U.S. patent application number 14/002061 was filed with the patent office on 2013-12-19 for high contrast grayscale and color displays.
This patent application is currently assigned to Dolby Laboratories Licensing Corporation. The applicant listed for this patent is John Gilbert, Christopher J. Seline. Invention is credited to John Gilbert, Christopher J. Seline.
Application Number | 20130335682 14/002061 |
Document ID | / |
Family ID | 46798735 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130335682 |
Kind Code |
A1 |
Gilbert; John ; et
al. |
December 19, 2013 |
High Contrast Grayscale and Color Displays
Abstract
A high contrast high resolution display is produced using an
image chain comprising a plurality of downstream high resolution
modulators. The modulators may be illuminated by a locally dimmed
backlight. Polarization control is maintained throughout the image
chain via reference and analyzing polarizers combined with
non-depolarizing layers. The modulators are grayscale and modulate
at the sub-pixel level. A color panel may be maintained for
embodiments that require color. Diffusion in the chain is matched
to a resolution of the image content carried in the light such that
the effects of local dimming and sub-pixel resolution are
preserved. Brightness enhancement films may be utilized to enhance
brightness and maintain polarization control.
Inventors: |
Gilbert; John; (Pacifica,
CA) ; Seline; Christopher J.; (San Francisco,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Gilbert; John
Seline; Christopher J. |
Pacifica
San Francisco |
CA
CA |
US
US |
|
|
Assignee: |
Dolby Laboratories Licensing
Corporation
San Francisco
CA
|
Family ID: |
46798735 |
Appl. No.: |
14/002061 |
Filed: |
March 5, 2012 |
PCT Filed: |
March 5, 2012 |
PCT NO: |
PCT/US12/27729 |
371 Date: |
August 28, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61450802 |
Mar 9, 2011 |
|
|
|
Current U.S.
Class: |
349/85 ;
345/89 |
Current CPC
Class: |
G02F 2203/30 20130101;
G02F 2001/133601 20130101; G09G 3/3607 20130101; G02F 1/133536
20130101; G02F 1/133528 20130101; H04N 13/356 20180501; G09G
2300/023 20130101; G09G 2320/0238 20130101; G02F 1/1323 20130101;
G02F 2203/34 20130101; G09G 2320/0242 20130101; G02F 1/133504
20130101; G02F 1/133606 20130101; G02F 2001/134345 20130101; H04N
13/361 20180501; G09G 3/3611 20130101; G02F 1/133609 20130101; H04N
13/351 20180501; G02F 2001/133622 20130101; G09G 3/003 20130101;
G09G 3/3426 20130101; H04N 13/332 20180501; G02F 1/13471 20130101;
G09G 2340/0457 20130101; G09G 2320/0646 20130101; G09G 2360/145
20130101; G02F 1/13318 20130101; G09G 2360/16 20130101; G02F
1/133611 20130101; H04N 13/337 20180501; H04N 13/324 20180501 |
Class at
Publication: |
349/85 ;
345/89 |
International
Class: |
G09G 3/36 20060101
G09G003/36; G02F 1/1335 20060101 G02F001/1335 |
Claims
1. A display, comprising a dual modulation architecture with local
dimming wherein modulated locally dimmed light is passed through
multiple downstream polarization controlled modulators.
2. The display according to claim 1, wherein the downstream
polarization controlled modulators comprise an LCD panel with color
filters removed such that each pixel of the LCD panel comprises 3
sub-pixels each covering approximately 1/3 of the pixel and a
analyzing polarizer intended to reflect upstream light rays
modulated by the LCD panel.
3. The display according to claim 2, further comprising a
de-polarizing reflector positioned around a source of the locally
dimmed light.
4. The display according to claim 1, further comprising an optical
stack comprising a reference polarizer and a series of films
configured to enhance brightness and reduce loss of light
transmitted through the stack.
5. The display according to claim 4, wherein the films comprise at
least one brightness enhancing layer.
6. The display according to claim 5, wherein the optical stack is
positioned after a source of the locally dimmed light and before a
first of the downstream modulators.
7. The display according to claim 6, wherein the stack comprises a
backlight resolution scale diffuser where the backlight resolution
comprises a resolution of a local dimming capability of sources of
the locally dimmed light.
8. The display according to claim 5, wherein the optical stack is
positioned between downstream modulators.
9. The display according to claim 8, wherein the stack comprises a
sub-pixel scale diffuser where the sub-pixel scale corresponds to
sub-pixels of an upstream one of the modulators surrounding the
stack.
10. The display according to claim 9, wherein the sub-pixel scale
diffuser comprises a diffuser that diffuses sub-pixels proportional
to sub-pixels generated by an LCD panel with color filters
removed.
11. The display according to claim 9, wherein subpixels of the
modulator comprise approximately 1/3 of a standard LCD pixel.
12. The display according to claim 5, wherein the stack is
positioned between a source of the locally dimmed light and a first
of the downstream modulators, and a similar stack is positioned
between the first and second of the downstream modulators.
13. The display according to claim 1, wherein the downstream
modulators comprise LCD panels with color filters removed.
14. A controller for a display, comprising a light field simulation
module configured to determine a light field incident on a
downstream modulator wherein the simulation takes into account a
sub-pixel level modulation of the light.
15. The controller according to claim 14, wherein the simulation
further takes into account a sub-pixel scale diffusion of the
sub-pixel modulated light.
16. The controller according to claim 14, wherein the simulation
further takes into account a source of the light that is locally
dimmed prior to the sub-pixel modulation.
17. The controller according to claim 14, wherein the simulation
further takes into account at least one optical stack comprising at
least one brightness enhancing film.
18. The controller according to claim 14, wherein the controller is
configured to provide energization signals to at least one
downstream modulator based on the simulation.
19. The controller according to claim 18, wherein the controller is
installed in a medical device and is configured to control a
display of the medical device with regard to high resolution and
contrast such that viewing angle traded for resolution and/or
contrast.
20. The controller according to claim 19, wherein the display is
grayscale.
