U.S. patent application number 11/984550 was filed with the patent office on 2009-02-05 for optical display system and method, active and passive dithering using birefringence, color image superpositioning and display enhancement with phase coordinated polarization switching.
Invention is credited to James L. Fergason.
Application Number | 20090033607 11/984550 |
Document ID | / |
Family ID | 33314492 |
Filed Date | 2009-02-05 |
United States Patent
Application |
20090033607 |
Kind Code |
A1 |
Fergason; James L. |
February 5, 2009 |
Optical display system and method, active and passive dithering
using birefringence, color image superpositioning and display
enhancement with phase coordinated polarization switching
Abstract
A display apparatus includes a passive display, a light source,
and a video signal input, in operation in response to a video
signal the passive display modulates light from the light source to
provide an image, and the intensity of the light source is
controlled by the video signal. A method of producing a displayed
image using a passive display illuminated by a light source is
characterized in controlling the light source to obtain a displayed
image with a desired amount of information, gray scale and/or color
characteristics. A method of reducing power consumption by a
display system in which a light modulating display modulates
incident light from a light source to provide images is
characterized in controlling power provided to the light source to
reduce output thereof for relatively dark images.
Inventors: |
Fergason; James L.;
(Atherton, CA) |
Correspondence
Address: |
MCKENNA LONG & ALDRIDGE LLP
1900 K STREET, NW
WASHINGTON
DC
20006
US
|
Family ID: |
33314492 |
Appl. No.: |
11/984550 |
Filed: |
November 19, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10983403 |
Nov 8, 2004 |
7352347 |
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11984550 |
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09676915 |
Oct 2, 2000 |
6816141 |
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10983403 |
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08817846 |
Apr 25, 1997 |
6184969 |
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PCT/US95/13722 |
Oct 25, 1995 |
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09676915 |
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08398292 |
Mar 3, 1995 |
5715029 |
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08817846 |
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08392055 |
Feb 22, 1995 |
5572341 |
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08398292 |
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08328375 |
Oct 25, 1994 |
5537256 |
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08392055 |
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60001972 |
Jul 23, 1995 |
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Current U.S.
Class: |
345/89 |
Current CPC
Class: |
G02B 5/3083 20130101;
H04N 9/3155 20130101; G09G 2340/0407 20130101; H04N 9/3173
20130101; G09G 3/2044 20130101; G09G 3/3406 20130101; G09G 2330/021
20130101; H04N 9/3167 20130101; H04N 9/3188 20130101; G02B
2027/0118 20130101; G09G 2310/0237 20130101; G09G 2320/0606
20130101; H01J 29/89 20130101; G09G 2360/144 20130101; H04N 13/324
20180501; G09G 3/3413 20130101; H01J 2229/8926 20130101; G09G
3/3611 20130101; H04N 13/341 20180501; G09G 3/2007 20130101; H04N
13/305 20180501; H04N 13/398 20180501; G02F 1/1347 20130101; G09G
2360/16 20130101; G09G 2310/061 20130101; H04N 9/3102 20130101;
G02F 2413/04 20130101; G09G 3/2051 20130101; G09G 3/36 20130101;
G02F 1/13363 20130101; G09G 3/3648 20130101; G09G 2320/0626
20130101; G09G 2320/066 20130101; H04N 13/31 20180501; H04N 13/395
20180501; H04N 5/66 20130101; H01J 2329/897 20130101; G02B 5/30
20130101; G02F 2203/62 20130101; H04N 13/344 20180501; G02B 27/017
20130101; G02B 27/283 20130101; G09G 3/2055 20130101; G09G
2320/0271 20130101; H04N 5/7441 20130101; H04N 9/30 20130101; G09G
3/007 20130101; H04N 9/16 20130101; G02B 2027/0112 20130101; G02F
1/133638 20210101; G09G 3/002 20130101; G09G 2320/0646 20130101;
G02F 1/133562 20210101; H04N 5/7491 20130101; G02F 2413/08
20130101; G09G 2310/0224 20130101; G09G 2310/0235 20130101 |
Class at
Publication: |
345/89 |
International
Class: |
G09G 3/36 20060101
G09G003/36 |
Claims
1. A display system, comprising a passive display for producing an
output image represented by an input signal that has contrast ratio
and brightness information representing an input image, and a
control operative to substantially maintain contrast ratio of the
output image produced by the passive display irrespective of the
brightness of the input image.
2. The display system of claim 1, further comprising a light source
for providing illumination to illuminate the passive display.
3. The display system of claim 2, wherein the light source is a
back light.
4. The display system of claim 2, wherein the light source is a
number of light emitting diodes.
5. The display system of claim 2, wherein the control is operative
to control the intensity of the light source based on brightness
information of the input signal.
6. The display system of claim 2, wherein the light source provides
plural colors of light.
7. The display system of claim 2, wherein the light source
comprises plural light sources respectively providing different
colors.
8. The display system of claim 2, wherein the control is operative
to lower the intensity of light produced by the light source to
produce a dim output image, thereby reducing the power requirements
to produce the output image.
9. The display system of claim 1, further comprising projection
optics for projecting an image produced by the passive display.
10. The display system of claim 1, further comprising optics for
providing an output image produced by the passive display for
viewing.
11. The display system of claim 10, wherein the control comprises a
computer control.
12. The display system according to claim 1, in the form of a
television or computer monitor.
13. A method of displaying images using a passive display for
producing an output image represented by an input signal that has
contrast ratio and brightness information representing an input
image, comprising substantially maintaining contrast ratio of the
output image produced by the passive display irrespective of the
brightness of the input image.
14. The method of claim 13, further comprising illuminating the
passive display.
15. The method of claim 14, said illuminating comprising
illuminating the passive display using a light source, and further
comprising controlling the intensity of the light source based on
brightness information of the input signal.
16. The method of claim 15, wherein said controlling the intensity
of the light source adjusts output image brightness.
17. The method of claim 15, wherein the input image has color
characteristics, and wherein said controlling the intensity of the
light source comprises controlling several light sources of
different respective colors.
18. The method of claim 15, further comprising lowering the
intensity of the light produced by the light source to produce a
dim output image, thereby reducing the power requirements to
produce the output image.
19-88. (canceled)
Description
[0001] This is a divisional of copending, commonly owned U.S.
patent application Ser. No. 10/983,403, filed Nov. 8, 2004, which
is a continuation of U.S. patent application Ser. No. 09/676,915,
filed Oct. 2, 2000, now U.S. Pat. No. 6,816,141; which is a
continuation of commonly owned U.S. patent application Ser. No.
08/817,846, filed Apr. 25, 1997, now U.S. Pat. No. 6,184,969; which
is the national stage of international application no.
PCT/US95/13722, filed Oct. 25, 1995, which claims the benefit under
35 USC .sctn. 119(e) of U.S. provisional application Ser. No.
60/001,972, filed Jul. 23, 1995 and which is a continuation-in-part
of copending, commonly owned U.S. patent application Ser. No.
08/398,292, filed Mar. 3, 1995, now U.S. Pat. No. 5,715,029; which
is a continuation-in-part of co-pending, commonly owned U.S. patent
application Ser. No. 08/392,055, filed Feb. 22, 1995, now U.S. Pat.
No. 5,572,341; which is a continuation-in-part of copending,
commonly owned U.S. patent application Ser. No. 08/328,375, filed
Oct. 25, 1994, now U.S. Pat. No. 5,537,256; all of which are
incorporated by reference for all purposes as set forth herein.
CROSS REFERENCE TO RELATED PATENTS AND PATENT APPLICATIONS
[0002] Reference is made to commonly owned U.S. patent application
Ser. No. 08/187,262, filed Jan. 25, 1994 (now U.S. Pat. No.
5,717,422 issued Feb. 10, 1998); Ser. No. 08/187,050, filed Jan.
25, 1994 (now U.S. Pat. No. 5,532,854, issued Jul. 2, 1996); Ser.
No. 08/187,163, filed Jan. 25, 1994; Ser. No. 08/275,907, filed
Jul. 5, 1994 (now U.S. Pat. No. 5,519,524, issued May 21, 1996),
Ser. No. 08/328,375, filed Oct. 25, 1994 (now U.S. Pat. No.
5,537,256, issued Jul. 16, 1996); Ser. No. 08/392,055, filed Feb.
22, 1995 (now U.S. Pat. No. 5,572,341, issued Nov. 5, 1996); Ser.
No. 08/398,292, filed Mar. 3, 1995 (now U.S. Pat. No. 5,715,029,
issued Feb. 3, 1998); Ser. No. 08/295,383, filed Aug. 24, 1994 (now
U.S. Pat. No. 5,621, 572, issued Apr. 15, 1997); Ser. No.
08/328,371, filed Oct. 25, 1994 (now U.S. Pat. No. 5,858,589,
issued Sep. 15, 1998); Ser. No. 08/383,466, filed Feb. 3, 1995 (now
U.S. Pat. No. 5,606,458, issued Feb. 5, 1997); and provisional
patent application Ser. No. 60/002,780 entitled Optical system and
method for a head mounted display providing both front and
peripheral fields of view and Ser. No. 60/002,779 entitled
Monocular viewing device with retroreflector display system,
telecommunication system, and method, both filed Jul. 19, 1995. The
entire disclosures thereof hereby are incorporated by
reference.
TECHNICAL FIELD
[0003] The present invention relates generally, as is indicated, to
optical display system and method, active and passive dithering
using birefringence, color image superpositioning, and display
enhancement with phase coordinated polarization switching.
[0004] The present invention also relates to dithering systems for
optical displays and methods, and, more particularly, to passive
dithering systems and methods for changing the location of an
optical signal and for improving an optical display. The present
invention also relates to the enhancing of optical displays and
methods to enhance such displays, and, more particularly, to
enhancing optical displays and methods by coordinating the phase of
switching light with the dynamic operation of the displayed image
developing device.
BACKGROUND
[0005] Dithering systems have been used in a number of technologies
in the past. The objective of a dithering system is to change a
characteristic of a particular signal in a periodic (or random)
fashion in order to provide a useful output. As is described in
further detail, the dithering system of the invention may be used
to change the relative location of an optical signal.
[0006] The present invention may be used with various types of
displays and systems. Exemplary displays are a CRT (sometimes
referred to herein as cathode ray tube) display, a liquid crystal
display (sometimes referred to herein as "LCD"), especially those
which modulate light transmitted therethrough, reflective liquid
crystal displays, light emitting displays, such as
electroluminescent displays, plasma displays and so on.
[0007] Conventional optical displays typically display graphic
visual information, such as computer generated graphics, and
pictures generated from video signals, such as from a VCR, from a
broadcast television signal, etc.; the pictures may be static or
still or they may be moving pictures, as in a movie or in a
cartoon, for example. Conventional displays also may present visual
information of the alphanumeric type, such as numbers, letters,
words, and/or other symbols (whether in the English language or in
another language). Visual information viewed by a person (or by a
machine or detector) usually is in the form of visible light. Such
visible light is referred to as a light signal or an optical
signal. The term optical signal with which the invention may be
used includes visible light, infrared light, and ultraviolet light,
the latter two sometimes being referred to as electromagnetic
radiation rather than light. The optical signal may be in the form
of a single light ray, a light beam made up of a plurality of light
rays, a light signal such as a logic one or a logic zero signal
used in an optical computer, for example, or the above-mentioned
alphanumeric or graphics type display. Thus, as the invention is
described herein, it is useful with optical signals of various
types used for various purposes. Therefore, in the present
invention reference to optical signal, light ray, light beam, light
signal, visual information, etc., may be used generally
equivalently and interchangeably.
[0008] In an exemplary liquid crystal display sometimes referred to
as an image source, there usually are a plurality of picture
elements, sometimes referred to as pixels or pels, and these pixels
can be selectively operated to produce a visual output in the form
of a picture, alphanumeric information, etc. Various techniques are
used to provide signals to the pixels. One technique is to use a
common electrode on one plate of a liquid crystal cell which forms
the display and an active matrix electrode array, such as that
formed by thin film transistors (TFT), on the other plate of the
liquid crystal cell. Various techniques are used to provide
electrical signals to the TFT array to cause a particular type of
optical output from respective pixels. Another technique to provide
signals to the pixels is to use two arrays of crossed electrodes on
respective substrates of an LCD; by applying or not applying a
voltage or electric field between a pair of crossed electrodes, a
particular optical output can be obtained.
[0009] One factor in determining resolution of a liquid crystal
display is the number of pixels per unit area of the liquid crystal
display. For example, Sony Corporation recently announced a 1.35
inch diagonal high resolution liquid crystal display which has
513,000 pixels arranged in 480 rows of 1,068 pixels per row.
[0010] Another factor affecting resolution is the space between
adjacent pixels sometimes referred to "as optical dead space". Such
space ordinarily is not useful to produce an optical signal output.
The space usually is provided to afford a separation between the
adjacent pixels to avoid electrical communication between them. The
space also is provided to accommodate circuitry, leads, and various
electrical components, such as capacitors, resistors, and even
transistors or parts of transistors. The proportion of optical dead
space to useful space of pixels that can produce optical output
tends to increase as the physical size of the image source is
decreased, for the space required to convey electrical signals, for
example, may remain approximately constant although the actual size
of the useful space of the pixels to produce optical output can be
reduced because of anticipated image magnification. However, upon
magnification of the image produced by such a miniature image
source both the optical dead space and the useful optical space of
the pixels are magnified. Thus, resolution tends to be decreased,
especially upon such magnification.
[0011] The picture elements (pixels or pels) may be discrete
pixels, blocks or areas where an optical signal can be developed by
emission, reflection, transmission, etc. such as the numerous
pixels in the miniature image source of Sony Corporation mentioned
above. The optical signal referred to may mean that light is "on"
or provided as an output from the device, or that the pixel has its
other condition of not producing or providing a light output, e.g.,
"off"; and the optical signal also may be various brightnesses of
light or shades of gray. Alternatively, the optical output or
optical signal produced by a pixel may be a color or light of a
particular color.
[0012] The pixels may be a plurality of blocks or dots arranged in
a number of lines or may be a number of blocks or dots randomly
located or grouped in a pattern on the display or image source
(source of the optical signal). The pixels may be a number of lines
or locations along the raster lines that are scanned in a CRT type
device or the pixels may be one or a group of phosphor dots or the
like at particular locations, such as along a line in a CRT or
other device. The optical signal produced by one or more pixels may
be the delivery of light from that pixel or the non-delivery of
light from that pixel, or various brightnesses or shades of gray.
To obtain operation of a pixel, for example, the pixel may be
energized or not. In some devices energizing the pixel may cause
the pixel to provide a light output, and in other devices the
non-energizing of the pixel may cause the providing of a light
output; and the other energized condition may cause the opposite
light output condition. It also is possible that the nature of the
light output may be dependent on the degree of energization of a
pixel, such as by providing the pixel with a relatively low voltage
or relatively high voltage to obtain respective optical output
signals (on and off or off and on, respectively).
[0013] For example, in a conventional twisted nematic liquid
crystal display device, polarized light is received by a liquid
crystal cell, and depending on whether the liquid crystal cell
receives or does not receive a satisfactory voltage input, the
plane of polarization of the light output by the liquid crystal
cell will or will not be rotated; and depending on that rotation
(or not) and the relative alignment of an output analyzer, light
will be transmitted or not. In an optical phase retardation device
that has variable birefringence, such as those disclosed in U.S.
Pat. Nos. 4,385,806, 4,540,243, and RE. 32,521 (sometimes referred
to as surface mode liquid crystal cells), depending on the optical
phase retardation provided by the liquid crystal cell, plane
polarized light may be rotated, and the optical output can be
determined as a function of the direction of the plane of
polarization. In a CRT light emission or not and brightness may be
determined by electrons incident on a phosphor at a pixel. In
electroluminescent displays and plasma displays light output may be
determined by electrical input at respective areas on pixels.
[0014] The interlacing of raster lines or display lines is a known
practice used in television and in other types of display systems.
For example, in NTSC and PAL television type cathode ray tube (CRT)
displays it is known that two interlaced fields of horizontal lines
are used to provide an entire image frame. First one raster or set
of lines is scanned to cause one subframe (sometimes referred to as
field) to be displayed; and then a second raster or set of lines is
scanned to cause a second subframe (field) to be displayed. The
electrical signals used to scan one line in one subframe and the
electrical signals used to scan the relatively adjacent line of the
subsequent subframe may be different, and, therefore, the optical
outputs of those lines may be different. The two raster subframes
are presented sufficiently fast that the eye of an observer usually
cannot distinguish between the respective images of the two
successive subframes but rather integrates the two subframes to see
a composite image (sometimes referred to as a frame or picture).
The two subframes are created sequentially by "writing" the image
to respective pixels formed by phosphors to which an electron beam
may be directed in response to electrical signals which control the
electron beam in on-off and/or intensity manner. After the electron
beam has reached the end of its scanning to create one subframe,
e.g., the last pixel or phosphor dot area of that field, there is a
period of time while the electron beam is moved or directed to the
first pixel of the next subframe. During that period of time a
blanking pulse is provided to prevent electrons from being directed
to phosphors or pixels causing undesired light emission. Sometimes
various circuits of a television or CRT display are synchronized to
the operative timing of the television, CRT, etc. by
synchronization with such blanking pulses.
[0015] The density of pixels, e.g., number of pixels per unit area,
in a CRT display usually is, in a sense, an analog function
depending on characteristics of the electron beam, drive and
control circuitry for the beam, phosphor dot layout, shadow
mask(s), etc., as is known. Usually a CRT is driven using the
interlaced lines forming the subframes mentioned above. In an LCD,
though, there is a fixed number of pixels per line or row; and
data, e.g., whether a given pixel in a row is to transmit light or
to block light transmission, usually is written to the pixels a row
at a time. The data is written to one row, then to the next, and so
on, and there usually is no interlacing of rows or of subframes as
there is in CRT driving techniques.
[0016] In some LCD's the two subframes mentioned above usually are
effectively averaged together, when driven by a CRT type of
interlaced signal, since there usually is no physical interlacing
of LCD pixels to form respective subframes as there are respective
scan lines of phosphor dots, for example, in a CRT. Rather, the
electrical signals for driving adjacent scan lines of different
respective interlaced subframes of a CRT display, both usually are
delivered to only a single row of pixels in an LCD. Each pixel
responds to the electrical signal applied thereto to transmit or to
block light, for example. Those two sets of electrical signals are
applied to the row of pixels at different times. Therefore, at one
time a given row of LCD pixels may present as an optical output
optical information from one subframe and at a later time present
optical information from the other subframe.
[0017] Since the optical information presented in one subframe is
expected to be displaced in space from the optical information
presented in the other subframe to obtain the interlacing pattern
of a CRT display, careful examination of the optical output from
the above-mentioned LCD will show an amount of "jittering" of the
image. This jittering is caused by the pixels of one row
periodically being changed so the optical output thereof
sequentially displays the result of energization by signals
representing one scan line of information from one subframe and
then energization by electrical signals representing the adjacent
scan line of information from the next subframe.
[0018] This jittering can degrade the displayed image and can make
viewing uncomfortable. Also, the problems, such as viewing
discomfort and/or image degrading, caused by jittering tend to
increase as the image is enlarged or magnified, e.g., when the
image is created by a relatively miniature image source, such as
the SONY display mentioned above, and is magnified for direct
viewing or for projection by a projector.
[0019] One technique for reducing the jittering is to use
relatively slow liquid crystal display devices. Therefore, the
liquid crystal display element or pixel tends to average the
electrical signals applied thereto. A disadvantage to this
technique, though, is that image resolution is reduced because the
information representing two scan lines is combined into a single
line. Also, a slow acting liquid crystal display element tends to
have undesirable hysteresis that slows motion being shown by the
display.
[0020] In a color display, such as a LCD (liquid crystal display),
there usually are red, green and blue pixels which form a color
triad (hereinafter referred to as triad). By operating the LCD in
such a way that one or more of the pixels forming a triad provides
(or produces) the respective color light of that pixel, different
respective colors and white can be produced as output light. For
example, if the red pixel of a triad were providing red output
light; and the green and blue pixels were not providing output
light, the light output from that triad would be red. Further, when
two or more pixels of a triad are providing light output, a
combination of those colors is seen by a person viewing (sometimes
referred to as the viewer) the light output or image. The viewer
usually visually superimposes the output light from the pixels of
the triad; and the combined or superimposed lights therefrom
provide the net effect or integrated light output of the triad. As
an example, to produce a white light output from a triad, the red,
green and blue pixels of that triad would provide, respectively,
red, green and blue light; and those lights would be, in effect,
superimposed by the viewer and seen as white light.
[0021] There is a continuing need and/or desire to improve
resolution of displays. It also would be desirable to facilitate
the placing of circuitry in a display while minimizing the optical
dead space caused by the circuitry. There also is a need to reduce
jitter.
[0022] In the above-mentioned patent applications are disclosed
techniques for actively dithering, moving an optical signal,
changing the location or optical path of an optical signal, etc.
for several purposes, such as to increase resolution, to reduce
jitter, and so on. There also are disclosed techniques for passive
dithering, moving of optical signals, etc., for example to increase
the fill factor of an image provided by a display by expanding the
image or pixels forming the image.
[0023] An LCD using the twisted nematic effect usually cannot
switch between transmission states as rapidly as changes occur in
the applied electrical signal which operates the LCD. For example,
the electrical input to a twisted nematic LCD can change nearly
instantly, but it takes a number of milliseconds for the LCD to
respond dynamically to the change in electrical input to change the
optical response of the LCD. When an LCD is used in a display
system that employs dithering to double, quadruple or otherwise to
change the effective number of pixels, for convenience hereinafter,
sometimes referred to as optical line doubling (or OLD), the
relatively slow response of the twisted nematic LCD compared to the
faster operation of the dithering optics can result in an optical
output that does not achieve the desired improvement in resolution
or other optical effect.