21. The controller according to claim 18, wherein the controller is
installed in a consumer display and is configured to control the
display in a manner that provides high contrast and resolution with
an industry standard viewing angle.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent
Application No. 61/450,802 filed 9 Mar. 2011, hereby incorporated
by reference in its entirety.
FIELD OF INVENTION
[0002] The present invention relates to High Dynamic Range Displays
(HDR), and more particularly to Grayscale HDR displays using dual
modulation.
DISCUSSION OF BACKGROUND
[0003] High Dynamic Range (HDR) displays are generally defined as
having a dynamic range of greater than 800 to 1. Recent advances in
technology have produced displays claiming contrast ratios of more
than 1,000,000 to 1.
[0004] Generally speaking, these higher contrast ratio HDR displays
utilize local dimming of the backlight that illuminates the LCD
panel. An early patent in this area, U.S. Pat. No. 6,891,672, by
Whitehead, Ward, Stuerzlinger, and Seetzen entitled "HIGH DYNAMIC
RANGE DISPLAY DEVICES" describes the fundamental techniques. Such
techniques include illuminating the LCD panel with an approximation
of a desired image and then further modulating the approximation
with the LCD panel so that it approaches the desired image.
[0005] Other forms of improving contrast have also been presented,
including "darkening" of an LCoS projected image through the use of
an LCD panel (Berman), and the use of multiple registered
modulating layers or premodulators (e.g., Blackham U.S. Pat. No.
5,978,142, Gibbon U.S. Pat. No. 7,050,122, and others). However,
commercially available HDR displays have deficiencies in
reproducing starfields and other challenging images mainly due to
parallax, backlight leakage, and other issues, and artifacts
resulting therefrom.
SUMMARY OF THE INVENTION
[0006] The present inventors have realized the need to improve
spatially localized contrast in LCD panels and other displays. The
displays of the invention are generally produced from multiple
modulation layers. The multiple modulation layers may be any of LCD
panels, grayscale LCD panels, and RGB color panels without the
color filters. The panels without color filters give higher
resolutions.
[0007] The panels may be, for example, illuminated with a backlight
that may be monochromatic, locally dimmed, edge-lit, CCFL, or
another backlight technology. The invention manages polarization
through all layers so that the maximum light is reused from one
layer to the next.
[0008] By using a very bright backlight, polarization management,
and unfiltered LCD panels, displays much brighter than normal are
possible. The use of two or more panels (e.g., LCD panels)
enhances, improves, and partially enables the achievement of high
contrast. With the additional control of the multiple panels,
higher total control of brightness per pixel is achieved.
[0009] Light efficiency of the panels or optical stack including
the panels (with color filters removed, or B&W versions) is
greater than a typical color LCD panel. In situations where high
brightness is not necessary, dimmer and less energy consuming
backlights can be used.
[0010] Resolution of a display according to the invention can be
more than the resolution of the LCD panels if a tighter viewing
angle is acceptable. The invention includes designing and utilizing
a tradeoff between resolution and viewing angle. The resolution of
color-filter-free displays that originate as RGB displays (or
similarly designed panel) is typically three times that of a
regular color LCD panel, and can be taken advantage of in various
embodiments of the invention.
[0011] Various aspects of the invention can achieve greater viewing
angles without visual artifacts by splitting the lower resolution
brightness features in an image from the higher resolution features
and displaying them on different panel layers.
[0012] In one embodiment, the invention may be described as a
display comprising (in order from inside components toward the
viewable part of the display): a light reflector, a light source
(backlight), a backlight diffuser, one or more layers of light
focusing films (optional but improves efficiency, brightness and
contrast), a reflective polarizer (also optional, but improves
efficiency and brightness), a biasing polarizer, a
color-filter-free LCD panel, a finishing polarizer (optional,
trades brightness for contrast), a second diffuser designed to
eliminate Moire interactions between the two LCD panels but
preserves as much polarization as possible, a second biasing
polarizer, a second color-filter-free LCD panel, a second finishing
polarizer. Additional layers of LCD panels, films, including BEFs,
polarizers, anti-glare coatings, etc., may be utilized.
[0013] In another embodiment, the two LCD panels can be of
differing resolutions, with the downstream LCD panel being a lower
resolution (possibly less expensive) than the upstream panel.
Preferably a low/non-artifact relationship between resolution of
the panels is utilized, as large scale resolution differences
create Moire features that are small enough to be masked by the mid
diffuser, and small scale differences are spread out over a large
area of the display and are not noticeable. Mid scale differences
however create mid scale Moire features that may not be maskable by
the diffuser and are therefore not desirable.
[0014] In certain kinds of LCD panels, the polarization angle
changes that the LCDs make on light passing through them is
dependent on the specific wavelengths of light as well as the LCD
control signal. This means that even with a LCD panel without color
filters, certain LCD control settings can create images with slight
amounts of color. This can be mitigated if desired by the addition
of a polarization retarding film that is color dependent. In dual
LCD systems with a one of the LCD panels containing color filters,
or dual color-filter-free LCD systems with an additional color LCD
panel, these slight color effects can be canceled out with the
correct countering signal to the color LCD. The invention includes
any such color correction methods applied in an optical path, such
as in a display.
[0015] In another embodiment, the two LCD panel display is equipped
with a backlight that is controllable to be able to switch colors
and brightness. Various images can be presented on the display with
different colors set on the backlight in rapid progression. This
allows the display to generate color images with much greater
control over the levels of brightness and saturation between
colors. This also allows for arbitrary numbers of primaries or base
colors to be able to hit much greater color gamuts.
[0016] In various embodiments, displays described in this document
can be used for developing and commercializing a low cost
consumer/prosumer grade high dynamic range display monitor. The
hardware elements and algorithmic components described in this
document can be developed into software plug-ins or as a software
module in existing graphics cards to perform relevant tasks to turn
existing displays (changing existing designs and/or retrofits) into
high dynamic range displays.
[0017] In one embodiment, the present invention provides a high
dynamic range display comprising a color LCD panel for generating
an image (the image-generating panel) and an LCD panel without
color filters (the contrast-improving panel) arranged to increase
the contrast ratio and improve black levels (either making them
darker or increasing the color and brightness fidelity of dark
areas that are not intended to be completely black) in the
generated image.