[0024] The displaying of a dark scene using a display device
(sometimes referred to as a passive display), which modulates light
received from a separate light source, encounters a disadvantage
which ordinarily is not present for displays which produce their
own light, such as a cathode ray tube (CRT). The problem has to do
with reduced resolution and/or contrast of the displayed image.
[0025] In a CRT, for example, when it is desired to display a dark
scene, the intensity of the output light can be reduced. The
different parts of the dark scene, then, all may be output at the
reduced brightness or illuminance level. All pixels (e.g., picture
elements, phosphor dots in a monochrome display or group of three
red, green and blue phosphor dots for a multicolor display, etc.)
of the CRT can be active so that resolution is maintained even
though intensity of the light produced by the phosphors is
reduced.
[0026] However, in a passive display device, such as a liquid
crystal display, an electrochromic display, etc., whether of the
light transmitting type or of the light reflecting type, the usual
practice to reduce brightness of a displayed image or scene is to
reduce the number of pixels which are transmitting light at a
particular moment. Such a reduction reduces the resolution of the
display. Also, such a reduction can reduce the contrast of the
display.
[0027] The human eye has difficulty distinguishing between seeing
or recognizing the difference between low and high brightness and
contrast ranges. This difficulty is increased when the number of
pixels is decreased and resolution is degraded.
[0028] It would be desirable to improve the contrast and resolution
of passive displays.
[0029] In U.S. patent application Ser. No. 08/187,163 is disclosed
a passive apparatus, such as an LCD, and method for displaying
images with high contrast by controlling the light input to the
display to control brightness of the output while operating
respective pixels of the display to obtain good contrast
substantially without regard to the output brightness. Different
color effects also are disclosed using, for example, field
sequential switching of respective color light. However, this is
another example of a passive optical device, in this case an LCD,
in which field sequential switching could be improved if
coordinated with the delays inherent in the dynamic optical
response of a liquid crystal cell, for example, relative to the
changes in operating signal, such as electric field, voltage,
etc.
[0030] As is described in application Ser. No. 08/187,163, an image
of a candlelit room would be dim. In the prior art devices a
relatively small number of pixels would be used, then, to transmit
light to create the image, whereas a relatively large number of
pixels would be used to block light transmission to give the effect
of the reduced intensity or dim room. In the invention of such
application, though, the number of pixels used to create the image
remains constant, and the contrast ratio between one portion and
another portion of the image remain constant; only the intensity of
the illuminating light changes thereby to diminish the brightness
of the room. Therefore, with the invention image data is not lost
regardless of the brightness of the image, whereas in the prior art
image data is lost because the additional pixels are used to
brighten or darken the brightness of the image.
[0031] The features of the invention as described in that patent
application can be used in a frame sequential basis. The features
of the invention can be used regardless of whether the display is
operated in reflective mode or in transmissive mode. Also, the
features of the invention can be used in a virtual reality type
display in order to provide a very wide range of contrast and of
image brightness characteristics. The picture information is used
to derive the brightness of the display, not the surrounding
ambient. Using the invention of that application, the amount of
information that can be conveyed by the display is substantially
increased over the prior art.
[0032] For example, if there were a grey scale of 100 shades of
grey and a display with 10 shades of grey, the intensity of the
illuminating source can be changed at 10 different levels, for
example, and there also can be 10 different shades of grey provided
by the display itself. Therefore, this provides 100 shades of grey.
This characteristic can be increased by another factor of 10 by
going to r, g, b (red, green, blue) modulation on a field
sequential basis, which allows the possibility of 10 to the 6th
different illumination levels and colors. The foregoing is
especially important in head mounted displays where immersion in
the image is extremely important. Using features of such patent
application, there can be high illumination of the scene, then, the
grey scale contrast ratio of the real image can be adjusted. As a
result, there is a high contrast image presented in a bright motif.
Another example using such invention is the ability to display a
sunrise scene in which the red image is enhanced and the blue and
green are minimized.
[0033] The invention of that application, then, can separate the
two functions of brightness and image. The image is a function of
the operation of the liquid crystal modulator and the illumination
brightness is the function of the light source intensity. The r, g,
b colors can be changed to give a candlelight or moonlight effect
with good resolution and color function, but the brightness of the
scene is a function of the background. As a result, it is possible
to photograph the scene in daylight to get good contrast; and then
by reducing the display illumination it is possible to give the
impression of a moonlit or candlelit environment.
SUMMARY
[0034] With the foregoing in mind, then, one aspect of the
invention is to increase the resolution of a display by
electro-optically dithering an optical signal.
[0035] Another aspect relates to use of electro-optical dithering
to obtain three dimensional images, especially using
auto-stereoscopic effect.
[0036] Another aspect relates to using electro-optical dithering to
effect beam switching of optical signals.
[0037] Another aspect is electro-optically to change selectively
the location at which an optical output signal is presented to
another location. A further aspect is to effect such change in more
than one direction, e.g., along more then one axis.
[0038] According to another aspect, a device for changing or
determining the location of an optical signal includes birefringent
means for selectively refracting light based on optical
polarization characteristic of the light, and means for changing
such optical polarization characteristic of light, the birefringent
means and the changing means being cooperative selectively to
change the location of the optical signal.
[0039] According to another aspect, a system for increasing the
resolution of an optical display having a plurality of picture
elements includes birefringent means for selectively refracting
light based on polarization characteristics of the light, changing
means for selectively changing the polarization characteristics of
light, and the birefringent means and the changing means being in
optical series and cooperative in response to selective operation
of the changing means to change the location of output optical
signals therefrom.
[0040] According to another aspect, a display system includes a
display for producing visual output information by selective
operation of a plurality of picture elements at respective
locations, and means for changing the location of the output
information as a function of optical polarization thereby
effectively to increase the number of picture elements.
[0041] According to another aspect, a display system includes a
display for producing visual output information by selective
operation of a plurality of picture elements at respective
locations, and means for changing the location of the output
information without physical realignment of a mechanical device
thereby effectively to increase the number of picture elements.
[0042] According to another aspect, a display system includes a
display for producing visual output information by selective
operation of a plurality of picture elements at respective
locations, and means for electro-optically changing the location of
the output information thereby effectively to increase the number
of picture elements.
[0043] According to another aspect, a method for displaying visual
information includes presenting a first optical output from a
source by providing plural optical signals arranged in a pattern,
presenting a second optical output from the source by providing
plural optical signals arranged in a pattern, and selectively
shifting the location of the pattern of the second optical output
relative to the location of the pattern of the first optical output
based on optical polarization.
[0044] According to another aspect, an electro-optical dithering
system for shifting polarized light includes birefringent means for
selectively refracting light as a function of a polarization
characteristic of the light, and changing means for changing the
polarization characteristic of polarized light to provide output
light that is shifted or not as a function of optical
polarization.
[0045] According to another aspect, a method of making a display
includes positioning in optical series an image source, a
birefringent means for selectively refracting light based on
optical polarization characteristic of the light, and a changing
means for changing such optical polarization characteristic.
[0046] Using principles of the invention, the location of an
optical signal can be changed, and the change can be used for a
number of purposes. For example, the change can be used to improve
resolution of a display, to provide an auto-stereoscopic output, to
interlace optical signals, to facilitate positioning and hiding of
circuitry used in a display, to facilitate overlapping of tiles or
pixels in a display, etc. A number of these examples are presented
below. The invention may be used to achieve one or more of those
and other uses. An aspect of the invention relates to an optical
line increaser, wherein the number of pixels in a optical display
can be increased by electro-optical means. An aspect of the
invention relates to an optical line increaser, wherein the number
of pixels in a optical display can be increased by electro-optical
means, for example, to double, triple, quadruple, or otherwise to
increase the effective number of pixels presenting output optical
information for viewing by a person, machine, other device, etc.,
and/or for other use.
[0047] Another aspect is to hide or to reduce optical dead space in
a display.
[0048] Another aspect is to use a switchable electro-optical device
to effect dithering (changing effective location) of an optical
signal.
[0049] Another aspect is to reduce jitter in an optical
display.
[0050] Another aspect is to drive a non-interlaced display using an
interlaced signal and electro-optically dithering the optical
output of the display to reduce jitter.
[0051] Another aspect is to increase the effective number of pixels
and/or lines of an optical display.
[0052] In accordance with a further aspect of the invention, a
passive dithering display system includes an optical display
including a plurality of pixels with optical dead space between the
pixels for producing an image, and a birefringent material for
shifting one polarization component of the image relative to a
second polarization component of the image such that the shifted
polarization component lies in the dead space.
[0053] In accordance with another aspect, a display system includes
an optical display for producing an image and a first birefringent
material for refracting one component of the image relative to a
second component of the image based on polarization characteristics
of the components to produce a plurality of adjacent images.
[0054] In accordance with a still further aspect of the invention,
a method of reducing optical background noise includes the steps of
displaying a plurality of pixels with optical dead space between
said pixels for producing an image and shifting one polarization
component of the image relative to a second polarization component
of the image such that the shifted polarization component lies in
the dead space.
[0055] Another aspect relates to expanding an image or pixels of an
image to increase the fill factor of the image, the fill factor
relating to the amount of area of the image actually occupied by
image compared to that part of the image occupied by optical dead
space.
[0056] Another aspect relates to using passive image or pixel
expanding to increase the fill factor of an image.
[0057] Another aspect relates to using active image or pixel
doubling (or other increasing) to increase fill factor and
resolution of an image.
[0058] Another aspect relates to techniques to superimpose color
pixel image light outputs to obtain respective color outputs for a
display.
[0059] Another aspect is to increase the amount of data able to be
displayed from a video signal or the like provided to a display
system, such as an LCD display system or other display system.
[0060] As is described further below, the invention is useful to
coordinate light output by an optical device, such as an LCD, for
example, and the dynamic operation of such optical device with
another optical device, such as one that switches or shifts the
location of the output light for use, such as viewing, projection,
etc., one that displays images in field (sometimes referred to as
frame or part of a frame) sequential operation to present images
with good contrast and/or color effect that are independent of the
brightness of the output light, and so on.
[0061] One or more of these and other objects, features and
advantages of the present invention are accomplished using the
invention described and claimed below.
[0062] To the accomplishment of the foregoing and related ends, the
invention, then, comprises the features hereinafter fully described
and particularly pointed out in the claims. The following
description and the annexed drawings set forth in detail certain
illustrative embodiments of the invention. These embodiments are
indicative, however, of but a few of the various ways in which the
principles of the invention may be employed.
[0063] Although the invention is shown and described with respect
to certain preferred embodiments, it is obvious that equivalents
and modifications will occur to others skilled in the art upon the
reading and understanding of the specification. The present
invention includes all such equivalents and modifications, and is
limited only by the scope of the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0064] In the annexed drawings:
[0065] FIG. 1 is a schematic side elevation view of a CRT display
including an electro-optical dithering system according to the
present invention;
[0066] FIG. 2 is a schematic illustration of the components of the
electro-optical dithering system of FIG. 1;
[0067] FIG. 3 is a schematic illustration of the double refraction
effect through a calcite crystal which may be used in the
electro-optical dithering system of the invention;
[0068] FIGS. 4A, 4B and 4C are, respectively, schematic
illustrations indicating exemplary axial alignment of the several
components of the electro-optical dithering system shown in FIG.
2;
[0069] FIGS. 5A, 5B and 5C are, respectively, schematic
illustrations similar to
[0070] FIG. 2 showing the operation of the electro-optical
dithering system on light in respective operational modes;
[0071] FIG. 6 is a schematic illustration of an alternate
embodiment of electro-optical dithering system;
[0072] FIG. 7 is a schematic front view of the face or display
output of a CRT showing exemplary raster lines;
[0073] FIG. 8 is a schematic side elevation view of the
electro-optical dithering system of the invention used in an
auto-stereoscopic display;
[0074] FIG. 9 is an enlarged view of a single lens element of the
auto-stereoscopic display of FIG. 8;
[0075] FIG. 10 is a schematic plan view of part of a liquid crystal
display showing areas where pixels are located and areas where
there is circuitry or dead space located between adjacent pixels
and including the electro-optical dithering system of the
invention;
[0076] FIG. 11 is a schematic top view of the display of FIG. 10
showing the paths of optical signals that are shifted in location
according to the on or off state of the electro-optical dithering
system of the display;
[0077] FIGS. 12 and 13 are schematic block diagrams of
synchronizing circuit techniques useful in the various display
systems of the invention;
[0078] FIGS. 14 and 15A-15E are schematic illustrations of a
display system and parts thereof with a double electro-optical
dithering system;
[0079] FIGS. 16A-16D are schematic illustrations of a pixel pattern
that is dithered or not in up to four different spatial pattern
locations;
[0080] FIG. 17 is a composite of the pixel patterns of FIGS.
16A-16D;
[0081] FIGS. 18 and 19 are schematic illustrations of a display
system with a double electro-optical dithering system and parts
thereof using switchable liquid crystal birefringent devices;
[0082] FIG. 20 is a schematic illustration of part of a red, green
and blue pixel arrangement for a multicolor display;
[0083] FIG. 21 is a schematic illustration of a segmented display
system with selective time sequenced dithering of respective
segments;
[0084] FIGS. 22A-22F are schematic illustrations of the segmented
display system of FIG. 21 showing the time sequence of operation
thereof;
[0085] FIG. 23 is a schematic illustration of a passive dithering
system used in connection with a display which produces a polarized
output;
[0086] FIG. 24 is a schematic illustration of the effect of
dithering in both horizontal and vertical directions;
[0087] FIG. 25 is a schematic illustration of the orientations of
the optic axes of the components of the passive dithering system of
FIG. 23;
[0088] FIG. 26 is a schematic illustration of the passive dithering
system of FIG. 23 used in connection with a display which produces
a nonpolarized (sometimes referred to as unpolarized) light
output;
[0089] FIG. 27 is a schematic illustration of the orientations of
the optic axes of the components of the passive dithering system of
FIG. 26;
[0090] FIG. 28 is a schematic illustration of an alternate
embodiment of a passive dithering system;
[0091] FIG. 29 is a schematic illustration of the orientations of
the optic axes of the components of the passive dithering system of
FIG. 28;
[0092] FIG. 30 is a schematic illustration of the passive dithering
system of FIG. 28 used in connection with a display which produces
a nonpolarized light output;
[0093] FIG. 31 is a schematic illustration of an optical display
system using an alternate embodiment of a passive dithering system
using unpolarized light input;
[0094] FIG. 32 is a schematic illustration of the orientations of
the optic axes of the components of the passive dithering system of
FIG. 31;
[0095] FIG. 33 is a schematic illustration of an alternate
embodiment of optical display system using an active dithering
system for diagonally displacing a pixel image;
[0096] FIG. 34 is a schematic illustration of the locations of the
original pixel images unshifted and of the shifted pixel images
using the dithering system of FIG. 33;
[0097] FIG. 35 is a schematic illustration of an alternate
embodiment of optical display system using active and passive
dithering system for displacing pixel images;
[0098] FIG. 36 is a schematic illustration of the locations of the
original pixel images unshifted and of the shifted pixel images
using the dithering system of FIG. 35 in four respective
operations;
[0099] FIG. 37 is a schematic illustration of the display output
from an optical display system of the type shown in FIG. 35, for
example, showing shifting of pixel images relative to each other to
obtain superpositioning of color pixel images and increased fill
factor;
[0100] FIGS. 38 and 39 are schematic illustrations of display
outputs from an optical display system of the type shown in FIG. 35
and or in other figures hereof, for example, showing shifting of
pixel images into gaps between pixels and in overlapping relative
to each other;
[0101] FIG. 40 is a schematic illustration of the display output
from an optical display system of the type shown in FIG. 41, for
example, showing shifting of pixel images according to an exemplary
prescribed pattern;
[0102] FIG. 41 is a schematic illustration of an optical display
system including the components to obtain the operation depicted in
FIG. 40 for a head mounted or boom mounted display system or other
display system;
[0103] FIG. 42 is a schematic illustration of a display system in
accordance with an embodiment of the invention including a head
mounted portion;
[0104] FIG. 43 is a schematic section elevation view showing the
various operational parts of the monocular viewing device used in
the display system of FIG. 1;
[0105] FIG. 44 is a compilation of graphs representing the response
of a twisted nematic LCD display pixel when addressed at 60 Hz
(Hertz);
[0106] FIG. 45 is a compilation of graphs representing the response
of a twisted nematic LCD display pixel when addressed at 120
Hz;
[0107] FIG. 46 is a compilation of graphs representing the response
of a surface mode type birefringent liquid crystal light shutter
operating as an optical rotator or switch coordinated with the
operation of a twisted nematic LCD display pixel which is addressed
at 120 Hz;
[0108] FIG. 47 is a schematic illustration of a display optical
system used in the viewing device of FIGS. 42-43, for example,
and/or in other viewing devices or display systems disclosed
herein;
[0109] FIG. 48 is a compilation of graphs showing the relationship
of timing signals for an optical line doubler system that provides
both horizontal and vertical doubling (e.g., quadrupling of
respective pixels), for example, as in the embodiment depicted in
FIGS. 14-17;
[0110] FIG. 49 is a schematic illustration of a light transmissive
display system according to an embodiment of the invention;
[0111] FIG. 50 is a schematic illustration of a light reflective
display system according to an embodiment of the invention;
[0112] FIG. 51 is a schematic view of a reflective field sequential
display and illumination system using plural cholesteric liquid
crystal reflectors and plural light sources of respective colors to
provide a multicolor or full color display useful in various
embodiments of the invention;
[0113] FIG. 52 is a schematic view of a head mounted display system
including a pair of display subsystems in accordance with various
embodiments of the invention; and
[0114] FIGS. 53-58 are schematic graphical illustrations depicting
operation of the invention.
DESCRIPTION
[0115] Referring, now in detail to the drawings wherein like
reference numerals designate like parts in the several figures and
initially to FIG. 1, an electro-optical dithering system in
accordance with an embodiment of the present invention is generally
indicated at 1 in use with a display 2 to form an optical display
system 3 for providing optical signals, visual information, etc.,
as the output therefrom. The display 2 provides a source of light
or optical signals, and such light is transmitted through the
electro-optical dithering system to provide optical signals at
respective locations for viewing or the like. Exemplary light is
represented by an arrow 4, such as an optical signal produced at a
particular location by the display 2 or produced by some other
source and modulated by the display 2 as the output therefrom.
[0116] The location of the output optical signal 5 is represented
by arrows 5a, 5b. Those arrows 5a, 5b represent the location of the
output optical signal 5 resulting from the optical signal 4 being
transmitted through the electro-optical dithering system 1 while
the electro-optical dithering system is in a respective one or the
other of the operative states thereof, such as off or on.
[0117] In the embodiment illustrated in FIG. 1 the display 2 is a
CRT. It will be appreciated that the display 2 may be an LCD or
another display, such as an electroluminescent display, plasma
display, flat panel display or other display.
[0118] Dithering may refer to the physical displacement of an
image. An electro-optical dithering system (EDS) refers to an
electro-optical means to physically shift, translate or to change
the location of an optical signal, such as an image. The image may
be shifted along an axis from one location to another and then back
to the first, e.g. up and then down, left and then right, etc. The
optical signal may be moved in another direction along a straight
or other axis or not along an axis at all. The dithering may be
repetitive or periodic or it may be asynchronous in moving an image
from one location to another and then holding it there, at least
for a set or non-predetermined time.
[0119] The electro-optical dithering system 1, as it is shown in
FIG. 1, includes birefringent material, which sometimes is referred
to as double refracting material, 10. An example of birefringent
material is a calcite crystal material. Other double refracting
(birefringent) materials also may be used. Birefringent material
may transmit light straight through or may refract the light which
is incident thereon, depending on a characteristic of the light
incident thereon, such as optical polarization characteristic. In
the illustrated embodiment the optical polarization characteristic
is the direction of the electric vector of plane polarized light.
Plane polarized light having one direction of electric vector
(sometimes referred to as direction of the polarization axis, the
transmission axis of the polarizer or of the light, the plane of
polarization of the light, the direction of polarization, etc.) may
transmit directly through the birefringent material 10 without
being refracted or bent, whereas light having a different direction
of plane of polarization may be refracted (bent) by the
birefringent material 10. For example, plane polarized light which
encounters one index of refraction characteristic, such as an
ordinary index of refraction characteristic, of the birefringent
material may be transmitted without refraction. However, plane
polarized light which encounters a different index of refraction
characteristic, such as the extraordinary index of refraction, of
the birefringent material will bend or refract at the interface
with the birefringent material, both upon entering and upon leaving
the birefringent material. Therefore, in a sense the birefringent
material 10 changes the direction of light transmitted through it,
for example, as it changes the location of the output optical
signal from location 5a to 5b.
[0120] In the optical display system 3 embodiment illustrated in
FIG. 1 the electro-optical dithering system 1 also includes a
switch 11 that can be operated to change the characteristic of
light relevant to the birefringent material 10 to change the
location of the output optical signal. In the exemplary embodiment
of FIG. 1 refraction of light or transmission of light without
refraction by the birefringent material 10 depends on the direction
of polarization of plane polarized light incident on the
birefringent material 10, and the switch 11 is able to switch the
direction of polarization of such light incident on the
birefringent material 10.
[0121] In the embodiment illustrated in FIG. 1 the switch 11 is a
liquid crystal cell or liquid crystal shutter type device which is
able to transmit light to the birefringent material 10 such that
the light incident on the birefringent material has a plane of
polarization that can be changed by the switch. Accordingly, if the
switch is in one operative state or mode, the light incident on the
birefringent material 10 may have a plane of polarization such that
the output optical signal 5 occurs at the location of the arrow 5a,
and with the switch 11 in a different state of energization the
plane of polarization of the light incident on the birefringent
material 10 can be changed (e.g., switched to an orthogonal
direction to the first-mentioned plane) thereby to cause the output
optical signal to occur at the location of the arrow 5b.
[0122] A linear polarizer (sometimes referred to as a plane
polarizer) 12 is between the switch 11 and the CRT display 2. The
light 4 provided by the display 2 is plane polarized by the
polarizer 12. The direction of polarization in cooperation with one
condition of the switch 11 will result in the light being
transmitted directly through the birefringent material 10 without
refraction so as to appear at location of arrow 5a. However, in
response to the other condition of the switch 11, the light will be
refracted by the birefringent material 10 so as to occur at the
location of the arrow 5b.
[0123] With the foregoing in mind, then, it will be appreciated
that the invention includes a material that can move the location
of an output optical signal relative to the location of an incident
(input) optical signal depending on a characteristic of the
incident optical signal, such as the direction of plane polarized
light. The electro-optical dithering system 1 of the invention
includes birefringent, double refracting, or equivalent material
and a means to switch or to discriminate the characteristic of the
incident optical signal.
[0124] In the embodiment illustrated in FIG. 1, the light 4 from a
CRT is unpolarized. The polarizer 12 gives the light a
characteristic of linear (plane) polarization. The switch 11 can
change the direction of polarization, e.g., the direction of the
electric vector of the polarized light. The birefringent material
provides the output optical signal at the location 5a, 5b,
depending on the characteristic of the light incident on the
birefringent material.
[0125] The switch 11 may be a liquid crystal cell or several liquid
crystal cells, such as twisted nematic liquid crystal cells,
birefringent liquid crystal cells, such as those disclosed in U.S.
Pat. Nos. 4,385,806, RE. 32,521, and 4,540,243, the entire
disclosures of which hereby are incorporated by reference. If
desired, the liquid crystal cells may be arranged in optical series
and operated as a push-pull arrangement to improve linearity of
response, and/or for other purposes, for example, as is disclosed
in one or more of the aforementioned patents. Other types of liquid
crystal cells also may be used for the switch 11. Further, other
types of devices that are able to switch the optical characteristic
of light, such as the direction of plane polarization, etc., may be
used for the switch 11; several examples include ferro-electric
liquid crystal cells, variable optical retarders, PLZT devices, and
so on.
[0126] An advantage to using a liquid crystal display (LCD) as the
display 2 with the dithering system 1 is that the output light from
an LCD usually already may have a characteristic of optical
polarization, such as linear polarization. In such a case, the
linear polarization characteristic provided by such displays may
eliminate the need for a separate linear polarizer 12.
[0127] In FIG. 2 the electro-optical dithering system 1 is shown in
use in an optical display system 13 having a transmissive LCD 20.
The LCD 20 may be a twisted nematic liquid crystal display,
birefringent liquid crystal display, or some other type of liquid
crystal display which produces in response to input light 21 from a
light source 22, output light represented by an arrow 23. The LCD
20 may be transmissive or reflective. The output light 23 may be,
for example, a graphic image, one or more light beams that are
selectively turned on or off depending on operation of the liquid
crystal display 20, etc. The graphic image may be a moving image,
an alphanumeric display, etc. The dithering system 1 includes a
birefringent material 10 and a switch 11. To simplify the following
description, the switch 11 may be referred to as a polarization
rotator, which rotates the plane of polarization of the light
represented by arrow 23 an amount depending upon the energization
state or condition of the polarization rotator. For example, if the
switch 11 were a twisted nematic liquid crystal cell, when it is
de-energized, it would rotate the plane of polarization by 90
degrees (or some other amount depending on the nature of the liquid
crystal cell), and when the twisted nematic liquid crystal cell is
in a fully energized condition, it would not rotate the plane of
polarization of the light incident thereon. Similar operation could
be obtained by using birefringent liquid crystal cells.
Additionally, if desired, compensation may be provided for residual
retardation in a liquid crystal cell, whether of the birefringent
or twisted nematic type; such compensation may be provided by a
wave plate or the like, such as a quarter wave plate positioned in
a particular orientation relative to the rub direction or axis of
the liquid crystal cell used in the switch 11.
[0128] Further, a wave plate, such as a half wave plate, may be
used to rotate the plane of polarization of light 23 so it is
appropriately aligned with the optic axis (sometimes referred to
herein as the rub direction, optical axis, or simply axis) of the
switch 11. For example, if the switch 11 were a twisted nematic
liquid crystal cell, the plane of polarization of the light 23 may
be parallel or perpendicular to the rub direction of one of the
plates of the liquid crystal cell. If the switch 11 were a
birefringent liquid crystal cell, such as a surface mode cell or a
pi-cell (e.g., as the above-mentioned patents or in U.S. Pat. No.
4,582,396, which is hereby incorporated by reference), the plane of
polarization of light 23 may be at 45 degrees to the rub direction.
In using a half wave plate to adjust plane of polarization, for
example, the axis of the half wave plate would be aligned to one
half the angular distance between the orientation of the plane of
polarization of the light incident on the half wave plate and the
angular orientation desired for the light output from the half wave
plate.
[0129] Turning to FIG. 3, there is shown an example of birefringent
material 10 in the form of the mineral calcite, also referred to as
a calcite crystal 30. Unpolarized light 31 enters the calcite 30 at
the left hand face 32 thereof. The light enters at a right angle to
the face 32. The light 31 is resolved into two orthogonally
polarized components 33, 34 in view of the birefringent nature of
the calcite. The optical axis of the light components 33, 34 are
oriented such that one component 33 has a plane of polarization or
electric vector direction into and out of the plane of the drawing
of FIG. 3, as is represented by the dots shown in FIG. 3, and such
light 33 experiences an index of refraction change between the
environment 35 outside the calcite 30 and the environment 36 inside
the calcite 30. However, the axis of the calcite crystal 30 is at a
right angle to the plane of polarization to the light 33, and,
therefore, this components of light 33 travels through the calcite
crystal 30 without deflection (refraction); sometimes this light is
referred to herein as the undithered light.
[0130] The light component 34 is polarized vertically in the plane
of the drawing of FIG. 3 and is represented by a double-headed
arrow in the drawing. The light component 34 experiences a change
in index of refraction as above; however, the light component 34
also encounters the calcite crystal axis at an angle which is other
than a right angle. Therefore, the light component 34 is refracted
and its path is deflected (direction is changed) as it enters and
leaves the crystal on its travel through the crystal 30, as is
shown in FIG. 3; sometimes this light is referred to herein as the
dithered light. This property of refraction of one polarization
component and no refraction of the other polarization component of
light incident on a birefringent material sometimes is called
double refraction, and it occurs in many materials. The amount of
physical displacement between the light components 33, 34 where
they exit the right hand face 37 of the calcite crystal 30 and
become, respectively, output light 33a, 34a represented by arrows
at locations 38a, 38b, respectively, depends on the thickness of
the calcite crystal, indices of refraction of the calcite crystal
and the external environment thereof, and the orientation of the
optical axis of the specific material, as is known.
[0131] In the optical display system 3 of FIG. 1 in which the
display 2 is a CRT and in the optical display system 13 of FIG. 2
which uses an LCD 20 the direction of polarization of light
incident on the switch 11 and the orientation of the switch 11 may
be related for optimal operation. In one example of the invention,
the switch 11 is a birefringent liquid crystal cell (or a pair of
them operating in push-pull manner), and such liquid crystal
cell(s) has (have) an axis which sometimes is referred to as the
rub direction, alignment direction, optic or optical axis, etc. of
the liquid crystal cell. Using such a liquid crystal cell in the
systems 3 or 13, for optimal operation the polarization direction
(transmission direction axis of the polarizer 12 or of the LCD 20,
for example) should be at 45 degrees relative to the axis of the
switch 11. Additionally, preferably the projection of the axis of
the calcite crystal 30 is oriented at 45 degrees to the axis of the
switch 11. These relationships are depicted in FIGS. 4A, 4B and
4C.
[0132] Briefly referring to FIGS. 4A, 4B and 4C, the
above-described relationships of axes is shown. In FIG. 4A the
transmission axis of the polarizer 12 or the plane of polarization
of light delivered by the liquid crystal display 20 or by CRT 2 and
polarizer 12 is shown as horizontal at 40. However, such direction
also may be vertical, because it is desired that the relationship
between that axis and the axis of the liquid crystal cell(s) of the
birefringent liquid crystal cell switch 11 be at a relative 45
degrees thereto. Such 45 degrees relationship is shown by the
respective axes 41, 42 for the switch 11. In fact, such axes 41, 42
may represent the axis of one liquid crystal cell and the axis of a
second liquid crystal cell, the two being arranged in optical
series and being operated in push-pull fashion. The axes 43, 44 of
the calcite crystal 30 are shown as horizontal and vertical.
However, the vertical axis actually is tipped in or out of the
plane of the drawing and it actually is the projection of that axes
which would appear as vertical; alternatively or additionally the
horizontal axis may be tipped. Such projection of the axes
preferably is at 45 degrees to the axes 41, 42 of the switch 11.
The described relative orientation of the axes of the various
components used in connection with the invention is exemplary, and
it will be appreciated that other arrangements may be used to
obtain a particular type of operation. However, in the ideal
simplified case described herein, the relationship described may be
employed. Also, it will be appreciated that compensation may be
provided to adjust the effective orientation of a particular axis.
Such compensation can be provided using a birefringent material, a
wave plate, such as a quarter wave plate or another one, etc., as
was mentioned above.
[0133] It will be appreciated that whether the axis of a
birefringent switch 11 is at plus or minus 45 degrees, represented
by the axis lines 41, 42, for example, and whether a respective
axis 43, 44 of the calcite 30 or other double refracting material
10 is at plus or minus 45 degrees to the axis of the birefringent
switch (and parallel or perpendicular to the plane of polarization
40) will determine whether the dithered optical signal will be
moved up, down, left or right relative to the undithered signal. If
the switch 11 were a twisted nematic liquid crystal cell, the axis
40 may be parallel or perpendicular to one of the axes of the
liquid crystal cell, and the orientation of the calcite 30 may be
as shown in FIG. 4C relative to the plane of polarization of the
light represented at 40 in FIG. 4A.
[0134] It will be appreciated that the arrangement of axes herein
described are exemplary. The alignment of the switch 11, whatever
that component is comprised of, preferably is such that the switch
is able to change a characteristic of light in the display system
3, 13 (and others described herein, for example) so that selective
dithering can be carried out by a double refraction or other
functionally equivalent material or device. Orientation of the
double refracting material may be such as to cause such selective
dithering depending on an optical characteristic of the light,
which is incident thereon and/or is transmitted therethrough,
relative to the double refracting material.
[0135] Quarter wave plates, other wave plates, etc. may be used in
conjunction with coupling of light along optical paths used in the
electro-optical dithering system 1 and/or the optical display
systems 3 or 13, etc. Also, such wave plates may be used to convert
plane polarized light to circularly polarize light or vice versa,
depending on the nature of the optical coupling occurring in the
various components and optical paths and/or the switch 11 used in
the invention.
[0136] Referring to FIGS. 5A, 5B and 5C, operation of the EDS1
according to the invention is depicted for use in the exemplary
systems 3, 13, etc., which are expressly described herein, and in
other display systems, too. Light 4, for example, from a CRT, is
horizontally polarized by the polarizer 12. Arrow 50 represents
such horizontal polarization, as does the dot in that arrow 50. The
switch 11 is a birefringent liquid crystal cell of the type
disclosed in the above-mentioned patents (such types sometimes
being referred to as "surface mode" or "pi-cell" liquid crystal
devices). When the switch 11 is in the high voltage state it does
not affect the state of polarization of the light 50. Therefore,
light 51 exiting the switch 11 also has horizontal polarization,
e.g., into and out of the plane of the paper of the drawing. The
light 51 enters the double refracting material (birefringent
material) 10 and is transmitted without any deflection and is
provided as output light 52 at the location and in the direction of
arrow 5a.
[0137] Referring to FIG. 5B, when the switch 11 is in the low
voltage state, it rotates the plane of polarization of the light 50
preferably 90 degrees, i.e., into the vertical plane, as is shown
by the vertical arrow 53 associated with the light 51. The
vertically polarized light enters the double refracting material 10
and its path is physically displaced, as is represented by dashed
line 54 resulting in output light 52 at the location and in the
direction of the arrow 5b.
[0138] Briefly referring to FIG. 5C, the electro-optical dithering
system 1 is shown having the light output 52 selectively switched
between the location of the arrows 5a when the switch 11 is in the
high voltage (no rotation of plane of polarization) state and the
location of the arrow 5b, which occurs when the switch 11 is in the
low voltage (polarization rotating) state. The light represented by
arrow 5a is horizontally polarized, and the light represented by
the arrow 5b is vertically polarized, as is represented in the
drawing of FIG. 5C. By selectively energizing and de-energizing or,
in any event, operating the switch 11 between two mentioned voltage
states, which switch the polarization characteristic of the light,
the location of the output optical signal 52 can be switched
between the locations represented by arrows 5a and 5b.
[0139] A modified optical display system 60 is shown in FIG. 6
using an electro-optical dithering system 1, as was described
above, in combination with an output polarizer (analyzer) 12'. The
analyzer 12' may be a linear (plane) polarizer or some other device
which can discriminate between the characteristics of light
incident therein, such as the direction of plane of polarization,
circular polarization, etc. The parts of the electro-optical
dithering system 1 include a birefringent material 10, such as a
calcite material described above, and a switch 11, such as one of
the liquid crystal cell devices described above, or some other
device, as will be appreciated.
[0140] The incident light 4 is received from a light source or
image source, such as a CRT 2 or some other device that delivers
unpolarized light output. Such unpolarized light 4 incident on the
birefringent material 10 is divided into two components 61, 62. The
light component 61 is horizontally polarized and it is transmitted
directly through the birefringent material 10 without deflection or
refraction. The light component 62 is polarized in the vertical
direction, and it is refracted so that its direction is changed
(path is deflected) in the manner shown representatively in FIG.
6.
[0141] It will be appreciated that here and elsewhere in this
description reference to directions is meant to be relative and
exemplary; for example, horizontal and vertical are meant to
indicate orthogonal relationship. Directions are exemplary and are
used to facilitate description and understanding of the
invention.
[0142] The horizontally polarized light component 61 and the
vertically polarized light component 62, the directions of
polarization being represented by the dots 63 and the arrow 64,
respectively, are incident on the switch 11. From the switch 11 the
light components 61, 62 are incident on the analyzer 12'. That
light component which has a polarization direction that is parallel
to the transmission axis of the analyzer 12' will be transmitted
through the analyzer, and the other light component will be
blocked. Depending on whether the switch 11 is in the operative
state to transmit light without rotation of the plane of
polarization or is in the operative mode to rotate the plane of
polarization of the light transmitted therethrough, one or the
other of the light components 61, 62 will be transmitted through
the analyzer 12' at a respective location represented by one of the
arrows 5a, 5b.
[0143] An exemplary use of the invention is illustrated in FIG. 7
for the CRT display 2 or for a liquid crystal display 20, for
example. The display 2, 20 has a resolution of some fixed number of
raster lines or rows of pixels that are updated periodically, for
example, 60 times per second.
[0144] Assume that the speed of the display is increased, for
example, is doubled to 120 times per second to re-scan the raster
lines and/or the rows of pixels. The switch 11 can be synchronized
with the switching of the display (CRT 2 or liquid crystal display
20) such that the raster images, for example, are alternately
displaced and not displaced, e.g., to locations 5a and 5b,
respectively. Such synchronization may be with respect to the
blanking pulse or some other signal.
[0145] The amount of such shifting or displacement can be adjusted
as aforesaid so that the displaced raster lines (or pixel rows)
interdigitate the non-displaced raster lines (pixel rows). The
information on the displaced and non-displaced rasters (pixel rows)
are selected to carry complementary information; and, therefore,
the resolution of the entire image displayed by the optical display
system 3 or 13 is increased by a factor of 2. The same technique
can be used to provide image coverage over the dead space between
adjacent pixels in a liquid crystal display (or in a CRT, e.g.,
where a shadow mask blocks transmission of electrons) or to cover
areas where conductors or other electrical connections or
components of a liquid crystal display, such as parts of an active
matrix array, are located, usually between adjacent pixels.
[0146] The display ordinarily would be refreshed or updated 60
times per second to cover both the odd and even raster lines.
However, by increasing the refresh or update rate to 120 times per
second and using the electro-optical dithering system to shift the
location of the output image or optical signal for part of the
time, essentially the odd and even raster lines, while unshifted,
can be refreshed or updated 60 times per second and the odd and
even raster lines, while shifted, can be refreshed or updated 60
times per second. The update or refresh times or rates presented
here are exemplary; others may be used.
[0147] In FIG. 7, assuming the display 2 is a CRT, the front face
70 has a plurality of odd raster lines and a plurality of even
raster lines. During operation of the CRT display 2, initially the
odd raster lines are scanned to produce a first subframe (field).
Subsequently, the even raster lines are scanned, and a second
subframe (field) is produced. The information produced during the
respective first and second subframes is referred to as
complementary and together complete an image (sometimes referred to
as a frame or picture) that is viewed. The time between producing
one subframe and the next is sufficiently fast that the eye of an
observer (viewer) integrates the respective first and second
subframe images to see one complete (composite) image. Similarly,
using the principles of the present invention, the space between
adjacent raster lines can in effect be scanned to produce
additional complementary image information. Thus, for example, the
odd lines can be scanned during the first subframe; the even lines
can be scanned during the second subframe; the odd lines can be
scanned during a third subframe but during which the switch 11 of
the electro-optical dithering system 1 is operative to cause
shifting of the image to the space between respective adjacent
pairs of odd and even raster lines; and finally during a fourth
subframe analogous to the third, the even raster lines can be
scanned while the electro-optical dithering system provides a shift
of optical output, to produce the shifted image between respective
pairs of odd and even raster lines. In this way resolution of the
output image produced by the optical display system 3 is increased
without having to increase the resolution or space between
relatively adjacent raster lines (scan lines) of the CRT display 2
and a similar technique can be used to increase the effective
number of the pixels, pixel rows, etc. to increase resolution of
the liquid crystal display 20.
[0148] Turning to FIGS. 8 and 9, an auto-stereoscopic display
system 80 is shown using the electro-optical dithering system 1 of
the invention. The principles of auto-stereoscopic display are well
known and will not be described in detail here. However, the
technique of obtaining the auto-stereoscopic display effect will be
described.
[0149] In the auto-stereoscopic display 80, there is a CRT display
2, which provides a light output 4, which is delivered to a linear
polarizer 12. The plane polarized light from the linear polarizer
12 is provided to the electro-optical dithering system 1, which
includes a surface mode device (surface mode liquid crystal cell)
switch 11 and double refracting material (birefringent material)
10. At the output of the electro-optical dithering system 11 is a
cylindrical lens array 81. The cylindrical lens array includes a
plurality of cylindrical lenses located in an appropriate
arrangement or pattern, as is known, to direct light to or toward
respective eyes 82, 83 of a person, or to some other device able to
detect or "see" the light received thereby. By providing a left eye
image to the left eye 82 and a right eye image to the right eye 83,
an individual viewing the auto-stereoscopic display system 80 will
discern a three dimensional or stereoscopic effect.
[0150] Using the electro-optical dithering system 1 of the
invention in combination with a display source, such as a CRT
display 2, a liquid crystal display 20, or some other display,
light beam steering can be accomplished to obtain the left eye and
right eye images. Therefore, auto-stereoscopic display systems can
be provided easily and relatively inexpensively.
[0151] In FIG. 9 the technique for obtaining beam steering for
auto-stereoscopic effect is illustrated. Incident light 4, which is
unpolarized, as is represented by the arrows and dots on the light
is incident on the plane polarizer 12. Alternatively, plane
polarized light can be provided from an image source or light
source, such as a liquid crystal display (and polarizer 12 may be
eliminated). In any event, the light which exits the polarizer 12
is plane polarized, for example, in a horizontal plane, as is
illustrated in FIG. 9. Such light then enters the switch 11 and
from there the light enters and transmits through the double
refracting material 10. Depending on whether the switch 11 rotates
the plane of polarization or it does not rotate the plane of
polarization of the light transmitted therethrough, the double
refracting material 10 will deflect or will not deflect the light
transmitted therethrough. In the case that the switch 11 does not
rotate the plane of polarization, and the above-described alignment
of the double refracting material 10 is provided, the light will
transmit directly through the material 10 without deflection as
light ray 90. When light ray 90 is transmitted through the
interface 91 between the cylindrical lens 92 of the cylindrical
lens array 81 and the external environment, such as air,
represented at 93, the light 90 will refract in the direction of
the arrow 94 toward the left eye 82 of the observer (viewer). The
light 90 traveling in the direction of the arrow 94 remains
polarized in the so-called horizontal direction, i.e., into and out
of the plane of the paper of the drawing.
[0152] However, when the switch 11 rotates the plane of
polarization of light transmitted therethrough, the double
refracting material 10 deflects the light, as was described above,
resulting in the light 95, which travels to a different location of
the interface 91 of the lens 92. The light 95 refracts at the
interface 91 and is bent or deflected in the direction of the arrow
96 toward the right eye 83 of the observer. The light 95 is
vertically polarized, i.e., the plane of polarization is parallel
with the plane of the paper of the drawing of FIG. 9.