[0018] In another embodiment, the present invention provides a
display comprising an image-generating panel and a
contrast-improving panel wherein the contrast-improving panel
comprises an LCD panel without color filters. The
contrast-improving panel may operate in combination with an
analyzing polarizer. The contrast-improving panel may be placed
downstream of the image-generating panel. The resolution of the
contrast-improving panel may be higher or lower than the
image-generating panel. The image-generating panel may comprise,
for example, a color filter based LCD panel having the same
polarization rotating design as the contrast-improving panel. The
contrast-improving panel may be, for example, abutted to the
image-generating panel.
[0019] The invention includes a controller comprised of an
image-generating panel energization module (e.g., a color module
and/or a color correction module) and a contrast-improving panel
energization module (e.g., a contrast-improving control module).
The controller may be connected, for example, to energize both the
image-generating LCD and the contrast-improving LCD with control
data produced by the corresponding energization module(s).
Energization of the image-generating panel may be based in part on
feedback from the contrast-improving panel energization module to
the image-generation panel energization module.
[0020] The controller may be configured, for example, to input data
from a media source of a standardized high resolution and contrast,
or higher (e.g., High Definition VDR), or other image types. The
image-generating panel may be selected to be capable of producing
an image of the standardized high (or other) resolution. The
contrast--improving layer is configured to increase contrast using,
for example, a different resolution than the image-generating
panel. Preferably, the resolution of the contrast enhancing panel
is higher than the image generating panel (but may be equivalent or
less).
[0021] The present invention includes a display comprising a
contrast-improving panel, which may comprise, for example, an LCD
panel without color filters. The display may include another
modulators such as a color-panel, and, the contrast-improving panel
may have a higher resolution than the other modulator or
modulators. The display may include, for example, a set of
diffusers, including a relatively coarse diffuser configured to
diffuse light from a backlight of the display, and a relatively
fine diffuser configured to mask high frequency details or
uncontrolled features in light modulated by the contrast-improving
panel. The contrast-improving panel may be located between the set
of diffusers and upstream of the other modulator(s).
[0022] The present invention includes displays where the
image-generating panel comprises a color filter layer, an active
layer, and a polarization filter layer, and the contrast-improving
panel comprises an active layer and a polarization filter layer.
The layers of the image-generating panel and the contrast-improving
panel may be preferably arranged, for example, so as to place the
active layers of the image-generating panel and the
contrast-improving panel as close together as possible.
[0023] The image-generating layer is backlit by at least one type
of light source. The light sources may comprise, for example, of
CCFLs, LEDs, and OLEDs. These may be directly illuminating or the
light can be carried through a light pipe, in the case of an edge
lit configuration. In one embodiment, the array of light sources
comprises at least one of the following: White or broad spectrum
light sources, RGB light sources, RGBW light sources, RGB plus one
or more additional primary light sources, or other multi-primary
light source color combinations. The array of light sources (e.g.,
edge-lit light sources) may be locally dimmed. In one embodiment,
the light sources comprise different colors and each color's
brightness is individually controllable.
[0024] In one embodiment, the display includes a contrast-improving
layer (e.g., contrast-improving panel) that is backlit by an array
of light sources, and the backlight and contrast-improving panels
are arranged such that light passing through the contrast-improving
panel from the backlight illuminates the image-generating panel.
The contrast-improving panel may produce, for example, a base
version of an image to be displayed by the display and the
image-producing panel further modulates the base image to produce
the image to be displayed. The base image comprises, for example,
brightness intensity in proportion to brightness intensities of the
image to be displayed. The brightness intensity of the base image
may be a sharper image than the image to be displayed.
[0025] In one embodiment, the base image is a blurred approximation
of brightness levels in proportion to brightness levels of the
image to be displayed. In similar and other embodiments, the
invention includes a controller connected to an image-generating
panel and a brightness-improving panel and is configured to provide
first-processed image data to the image-generating panel and
second-processed image data to the brightness-improving panel,
wherein the first-processed image data is produced in part based on
image data input from a media source and feedback from production
of the second-processed image data. The first-processed image data
may comprise a full-color high-resolution version of the input
image data, and the second-processed image data may comprise a
mapping of brightness levels proportional to the input image
data.
[0026] The invention may be implemented as a display or as a system
and portions of the invention may be conveniently implemented as a
method, for example, in programming on a general purpose computer,
or networked computers, and the results may be displayed on an
output device connected to any of the general purpose, networked
computers, or transmitted to a remote device for output or display.