[0153] In operation of the auto-stereoscopic display 80, left eye
and right eye images sequentially are produced by the display 2
(20) for example. When the left eye image is displayed, the switch
11 does not rotate the plane of polarization, and the light 90
follows the direction of the arrow 94 to the left eye 82 of the
observer. When the right eye image is produced by the display, the
switch 11 does rotate the plane of polarization so that the
material 10 deflects the light as light 95 which is refracted to
the direction of the arrow 96 to the right eye 83 of the observer.
For convenience of this description, it is understood that the
indices of refraction of the material 10 and the material of which
the lens 92 is made would be the same or about the same to avoid
further refraction at the interface therebetween; however, if there
is refraction there, such refraction can be taken into account, as
will be appreciated by those having ordinary skill in the art.
[0154] Referring to FIGS. 10 and 11, a display system 99, which
includes a liquid crystal display 100, is shown in top plan and top
section views. The display system 99 is similar to the several
other display systems described herein, such as those designated 3,
13, etc. The LCD 100 has a plurality of pixels 101 arranged in
respective rows 102 with dead space 103 between respective rows and
also at the edge 104 of the display 100. As is seen in FIG. 11, the
liquid crystal display 100 includes a substrate 105 on which an
active matrix array 106 is located. The liquid crystal display also
includes a further substrate 107, a space 108 between substrates
where liquid crystal material 109 is located, a seal 110 to close
the space between the substrates, and (not shown) appropriate
driving circuitry, as is well known. Light 120 represented by
respective arrows illustrated in FIG. 11 is provided by a light
source 121 and is selectively transmitted or not through the liquid
crystal display. The light 120 is plane polarized by a plane
polarizer 122 located between the light source 121 and the liquid
crystal display 100, and the light 120 is transmitted or is not
transmitted as a function of the plane of polarization thereof
relative to an analyzer 123, as is well known. An electrode 124 on
the substrate 107 and respective transistors and electrodes of the
active matrix array 106 on the substrate 105 apply or do not apply
electric field to liquid crystal material 109 at respective pixels
101 to determine whether or not the plane of polarization of light
120 is rotated and, thus, whether such light will be transmitted or
will not be transmitted through the analyzer 123.
[0155] The light 120 which is transmitted through the analyzer 123
is incident on the electro-optical dithering system (EDS) 1. The
electro-optical dithering system may be operated to not shift or to
shift the location of the light 120 to locations 5a, 5b in the
manner described above. If the optical signal at locations 5a, 5b
is complementary, as was described above, the resolution of the
optical display system 99 shown in FIG. 11 can be increased.
Moreover, as part of such increased resolution, the dead space 103
where transistors 131 and/or other components that are not light
transmissive in the active matrix array 106 effectively are covered
over by the shifted light 5b, for example. Therefore, using the
electro-optical dithering system 1 in a display system 99 as
described, the light blocking portions of the active matrix array,
of conductors, etc., can be in effect overcome or negated while the
overall resolution of the display is improved.
[0156] The parts shown in FIGS. 10 and 11 are in a relatively
horizontal relation showing dithering in a vertical direction. It
will be appreciated that dithering can alternatively be in a
horizontal direction or, if desired, multiple electro-optical
dithering systems 1 can be used in optical series in order to
obtain both vertical dithering and horizontal dithering.
[0157] The LCD 100 preferably is relatively fast acting to turn on
and off. Therefore, using the combination of the fast acting LCD
with the EDS1 the respective lines of one subframe of information
can be displayed by the respective rows of pixels of the LCD and
subsequently the interlaced lines of the next subframe can be
displayed by the same respective rows of pixels of the LCD.
[0158] The light source for the LCD 100 may be a pulsed source,
which produces light output in pulses or sequential bursts. In such
case, it is desirable to synchronize the light pulses or bursts of
the light source with the LCD and/or with the EDS1. Therefore, the
respective pixels of the LCD would transmit or block light when the
light source is producing a desired light output. The amount of
time that the light source is transitioning between a light
transmitting or light blocking state may be reduced and preferably
is minimized. Also, the LCD would be operative to transmit or to
block light when the light source is producing its intended light
output rather than when the light source is not producing a burst
of light or a desired light output. This tends to increase the
contrast of the output image, since the shutter element (LCD 100)
is not changing state when the light is pulsed, e.g. is changing
its state from light producing to not producing or vice versa.
[0159] The EDS1 and the LCD 100 preferably are synchronized.
Therefore, when the LCD is producing scan lines of information from
one subframe the EDS is in one state, and when the LCD is producing
scan lines of information from the other subframe, the EDS is in
its other state thereby causing the lines of one subframe to be
interlaced with the lines of the other subframe. The EDS and a
pulsating type light source also may be synchronized so that the
EDS switches states during the time that no light output or
non-optimal light output is produced by the light source. This
further enhances contrast of the display system 3, 13, 99.
[0160] Various circuitry may be used to obtain the aforementioned
synchronization. Two examples are shown, respectively, in FIGS. 12
and 13. In FIG. 12 an exemplary display system 140 is shown. In the
display system 140 a blanking pulse from a source 141 is supplied
to respective LCD buffer and EDS buffer circuits 142, 143 to
synchronize operation of them. The actual information signals from
line 144 indicating the light transmitting or blocking state, for
example, of the pixels of the LCD 100, for example, as is shown in
FIGS. 10 and 11, are provided the LCD buffer 142. Those information
signals are not delivered to the LCD 100, though, until
appropriately coordinated or synchronized with the blanking pulses.
The EDS 1 is connected to the EDS buffer 143 and receives its drive
signal from line 145 to dither or not the optical output from the
LCD 100. The EDS buffer also receives the blanking pulse from the
source 141 to synchronize delivery of the signals to the EDS with
such blanking pulses and/or with the operation of the LCD buffer
and information signals delivered to the LCD. The buffers 142, 143
can be synchronized with respect to each other by appropriate timed
operation thereof with respect to the blanking pulse; or,
alternatively, the buffers can be directly coupled to each other to
synchronize operation thereof so that the dithering function is
coordinated with switching of pixels or writing of information to
the LCD.
[0161] As another example of synchronization, FIG. 13 depicts a
display system 150 in which a pulsed light source 121, for example,
receives pulsed power from a power supply 151. A signal
representing the characteristics of the pulsed power from the
powers supply 151 is provided to the LCD buffer 142 and EDS buffer
143, which respectively receive information and power signals on
lines 144, 145 as described above. By synchronizing the LCD 100 and
EDS 1 with respect to each other and/or with respect to the pulsing
light source, the LCD can switch states as new information is
written thereto when the light source is not producing significant
light output, and/or the EDS can switch from direct transmission to
dithered transmission of light states when the light source is not
producing a bright output and/or the LCD is not in the process of
switching display states.
[0162] The foregoing are but two examples of synchronization useful
in the various display systems and embodiments of the invention. It
will be appreciated by those having ordinary skill in the art that
many other types of synchronizing techniques may be used to obtain
the desired synchronization.
[0163] Although it may be desired to obtain full interlacing and
separation of respective lines as in a CRT display, for example,
even less than full interlacing, e.g., an amount of displacement
that does not fully separate the lines but nevertheless reduces the
amount of overlap thereof, will tend to reduce the above-mentioned
jitter and improve the optical output of the LCD.
[0164] Interlacing or dithering can be used to effect vertical
displacement (changing of location of the optical output signal),
horizontal (lateral) displacement, and/or diagonal displacement of
the optical signal, such as that produced as the output from a
pixel of a display, e.g., a CRT, LCD, or any other type of display.
The direction of displacement will depend on the orientation of the
various components of the optical system. For example, in the EDS
of FIG. 1 having orientation of axes of components shown in FIGS.
4A, 4B and 4C, vertical displacement will occur. However, by
changing the relative orientation of the axes by 45 degrees or 90
degrees, the displacement as a function of the state of the switch
11, for example, can be changed to diagonal or horizontal.
[0165] Using the vertical displacement of optical signals by the
EDS1 in combination with a display, such as an LCD, for example, it
possible in effect to double the resolution of the display in the
manner described above. Thus, in a sense, the EDS becomes an
optical line doubler which doubles the number of horizontal lines
of resolution of the display system. However, by using both
vertical and horizontal displacement functions in a display system,
it is possible to obtain in effect up to quadruple the resolution
of the display relative to operation of the display absent the
EDS.
[0166] Referring to FIGS. 14 and 15A-15E an EDS system 201 used
with a display 202, in the illustrated embodiment an LCD (although
other types of displays can be used), is shown as a display system
203. In FIGS. 14 and 15A-15E reference numerals which designate
parts that are the same or similar to those described above are the
same as the reference numerals that designate such above-described
parts except being increased by the value 200. Thus, display system
203 is similar to display systems 3, 13, 99, etc. mentioned
herein.
[0167] However, the EDS system 201 of display system 203 includes
two EDS portions 201v and 201h, which respectively can be operated
to obtain vertical and horizontal displacement of the optical
signal transmitted therethrough. Each EDS 201v, 201h includes,
respectively, a double refracting material 210v, 210h and a switch
211v, 211h. For example, each double refracting material may be a
calcite crystal and each switch may be a surface mode
(birefringent) liquid crystal cell. The source of optical signals
in display system 203 is a flat panel liquid crystal display 202,
although other types of displays may be used. The LCD 202 provides
light output that is plane polarized, and, therefore, a separate
polarizer like the polarizer 12 of FIG. 1, for example, may be
unnecessary in the illustrated embodiment of display system 203. It
will be appreciated that although the display system 203 uses two
EDS devices or portions, the principles of the invention may be
used with more than two EDS portions to obtain not only horizontal
and vertical displacement but also displacement in even another
direction.
[0168] The relative orientation of the axes of the respective
components of the display system 203 is shown in FIGS. 15A-15E.
Plane (linear) polarized light having a horizontal plane of
polarization is provided by the LCD 202, as is seen in FIG. 15A. In
the vertical displacement EDS 201v, the axis of the birefringent
liquid crystal switch 211v shown in FIG. 15B is oriented at 45
degrees to the plane of polarization of light from the source 203;
in the illustrated embodiment, such orientation is actually -45
degrees relative to vertical, for example. The projection of the
axis of the double refracting material 210v is vertical, as is seen
in FIG. 15C. In the horizontal displacement EDS 201h, the axis of
the birefringent liquid crystal switch 211v is oriented at +45
degrees to the vertical (FIG. 15D), and the projection of the axis
of the double refracting material 210h is horizontal (FIG. 15E).
The actual alignments may be slightly different from those
illustrated to accommodate or to compensate for residual
birefringence in the liquid crystal switches and/or for other
purposes. Also, if desired wave plates and/or other optical
components may be included with one or more of the EDS devices
201h, 201v to compensate for such residual retardation and/or other
factors.
[0169] The display system 203 can be operated in four different
states. In one state shown in FIG. 16A with both EDS devices 201v,
201h of FIG. 14 not displacing light, the light from the display
source 202 is transmitted without being displaced; this may occur
with birefringent switches 211v, 211h being in high voltage,
non-polarization rotating state and low, polarization rotating
states, respectively. In a second state shown in FIG. 16B with EDS
device 201v, 201h respectively not displacing and displacing light,
the light from the display source 202 is transmitted while being
horizontally, but not vertically displaced; this may occur with
both birefringent switches 211v, 211h being in high voltage,
non-polarization rotating state. In a third state shown in FIG. 16C
with both EDS devices 201v, 201h displacing light, the light from
the display source 202 is transmitted while being displaced both
horizontally and vertically; this may occur with both birefringent
switches 211v, 211h being in low voltage, polarization rotating
state. In a fourth state shown in FIG. 16D with EDS device 201v,
201h respectively displacing and not displacing light, the light
from the display source 202 is transmitted while being vertically,
but not horizontally displaced; this may occur with EDS 211v in the
low voltage, polarization rotating state and birefringent switch
211h being in high voltage, non-polarization rotating state.
[0170] In FIG. 17 is illustrated a composite of the display
conditions depicted in FIGS. 16A through 16D. By using relatively
fast acting LCD as the display source 202 and two EDS devices 201h,
201v synchronized and operated in the manner just described so that
the pixels first are shown in the manner in FIG. 16A, then as in
FIG. 16B, etc., sufficiently quickly that the observer's eyes tend
to integrate the respective images, a high resolution image with a
pixel density like that shown in FIG. 17 can be obtained. It will
be appreciated that an exemplary optimum improvement in resolution
using the display system 203 in the described manner can increase
resolution of the display 202 by approximately a factor of 4.
[0171] Thus, it will be appreciated that the respective switches
211v, 211h may be operated according to the following table to
obtain the above-described operation controllably to vertically
shift or displace and/or to horizontally shift or displace the
optical signals from the display 202. High means electrically
operated so as to be not polarization rotating and low means
electrically operated so as to be polarization rotating, although
other conventions may be used.
TABLE-US-00001 TABLE 1 Switch 211v Switch 211h High Low High High
Low Low Low High
[0172] In the present invention the switches and double refracting
material may be substantially optically transparent. Therefore,
those components do not tend to absorb light. The use of such
components in a display system 203, for example, does not
ordinarily significantly reduce the brightness of the display
output. Although two or more images are placed sequentially in the
field of view provided by the display system 3, 13, 99, 203, etc.,
brightness of the display output is not diminished; rather, image
resolution can be increased.
[0173] Other types of birefringent materials and/or devices may be
used in place of or in addition to the calcite material double
refracting device 10 described above. For example, other types of
crystal materials and/or minerals may be used; the amount of
displacement between an unrefracted optical signal and a refracted
optical signal by such double refracting material would depend on
index of refraction characteristics of the double refracting
material, the index of refraction of the environment external of
the double refracting material, wavelength of optical signal, and
distance the optical signal travels in the double refracting
material.
[0174] Another double refracting material which may be used in the
invention as component 10, for example, is liquid crystal material.
Liquid crystal material, such as nematic liquid crystal and smectic
liquid crystal material may be birefringent and may be used. Other
types of birefringent liquid crystal materials also may be used. By
organizing or orienting the liquid crystal material in a particular
organization or orientation, the transmission of light therethrough
with or without refracting the light can be dependent on the
direction of electric vector of the light, e.g., the plane of
polarization of plane polarized light.
[0175] A polymer liquid crystal may be especially useful as such a
double refracting material, for such material both can have a
relatively large birefringence and also can be formed into a solid
material which maintains the orientation of the structure of the
liquid crystal material thereof. Polymer liquid crystal materials
are known.
[0176] However, if the double refracting material were of a liquid
crystal material whose structural orientation or organization could
be switched, e.g., in response to application of a prescribed input
such as an electric field (or removal of such field or changing
voltage or some other characteristic of the field, etc.), then the
function of the two components of an EDS may be replaced by a
single switchable liquid crystal shutter type device. In this case
the liquid crystal shutter could provide one index of refraction or
birefringence characteristic to refract light transmitted
therethrough a given amount and a different index of refraction
characteristic with no birefringence so as not to refract such
light or with parameters to refract the light a different
amount.
[0177] An embodiment of display system 203' which uses a pair of
switchable liquid crystal cells 270, 271 associated with a liquid
crystal display 202' is shown in FIGS. 18 and 19. Each of the
liquid crystal cells 270, 271 functions as a combination of
birefringent or double refracting material 210h, 210v and as a
switch 211h,211v. The liquid crystal cells may be, for example,
aligned like a birefringent liquid crystal cell using nematic or
smectic liquid crystal material between a pair of glass plates. The
plates are treated so the liquid crystal is aligned generally in
the same direction at both plates without twisting; and, therefore
is so aligned throughout the cell. The liquid crystal material
preferably is tilted, e.g., at 45 degrees, to obtain a desired
birefringence characteristic; but although tilted, the projection
of the axis of the liquid crystal structure would be in the same
plane as the plane of polarization of incident light thereon to
obtain the desired birefringence characteristic. The exemplary
arrangement of axes of the display system 203' is shown in FIG.
19.
[0178] By changing the electrical drive signal to the respective
liquid crystal cells 270, 271, the index of refraction
characteristics thereof can be changed, and, as a result, the
location of the optical signal transmitted therethrough can be
changed, e.g., dithered as described herein. For example, for plane
polarized light incident on liquid crystal cell 270 which has
liquid crystal therein structurally aligned such that the light
experiences the ordinary index of refraction of the liquid crystal
and no birefringence, the light will transmit directly through the
liquid crystal cell without refraction. However, if the liquid
crystal is structurally aligned such that the light experiences the
extraordinary index of refraction and, thus, birefringence, the
light will be refracted at the interface between the liquid crystal
material and the glass plate or the like forming or at one surface
of the liquid crystal cell 270 at one side; and the light will be
refracted again at the interface between the liquid crystal and the
glass plate etc. at the other surface of the liquid crystal cell so
as to be parallel with the light incident on the liquid crystal
cell 270 but displaced from the extension of the transmission axis
of the incident light.
[0179] Thus, by selectively operating, e.g., energizing and
deenergizing or changing energization level, the liquid crystal
cells 270, 271, then, can change the location of the optical signal
output by the display system 203'. The liquid crystal should be
aligned to present to the light transmitted therethrough either the
ordinary or extraordinary axis or index of refraction and
appropriate birefringence characteristic as described above. If
only one liquid crystal cell 270 is used, the optical signal can be
changed back and forth in one plane or direction. If two liquid
crystal cells 270, 271 (like the cell 270, for example) are used
and are arranged such that the axes thereof are non parallel, then
the optical signal can be changed back and forth in two planes or
directions. Such non-parallel alignment may be perpendicular
alignment to obtain up/down dithering and left/right dithering
relationships. Since the plane of polarization of light incident on
the liquid crystal cell 271 should be parallel to the axis of that
cell, a half wave plate 272 may be placed between the liquid
crystal cells 270, 271 to rotate the plane of polarization of the
light exiting the liquid crystal cell 270. For example, the axis of
such half wave plate may be oriented at 45 degrees relative to the
plane of polarization, i.e., half way between the 90 degrees
desired rotation. It is noted that a polarizer 12 is shown in FIGS.
18 and 19; such polarizer helps assure the quality of polarization
of the light from the display; but such polarizer can be eliminated
if the output from the display is of sufficient quality of
polarization, e.g., minimal amount of unpolarized light included
therein.
[0180] The EDS1, 201 may be used in a display system 3, 13, 99,
203, 203', etc. which is monochrome or multicolor. Operation for a
monochrome display system would be, for example, as is described
above. One embodiment exemplifying operation for a multicolor, such
as a red, green and blue (rgb), display system can employ the
above-described type of operation for each color. Therefore, when
one color or a group of colors is being displayed by respective
pixels of such a color display, the optical signal output can be
either transmitted without displacement or with displacement in the
manner described above. As is depicted schematically in FIG. 20,
part of a display 202', e.g., similar to display 202, is shown
including three representative adjacent pixel triads 281, 282, 283,
each including a red, green and blue pixel portion. The display
202' may be operated in a color frame sequential mode in which
respective red, green and blue frames or images are produced in
time sequence. In this case all red pixels of respective pixel
triads 281, 282, 283, etc. would be red where it is desired in the
final image to have red light; subsequently green and then blue
pixels of the image would be created. Alternatively, the respective
red, green and blue pixels of respective triads can be displaying
respective colors simultaneously. In either case, the principles of
the invention using the EDS1, 101, etc. may be used to increase
resolution of the output image in the above-described manner.
[0181] However, the EDS may be used for the purpose of selectively
dithering (displacing) less than all of the color frames of a
multicolor display, especially if the display is operated in a
color frame sequential mode. For example, the dithering function
can be used selectively to displace or not the green optical signal
(light produced during the green frame) of the display 3, 13, 99,
203, 200'; however, the EDS may be used so it does not selectively
to dither the optical signal during one or both of the other color
frames. Since the human eye is more sensitive to green light than
to red or blue light, a significant enhancement of the apparent
resolution of the multicolor display can be achieved by only
selectively dithering the green light optical signal. If desired,
the green and red optical signals can be selectively dithered
without selectively dithering the blue optical signal; and this
will result in an even greater apparent resolution of the
multicolor display than if only the green optical signal were
selectively dithered. Since the human eye is not as sensitive to
blue light as it is to red or green light, the fact that resolution
of the blue light or blue frame component of the overall image is
not enhanced by the dithering of the invention may not
significantly reduce the resolution of the composite multicolor
output image. By reducing the amount of dithering required, it is
possible that the complexity and/or cost of the electronic drive
and timing circuitry employed in the invention can be reduced.
[0182] Referring to FIGS. 21, and 22A-22F, there is shown a
schematic illustration depicting a time sequence of operation of
the invention using a segmented display system 403. FIG. 22A
represents the output operation of the display system 403 at one
period of time; FIG. 22B represents operation at the next period of
time; and so on. In FIGS. 21 and 22A-22F the various parts which
correspond to parts described above are identified by the same
reference numerals but increased to a 400 series. Thus, display
system 3, 13, 99, 203, 203', etc. in FIGS. 21 and 22A-22F is
designated 403, for example.
[0183] The face 470 of the display system 403 in FIGS. 21 and
22A-22F is divided into three separate segments 470a, 470b, 470c.
More specifically, the display 402 may include a CRT or an LCD 2,
20, 102, etc., and between the display and the viewer, for example,
is at least one, and possibly several in series, electro-optical
dithering system 1, 11, 21, 101, as was described in the several
embodiments above. For simplicity of description here the display
system 403 is described with only one EDS, though.
[0184] The EDS 401 includes, for example, a double refracting
material 410 and a switch 411 such as a surface mode liquid crystal
cell. However, the switch 411 is segmented into several areas which
can be separately addressed to change the optical characteristics
thereof. The switch 411 is shown in FIGS. 21 and 22A-22F as having
three separate segments 411a, 411b, 411c; but it will be
appreciated that the switch may have fewer or more segments. Each
segment 411a, 411b, 411c can be separately operated to change or
not to change the direction of plane of polarization of light
transmitted therethrough. Each segment can be a separate liquid
crystal cell or each can be part of the same liquid crystal cell
which has an electrode arrangement which permits operating of the
different parts separately.
[0185] In FIGS. 22A, 22B, 22C, respectively, (with reference also
to FIG. 21) the first subframe (field) of information is written
sequentially to the upper, middle and lower thirds 402a, 402b, 402c
of the display 402 for direct transmission without being dithered
or shifted in position. By the time the information is being
written to the middle third of the display 402, the information
written to the top third begins fading; and by the time the
information is being written to the bottom third, the information
at the top third is substantially fully faded and that at the
middle third is beginning to fade.
[0186] In FIG. 22D the start of information representing the second
subframe (field) being written to the display 402, initially to the
top third 402a of the display, is shown. The dithered information
optical signal in the top third of FIG. 22D is represented by the
illustrated dashed lines. Since such information is for the second
subframe, the optical signal output is intended to be
dithered/changed; however, at this time the image or optical output
presented by the middle third 402b of the display 402 has not
completely faded. Therefore, if the optical output of the entire
display 402 were dithered at this time, the optical information or
optical output signal still being displayed at the middle third
would be shifted to an incorrect location. To avoid this wrongful
shifting of the optical signal from the middle third at this time,
only the top third 402a of the display 402 is dithered. Preferably
the top third actually is dithered when the previous image there
has faded; and that actually can occur at the time period
represented in FIG. 22C.
[0187] At the time period represented by FIG. 22D the middle third
of the display 402 has faded, and is dithered; and at the time
period represented by FIG. 22E, information is written to that
dithered middle third of the display, and the bottom third which
has faded is dithered. At the time period represented by FIG. 22F,
the dithered image information is written to the bottom third of
the display 402 and the top third is dithered since the information
previously written there by now has faded.
[0188] The above-described operation of the display system 403 can
continue sequentially as the respective subframes are sequentially
displayed, e.g., the optical signals comprising such subframes are
presented as the output of the display system. In each subframe the
different respective parts or segments are sequentially dithered or
not preferably so that a segment is already undithered or dithered
before the raster, line, row, etc. of information to form the
optical signal is written to the respective pixels of that segment.
The dithering or undithering switching action, e.g., operation of
the respective switches 411a, 411b, 411c from one state to the
other, also can be carried out as the action of writing information
to a segment is carried out; but ordinarily it would be better to
effect the dithering or undithering when the segment is relatively
blank (e.g., information there has faded) to avoid undertaking a
dithering or undithering action while an optical output is being
displayed.
[0189] It will be appreciated that the segmentation technique may
be used with display system which uses a CRT display, a liquid
crystal display or some other type of display. The segmented switch
411 approach also is useful to remove artifacts caused by a
relatively slow acting LCD.
[0190] Further, it will be appreciated that the various EDS
embodiments of the present invention and display systems using such
EDS embodiments are operative to move, shift, translate, etc. an
output optical signal from one location to another without
substantially affecting brightness of the display system or optical
signal. The components of the EDS generally are optically
transparent, and, therefore, other than a relatively minor amount
of absorption of light transmitted therethrough, there may be
otherwise relatively little reduction in light intensity.
Therefore, the features of the invention may be used for the
various purposes described herein, for example, to increase
resolution, to cover or to reduce the effective optical dead space,
etc., without reducing brightness of the optical output.
[0191] A passive dithering system 500 in accordance with one aspect
of the present invention is illustrated schematically in FIG. 23 in
an optical display system 501. The passive dithering system 500 as
shown is used in connection with a display 502 which produces an
output of polarized light, such as might be produced by a twisted
nematic (TN) based flat panel liquid crystal display 504
incorporating a linear polarizer 506 or by a CRT display with an
added linear polarizer interposed, as is the polarizer 506, between
the CRT display and the dithering system 500. The dithering system
500 includes a pair of double refracting or birefringent material
layers 508h, 508v, such as a calcite crystal material, separated by
a half wave plate 510. A wave plate 512, such as a quarter wave
plate, turns plane polarized light into circularly polarized light;
circularly polarized light can mathematically be resolved into
equal amplitudes of vertical and horizontal plane polarization
separated in phase by 90.quadrature.. Thus, the quarter wave plate
in a sense separates incident plane polarized light into relatively
orthogonal plane polarized components for delivery to the
birefringent material 508h as an input for the dithering system
500. The effect of the passive dithering system 500 can be to
enhance the resolution of the display output by reducing fixed
pattern noise in the display. The passive dithering system 500 can
increase the number of output pixels provided simultaneously by an
optical display system.
[0192] In FIG. 24a a very generalized example of the function of
the passive dithering system 500 is shown considering an image 520a
created by a single pixel 520 of the flat panel liquid crystal
display 504 separated from adjacent pixels 522 in the display by
optical dead space 524. The birefringent material 508h effectively
creates a double image 520b of the image 520a which is displaced or
dithered in, for example, a horizontal direction, as is shown in
FIG. 24b. The second birefringent material 508v, which receives
both images 520a and 520b, creates a second pair of images 520c,
520d displaced vertically from the first pair of images as is shown
in FIG. 24c. In this way, the image produced by a single pixel,
such as exemplary pixel 520, can be made to fill or at least to
increase the fill of the optical dead space 524 between the pixels
522 which is typically used to electrically isolate adjacent pixels
and to accommodate circuitry and electrical components. In other
words, the dithering system 500 increases the fill factor of the
display 502 as viewed. Therefore, the passive dithering system 500
expands or enlarges the respective pixels. In the example of FIGS.
24a, 24b, 24c, the pixel 520a can be said to have been expanded or
enlarged to cover the area shown in FIG. 24c being occupied by
images 520a, b, c, d.
[0193] If desired, the locations at which the passively dithered or
created images 520b, c, d are placed may be other than or in
addition to the optical dead space 524. For example, such image may
be placed to overlap another image or pixel, to overlap several
images or pixels, image(s) and optical dead space, etc., for
example, as is described further below.
[0194] One possible manner of orienting the axes of the optical
components of the passive dithering system 500 in the optical
display system 501 is shown in FIG. 25a. The linear polarizer 506
or polarized display output is oriented vertically so that an image
of a pixel emerging from the polarizer or display will be linearly
polarized in a vertical direction, as is shown at pixel 520a in
FIG. 25b. In FIGS. 25b-g the respective arrows represent direction
or plane of polarization of light. The quarter wave plate 512 is
aligned with its axis 512' at 45.quadrature. to the plane of
polarization of the plane (linearly) polarized light incident
thereon, e.g., from the polarizer 506. With this arrangement the
quarter wave plate 512 converts the incident plane polarized light
to circularly polarized light. Circularly polarized light in effect
can be resolved into two orthogonal plane polarized components
520a', 520a'' which are out of phase by 90.quadrature., and such
resolution is shown for pixel 520a in FIG. 25c. The birefringent
material 508h is arranged relative to the linear polarizer 506 and
quarter wave plate 512 with the projection of its optic axis 508h'
into the plane of the polarizer 506 and quarter wave plate 512
being horizontal, e.g., parallel to the polarized light component
520a'' and perpendicular to the polarized light component 520a'.
The axis 510' of the half wave plate 510 is oriented at +22.5
degrees to vertical, and the second birefringent material 508v is
oriented with the projection of its optic axis 508v' into the plane
of the polarizer 506, etc. being vertical. It will be appreciated,
however, that this arrangement is only one of many possible
arrangements of the axes of the components which would produce the
dithering or pixel expanding or enlarging effect described herein
and/or similar or equivalent effects.
[0195] With further reference to FIGS. 25a-g, which additionally
illustrates the path of an image through the passive dithering
system 500, the path of the exemplary pixel image 520a through the
system will be described in greater detail. As oriented, the linear
polarizer 506 transmits optical information in the form of pixel
images from pixels in the display which have effected the light
transmitted therethrough so as to be polarized in the direction of
the transmissive axis 506' of the linear polarizer. For the
exemplary image 520a in FIG. 25b, the light would thus be polarized
in a vertical direction represented by arrow 520a'.
[0196] Since the plane of polarization of the image 520a is at a 45
degree angle to the optic axis 512' of the quarter wave plate 512,
the quarter wave plate converts the plane polarized incident light
to circularly polarized light. The circularly polarized light can
be resolved or considered as two plane polarized light components
520a', 520a'' (FIG. 25c) the planes of polarization of which are
orthogonal and the phases of which are 90.dbd. out of phase. It
will be appreciated that other means or techniques may be used to
divide the plane polarized light, which is delivered to the
birefringent material 508h, into plural components which are acted
on differently by the birefringent material, for example acted on
in the manner illustrated in FIGS. 25a-g or in some other
manner.
[0197] Since the plane of polarization 520a'' of some of the light
representing pixel 520a in FIG. 25c, which is incident on the
birefringent material 508h, is in the place of the optic axis 508h'
and encounters birefringence due to the tilting of the optic axis
508h' as was described above, e.g., with respect to FIGS. 1-6, such
light is refracted by the birefringent material to form the pixel
520b at a location displaced, for example, to the right from pixel
520a, as is seen in FIG. 25d. Also, since the plane of polarization
520a' of some of the light representing pixel 520a in FIG. 25c,
which is incident on the birefringent material, 508h, is
perpendicular to the optic axis 508h', the path of such light is
not altered by the birefringent material, and pixel 520a is located
as is shown in FIG. 25d. Summarizing, as the orthogonally related
polarized components pass through the birefringent material 508h,
one of the polarized components will be refracted and deflected
horizontally while the other component will be unaffected. As a
result, the birefringent material 508h will yield two images, an
image 520a in its original location and a horizontally displaced
image 520b with the images being polarized orthogonally to one
another.
[0198] The images 520a and 520b then pass through the next optical
component in the passive dithering system 500, the half wave plate
510, where the plane of polarization of each of the images 520a and
520b is effectively rotated +45 degrees so that the plane of
polarization of each image is as shown in FIG. 25e. The
polarizations represented by arrows 520a''' and 520b'' for pixel
images 520a, 520b in FIG. 25e are the vector equivalents to the
polarizations represented by the respective arrows 520a', 520a'',
520b', 520b'' for pixels 520a, 520b in FIG. 25f. Two of such vector
equivalent polarizations of FIG. 25f are parallel to the optic axis
508v' of the second birefringent material 508v, and two are
perpendicular to the optical axis 508v'. Due to such relationships
of the planes of polarization of each of the images 520a and 520b
in FIG. 25f to the axis 508v' of the birefringent material 508v,
the images 520a and 520b will be resolved into their orthogonally
polarized components 520c, 520d, respectively, as these components
pass through the birefringent material 508v. The polarized
components of each image 520a, 520b which are parallel (520a',
520b''') to the plane containing the axis 508v' will be refracted
and deflected vertically to result in images 520c and 520d while
the other polarized components 520a'', 520b', which are
perpendicular to the axis 508v' (or the plane containing that axis)
will be unaffected. As a result, the original image 520a is
dithered into four images 520a, 520b, 520c and 520d. These images
may be of substantially equal intensity.
[0199] While the passive dithering system 500 discussed above was
illustrated as doubling images in two directions, horizontal and
vertical, a passive dithering system that doubles the image in only
a single direction only is also possible. Such a system may include
a single birefringent material used in conjunction with a display
producing a polarized or non-polarized output to result in a
doubled pixel image or to perform passive line doubling.
[0200] Also, it will be appreciated that the above description with
respect to FIGS. 23, 24a-c, and 25a-g is exemplary, and other
arrangements of components to compose a passive dithering system to
obtain a desired pixel enlarging, expanding, shifting, etc. may be
employed. For example, a birefringent liquid crystal cell may be
used as a wave plate: a surface mode liquid crystal (e.g., U.S.
Pat. No. Re. 32,521) cell or a pi-cell liquid crystal cell (e.g.,
U.S. Pat. No. 4,582,396) which is tuned to the desired retardation
of quarter wave or half wave are examples. The birefringent
material may be liquid crystal cells. Various crystals, prisms, or
other devices may be used to provide birefringence and/or
polarizing functions. By changing the amount of birefringence and
optical path length through a birefringent material the amount of
deflection of a pixel image can be determined. Changing relative
orientation of axis of one or more components can change the
direction a pixel is shifted. Of course, the illustrated alignment
of components is relative and reference to vertical, horizontal,
into or out of the plane of the paper or drawing only is for
convenience of description. All such equivalent and alternate or
additional materials and/or alignments of components and functional
operation are considered within the scope of the present
invention.
[0201] As is evident from the description above with respect to
FIGS. 23-25 and the description below with respect to FIGS. 26-32,
in an exemplary passive dithering system of the invention,
birefringent material may be used to change location of light
representing a pixel, an image of a pixel, or another optical
signal (for convenience sometimes simply referred to as pixel). The
passive dithering system, therefore, is able to change the apparent
location of the pixel. Such change may result in an increase in or
enlarging of the pixel size, in a doubling or duplicating of the
pixel, etc; such change in location may simply be a change in the
apparent location of the pixel without any doubling, duplicating,
changing of size, etc.
[0202] When the passive dithering system is used to dither a pixel
to change size, e.g., effectively to enlarge the pixel, the
dithering system may cause there to be multiple spaced apart pixels
derived from the original pixel or pixels. Alternatively, one or
more of the multiple pixels may overlap or be sufficiently adjacent
to another pixel as to be considered touching or in any event not
spaced apart. As an example, by enlarging a pixel to cover optical
dead space of a display, the apparent resolution of the display
usually is increased even without increasing the actual number of
pixels driven by the display.
[0203] In the case of a pixel being expanded using an exemplary
passive dithering system according to the invention, light from the
original pixel is distributed over a viewed area that is larger
than the area of the original pixel of the display. However, the
total amount of light reaching the eye of an observer, for example,
remains substantially the same as that provided by the original
pixel before being expanded because the components of the passive
dithering system are not the light absorbing or blocking type.
Therefore, the apparent brightness of a display when used in
combination with such a passive dithering system would tend not to
be diminished.
[0204] The passive dithering system of the invention is described
with respect to several embodiments. These embodiments are examples
of components and arrangements of components to obtain the passive
dithering effect of the invention. Many other components and
arrangements of components also may be used to obtain passive
dithering, as will be appreciated by those who have ordinary skill
in the art.
[0205] For example, in the embodiments of passive dithering systems
illustrated in FIGS. 23-27 a half wave plate is used to set up
particular plane polarization conditions, such as direction of
plane of polarization; and in the embodiments illustrated in FIGS.
28-32 a quarter wave plate is used to set up particular plane
polarization conditions. In the embodiments of passive dithering
systems illustrated in FIGS. 23-25 and 28-30 the passive dithering
systems receive plane polarized light input from a liquid crystal
display that provides plane polarized light output or from another
display which may not provide a plane polarized light output but
which is used in combination with a plane polarizer to obtain the
desired polarized light input to the dithering system. However, in
the embodiments illustrated in FIGS. 26, 27, 31 and 32 the passive
dithering systems receive and operate on unpolarized light.
[0206] The components of the respective passive dithering systems
described with respect to FIGS. 23-32 are arranged to expand a
single pixel or light forming that pixel to four pixels which are
arranged in a two by two rectilinear array, such as that depicted
by pixels 524a-d in FIG. 24c. However, it will be appreciated by
those who have ordinary skill in the art that the passive dithering
systems of the invention may be adjusted, including changing of
optical axes orientations, changing of birefringence value, adding
or deleting components, etc., to expand the single pixel to fewer
or to more than four pixels and to arrange those pixels in a
rectilinear array or in another pattern or arrangement. Also,
although quarter wave plates and half wave plates are disclosed
useful in passive dithering systems, it will be appreciated that
other types of wave plates or appropriate means may be used, too.
Preferably the wave plates and/or other appropriate means provide
the same or substantially the same wave plate function, such as
optical retardation, for all, for a relatively wide range of
wavelengths of light or at least for the wavelength range intended
to be used.
[0207] Using the principles of the invention to expand a pixel
formed of plane polarized light, the incident plane polarized light
is divided into two orthogonally related plane polarized
components. A quarter wave plate may be used for this function. A
quarter wave plate having its optic axis aligned at 45.quadrature.
to the plane of polarization of incident plane polarized light
converts the plane polarized light to circular polarized light,
which can be resolved to orthogonally related plane polarized
components which are of equal amplitude but are out of phase by
90.quadrature.. If the quarter wave plate is oriented at other than
45.quadrature. to the plane of the incident plane polarized light,
the output therefrom will be elliptically polarized, which also may
be resolved to respective plane polarized components possibly with
phases that differ by other than 90.quadrature. and/or amplitudes
which are not equivalent. Means other than a quarter wave plate
also may be used to effect such separating of the incident plane
polarized light into respective distinguishable components. The
incident plane polarized light, which is resolved to respective
distinguishable components, is directed to the birefringent
material, which separates the components in effect by directing
them to different locations and thereby expands the apparent area
of the pixel.
[0208] For unpolarized light input to a passive dithering system of
the invention used, for example, to expand a pixel, the incident
light is directed to birefringent material usually without the need
to plane polarize the incident light. Since the incident light
already includes or can be considered as being resolved to two
orthogonally related plane polarized components, the birefringent
material separates the respective orthogonally plane polarized
components in effect by directing them to different locations and
thereby expands the apparent area of the pixel.
[0209] Referring to FIG. 26, there is shown a passive dithering
system 500' of an optical display system 501' used in connection
with a display 532 which produces non-polarized (unpolarized)
light, such as a nematic curvilinear aligned phase liquid crystal
(NCAP), polymer dispersed liquid crystal (PDLC) or liquid crystal
polymer composite (LCPC) based flat panel liquid crystal display.
The passive dithering system 500' of FIG. 26 includes the same
optical components as the dithering system 500 described above
relative to FIG. 23-25, such as a birefringent material 508h, a
wave plate 510 and a second birefringent material 508v. In this
instance, neither the passive dithering system 500' nor the display
532 is provided with a linear polarizer to polarize the output
light from the display.
[0210] In operation, the passive dithering system 500' when used in
connection with a display producing non-polarized light will result
in horizontal and vertical pixel image doubling similar to that
produced by the passive dithering system 500 and shown in FIGS.
23-25. In fact, the orientations of the optic axes 508h', 510' and
508v' of the components 508h, 510, 508v, shown in FIGS. 26 and 27
may be the same as when those components are used in connection
with a display producing a polarized output. (If it were desired to
use the dithering system 500 with an unpolarized light producing
display 532, the polarizer 506 could be placed optically between
the display 532 and the dithering system 500 in the manner shown in
FIGS. 23-25, for example).
[0211] One possible set of orientations for the optic axes of these
components is shown in FIG. 27. The optic axis 508v' of the first
birefringent material 508v is vertical and is tipped as was
described above, the axis 510' of the half wave plate 510 is at
+22.5.quadrature. to vertical and the projection of the optic axis
508h' of the second birefringent material 508h into the plane of
the page is horizontal and is tipped as was described above.
Although the light which enters the first birefringent material
508v is non-polarized, it can be visualized as polarized light
resolved into two orthogonal components such as a vertical and
horizontal polarized component as shown by arrows in the exemplary
pixel image 534a created by a corresponding pixel 534 in the
display 532.
[0212] The components 508v, 510 and 508h then function basically as
described above in FIG. 25. The first birefringent material 508v
will resolve the individual components of the pixel image 534a into
their orthogonal components and will dither (shift location of) one
polarized component relative to the other polarized component to
produce a vertically displaced double image of the pixel image
534a. The half wave plate 510 will then rotate the polarization
components of those images as in FIG. 25e so they are at
45.quadrature. angles to the optic axis 508h' of the second
birefringent material 508h where the images will be doubled and
displaced in a horizontal direction as in FIG. 25g. As a result,
the initial image 534a is doubled in the vertical direction and
then the initial image and the doubled image are doubled in the
horizontal direction to produce four adjacent images which may
substantially cover the portion of the original pixel 534a in the
display and dead space surrounding the pixel in one vertical and
horizontal direction.
[0213] FIG. 28 illustrates an alternate embodiment of a passive
dithering system 540 of an optical display system 541 shown with an
optical display which produces linearly polarized output light,
such as by a twisted nematic based flat panel liquid crystal
display 542 incorporating a linear polarizer 544. The passive
dithering system 540 includes a first birefringent material 546v, a
second birefringent material 546h and quarter wave plates 548, 549,
respectively, interposed between the source of polarized light
(display 542 and, if used, polarizer 544) and the first
birefringent material 546v and between the birefringent materials
546h and 546v. One possible set of orientations for the axes of the
linear polarizer 544 of the display, the birefringent materials
546v and 546h and the quarter wave plates 548, 549 is shown in FIG.
29. The linear polarizer 544 has a transmissive axis in the
vertical direction. The projection of the optic axis of the first
birefringent material 546h into the plane of the transmission axis
of the linear polarizer also is vertical, i.e., parallel to the
axis of the polarizer. The axes of the quarter wave plates 548, 549
are oriented +45.quadrature. to vertical and the projection of the
optic axis of the second birefringent material 546h into the plane
of the linear polarizer is at +90.quadrature. to vertical, i.e.,
horizontal.