In addition, any components of the present invention represented in
a computer program, data sequences, and/or control signals may be
embodied as an electronic signal broadcast (or transmitted) at any
frequency in any medium including, but not limited to, wireless
broadcasts, and transmissions over copper wire(s), fiber optic
cable(s), and co-ax cable(s), etc.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0028] FIG. 1 is a schematic diagram of a high dynamic range
display according to an embodiment of the present invention;
[0029] FIG. 2A is a schematic diagram of a high dynamic range
display according to another embodiment of the present
invention;
[0030] FIG. 2B is a schematic diagram of a high dynamic range
display according to another embodiment of the present
invention;
[0031] FIG. 2C is a graph illustrating high frequency features and
diffusion according to an embodiment of the present invention;
[0032] FIG. 3A is a drawing illustrating an arrangement of layers
in a typical LCD panel;
[0033] FIG. 3B is a drawing illustrating an arrangement of layers
in an LCD panel and a brightness-improving panel according to an
embodiment of the present invention;
[0034] FIG. 4A is an architecture and an alternative architecture
of an electronic device that generates energization signals for LCD
panels and contrast-improving panels according to an embodiment of
the present invention;
[0035] FIG. 4B is an architecture of another electronic device that
generates energization signals for LCD panels and
contrast-improving panels according to an embodiment of the present
invention;
[0036] FIG. 4C is an architecture of yet another electronic device
that generates energization signals for LCD panels and
contrast-improving panels according to an embodiment of the present
invention;
[0037] FIG. 4D is an architecture of still yet another electronic
device that generates energization signals for LCD panels and
contrast-improving panels according to an embodiment of the present
invention;
[0038] FIG. 5 is a flow chart of a process for energizing a high
dynamic range display according to various embodiments of the
present invention;
[0039] FIG. 6 is an illustration of a color diagram describing
aspects of various embodiments of the invention;
[0040] FIG. 7A is an arrangement of controllable panels according
to an embodiment of the present invention;
[0041] FIG. 7B is an arrangement of pixels on panels according to
an embodiment of the present invention;
[0042] FIG. 8 is an arrangement of controllable panels according to
various embodiments, including simultaneous 2D and 3D displays, of
the present invention;
[0043] FIG. 9 is a drawing of one possible embodiment of a
simultaneous 2D and 3D display according to the present invention;
and
[0044] FIG. 10 is an arrangement of controllable panels according
to an embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] Referring now to the drawings, wherein like reference
numerals designate identical or corresponding parts, and more
particularly to FIG. 1 thereof, there is illustrated a new
construction for a high dynamic range display 100 according to an
embodiment of the present invention. The display 100 includes a
backlight 110 which may be a standard CCFL or other broadband
lighting source (e.g., LEDs, OLEDs, etc.). In addition, the
backlight may be direct lit (light source(s) directly illuminating
downstream modulation panels) or edge lit (as is popular in many
thin screen LCD display designs). Further yet, the backlight may be
constant, globally dimmed, or locally dimmed. The light source for
this display can be white, controllable luminance, or multiple
color driven.
[0046] The backlight 110 illuminates downstream modulators,
including, in this example, an LCD panel 120 which modulates the
backlight in intensity and color. A controllable polarizer (or
contrast-improving panel) 130 further modulates the light as to
polarity (and which may then be attenuated by a polarization layer
to effect an intensity modulation of the output light).
[0047] The LCD panel 120 is constructed to include an initial
polarizing layer 122, which may be for example, any of a reflective
polarizer, an absorptive polarizer, or a polarization converter, or
another device that provides an initial uniform polarization
orientation from which downstream modulations are to be based.
Preferably, the initial polarizing layer 122 is a reflective
polarizer so that light that the reflected light may be "re-cycled"
by reflection into and then back out of the optical cavity of the
backlight 110. An active layer 124 comprises liquid crystals (e.g.,
twisted nematic) and color filters (e.g., typically RGB). The
liquid crystals are oriented based on an energization of the active
layer intended to rotate or change polarization of light passing
through the filters. A passive polarization analyzer 126, which may
be, for example, an absorptive polarizing layer that filters out
(or passes) light of a predefined polarization as changed by the
liquid crystals.
[0048] The controllable polarizer (contrast-improving panel) 130,
may be, for example, the active elements of an LCD panel (e.g., a
TN layer) combined with a passive polarizer (e.g., active layer, or
active elements 134 and passive polarizer 136). The controllable
polarizer 130 may be, for example, an LCD panel without color
filters. As shown, the initial polarizer of this second LCD panel
may be removed, relying, in this specific case, on the passive
polarizing analyzer 126 for an initial uniform polarization.
[0049] In the case of a constant backlight, the backlight 110
produces an initial light 112 which is constant or uniform. In
other embodiments, the initial light 112 may be modulated, e.g.,
any of spatially modulated light, pre-modulated light, globally
dimmed light, individual RGB dimmed, temporally modulated light, or
others, and/or a combination of the above. The initial light 112
illuminates the first downstream modulator (note that additional
optical elements may be placed at virtually any point in the
light/image chain, including any of diffusers, collimators, DEV,
Brightness Enhancement Films (BEFs), etc). Other optical elements
including reflectors may also be utilized depending on the design
(e.g., side lit display designs may utilize, for example, a
reflector/diffuser combination to redirect and diffuse light from a
side light path that is mainly parallel to a display screen to a
light path that is mainly perpendicular to the display screen.
[0050] The image-generating panel 120 modulates the initial light
112 in a manner that is physically similar to a standard LCD
display. The energization of the image-generating panel 120 is
calculated to accommodate the design and use of the controllable
polarizer 130 and is discussed in more detail further below. 1st
modulated light 128 is emitted from the image-generating panel 120
and illuminates the contrast-improving panel 130.
[0051] The contrast-improving panel 130 further modulates the
1.sup.st modulated light 128 in a manner that increases the
contrast and, for example, resolution of the modulated light,
resulting in a 2.sup.nd modulated light, or, in this case, better
described as final image light 138. The increased resolution
results, for example, when the contrast-improving panel 130 has
more pixels for a given area than the image-generating panel
120.
[0052] Increased spatial resolution may also result when the active
elements 134 are of similar/same construction as active elements of
the image-generating panel 120 (e.g., LCD panel 120 and
contrast-improving panel 130 are the same except that the
contrast-improving panel 130 has the color filters removed).
Benefits may also be obtained when the pixels of the
contrast-improving panel are of a different shape, offset, size
(e.g., smaller or larger), orientation (e.g., 0, 45, or 90
degrees), or layout compared to the image-generating panel.
[0053] The active elements 134 rotate polarization of individual
"pixels" of the 1.sup.st modulated light 128 based on a desired
local dimming effect. Pixels in quotations because the pixels of
first modulated light 128 may be different from pixels of the
active elements 134. In the case where a design utilizes an LCD
panel (e.g., LCD panel 120) having active elements that are the
same as active elements 134, the pixels of the active elements 134
are still different from the pixels of the LCD panel 120 because
the pixels of the LCD panel 120 each include three active elements
(one for each Red, Green, and Blue filter that forms each LCD
pixel), where each element of the active elements 134 may be
defined as a single pixel.
[0054] The active elements 134 further modulate the 1.sup.st
modulated light 128 on a pixel-by-pixel basis via the pixels of the
active elements 134 by imposing a prescribed amount of polarization
rotation. The modulation is then effected by passive polarizer 136
that absorbs amounts of light proportional to the light's
difference in polarization as modulated upstream. The
contrast-improving panel 130 is shown downstream from the
image-generating panel 115, but may be placed upstream of the
image-generating panel 115.