[0214] The passive dithering system 540 functions basically the
same way as the passive dithering system 500 is described above
relative to FIG. 25. The function of the half wave plate 510 in the
passive dithering system 500 has been replaced in the system 540 by
a quarter wave plate 549. The quarter wave plate 548 and
birefringent material 546v function as the quarter wave plate 512
and birefringent material 508h of FIGS. 23-25. The quarter wave
plate 549 effectively divides the polarized light components of
light passing through the wave plate 549 by converting the light to
circularly polarized light and its respective equivalent orthogonal
plane polarized components like the quarter wave plates 512, 548
do. The components of the circularly polarized light are then
dithered by the second birefringent material 546h in a horizontal
direction as explained above for the passive dithering system 500.
One advantage of using the quarter wave plate 549 as opposed to the
half wave plate 510 or 510' is that the quarter wave plate 549 will
tend to introduce less chromatic aberration on the light passing
therethrough since a quarter wave plate usually is thinner material
than a half wave plate and, therefore, usually is less dispersive,
e.g., exhibits less optical dispersion.
[0215] In FIGS. 30a-30e are shown the operation of the passive
dithering system 540 of FIGS. 28 and 29. In FIG. 30a a pixel 542a
of display 542 is shown. Light from pixel 542a is vertically
polarized and is represented by the vertical arrow therein. The
linear polarization is produced by the display 542 and/or is due to
the polarizer 544. A separate polarizer 544 ordinarily is
unnecessary if the display 542 produces polarized light output.
Optical dead space 550 surrounds the pixel 542a.
[0216] The quarter wave plate 548 divides the vertically polarized
light from the polarizer 544 to obtain two orthogonal plane
polarized components, as is seen in FIG. 30b. In FIG. 30c it can be
seen that the birefringent material 546v changes the location of
the vertically polarized light component portion of light incident
thereon moving that light vertically relative to the location of
the vertically polarized light component portion. Therefore, pixel
542a is expanded, e.g., is doubled, in that pixel area 542b now has
been created. The quarter wave plate 549 divides (resolves) the
plane polarized light from the birefringent material 546v so that
each pixel 542a, 542b has both orthogonal plane polarized light
components, e.g., horizontal and vertical, as is shown in FIG. 30d.
In the manner described above, the double refracting material 546h
expands, e.g., doubles, the pixels 542a, 542b to create pixel areas
542a, 542b, 542c, 542d shown in FIG. 30e.
[0217] FIGS. 31 and 32 illustrate a passive dithering system 540'
which is identical to the passive dithering system 540 shown in
FIGS. 28-30 but it is used in an optical display system 541' with a
display producing non-polarized (unpolarized) output light, such as
an NCAP, PDLC or LCPC based flat panel liquid crystal display 560
e.g., like the display 532 and pixels 534 of FIGS. 26 and 27. The
orientation of the birefringent materials 546v and 546h and the
quarter wave plate 549, which are represented in FIG. 32, may be
the same as those described for the like components for the passive
dithering system 540 although it would be appreciated that this is
only one possible set of orientations for the axes of the
components which would dither an image in the manner described
above. The passive dithering system 540' functions in basically the
same way described above for the system 540 but on unpolarized
input light, which is resolved as orthogonally related plane
polarized light components (see the description above concerning
FIGS. 26 and 27), as opposed to the linearly polarized light which
the system 540 receives from the display 542.
[0218] It also will be appreciated that the several features and
embodiments of the invention illustrated and/or described herein
may be used with other features and embodiments that are
illustrated and/or described herein as well as equivalents thereof.
For example, in the segmented display system described the EDS may
be formed by a calcite crystal and a surface mode liquid crystal
cell, by a calcite crystal and a twisted nematic liquid crystal
cell or by some other type of switch and/or some other type of
double refracting material. Also, the EDS may be a liquid crystal
EDS in which both the switch function and the double refracting
function can be carried out by the same device, e.g., as in the
embodiment of FIGS. 18 and 19. Moreover, in many instances passive
dithering systems may be used in conjunction with or as a
substitute for some of all of the components described for the EDS.
These are simply examples of combining features and it will be
appreciated that other combinations also may be made consistent
with the spirit and scope of the invention.
[0219] From the foregoing it will be appreciated that various
embodiments of the invention using principles described herein may
be employed with polarized light or unpolarized light. If it
possible to operate based on an unpolarized light as an input to
the dithering system, e.g., using an NCAP display, there is no need
for a polarizer and the undesirable effect that a polarizer has in
blocking approximately 50% of the transmitted light. It also will
be appreciated that in various embodiments described herein a
quarter wave plate may be used, a half wave plate may be used,
and/or a combination thereof may be used. In various embodiments a
half wave plate may be substituted for one or more quarter wave
plates and vice versa. A quarter wave plate may be used to convert
plane polarized light to circular polarized light or to orthogonal
components of plane polarized light. A quarter wave plate also may
be used to convert plane polarized light to elliptically polarized
light. A half wave plate is used to rotate the plane of
polarization of plane polarized light. Usually the half wave plate
will rotate the plane of polarization by twice the angle between
the plane of incident plane polarized light and the axis of the
half wave plate.
[0220] Turning to FIG. 33 an active dithering system 601 is used
with a display 602 in an optical display system 603. The dithering
system includes a birefringent material 610, such as a calcite
crystal, having an axis 610' that is oriented at an angle theta
relative to horizontal, as is depicted in FIG. 33. The dithering
system 601 also includes a switch 611, such as a birefringent
liquid crystal cell of the type described above. The display 602
may be a liquid crystal display that provides plane polarized light
output that has a vertical plane of polarization represented by the
arrow 602'. Alternatively, the display 602 may provide other than
plane polarized light output, and in that case a plane polarizer
612 may be used to provide such vertical polarization of the light
delivered from the display and polarizer to the switch 611. The
orientation of the axis of the birefringent liquid crystal switch
611 is at 45.quadrature. to the vertical plane of polarization
602', as is represented by the arrow 611'. As was described, as the
switch 611 is energized or not, the plane of polarization of the
light output therefrom will be the same as the direction of the
arrow 602' or not, i.e., vertical, or horizontal. A half wave plate
615 between the switch 611 and the birefringent material 610 has
its axis 615' oriented at an angle relative to horizontal that is
1/2 theta.
[0221] With reference to FIGS. 33 and 34, which presents
representative operation of the dithering system 601, when the
light transmitted through the switch 611 has a given plane of
polarization, such light will be transmitted through the half wave
plate 615 and birefringent plate (calcite) 610 to appear at the
same relative positions as they originally appear in the display
602. If such pixels are, respectively, red, green and blue pixels
of a triad, such pixels may be at the locations of the pixel images
620r, 620g, 620b shown in FIG. 34. However, when the plane of
polarization of the light exiting the switch 611 is such that it is
appropriately rotated by the half wave plate 615 so as to impinge
on the calcite 610 in a direction relative to the axis 610' to
cause shifting of the light output, such pixels will appear as
images 620r', 620g', 620b'. Thus, it will be seen that the offset
or shifting is in a sense diagonal rather than horizontal or
vertical. The angle at which such diagonal occurs relative to
horizontal, for example, depends on the magnitude of the angle
theta. Thus, it will be appreciated by appropriately selecting the
angles of the respective axis of the components and their
relationship to each other, whereas desired directions of shifting
can be obtained. Also, the extent or distance of such shifting can
be determined, for example, by the thickness of the birefringent
device 610, i.e., the effect of optical thickness thereof having an
affect on the light transmitted therethrough.
[0222] Referring to FIGS. 35 and 36 and the Chart I below, an
optical display system 640, which includes two active dithering
systems 641, 642 and one passive dithering system 643 is
illustrated. The optical system 640 receives plane polarized light
input 644 from a display 645. If the display 645 is not the type
that provides a plane polarized light output, than an additional
polarizer 646 may be used to provide such plane polarization. The
orientation of respective components of the display system 640 is
depicted by respective double-headed arrows above the various
components.
[0223] The display system 640 may be used to provide a video output
display operation. In an exemplary video display system, such as an
NTSC or PAL system, it is conventional to compose a picture or a
frame from two interlaced and sequentially presented fields
(sometimes referred to as sub-frames). The optical display is able
to produce four output conditions and signals in the manner
described below. Such four output conditions may correlate to two
respective frames and the two respective fields in each frame in a
video display system, such as a television system using a liquid
crystal display or some other display as the image source. However,
it will be appreciated that the four output conditions described
below may be correlated with the operation of other types of
display systems or with a video display system in a way different
from the exemplary operation described below.
[0224] In the optical system 640 the active dithering system 641
includes a switch 650 and a birefringent device 651. The active
dithering system 642 includes a switch 652 and a birefringent
device 653. The passive dithering system 643 includes a quarter
wave plate 654 and a third birefringent device or material 655. The
first and second switches 650, 652 may be respective surface mode
birefringent liquid crystal cells or some other switch as is
described elsewhere herein. The first, second and third
birefringent devices 651, 653, 655 may be calcite material or some
other birefringent material having axis oriented generally in the
manner illustrated and tipped in the manner described above.
[0225] In describing operation of the optical display system 640,
reference is made to a pixel of the display and light representing
that pixel. The passive dithering system 643 effectively doubles
the size of the pixel received by it from the display 645 and via
the respective active dithering systems 641, 642. Therefore, as is
seen in FIG. 36, each pixel input to the passive dithering system
643 is shown in solid lines and the doubled image thereof is shown
in dotted lines adjacent thereto. For example, the pixel provided
the passive dithering system 643 for the first field of the first
frame is represented at 660, and the dithered image 660' is shown
adjacent thereto in dotted lines. The passive dithering system
operates in the manner of the passive dithering systems described
above, for example.
[0226] Referring to the Chart I below, at frame 1, field 1, the
voltage or energization of the first switch 650 is low so that the
switch rotates the plane of polarization of the input vertically
polarized light to horizontally polarized light as the output
therefrom; see the column labeled "polarization direction output 1"
having the letter "H" representing such horizontal polarization.
Delivery of that horizontally polarized light to the first calcite
651 results in no shift of location. Continuing in the first line
for frame 1, field 1 in the Chart I below, the voltage of the
second switch 652 is low, whereby that switch rotates the plane of
polarization back to vertical, as is represented by the letter "V"
in the column labeled polarization direction output 2; and,
therefore, the second calcite member 653 does not shift the
location of the pixel. When the vertically polarized light output
from the second calcite 653 enters the quarter wave plate 654, such
light is divided into horizontal and vertical polarized components;
the vertically polarized component transmits through the third
calcite material 655, and the horizontally polarized component is
shifted horizontally thereby effectively doubling the size of the
pixel and producing the image 660', as is represented in the last
column of the table designated calcite 3 shifting and doubling in
the horizontal direction the particular pixel.
[0227] The second field of the first frame, for example, each pixel
of the second frame, is displaced vertically relative to the
corresponding pixel of the first field of the first frame. The
pixel 661 represents the location of such downwardly vertically
displaced pixel for the second field of the first frame when the
display system is a video type using interlaced fields to produce a
frame. The second line of the Chart I below shows the conditions of
the surface mode switches 650, 652, both being at high voltage so
as not to rotate the plane of polarization of light transmitted
therethrough, the resulting vertical downward displacement caused
by the first calcite 651, and the doubling of the pixel by the
passive dithering system 643 to produce not only pixel 661 but also
the dithered pixel 661'. In pixels 660, 660', the two digits one in
each represent, respectively, first frame, first field; and in the
pixels 661, 661', the digits one and two represent first frame,
second field, respectively.
[0228] Lines three and four of the Chart I below represent
conditions and shifting resulting from those conditions of the
switches 650, 652, direction of plane of polarization, etc. as was
described above with respect to the first two lines of the Chart I
below in order to achieve pixels 662, 662' and 663, 663', the
primed pixels representing the dithered images that doubles the
effective size of the overall pixel, such as the doubled size 663
plus 663'. As was mentioned above, the amount of shifting or
translating of a particular pixel may be a function of the
birefringence and/or optical thickness of the respective
birefringent device, such as the respective calcite plates 651,
653, 655. Also, in a conventional video system there usually is no
horizontal interlacing. The two field of the second frame
represented by pixels 662, 662', 663, 663' may represent images
moved to fill optical dead space, images to effect super imposing
respective colors, as is described further below, or some other
purpose. The increasingly effective size of each pixel, such as by
doubling it to increase pixel 660 to the effective size of the sum
of pixels 660, 660', can be used to improve resolution by
effectively covering optical dead space in the display. The
vertical displacing of pixels can be used to cause a liquid crystal
display to provide a true or more nearly true interlaced operation
whereby a pixel presented in one field of a frame is presented at a
different location when the second field of that same frame is
produced.
[0229] An advantage to the use of a dithering system with a
display, such as a liquid crystal display, wherein the location of
a pixel in the output can be shifted even though the actual
location of the pixel in the display itself, such as an LCD,
remains fixed is that correct data can be used to drive the pixel
to provide the desired image output with relatively accurate
following of the video signal. In a conventional LCD used to
provide a video output a particular pixel may average the two
fields of a frame; the average is not an accurate representation of
the data received from the video signal. However, using a dithering
system in accordance with the present invention, a pixel of the LCD
may be driven based on information from the video signal intended
to drive that pixel for a particular field of a frame to provide a
visual output from the display system, such as display system 640.
Subsequently when the image output of the respective pixel is
shifted so that it is in the location desired for the second field
of the particular frame, the actual information from the video
signal that ordinarily would be used, say in a CRT, for example,
could be the information that is used to operate or to drive the
pixel which then provides a relatively accurate output
representative of the appropriate input signal.
[0230] Using the two active and one passive dithering systems of
the optical display system 640 is it possible to obtain eight
copies of the original image, if desired, namely that provided at
pixel 660, for example. Such eight copies may be obtained for every
field for every frame, if desired and, thus, provide a macro pixel
effectively about eight times the size of the pixel 660. In another
embodiment, the data picked off the incoming analog signal or other
video signal that operates the pixel 660, e.g., to turn it on or
off, may be selected at the appropriate time to drive the pixel
660; and subsequently the pixel 661 may be operated as a function
of information picked off the incoming video or analog signal
representing the desired operation of the pixel 661 for interlaced
fields operation of a conventional NTS or PAL system. However,
additionally, if desired, the information from the incoming signal
also could be picked off to represent the on/off or intensity
effect of a pixel presented at location of pixel 662 accurately to
represent that pixel even though that pixel physically may not be
in the display 645 but rather is represented by the pixel of the
display 645 that produces pixel image 660 shifted to the location
of pixel 662. In other words, in an exemplary LCD there may be two
relatively adjacent pixels, and the information from the incoming
video signal would be picked off from that video signal to drive
the respective pixels at the appropriate times. However, there also
may be information contained in the video signal that would
represent a desired optical output from the optical display system
640 from a pixel located between the two mentioned pixels. The
present invention allows the information from the video signal that
would be used to drive such intermediate pixel to be delivered to
the pixel of the display 645 that would produce pixel image 660
while the dithering systems in the optical display system 640
effect horizontal or lateral displacement of the optical output to
a location where such intermediate pixel might otherwise appear in
the output image from the optical display system 640. This
operation can enhance the resolution provided by the optical
display system 640 and the accuracy of representation of the
information carried by the input video signal, etc.
Superimposed Color Operation
[0231] Referring to FIG. 37 there is a shown a layout of an
exemplary group of red, green and blue pixels of an exemplary
liquid crystal display. The pixels are arranged in respective
parallel rows and columns. Capital letters represent the color of
the pixel, e.g., whether the pixel will deliver output like that is
red, green or blue. Portions of two rows are shown.
[0232] In the viewing of a color liquid crystal display the eye of
the viewer, i.e., a human eye, may receive light input from many
different pixels, and the eye effectively integrates the light
inputs. One way of considering such viewing is to analogize the
adjacent pixels, which are extremely small, effectively being
superimposed so that the light therefrom is superimposed.
Therefore, the combination of red, green and blue light that is
superimposed would provide a white light as seen by the viewer.
[0233] The various embodiments of dithering systems in accordance
with the present invention, including those disclosed and
equivalents thereof, may be used to effect real superimposing of
respective pixels, thereby enhancing the color output or color
response of a color liquid crystal display. Such superimposition is
depicted in FIG. 37 and now is described. The two rows of pixels
shown in FIG. 37 are portions of respective rows of pixels in a
color liquid crystal display. In the first row shown there are five
pixels of the indicated colors; and in the second row there also
are five pixels of the indicated colors. The sequence of colors is
red, green and blue in both rows, but the sequence is offset by one
pixel one row to the other. Therefore, in the first (top) row the
first pixel row, and in the second row the first pixel is green.
The arrangement of pixels in FIG. 37 is exemplary. Many other types
of arrangements of pixels may be used whether in parallel rows and
columns in the manner shown, in a so called delta configuration or
pattern wherein there is an offset of rows, such as in FIG. 40,
etc.
[0234] Using the optical display system 640, for example, the red
pixel Ra at the top left of FIG. 37 is duplicated by the passive
dithering system 643 to produce a red pixel or ra, which is
represented in dash lines. Operation of the first dithering system
641 produces a second copy of both those red pixels displaced
downward to locations of dash red pixels designated ra'. Such
operation of the first dithering system 641 is coordinated with the
second dithering system 642 to effect such downward shift.
Similarly, horizontal shifting of all four red pixels just
mentioned, namely Ra, ra, and the two designated ra' to a
horizontally shifted or laterally shifted place results in the red
pixels represented by dash lines and designated ra'', one of which
is superimposed over the green pixel Ga and one of which is
superimposed on the blue pixel Ba. Such shifting may occur in a
time sequence that is sufficiently fast that the human eye does not
perceive the various shifts. Additionally, such shifting occurs in
a time sequence coordinated with the desired color output from the
display as represented by the input video signals to the display so
that the superimposed colors provide a good quality and accurate
representation of the color output from the display intended as a
result of the input video signal. Similarly to the just described
shifting of the red pixel Ra, shifting of the green pixel Ga also
occurs, and such shifted pixels are represented by dotted outline
at pixel locations represented by Ga due to the passive dithering
system 643, and the other shifted pixels represented by dotted
lines labeled ga' and ga'' resulting from coordinated operation of
the active dithering systems 641, 642. Furthermore, similar
operation occurs for the blue pixel Ba, which is represented by
phantom lines at pixels or pixel locations designed ba, ba', and
ba''. The four blue pixels represented by respective designations
ba' and ba'' near the bottom of FIG. 37 would overly or be
superimposed on other pixels which are not shown in order to
simplify the drawing and description.
[0235] Briefly referring to FIG. 38, shifting of the red pixel R
into respective gaps and also superimposed on other pixels is shown
schematically and simply. Specifically, pixel R is doubled by the
passive dithering system 643 of the optical display system 640 in
FIG. 35, for example to provide pixel r. Both pixels R and r are
duplicated also at pixel image locations r' shown in FIG. 38 in the
gap between respective parallel rows of actual pixels. Pixels R, r
and r' also are duplicated to the right relative to the
illustration of FIG. 38 as pixel images r'', some of which are in
the same gap as pixel images r' and one of which overlies or is
superimposed on the green pixel G. Thus, it will be seen that the
pixels can be shifted to various locations in the display to
achieve the desired optical output.
[0236] As the display of FIG. 38 is operated as part of the optical
display system 640 to duplicate pixel images and/or to translate
pixel images, so, too, the display shown in FIG. 39 represents
similar modified operation of the optical display system 640. In
particular, in FIG. 39 lateral shifting occurs like that in FIG.
38; but in FIG. 39 the vertical shifting of images results in the
shifted image overlying the gap between adjacent rows of pixels of
the display 645 and also overlying at least a portion of the pixel
of the display 645 which is vertically displaced beyond such gap
between pixel rows. Placing the pixel image in a gap increases the
fill factor of the display. As was mentioned above, the shifting
may result in superimposing pixel images to achieve the
superimposed color response described above. Also, if desired, the
vertical shifting may result in a portion of the shifted pixel
image still overlapping a portion of the image in the original row,
such as the illustrated pixel R and shifted pixel image r'
therebelow. Such superimposing of pixels may provide a desired type
of visual output for the optical display system 340.
[0237] Briefly referring to FIGS. 40 and 41, there is shown a delta
design of pixel layout for a display in FIG. 40, such as an LCD 645
and the output images therefrom after transmitting through an
optical display system 680, which includes one active dithering
system 681 and two passive dithering systems 682, 683. The active
dithering system 681 includes a switch, 684, such as a birefringent
liquid crystal cell, and a calcite crystal 685 able to transmit an
image or to shift the image vertically 1/2 pixel, depending on the
direction of plane of polarization of light incident thereon. The
passive dithering system 682 includes a half wave plate 686, which
rotates the plane of polarization of incident light 45 degrees, and
a second calcite crystal 687, which can transmit the incident pixel
image and has a thickness, birefringence, axial orientation and
tipped to displace the image 1/2 triad pitch horizontally. The
passive dithering system 683 includes a half wave plate 688, which
rotates the plane of polarization of incident light 45 degrees, and
a second calcite crystal 689, which can transmit the incident pixel
image and has a thickness, birefringence and axial orientation and
tip to be able to displace the image 1 pixel pitch
horizontally.
[0238] The optical display system 680 and dithering systems 681,
682, 683 thereof are set up to effect shifting 1/2 triad pitch to
the right; 1 pixel pitch left and 1/2 pixel vertical pitch down.
This arrangement is represented by only the blue pixel Ba. In
shifting that pixel 1/2 triad pitch to the right, pixel ba results.
In shifting both pixel Ba and ba 1 pixel pitch to the left, two
respective pixel images ba' are produced--one is superimposed over
the green pixel G, and one is in the gap between the blue pixel Ba
and the red pixel R horizontally adjacent to the blue pixel Ba.
Such shifting provides both for filling the optically dead space
and effecting a superimposing of respective color pixel images as
was described above. The shifting of pixel images vertically to
form the four pixel images ba'' places some of those in the gaps
between rows of pixels and some in superimposed relation to the
same and/or other pixels or shifted pixel images.
[0239] Referring to FIG. 42, a person 704 is shown wearing a head
mounted viewing system 705 in accordance with the present
invention. The viewing system may be part of a virtual reality
viewing system having one or more displays which are viewed by the
person. The viewing system may be part of a telecommunications
system, entertainment system, or some other device in which light,
optical, etc. information can be presented for viewing, projecting,
photographing, or other use. Exemplary systems in which the
invention may be used are disclosed in the above-mentioned patent
applications; of course there may be other uses, too.
[0240] The head mounted viewing system 705 includes a housing 705h
in which the various components of the viewing system 705 are
included, and a mounting device 705m, such as a strap, eyeglass or
goggles type frame support structure, etc. The mounting device 705m
mounts the housing 705h for support from the head of the individual
704 placing the viewing system 705 in position in front of one of
the eyes for viewing of an image presented by the viewing system
705. Whether the viewing system 705 is hand held, head mounted, or
otherwise supported, for example, from a pedestal, tripod, frame,
etc., from a table, from the floor, from a console 9, etc.,
preferably the viewing system 705 and housing 705h thereof is
relatively small and sufficiently lightweight to facilitate moving,
transporting, mounting, and/or holding. If the viewing system 705
is to be hand held or head mounted, it especially should be
relatively lightweight to avoid being a weight burden on the hand
or head of the individual using the viewing system 705. Also, to
facilitate holding the viewing system 705 manually or head mounting
the viewing system, the viewing system 705 should be relatively
small. An exemplary viewing system may be, for example,
approximately 4 to 5 inches in height, approximately 2 to 3 inches
wide, and approximately 1/2 to 2 inches deep. These are exemplary
only, and it will be appreciated that other dimensions may be
used.
[0241] In using the viewing system 705 it may be head mounted, hand
held, coupled to a control box, console or the like, for example,
similar to the main body of the conventional telephone when used in
a telecommunication system.
[0242] Turning to FIG. 43, the viewing system 705 is shown in
detail as a monocular viewing system. The housing 705h includes a
viewing portion 711 and a support portion 712. The viewing portion
711 is intended to be viewed by an eye 713 of a person 704 (FIG.
42), and the support portion 712 is intended to be held in the hand
of that individual. As was mentioned above, a head mount 705m may
be provided to support the viewing system 705 from the head of a
person. Thus, the housing 705h may be hand held, supported by a
strap, cap, temple piece as in eyeglasses, or otherwise mounted for
viewing by a person.
[0243] The viewing system 705 includes an optical system 714 in the
housing 705h. The optical system 714 includes an image source 715,
such as an LCD, that provides images for viewing by the eye 713
through a viewing port 716. A viewing lens 717 (or group of lens)
presents to the eye 713 an image which appears at a comfortable
viewing distance, such as about 20 inches or more away. An image
resolution enhancing device 18 (sometimes referred to as an optical
line doubler or OLD, dithering device or system, EDS, etc.)
optionally included in the optical system 714 may be used to
enhance the resolution or other qualities of the image produced by
the image source 715.
[0244] A number of optical components 720 are included in the
optical system 714. The optical components include focusing optics
721 (sometimes referred to simply as "lens" or as projection optics
or as a projector), a beam splitter 722, and one or more
retroreflectors 23, 23'.
[0245] The image source 715 includes a display 724d and a source of
incident light 724i. The light source illuminates the display 724d,
and the display in turn presents images which can be projected for
viewing by the eye 713, as will be described in greater detail
below. It will be appreciated that other types of image sources may
be used, examples being cathode ray tube displays, other liquid
crystal displays, plasma displays, etc. Examples of several
displays and light sources are presented in the above-referenced
co-pending patent applications. A connection cable 28 provides
electrical and/or optical signals and/or power to the optical
system 714, and is particular to the image source 715 and OLD 18 to
develop the above-mentioned images for viewing by the eye 713. A
control system 729 is coupled to the cable to provide such
electrical signals for controlling operation of the display system
705, as is described in further detail below.
[0246] Summarizing such controlled operation, though, the display
724d may be a twisted nematic liquid crystal display, and the OLD
18 includes an optical switch, such as a surface mode liquid
crystal cell, that switches polarization characteristics of light
to cause the light output to viewed by the eye 713 to be, for
example, of enhanced resolution, as is described further below.
Therefore, the control system 729 provides signals to generate the
image by the display 724d; and the control system 729 also controls
the optical switch to effect a synchronization such that there is a
phase or time delay between the signals to the twisted nematic LCD
and the signals to the optical switch. Accordingly, the optical
switch which operates at a different speed, e.g., faster or in
shorter time than the twisted nematic LCD will be coordinated with
the operation of the twisted nematic LCD to improve operation and
optical output of the display system 705. Detailed operation of the
control system is described further below, for example, with
respect to FIGS. 44-46 and 48.
[0247] Dithering may refer to the physical displacement of an
image. The dithering system 718 may be an electro-optical dithering
system (EDS), which refers to an electro-optical means to
physically shift or to change the location of an optical signal,
such as an image. The shifting may result in doubling of the number
of pixels or scan lines of a display--thus, reference to OLD
(optical line doubler). The shifting also may result in quadrupling
(or more or less increase) pixels or scan lines; and in such case
OLD also may be used as a generic label. The shifting may be active
in response to an electrical, magnetic or other input. The
dithering system 718 may be passive, e.g., in which shifting occurs
constantly or substantially constantly (or continuously); in other
words such shifting may occur all the time without the need for a
separate input to cause shifting. Various embodiments of dithering
systems useful in the invention are described above.
[0248] The image may be shifted along an axis from one location to
another and then back to the first, e.g. up and then down, left and
then right, or both, etc. The optical signal may be moved in
another direction. The dithering may be repetitive or periodic or
it may be asynchronous in moving an image from one location to
another and then holding it there, at least for a set or
non-predetermined time. Also, as was mentioned, the dithering may
be passive, and, thus, constant, e.g., without changing. When the
dithering is passive there usually are provided simultaneously the
original image at the undithered location and a second or dithered
image at another location, e.g., located adjacent or spaced apart
from the undithered image.
[0249] Referring to FIG. 44, the top line A in the graph represents
an electrical signal, namely the voltage applied to a given display
pixel (sometimes referred to as picture element or component) as a
function of time. The pixel may be a part of a twisted nematic type
LCD, such as part of the display 724d, especially an active matrix
LCD, although the pixel may be a part of some other type of
display, optical device, etc. When the voltage is applied to an
active matrix display, it results in an electric field being
applied across the liquid crystal material causing a particular
type of operation, e.g., alignment with respect to the field or
when no field is applied relaxing to an alignment which may be
influenced, for example, by the surfaces, surface coatings, etc.,
of the liquid crystal cell or device forming LCD. The voltage A
illustrated in FIG. 44 is applied at a frequency of 60 Hz.
[0250] The second line B in FIG. 44 represents the desired light
transmission characteristic of an ideal pixel as a function of
time. In the illustrated example, the pixel is switched between
clear (sometimes referred to as the white state) and dark
(sometimes referred to as the black state). As illustrated, the
clear state would occur when the voltage A is high, and the dark
state would occur when the voltage A is high.
[0251] In the illustrated case of an ideal pixel in FIG. 44, the
pixel switches transmission B from dark to clear at the same time
the voltage switches from high to low. That is, the ideal pixel
switches in phase with the applied voltage A. Furthermore, in the
OLD or EDS1, etc. (FIGS. 1, 2-6, 11-12, etc.) hereof (hereinafter
referred to as EDS1 for brevity although such reference includes
the various embodiments of active and passive dithering systems
disclosed herein), the position of the pixel changes by switching
the voltage applied to the surface mode birefringent liquid crystal
cell, optical switch or polarization rotator 11 (FIGS. 1, 5 and 6,
for example). Therefore, it follows that in the ideal case, i.e.,
for use with the ideal pixel, the voltage applied to the optical
switch 11 also would be switched synchronously with the voltage A
applied to the ideal pixel and in phase.
[0252] However, a real liquid crystal display 20, 724d utilizing
the twisted nematic effect cannot switch between transmission
states as rapidly as indicated in the second line B of FIG. 44. For
example, the active matrix liquid crystal display used in the Sony
XC-M07 monitor can switch from dark to clear in about 20
milliseconds and from clear to dark in about 11 milliseconds.
Switching time is defined conventionally as the time required for
the transmission to change between 10% and 90% of the final values.
This real switching behavior is illustrated in the third line C of
FIG. 44. In this third line C depicting light transmission, the
transmission of the clear state has been normalized to 100% and the
transmission of the dark state has been normalized to 0%. It will
be appreciated that the graph line C is schematic only, and the
precise times mentioned above are not necessarily accurate.
[0253] In FIG. 45 the graphs present information similar to that
presented in the graphs of FIG. 44 except that in the graphs of
FIG. 45 the frequency of the applied voltage A' to the pixel, e.g.,
of the display 724d, is doubled to 120 Hz. The transmission B' of
the ideal pixel in FIG. 45 is shown synchronized and in phase with
the applied voltage A'. However, the actual transmission C' of a
real pixel is illustrated in the third line of FIG. 45. As is
shown, within the available time of respective half cycles of the
applied voltage A', the real pixel is able to switch transmission
between about 25% and 75%. This means that the contrast ratio would
be reduced by a factor of about one half (1/2) compared to the 60
Hz case of FIG. 44. This behavior is characteristic of many twisted
nematic effect LCDs; starting at a modulation of about 60 Hz. every
increase in the frequency of the applied voltage by a factor of two
(2) usually results in a reduction in the contrast ratio by a
factor of about one half (1/2).
[0254] Referring to FIG. 46, line A'' represents the applied
voltage to the pixel at 120 Hz. The second line C'' represents the
transmission response of a real pixel of an active matrix twisted
nematic LCD. Note that line C'' is similar to line C' in FIG. 45. A
guide line D has been drawn in the graph of line C'' in FIG. 46 at
50% transmission. That portion of a particular frame, in which the
real pixel is presenting an image of clear or dark, having a
transmission greater than 50% is defined here as the clear state.
That portion of the frame having a transmission less than 50% is
defined here as the dark state. As seen, the real pixel does
shutter light at 120 Hz but the transmission modulates between 25%
and 75% rather than the 0% to 100% experienced when the frequency
of the applied voltage signal A was 60 Hz. in FIG. 44.
[0255] Another feature of the 120 Hz response of the real pixel is
shown in FIG. 46. Consider the point marked along the time scale by
the double headed arrow E. The bottom part of the arrow E indicates
the point in time that the transmission of the real pixel switches
from dark to clear; the top of the arrow E indicates the
corresponding applied voltage. It can be seen that the applied
voltage A'' is out of phase with the transmission characteristics
of the pixel, i.e., when the real pixel switches between what is
considered the clear state and the black state, by
90.quadrature..
[0256] In the present invention the EDS1 may be adjusted to
introduce a similar phase shift in the voltage F (FIG. 46) applied
to the optical switch 11. An exemplary optical switch 11 is a
surface mode birefringent liquid crystal cell. Such device usually
can switch between states in response to a change in input signal
much faster than does a twisted nematic liquid crystal cell or LCD.
Therefore, by introducing the indicated phase shift in the driving
of the surface mode liquid crystal cell and the twisted nematic
LCD, the optical switch can be coordinated to switch optically at
the same time that the LCD 724d, for example, switches optically
from what is considered its clear state to what is considered its
dark state or vice versa. As a result, as the EDS1 operates in
coordination with the LCD 724d, for example, to crispness or
sharpness of the output image can be improved and there is less
likelihood of a bleeding effect between images produced by pixels
which are periodically optically shifted using the dithering
principles of an OLD or the like.
[0257] After the phase of the surface mode liquid crystal cell
optical switch 11 has been adjusted as described, the contrast of
the display 724d would be reduced by a factor of about one half
(1/2) when the display is optically doubled and one fourth (1/4)
when the display is optically quadrupled. The decrease in contrast
is due to the increased frequency at which the display liquid
crystal cell (LCD) is driven, not due to the EDS or how it is
driven. It has been found that the contrast reduction is nearly
undetectable by the human eye and, therefore, has been found
acceptable for many applications.
[0258] It will be appreciated that although the above description
regarding FIGS. 44-46 presents phase shift of 90.quadrature. for
the indicated purpose, the principles of the invention may be used
to introduce other phase shifts to achieve a similar coordination
between two optical devices which have different response
characteristics, such as, for example, change in light transmission
or polarization as a function of change in electrical input, or
other input, e.g., magnetic input.
[0259] In FIG. 47 details of optical components of the optical
system 714 of the display system 705 are shown. The optical
components shown in FIG. 47 are similar to those included in the
housing 705h of FIG. 43; however, in FIG. 47 the housing 705h and
support 705m are not shown to facilitate illustrating the invention
and to simplify the drawing.
[0260] The optical components 720 of the optical system 714 include
focusing optics 721 (sometimes referred to simply as "lens" or as
projection optics or as a projector), a beamsplitter 722 and
retro-reflector 723. The display system 705 also may include an
image source 715 (FIG. 43) which provides images or light having
characteristics of an image and, if desired, may be part of the
mentioned projector. An exemplary image source is a liquid crystal
display, such as a small liquid crystal television having a
cross-sectional display area on the order of about one square inch
or less. As shown, the image source 715 includes a liquid crystal
display 724d which modulates light from the light source 724i to
form images for viewing by the eye 713. Alternatively, the image
source may be separate and simply used to provide one or more
images or light having image characteristics that can be provided
by the viewing system 705, such as that shown in FIG. 1, or a head
mounted display, sometimes referred to as HMD to the eye 713.
Additional optical components of the optical system 714 may include
linear polarizers, circular polarizers, wave plates, focusing
elements, such as lenses or mirrors, prisms, filters, shutters,
apertures, diaphragms, and/or other components that may be used to
provide a particular type of output image for viewing by the eye
713. Examples of several embodiments using such additional optical
components are described below with respect to other drawing
figures.
[0261] The invention is useful with virtually any type of image
source or display source. An example of such a display source is a
compact flat panel display, and especially one utilizing a
reflective liquid crystal display made from a single crystal
silicon active matrix array.
[0262] In FIG. 47 the image source 715 displays an image 825, which
is shown in the drawing as an arrow 826. The light 827 leaving the
image source 724 represents an image or has characteristics of an
image, and that light is collected by the focusing optics 721 of
the optical system 714 of the display system 705 and travels to the
beamsplitter 722. In FIG. 47 and in a number of the other drawing
figures hereof the focusing optics 721 is represented as a single
lens. However, it will be appreciated that the focusing optics 721
may include one or more other components, such as lenses,
reflectors, filters, polarizers, wave plates, etc.
[0263] Although the image source(s) 715 is shown in FIG. 47 located
relatively above the beamsplitter 722, the image source may
alternatively be located below the beamsplitter as is shown in FIG.
2.
[0264] At least some of the light 827a incident on the beamsplitter
722 is reflected by the beamsplitter as light 827b toward the
retro-reflector 723. The retro-reflector may be, for example, a
screen made of retro-reflecting material. Exemplary
retro-reflectors are well known. One example is that known as a
corner reflector or a sheet having a plurality of corner
reflectors. Another example is a material having plural glass beads
or other refracting and/or reflecting devices on or in a support.
An example of a retro-reflector is a film or sheet material having
a plurality of corner cubes which material is sold by Reflexite
Corporation of New Britain, Conn. Such material is available having
about forty-seven thousand corner reflectors per square inch.
[0265] The light (light rays) 827c, which are shown as broken
lines, are reflected by the retro-reflector 723 such that their
path is exactly back along their direction of incidence on the
retro-reflector. In this way some of the light rays 827c pass
through the beamsplitter 722 and are directed toward a location in
space designated 828 in the illustration of FIG. 47. The eye 713 of
a viewer (person) can be placed approximately at location 828 to
see the image, and the pupil and lens, individually and
collectively designated 713a, of the eye, accordingly, are shown at
that point. The lens 713a focuses the light incident thereon as an
image on the retina of the eye 713.
[0266] The projection lens 720 projects light toward the
retro-reflector 723 to cause a real image to be formed at the
retro-reflector or in front or behind the retro-reflector. As is
defined in Jenkins & White, Fundamentals Of Optics,
McGraw-Hill, 1976, for example, using an exemplary projection lens,
an image is real if it can be visible on a screen. The rays of
light are actually brought to a focus in the plane of the image. A
real image is formed when an object is placed beyond the focal
plane of a lens; the real image is formed at the opposite side of
the lens. If the object is moved closer to the focal plane of the
lens, the image moves farther and is enlarged. In contrast, a
virtual image occurs if an object is between the focal point of a
lens and the lens itself.
[0267] In FIG. 47 the broken lines represent light rays which
travel after reflection by the retro-reflector along the same or
substantially the same path, but in the opposite direction to,
respective incident light rays impinging on the retro-reflector.
Thus, the retro-reflector 723 is part of a conjugate optics path
823a in which light incident thereon is reflected in the same path
and opposite direction as reflected light. The beamsplitter 722
directs light from the focusing optics 721 into that conjugate
optics path and toward the retro-reflector; and the beamsplitter
also passes light in the conjugate optics path from the
retro-reflector to the output port 16 (FIG. 2) for viewing by the
eye 713. The beamsplitter 722 and retro-reflector 723 cooperate as
a conjugate optics system to provide that conjugate optics
path.
[0268] Using the described conjugate optics path and system,
relatively minimal amount of the light from the image source 724
and focusing optics 721 is lost and, conversely, relatively maximum
amount of light is directed to the eye 713. Also, there is
substantial accuracy of image and image resolution conveyed to the
eye. Furthermore, especially if a relatively good quality
retro-reflector is used so that the precise location at which the
image 830 is in focus will not be critical, e.g., it can be behind
or in front of the retro-reflector, the tolerance required for the
relative positioning of the components of the optical system 714 is
less severe. This makes the HMD display system 705 relatively
robust and reliable.
[0269] In FIG. 47 the viewed image 830 is represented by an
enlarged arrow 831. Such arrow 831 is shown in FIG. 47 as a
magnified focused image of the image 825 from the image source 724.
The image 830 may be in focus at or approximately at the
retro-reflector 723, and this is especially desirable for good
quality images to be provided the eye 713 when a relatively low
quality retro-reflector is used. A low quality retro-reflector is
one which has relatively low resolution or accuracy of reflecting
light in a conjugate manner in the same path but opposite direction
relative to the incident light. With a low or poor quality
retro-reflector and the image not being focused at the
retro-reflector, it is possible that too much light may be lost
from the desired conjugate optics path back to the eye 713, and
this can reduce the quality of the image seen. However, the image
830 may be in focus at another location or plane either behind the
retro-reflector (relative to the eye) or in front of the
retro-reflector, and this is easier to do while maintaining a good
quality image for viewing when the retro-reflector is a good
quality one. The better the retro-reflector, the more
self-conjugating is the optical system 714 and the less the need to
focus with precision at the retro-reflector.
[0270] Retro-reflector quality may be indicated by the radians of
beam spread of light reflected. For example, a relatively good
quality retro-reflector may have from zero or about zero radians of
beam spread to a few milliradians of beam spread. The quality
usually is considered as decreasing in proportion to increasing
beam spread of reflected light.
[0271] In considering the brightness of the image seen by the
viewer, the nature of the beamsplitter 722 plays a role. The light
produced by the image source 724 may be polarized or unpolarized.
If the beamsplitter 722 is of a non-polarizing type, then a
balanced situation is to have 50% of the light incident on the
beamsplitter 722 be reflected and 50% transmitted. Thus, of the
light 827a incident on the beamsplitter 722, 50% is reflected and
sent toward the retro-reflector screen 723 as light 827b. Of the
reflected light 827c from the retro-reflector 723, 50% of the light
will be transmitted through the beamsplitter 722 and will travel to
the viewer's eye 713. This configuration of the optical components
720 of the display system 705 can transfer to the viewer's eye a
maximum of 25% of the light produced by the image source 724. If
desired, the beamsplitter 722 can be modified in ways that are well
known to change the ratio of the reflected light to transmitted
light thereby. Also, the beamsplitter 722 may include an
anti-reflection coating so that all or an increased amount of the
image comes from one side of the beamsplitter and thus to reduce
the likelihood of a double image.
[0272] Since the optical system 714 of the display system 705
provides good resolution of the image and maintains the
characteristics thereof, the image source can be a relatively
inexpensive one that does not have to compensate for substantial
loss of image quality that may occur in prior display systems.
Furthermore, since a relatively large amount of the light provided
by the image source 724 is provided to the eye 713 for viewing,
e.g., since the retro-reflector can virtually focus the light for
viewing at the eye, additional brightness compensation for loss of
light, as may be needed in prior display systems, especially
portable, e.g., hand held or head mounted, ordinarily would not be
required.
[0273] For exemplary purposes, in FIG. 47 three light rays 840a,
840b, 840c (collectively 840) originating at the tip of the arrow
826 constitute a portion of the light 827. Three light rays
schematically shown at 841a, 841b, 841c (collectively 841) also are
examples of light emanating at the tail of the arrow 826. The light
827 has characteristics of the image 825 from or provided by or at
the image source 715, and represented by the exemplary light rays
840 and 841, is focused by the focusing optics 721 onto the
retro-reflector 723. The size of the image 830 seen as the arrow
831 on the retro-reflector 723 depends on the focal length of the
focusing optics 721 and the distances between the image source 724
and the retro-reflector 723 from the focal points 843, 844 of the
focusing optics 721. Thus, magnification can depend on such focal
length. The image source 715 should be located relative to the
focusing optics 721 such that an image can be focused, e.g., in
focus as is shown in FIG. 47, at or approximately at the
retro-reflector. For example, the image source 715 may be beyond
the focal point 843 of the focusing optics 721, and the
retro-reflector likewise preferably is beyond the focal point 844
of the focusing optics so that the image can be focused at the
retro-reflector.