[0055] FIG. 2A is a schematic diagram of a high dynamic range
display 200 according to another embodiment of the present
invention. In FIG. 2A, a contrast-improving panel 240 (e.g., a
controllable polarizer or modified controllable polarizer) is
placed upstream of an image-generating panel 250. Backlight 210
illuminates the contrast-improving panel with light 218. The
contrast-improving panel 240 produces modulated light 248, which is
a locally dimmed version of the backlight 218. Modulated light 248
is further modulated for color and brightness by a color panel 250
(e.g., an LCD panel), producing final image light 258.
[0056] As shown, the contrast-improving panel 240 includes an
initial polarizer 242, and an active elements panel 242 (e.g., TN
layer w/o color filters). The color panel 250 is constructed with a
polarizer 246 (e.g., an absorptive polarizer) which operates as
both an initial polarizer for the color panel and as an analyzer
for the active elements panel 242. A color active layer 254 (e.g.,
TN layer+color filters) modulate the light as to intensity and
color, and a passive polarizer 256 effects the modulation by
polarization based filtering.
[0057] FIG. 2A is a schematic diagram of a high dynamic range
display 260 according to another embodiment of the present
invention. The display 260 improves performance by the addition of
appropriately designed diffusers. The additional diffusers include
an upstream diffuser 272 and a mid-stream diffuser 274. Upstream
diffuser is a "rough" diffuser that is designed to diffuse the
backlight into an evenly distributed light source. In the case of
locally dimmed backlight embodiment, the upstream diffuser is
designed to cause the backlight to smoothly vary across pixels of
the upstream modulator (e.g., contrast-improving panel 244 in this
example).
The midstream diffuser is specifically designed to smooth light
emitted from the upstream modulator (e.g., contrast-improving panel
244 in this example).
[0058] Preferably, the midstream diffuser operates to remove and
smooth rough edges of the lights emitted from each pixel of the
upstream modulator. To do so, the midstream diffuser is, for
example, a diffuser that is of higher diffusion resolution (e.g.,
diffuses smaller features) than the upstream diffuser and is
capable of maintaining the modulated resolution of light emitted
from the upstream modulator. For example, FIG. 2C provides graphs
that illustrate an approximate resolution of modulated light 280 in
an on-off pattern as might be emitted from a contrast-improving
panel or other upstream modulator.
[0059] The midstream diffuser then operates to remove sharp edges
and smooth the emitted light while preferably maintaining as much
peak brightness and darkness as possible as shown by diffused light
285.
[0060] Diffused light 285 takes away the sharp edges (e.g. higher
frequencies) of the upstream-modulated light and is sufficient to
"break-up" or prevent the formation of moire patterns that
typically develop as artifacts in displays with various
combinations of grid like panels and/or other optical elements.
Also worth further discussion is that the diffused light 285
emitted from the mid-stream diffuser 274 is preferably at an
entirely different level of diffusion compared to the diffused
light emitted from the upstream diffuser 272. The upstream diffuser
may, for example, cause the backlight to smoothly vary from one
lighting element in the backlight to the next. In contrast, the
mid-stream diffuser may, for example, provide smooth variances of
lighting within a single pixel and mix light only from directly
adjacent pixels. In one embodiment, the upstream and mid-stream
diffusers differ in diffusion coarseness by, for example, an order
of magnitude or more. In fact, best results may occur with an even
much greater differential in resolution between the upstream and
midstream diffusers.
[0061] In one embodiment, the upstream diffuser mixes and smoothes
light from multiple light sources in the backlight while the
midstream diffuser smoothes light on the order of single
contrast-improving size pixels. In another embodiment, the upstream
diffuser may be described as mixing light such that a single pixel
of the upstream diffuser is illuminated by a plurality of light
sources in the backlight, and the mid-stream diffuser may be
described as mixing light on a sub-pixel level (sub-pixels of the
upstream modulator). In one embodiment, the upstream diffuser is a
rough diffuser compared to a relatively fine mid-stream diffuser.
In one embodiment, the mid-stream diffuser provides diffusion at
less than a sub-pixel resolution. In another embodiment, the
mid-stream diffuser comprises a diffuser with a spatial transfer
function that either cuts-off, removes, repositions, or eliminates
high frequency elements of light that would otherwise be emitted.
In another embodiment, the mid-stream diffuser may consist of a
material that diffuses light more in one direction than in another
to compensate for the non-squareness of the upstream pixels.
[0062] In yet another embodiment, the mid-stream diffuser comprises
a diffuser that preserves enough detail such that the resolution of
the modulated light is not altered (e.g., resolution not altered,
but higher frequency details are no longer present). The mid-stream
diffuser may be designed to mask high frequency details in the
light modulated by the contrast-improving panel. For example, the
mid-stream diffuser may comprise an optical low-pass filter that
passes the lowest 4 harmonics (e.g., See FIG. 2C, the 4 lowest
harmonics of 280 which approximately reproduces 285), but may be,
for example, between 2-8 harmonics of the fundamental frequency.
The mid-stream diffuser removes, for example, sub-pixel level
features placed into the light stream by the contrast-improving
panel.
[0063] In most embodiments, the size of a pixel in the
contrast-improving panel is smaller than a distance between the
active panels (e.g., distance between the contrast-improving panel
and the image-generating panel).
[0064] The coarseness of the mid-stream diffuser may, for example,
be determined in part by a geometry of cells and surrounding areas
of the contrast-improving panel. For example, if the
contrast-improving panel comprises cells that are square with
equivalent amounts of hardware (wires, cell walls, etc) on all
sizes, then the coarseness of the midstream diffuser would
generally be uniform in all directions. If the cells of the
contrast-improving panel are rectangular then the coarseness of the
midstream diffuser, assuming all other factors being equal, would
be coarser in the direction corresponding to the longer side of the
rectangle and finer in the direction corresponding to the shorter
side of the rectangle.
[0065] The coarseness of the mid-stream diffuser may also be
determined, for example, by a scale and/or physical or other
measurable un-controlled features and/or imperfections in the cells
of the contrast-improving panel. The coarseness is determined at a
resolution that masks the uncontrollable features but still allows
the resolution of the panel (in the form of modulated light) to
pass mostly unaltered. For example, space between the cells of the
contrast-improving panel may, for example, block light or pass some
amount of un-modulated light. Blocked light or un-modulated light
passed by the contrast-improving panel results in an uncontrolled
or un controllable in the image being formed.
[0066] Other uncontrollable features may include, for example,
differences in modulation in a cell not attributable to its
energization level and/or non-uniformity within a cell--any of
which may be due to, for example, manufacturing or component
quality variances. In one embodiment, the coarseness of the
mid-stream modulator is selected so that one or more of the
uncontrollable features are at least one of removed, masked, or
otherwise minimized through diffusion. In one embodiment, the
uncontrollable features are different depending on a direction
(e.g., horizontal and vertical), and each direction (at least two
directions in a single diffuser) having different diffusion
properties related to the different amounts of uncontrollable
features found in those directions.
[0067] Note that above, the polarizer 246 had been used as both an
analyzer for the up-stream modulator 244 and an initial orientation
polarizer for downstream modulator 254. The mid-stream diffuser 274
may be specially constructed to include polarization or to maintain
existing polarization. In the case where mid-stream diffuser 274
maintains polarization (e.g., a diffuser that does not
substantially alter the polarization of light being diffused), then
polarizer 246 operates as both the analyzer and initial orientation
polarizer as described above. However, diffusers typically will
impart more polarization alteration than is desirable and therefore
the addition of a polarizer to diffusion layer 274 is desirable so
that the light may be analyzed prior to diffusion and accompanying
polarization changes. This additional polarizer will increase
contrast at the expense of brightness. The present invention
includes designing a display for either increased contrast or
brightness by respectively including or forgoing an additional
polarizer between active layers.
[0068] The embodiments of FIG. 1, FIG. 2A, and FIG. 2B are
constructed so that the modulators (e.g., contrast-improving panel
240 and image-generating panel 250) are in close proximity to each
other, which, as one benefit, reduces parallax caused by a
separation between the panels. In the present invention, the
modulators are sandwiched together either directly or separated by
thin films, air gaps, or optical stack items such as diffusers,
collimators or other optical elements that are relatively thin
compared to glass and other layers of an LCD panel.
[0069] Even with the close proximity of the panels, parallax may
occur, particularly when difficult images or patterns are displayed
and viewed at off-normal angles. The present inventors have
realized that a specific configuration of panels brings the active
layers of the contrast-improving panel and the image-generating
panel closer together, further reducing parallax effects.
[0070] Construction of a typical LCD panel 310 is illustrated in
FIG. 3A. A first layer from the viewing side is a polarizing
(analyzing) layer 312. Next, a relatively thick transparent
substrate 314 (e.g., glass) is shown. Etched on the non-viewing
side of the glass are, for example, wires and/or electronics for
controlling a liquid crystal layer 316. Laminated together with the
substrate and liquid crystal layer(s) is a color filter layer 318
and an initial polarizing layer 320. In operation, a backlight
illuminates the panel 310, polarizing layer 320 sets an initial
polarization, color filters 318 provide the primary colors Red,
Green, and Blue, and liquid crystal layer 316 rotates polarization
of each R, G, and B light by an amount that each light is to be
attenuated. The analyzing layer then absorbs amounts of the R, G,
and B lights based on their respective polarizations as imparted by
the liquid crystal layer.
[0071] FIG. 3B is a drawing illustrating an arrangement of layers
in an image-generating panel and a contrast-improving panel
according to an embodiment of the present invention. The
arrangement is specifically designed to place the active layer of a
contrast-improving panel 350 as close as possible to the active
layer of the image-generating panel 370.
[0072] The layers of the contrast-improving panel 350 (from the
backlight side) comprise a transparent substrate 352, an initial
polarization layer 354, and an active layer 356 (e.g., controllable
polarizing layer). A polarizer 360 (which may be a separate
component or laminated together with either a contrast-improving
panel 350 or an image-generating panel 370) performs double duty as
both an analyzing polarizer for the contrast-improving panel 350
and an initial polarizing layer for the image-generating panel
370.
[0073] Continuing from the backlight side, the layers of the
image-generating panel 370 comprise a color filter layer 372,
active layer 374, substrate 376, and a polarization (analyzing
layer) 378. Other arrangements of the layers may be utilized,
including, for example, placing the polarization (analyzing) layer
378 on the backlight side of the substrate 376. The polarization
(analyzing) layer 378 may also be placed on the backlight side of
the color filter layer 372 and the active layer 374 may be placed
as the first layer on the backlight side of the image-generating
panel 370 (e.g., active layer-color filter layer-polarization
(analyzing layer).
[0074] In an embodiment of the present invention, a
contrast-improving panel and an image-generating panel are provided
from similarly constructed LCD panels. The contrast-improving panel
may, for example, be oriented backwards or upside down (flipped or
inverted) relative to the LCD panel. This arrangement places the
active layers of the contrast-improving panel and the
image-generating panel closer together than would be in the case of
similarly oriented panels of typical commercially available
construction.
[0075] FIG. 4A provides an architecture of an electronic device 400
(e.g., electronic circuitry, software architecture, programmable
device architecture, plug-in, etc., or combinations thereof) that
generates energization signals for image-generating panels and
contrast-improving panels according to an embodiment of the present
invention. A signal comprising, for example,
R.sub.inG.sub.inB.sub.in, is provided and/or extracted from an
image or video source (e.g., DVD, Cable, Broadcast, Satellite,
Streaming video, Internet, removable media, thumb drive, etc.) to
an LCD Color Correction module 410 and a Polarization Control
module 420. The polarization control module prepares a P.sub.out
signal 425 that is connected to a contrast-improving panel (e.g.,
controllable polarization panel). In essence, the P.sub.out signal
425 indicates which pixels of the contrast-improving panel should
be attenuated and the amount of attenuation. When using a
controllable polarizer as the contrast-improving panel, this is
performed, for example, by rotating the polarization of pixels to
be attenuated by an amount proportional to the amount of desired
attenuation for that pixel. The P.sub.out signal 425 may be, for
example, a luminance calculation from a desired image defined by
the R.sub.inG.sub.inB.sub.in data.