[0274] In the illustration of FIG. 47 the image 830 on the
retro-reflector 723 is magnified relative to the size of the image
at the image source display 724d; it does not have to be magnified.
The image 830 may be the same size as the image 825 or it may be
smaller. Thus, although the image source display 724d may be
relatively small and/or may provide a relatively small size image
825 at its output, the size of the image 830 viewed by the eye 713
may be different.
[0275] The optical system 714 is operable to place the image plane
effectively at the retina of the viewer's eye 713. This is
accomplished by effectively putting the plane of the eye lens (or
pupil) 713a effectively at the position occupied by the focusing
optics 721 relative to the source of the image provided to the
focusing optics. In a sense the lens 721 is optically superimposed
on the lens 713a of the eye 713.
[0276] The invention provides an optical system in which there are
conjugate paths from a lens, such as focusing optics 714, which
corresponds to the "lens means" of an optical sensor, e.g., the eye
713. Stated in another way, the invention presents visual
information or optical data with a wide field of view by taking the
output from a lens (focusing optics 721) and reflecting the light
back along a conjugate path toward a location corresponding to that
of the same lens which was in the original path, but actually
direct that reflected light onto the eye placed at such
corresponding location. This is obtained by using the conjugate
optics arrangement disclosed herein.
[0277] The human eye is most comfortable when viewing an image at a
distance of about twenty inches, approximately at the distance at
which one would place a book, document, etc. to be read. It is
desirable that the final image as seen by the viewer be located at
such distance, e.g., approximately twenty inches from the pupil
713a of the eye. This can be accomplished in the manner, if
desired, by adding an additional lens 717 (FIG. 43) or other
optical system (not shown) between the beamsplitter 722 and the eye
713. Such lens may cause the person to see a virtual image behind
the retro-reflector, as is described in several of the above patent
applications. Although in many viewing devices further spacing
between the eye and the optical component of the optical system
nearest the eye may be desired to obtain desired eye relief, the
use of the lens 717 at the indicated distance of about 1/2 to 1
inch from the eye usually is acceptable and reasonably comfortable
because that is the approximate spacing of ordinary eye glasses to
which people ordinarily relatively easily become accustomed.
[0278] The function of the lens 717 may be obtained by using a
negative lens at the focusing optics 721.
[0279] Referring to FIG. 14 an EDS 201 in the form of an
electro-optical dithering system which includes two line doublers
in optical series is shown used with a display 202, in the
illustrated embodiment an LCD (although other types of displays can
be used), as a display system 203. The display 202 and the EDS 201
may be substituted for the display 724d and EDS1 in the display
system 705 of FIGS. 42 and 43. The display 202 may include a light
source or a separate light source 724i may be used to illuminate
the display 202.
[0280] FIG. 48 presents a number of graphs representing signals in
the control system 729 for the display system 705 or display system
203 to present an image that is enhanced by optical dithering
(optical line doubling, in fact quadrupling) and that is enhanced
by the phase shifting of the invention as described herein. The
respective signals are shown on a time scale presented on the "x"
axis. Vertical sync pulses G from a conventional video signal used
for driving a television, CRT, LCD, etc., are presented at periodic
intervals, e.g., at a frequency of 60 Hz. (one pulse each about
16.67 milliseconds (ms)). An odd/even frame signal H also is
presented; this signal is approximately a square wave having high
and low half cycle portions, each half cycle occurring over a
period of about 16.67 ms. The high portion of the frame signal
represents an odd or even frame, and low represents the other
frame. A video data delay signal I controls delivery of video data;
high is on and low is off.
[0281] In the display system 203 there are two surface mode liquid
crystal cells 211v, 211h, hereinafter sometimes abbreviated SMD
(for surface mode device), which serve as respective polarization
rotators or optical switches. It will be evident that other types
of switches may be used. As is known, one type of operation of an
SMD results in the SMD having two states, one in which it provides
substantially no optical phase retardation of light, for example,
zero or near zero, and one in which it provides a relative maximum
amount of optical phase retardation, for example, 90 degrees, 45
degrees, etc., depending on the optical thickness of the SMD and/or
on other properties of the particular SMD. Usually the minimum and
maximum optical phase retardations are produced, respectively, when
a respective relative maximum and minimum voltage is applied across
the liquid crystal cell forming the SMD. Usually, the minimum
voltage is a non-zero rms voltage which preconditions the liquid
SMD crystal cell, sometimes referred to as biasing the SMD, to help
maintain the alignment of the liquid crystal material in the
maximum optical retardation condition. In one example, the
preconditioning is provided by a constantly applied voltage in the
"low voltage" or maximum optical retardation state. In another
example, the precondition is provided by the effect of an rms
voltage occurring as a result of periodically driving the liquid
crystal cell with a voltage that varies between an instantaneous
value of a maximum level and zero. In this case, the voltage is
reapplied before the liquid crystal cell can relax fully. Other
techniques for driving an SMD also may be possible.
[0282] As is seen in curve J, the voltage waveform applied to the
SMD 211v (FIG. 14) varies at the extremes J' between -15 volts and
+15 volts which provides minimal optical phase retardation
(rotation of the plane of polarization). Portions J'' of the
voltage J also are at plus and minus a small voltage that is
slightly above and below, respectively, the zero voltage level;
these portions J'' are the voltage of the SMD when it is in the
maximum optical phase retardation condition (providing maximum
rotation of plane of polarization). Each portion J' and j'' of the
voltage J is the same duration as the respective half cycle of the
odd/even signal H and the same duration as the time period between
vertical sync pulses G. However, the phase of the voltage waveform
J is shifted from the phase of the vertical sync G and odd/even
frame signal H by an amount which is determined in the manner
described above with respect to FIGS. 44-46, for example. That
phase shift in the illustrated example is 13.2 milliseconds, as is
evident from the scale at the bottom of FIG. 48. Waveform signal or
voltage K in FIG. 48 is applied to the SMD 211h (FIG. 14). It
varies only at one half (1/2) the frequency of the waveform J.
[0283] As an example of operation of the display system 203, which
is not necessarily coordinated with the sequence of FIGS. 16A-16D,
although producing the result of FIG. 17, incident plane polarized
light is provided to and transmitted through the SMD's 211h and
211v, which are operated generally according to the waveforms J and
K. Therefore, the polarization of light respectively entering the
birefringent crystals, e.g., calcite or other birefringent
material, 210h, 210v will vary generally in the manner depicted by
curves L and M, which is synchronized and in phase or approximately
in phase with the operation of the SMD's 211h, 211v. As light
transmits through the respective birefringent crystals 210h, 210v,
the location of the image from respective pixels of the display 202
will vary generally along the lines of the curves N and O. The
description herein refers to direction, e.g., horizontal and
vertical; it will be appreciated that such reference only is
exemplary, and where vertical shifting or orientation is referred
to, horizontal could be substituted, and vice versa.
[0284] The phase shifting for coordination of optical switching
with an optical display, for example, as described above, also may
be used in a display system that provides multicolor output with
good contrast even though brightness or intensity of the output
light is varied, for example, of the type disclosed in
above-referenced patent application Ser. No. 08/187,163. Using such
phase shifting in coordination with the liquid crystal display
system of such patent application and/or with the dithering of
others of the patent applications referenced above to provide a
multicolor output can increase the resolution, sharpness and
crispness of the viewed image, for example.
[0285] Referring to FIG. 49, a light transmissive display system
according to an embodiment of the invention is illustrated at 901.
The display system 901 includes a light source 902, liquid crystal
display 903, such as that shown at 724d in FIG. 43, optics 904,
such as that shown at 14 in FIG. 43, for projection or viewing of
the images created by the liquid crystal display, a computer
control 905, such as the control 729 in FIG. 43, and an image
signal source 906, which may be part of the control 905 or a
separate source of video signals or other signals as may be
appropriate. A photodetector 907 also may be included in the system
901.
[0286] The light source 902 may be one or more light emitting
diodes, incandescent light source, fluorescent light source, light
received via fiber optics or other means, a metal halide lamp,
etc.
[0287] The liquid crystal display 903 may be a twisted nematic
liquid crystal cell, a variable birefringence liquid crystal cell,
a supertwist liquid crystal cell, or some other type or liquid
crystal cell able to modulate light. The liquid crystal display 903
may include polarizers, wave plates, such as quarter wave plates or
other wave plates, means for compensating for residual
birefringence or for problems encountered during off axis viewing,
etc. Other types of display devices which modulate light as a
function of some type of controlled input can be used in place of
the liquid crystal cell 903. Exemplary liquid crystal cells and
display devices which may be used for the liquid crystal cell 903
are disclosed in U.S. Pat. Nos. 4,385,806, 4,436,376, 4,540,243,
Re. 32,521, and 4,582,396, which disclose surface mode and pi-cell
liquid crystal devices, and in concurrently filed, commonly owned
U.S. patent application Ser. No. 08/187,050, entitled "Folded
Variable Birefringence Liquid Crystal Apparatus."
[0288] The optics 904 may be one or more lenses separate from
and/or included as part of the liquid crystal display for the
purpose of providing an output image for viewing or for projection.
If for viewing, such optics 904 may be one or more lenses which
focus an image for close, e.g., as in a head mounted display of the
heads up display type, virtual reality type or multimedia type, or
far viewing, e.g., as in a slide viewer or a television. If for
projection, such optics 904 may include projection optics which
project an image formed by the display 903 onto a screen for
transmissive viewing or reflective viewing.
[0289] The image signal source 906 may be a source of computer
graphics signals, NTSC type television (video) signals, or other
signals intended to produce an image on the display 903. Such
signals are decoded in conventional manner by the computer control
905, for example, as is the case in many display systems, and in
response to such decoding or deciphering, the computer control 905
(or some other appropriate control, circuit, etc.) operates the
display 903 to produce desired images. If desired, the computer
control 905 can operate the display 903 in sequential manner to
produce multiple images in sequence while the display is being
illuminated by only a single light source or color of light, e.g.,
a monochromatic type of operation. Exemplary operation of this type
is summarized in the above '396 patent. Other exemplary types of
operation of the computer control 905 include those employed in
conventional liquid crystal display televisions of the hand-held or
larger type and/or liquid crystal type computer monitors.
Alternatively, the computer control can operate the display 903 in
a field sequential or frame sequential manner whereby a particular
image is formed in several parts; while one part is formed, the
display is illuminated by light of one color; while another part is
formed, the display is illuminated by light of a different color;
and so on. Using this field sequential type operation, multicolor
images can be produced by the display system apparatus 901.
[0290] In a typical input signal to a television or liquid crystal
television, there is information indicating brightness of the light
to be transmitted (or reflected) at a particular pixel. The
computer control 905 is operative to compute the brightness
information of a particular image or scene and in response to such
computation to control the intensity or brightness of the light
source 902. While intensity or brightness of the light source is
controlled in this manner, the computer control 905 operates the
liquid crystal display 903 to modulate light without having to
reduce the number of pixels used to transmit light. Therefore, the
full number or a relatively large number of pixels can be used to
form the image or scene even if the brightness of the scene as
controlled by the controlled light source is relatively dark.
[0291] Information coming through from the image signal source 906
may indicate various levels of illumination. There usually is a
blanking pulse and a data line pulse. The computer control 905 can
take the integral of the data line electrically or an integral of
the whole set of data (from all of the data lines of the scene) or
all of the pixels while electrically skipping the blanking. Based
on that integral, the brightness of the light incident on the
display 903 is controlled by the computer control 905. It will be
appreciated that a person having ordinary skill in the art would be
able to prepare an appropriate computer program to provide the
integral functions and to use the results of such integration to
provide brightness control for the light source 902.
[0292] From the foregoing, then, it will be appreciated that the
apparatus 901, including the computer control 905, is operative to
control or to adjust the brightness of a scene without degrading
the contrast ratio. Thus, the same contrast ratio can be maintained
while brightness of a scene or image is adjusted. For example, the
same contrast ratio or substantially the same contrast ratio can be
maintained by the apparatus 901, whether depicting a scene of a
bright sunlit environment or of the inside of a dark cave.
Therefore, the scene will have the appearance of illumination under
natural illumination conditions.
[0293] The features of the invention described below can be used in
virtually any passive display system.
[0294] Power requirements of the apparatus 901 can be reduced over
prior display systems because the intensity of light produced by
the source 902 is controlled to create dark images. In prior
systems, though, the intensity of the light produced by the source
was maintained substantially constant while the amount of light
permitted to be transmitted through the passive display would be
reduced to create a dark scene image.
[0295] In addition to controlling intensity of the light source 902
as a function of brightness of a scene, the computer control 905
also may be responsive to measurement or detection of the ambient
environment in which the apparatus 901 is located. The brightness
of such ambient environment may be detected by the photodetector
907. The photodetector 907 may be place in a room or elsewhere
where the image created by the display 903 is to be viewed; and the
brightness of the source 902 can be adjusted appropriately. For
example, if the room is dark, it usually is desirable to reduce
brightness of the source; and if the room is bright or the
apparatus is being used in sunlight, the brightness of the source
may be increased.
[0296] Turning to FIG. 50, a light reflective display system
according to the invention is illustrated at 901'. The display
system 901' includes a light source 902', liquid crystal display
903', optics 904' for projection or viewing of the images created
by the liquid crystal display 903', a computer control 905', and an
image signal source 906. A photodetector 907 also may be included
in the system 901. The various parts of the display 903' and optics
904' may be the same or similar to those disclosed in the U.S.
patent applications referred to above. The light source 902' and
display 903' may be of the type disclosed in concurrently filed,
commonly owned U.S. patent application Ser. No. 08/187,262,
entitled "Illumination System For A Display."
[0297] For example, the light source 902' may include a source of
circularly polarized light 902a' and a cholesteric liquid crystal
reflector 908. The liquid crystal display 903' may be a reflective
variable birefringence liquid crystal display device.
Full Color Frame Sequential Illumination System and Display.
[0298] Turning to FIG. 51 a full color display subsystem 919
including illumination system 920 is shown. However, in the display
subsystem 919 the illumination system 920 includes several sources
of light, each having a different wavelength. For example, three
separate light sources 902r, 902g, 902b provide red, green and blue
wavelength light, respectively, or light that is in respective
wavelength bands or ranges that include red, green and blue,
respectively. The light sources may be respective light emitting
diodes or they may be other sources of red, green and blue light or
other respective wavelengths of light, as may be desired for use in
the display subsystem 919. The cholesteric liquid crystal reflector
908 is able to reflect green light; the reflector 908a is able to
reflect red light; the reflector 908b is able to reflect blue
light. Such reflection occurs when the circular polarization
characteristic of the light is the same direction as the twist
direction of the cholesteric liquid crystal material in the
respective reflector. The reflectors 908, 908a, 908b are
transparent to the other polarizations of incident light and to the
other wavelengths of incident light.
[0299] The illumination system 920 is intended sequentially to
illuminate the display 903', which may include a wave plate, such
as a quarter wave plate, (or respective portions of the display)
with respective wavelengths of light. For example, for a period of
time the display 903' (or portion thereof) is illuminated with red
light; subsequently illumination is by either green or blue light;
and still subsequently illumination is by the other of green or
blue light. Such sequential illumination may be carried out
sufficiently rapidly so that respective red, green and blue images
created by the display 903' when illuminated by the respective
colors of light are output from the display subsystem 961 and are
integrated by the human eye. As a result, the human eye effectively
sees a multicolor image. Other examples of frame sequential
switching to provide multicolor and/or full color outputs are known
in the art. Various advantages inure to a frame sequential
multicolor display, including the ability to provide high
resolution with approximately one-third the number of picture
elements required for a full color r, g, b display system in which
respective pixels are red, green or blue.
[0300] The sequential delivering of red, green and blue light to
the display 903' is coordinated by the control system 905 with the
driving of the display 903'. Therefore, when a red image or a
portion of a red image is to be produced by the display 903', it is
done when red light is incident on the display 903'; and the
similar type of operation occurs with respect to green and blue
images.
[0301] If the respective light sources 902r, 902g, 902b are light
emitting diodes, they may be sequentially operated or energized to
provide light in coordination with the operation of the display
903' under direct control and/or energization by the control system
905. Alternatively, the control system 905 may be coordinated with
whatever other means are used to provide the respective red, green
and blue color lights of the light source.
[0302] Another example of frame sequential or field sequential
operation of a displays subsystem like that shown at 961 herein is
described in the above-referenced patent applications. Another
example of field sequential operation is described in U.S. Pat. No.
4,582,396, which is mentioned above and incorporated by
reference.
[0303] Referring to FIG. 52, a head mounted display 960 includes a
pair of display systems 961, 962 and a control system 705 for
creating images intended to be viewed by the eyes 964, 965 of a
person. The display systems 961, 962 may be positioned in
relatively close proximity, for example, at approximately one inch
distance, to the respective eyes 964, 965. A mounting mechanism,
such as temple pieces 966, 967 and a nose bridge 968 may be
provided to mount the display 960 on the head of the person.
[0304] The control system 905 in conjunction with the display
systems 961, 962 are intended to create images for viewing by the
eyes. Those images may be monochromatic. The images may be
multicolor. The images may be two-dimensional or they may provide a
three dimensional, stereoscopic effect. Stereoscopic effect viewing
is obtained when the control system 905 operates the display
systems 961, 962 to provide, respectively, right eye and left eye
images that are sufficiently distinct to provide depth perception.
Right eye, left eye imaging and depth perception are techniques
used in some stereoscopic imaging and viewing systems which are
commercially available.
[0305] The display systems 961, 962 may be identical. The control
system 905 provides control and/or power input to the display
systems 961, 962 to create images for display to the eyes 964, 965.
The display 960 may be a head mounted display, such as a heads-up
display, a virtual reality display, or a multimedia display. The
control system 905 may be generally a control system of the type
used in known head mounted displays to create such images. Such a
control system may provide for control of color, light intensity,
image generating, gamma, etc. The display systems 961, 962 may
include focusing optics so as to focus the image created by the
display systems for comfortable viewing, for example from a few
inches up to a few feet in front of the eyes, say, from about 20
inches to about several feet in front of the eyes.
[0306] It will be appreciated that the features of the liquid
crystal cell 903' may be used in the display 960 of the head
mounted type. Also, features of the invention may also be employed
in other types of display systems. One example is a display system
that uses only a single display system of the type described
herein. Such display system may be located in proximity to an eye
for direct viewing. Alternatively, such display system may be used
as part of a projection type display in which light from the
display system is projected onto a surface where the image is
formed for viewing. Various lenses and/other optical components may
be used to direct from the display system light to create an
appropriate image at a desired location.
[0307] Turning to FIGS. 53-58, operation of the apparatus is
described. In FIG. 53, a plan view of a dot matrix liquid crystal
display is shown. The shade of grey measured at several pixels is
indicated. According to the bottom graph in FIG. 53, the actual
shade is shown; according to the dot matrix image at the side and
top of FIG. 53, the actual shade of the pixel is shown. Thus, at
location 1 on the graph at the bottom of FIG. 53, there is a shade
2. At location 2, there is a shade 1. At location 3 there is a
shade 0, and so on. In pixel 1 marked in the top of FIG. 53, the
pixel is a shade of gray of 2; and at the adjacent pixel the pixel
is a shade gray of 1, and so on. This is conventional. This would
indicate the signals coming in to the computer control 905.
[0308] In FIG. 54, an example of a bright image scene produced by
back light at a medium (normal) illumination level is illustrated
at the top; the shades of gray are shown at the middle left; and
the lamp light level is constant at the bottom left. The viewer
sees a bright/low contrast image of a person as seen at the top
right of the drawing. A side view of the display representing
respective pixels and the gray levels thereof is shown at the
bottom right of the figure.
[0309] FIG. 55 is similar to FIG. 54 again with average constant
lamp light level. The average light level is produced; the average
brightness output from the display is to be produced; and the
viewer sees an average brightness high contrast image because all
conditions are optimized.
[0310] FIG. 56 is similar to FIG. 54 again with average constant
lamp light level and a dark transmission provided by the liquid
crystal cell; the viewer sees a dim low contrast image.
[0311] FIGS. 54-56 represent operation of a standard display
apparatus. FIGS. 57 and 58 represent applying the principles of the
present invention to develop high contrast images. In FIG. 57 it is
seen that there is the intent to produce a wide range of gray
levels; and this is possible by using a high intensity lamp level;
the result is a bright high contrast image. In FIG. 58 it is
intended that the viewer see a dim image; the same range of grey
shades are provided as is depicted in the middle left graph of the
drawing; but the lamp level is low. Therefore, there is a good
contrast ratio provide to the viewer; from 0 to about 7 at the
brightness level shown in the graph at the upper left of the
drawing.
TABLE-US-00002 CHART I CALC3 SHIFT POL POL 1/4 X DOUBLES VOLT. DIR
CALC1 VOLT DIR CALC2 POL DIR HORIZ FRAME FIELD SMD1 OUT1 SHIFT SMD2
OUT2 SHIFT OUT / 2 PIXEL 1 1 Lo H None Lo V None H, V X2 1 2 Hi V
Vert. Hi V Non H, V X2 Down 2 1 Lo H None Hi H Horiz. H, V X2 Right
2 2 Hi V Vert. Lo H Horiz. H, V X2 Down Right
* * * * *