[0076] Processing in the Polarization Control Module, may include,
for example, both a characterization that produces a corrected
response curve (e.g., correcting RGB values for a given luminance)
and a non-linear function (e.g., transfer function) that increases
or decreases local contrast (makes pixels darker or lighter). The
non-linear function may, for example, brighten or darken pixels in
a manner that take into account the relative brightness of
neighboring pixels. As shown, P.sub.out is then forwarded (fed
into) the LCD Color Correction module 410 (via line 422).
Alternatively, intermediate data may be exclusively or additionally
forwarded to the LCD Color Correction module (via 424). The
intermediate data, may be, for example, partially processed data
including any one or more steps performed to produce P.sub.out
(e.g., characterization without applying the non-linear
function).
[0077] Along with the R.sub.inG.sub.inB.sub.in data, the LCD Color
Correction module prepares an R.sub.outG.sub.outB.sub.out signal
430 that is connected to control an image-generating panel (e.g.,
an LCD panel). The image-generating panel may be an LCD display,
plasma display, or other type of display device.
In another embodiment, an electronic device 440 (e.g., electronic
circuitry, software architecture, programmable device architecture,
plug-in, etc., or combinations thereof) that generates energization
signals for image-generating panels and contrast-improving panels
according to an embodiment of the present invention. A signal
comprising, for example, R.sub.inG.sub.inB.sub.in, is provided from
an image or video source (e.g., DVD, Cable, Broadcast, Satellite,
Streaming video, Internet, removable media, thumb drive, etc.) to a
Polarization Control Module 442 and an LCD Color Correction module
446. The Polarization Control Module 442 controls, for example, a
polarizer that is physically located in a display and upstream of a
corresponding color panel. The Polarization Control Module 442 may
be configured to prepare modulation signals for a higher resolution
than the resolution of the color panel (e.g., higher resolution in
the number of controllable pixels and higher resolution in the
total number of controllable elements in a given area of the
corresponding panels). The polarization control module may be
configured, for example, to control the active elements of a
1680.times.1050 active element panel.
[0078] An output luminance P.sub.out 442 is produced. In turn, an
LCD Color Correction module 446 provides signals to control the
corresponding color panel, which may be, for example, a
1920.times.1080 panel. The LCD Color Correction module 446 utilizes
the video-in (RGB) signal plus results from the Polarization
Control Module (e.g., luminance controlled by the upstream
panels).
[0079] FIG. 4B is an architecture of an electronic device 450
(e.g., electronic circuitry, software architecture, programmable
device architecture, plug-in, etc., or combinations thereof) that
generates energization signals for image-generating panels and
contrast-improving panels according to an embodiment of the present
invention. A source image/video signal comprising, for example,
R.sub.inG.sub.inB.sub.in, is provided an image or video source
(e.g., DVD, Cable, Broadcast, Satellite, Streaming video, Internet,
removable media, thumb drive, etc.) to a global brightness
computation module 452, which separates the light into its primary
color components (e.g., R, G, and B) and provides that information
to a backlight controller 454. A backlight control signal is
generated, which may be, for example, a globally dimmed backlight
value that is calculated (e.g., for each primary color value),
which comprises, for example, an energization amount (or intensity)
of individual primary colored lights in a backlight 456. The
backlight is then energized according to the calculated backlight
values for each primary.
[0080] In one embodiment, in the case of a locally dimmable
backlight (e.g., a backlight that includes locally dimmed (or
dimmable) light sources), the backlight controller may generate a
spatially modulated backlight that illuminates downstream panels
according to relative brightness in areas of the image (e.g., areas
comprising, for example, each backlight pixel). The relative
brightness may be computed, for example, based on the relative
intensities of each primary color in a corresponding backlight
pixel. Production of the spatially modulated backlight may also
include, for example, consideration of the brightness of
neighboring or nearby backlight pixels, and/or, in the case of
video, brightness of pixels in preceding and/or subsequent image
frames.
[0081] A Dimming/Polarization Controller 458 receives the backlight
control signal and the input video/image signal, which are utilized
to produce a contrast-improving control signal. The
contrast-improving control signal specifies an amount of dimming
produced by a contrast-improving panel 460. In various embodiments,
the contrast-improving panel is of higher resolution than the
image-generating panel (e.g., LCD panel) and may produce, for
example, a very precise illumination profile.
[0082] In one embodiment, the image-generating panel is downstream
from the contrast-improving panel and the higher resolution
contrast-improving panel is utilized to produce an illumination
profile that is intentionally blurred (blurred using the higher
resolution capabilities of the contrast-improving panel as opposed
to blurred because the contrast-improving panel is of lower
resolution). The intentionally blurred image is blurred using the
higher resolution capabilities of the display separate and apart
from any blurring that occurs among or due to mixing of the
backlights due to point spread functions or other
qualities/orientations of the backlight or individual lights in the
backlight. Although the aforementioned blurring is separate and
apart from backlight blurring or mixing, embodiments of the
invention may nonetheless include amounts of mixing or blurring of
individual elements of the backlight.
[0083] A Color LCD Controller 462 receives the contrast-improving
control signal, the backlight control signal, and the image/video
signal which are utilized to produce an image-generating control
signal that specifies the energization of the color panel 485
relative to the upstream illumination (e.g., in various embodiments
the combined backlight and contrast-improving panel produce the
upstream illumination) provided to the color panel 464.
[0084] FIG. 4C is an architecture of controllers according to an
embodiment of the present invention. An RGBin signal is provided to
both a Polarization Control Module 466 and an LCD Color Correction
Module 468. The LCD Color Correction Module may be configured to
correct and produce an output for a 1920.times.1080 array of RGB
pixels. The Polarization Control Module may be configured to
control other resolutions, for example, 1680.times.1050
polarization cells.
[0085] The Polarization Control Module outputs to each of: the LCD
Color Correction Module, a sub-pixel Interpolation and Registration
module, and a filtering module. The sub-pixel interpolation module
interpolates values for each pixel of the polarization control
panel (e.g., each pixel may be considered a sub-pixel relative to
the larger pixels of the image-generating panel). The interpolation
and registration module allows the embodiment to handle multiple
panels with different control resolutions and sizes. The spatial
and range filtering module allows us to smooth the energization on
the contrast-improving panel to get better viewing angle
performance while maintaining edges and preserving the high
frequency details in the image. This module also enhances the local
contrast of this embodiment. Filtering is performed based on the
polarization control and preceding sub-pixel operations. The result
is a P1, P2, and P3 output for controlling the controllable
polarizer, and an output for controlling the color panel.
[0086] FIG. 4D is an architecture of controllers according to an
embodiment of the present invention that provides a framework for
utilization of a High Dynamic Range (HDR) signal. The HDR signal
could comprise an image and/or images (e.g., video) having a
dynamic range that is equivalent to the dynamic range of the human
visual system (HVS) on average. Since, on average, the HVS has
greater dynamic range than most displays, a tone mapping algorithm
is utilized to change the dynamic range of the image(s) or portions
of the images so that they are within luminance range of the
proposed display system. An HDR frame sequence {XinYinZin} is
provided to a Global Tone Mapping Module 482, which outputs an RGB
signal which is then fed to Polarization Control and LCD Color
Correction Modules.
[0087] FIG. 5 is a flow chart of a process for energizing a high
dynamic range display according to various embodiments of the
present invention. At step 510 Image and/or video data (the method
repeated in real time for each frame) is received. Luminance values
are extracted from the image data and used to drive a
contrast-improving panel (see step 520). An image-generating panel
optically co-joined with the contrast-improving panel is driven
based on the image data and the global or local dimming levels
(step 530), or constant values representing the backlight
color.
[0088] More details on a specific algorithm for driving the
contrast-improving and image-generating panels are now discussed
for producing a pixel accurate dual modulation displays. The
architecture of two modulators of perhaps similar construction
allows performance of local dimming in a sub-pixel (or higher
resolution) fashion. Additionally, one of the modulators could have
a different or the same resolution than the other in either
dimension.
[0089] Pixels in the contrast-improving panel can be driven based
on the luminance of a corresponding (or related) input pixel. The
contrast-improving pixel may be a sub-pixel of an input pixel, a
portion of an input pixel, or a pixel optically and precisely
corresponding to an input pixel. Accurate characterization of the
local dimming panel's output luminance response could be used to
map the input RGB pixel values to a specific drive level (e.g.,
specific polarization rotation in this example).
[0090] Drive values may be provided, for example, via:
Y.sub.max=Y.sub.R+Y.sub.G+Y.sub.B
Y.sub.out=Y.sub.R*R.sub.in+Y.sub.G*G.sub.inY.sub.B*B.sub.in
drive.sub.polarizer=f.sub.2(f.sub.1(Y.sub.out/Y.sub.max))
The function f.sub.1 is the polynomial characterizing the luminance
response of the combined dual modulation system while linearly
varying the local dimming panel's (polarizer's) control with the
RGB color LCD drive is set to full white (maximum codewords).
[0091] The function f.sub.2 a nonlinear transfer function that
could represent the skew of the codewords with the luminance
representing the nonlinear nature of the drive. The function could
be approximated with either a simple gamma curve or a polynomial
function. This drive computation can be used to calculate the drive
for pixels of the contrast-improving panel (sub-pixels (P.sub.1,
P.sub.2, P.sub.3) of input pixels in the case where the
contrast-improving panel has a similar construction and orientation
to the image-generating panel). This function could also be used to
improve the local contrast of the display using a nonlinear
input-output relationship making dark regions darker and bright
regions brighter.
[0092] The interaction between the image-generating panel and the
contrast-improving panel (e.g., controllable polarizer) is
represented in the color correction function. This function may
utilize, for example, surfaces mapped from the characterization of
the color primaries of the image-generating panel with the
corresponding amount of local dimming (e.g., polarization) from the
contrast-improving panel.
[0093] The resulting RGB drive may, for example, be calculated as
follows:
R.sub.out=f.sub.3(R.sub.in,f.sub.4(R.sub.in,Y.sub.out))
G.sub.out=f.sub.5(G.sub.in,f.sub.6(G.sub.in,Y.sub.out))
B.sub.out=f.sub.7(B.sub.in,f.sub.8(B.sub.in,Y.sub.out))
Here, f.sub.4, f.sub.6 and f.sub.8 define the characterization
functions that define the output primary for an input primary pixel
values and a computed Y.sub.out. f.sub.3, f.sub.6 and f.sub.7
define the nonlinear combination functions for combining the input
primary and the output from the characterization functions. The
polarization control could be pre-computed in the LCD correction
system to drive the LCD control plane independent of the
polarization control signals computed in the dimming plane
drive.
[0094] Sub-pixel control of the contrast-improving panel can be
used to smooth out any parallax errors that are incurred by it use.
Since sub-pixel control increases the implied resolution of the
local dimming panel (e.g., polarizer), smoothing/dithering
operations shall be more refined and accurate. By using a smoothing
mask on the drive image to the modulating polarizer, such as, for
example:
[drive.sub.polarizer].sub.(i,j)=f.sub.int
R(drive.sub.polarizer].sub.(i,j))
where f.sub.int is the smoothing operator applied on a spatial
radius of R sub-pixels. In a construction with 4 sub-pixels on the
polarizer corresponding to every pixel on the color RGB LCD, the
applied quad design would increase the resolution of the
contrast-improving panel to twice that of the image-generating
panel along both the width and the height directions.
[0095] In an embodiment, a source image may be processed through a
nonlinear function to modulate the contrast-improving panel. This
can create a perceived effect of contrast stretching. Existing tone
mapping algorithms rely exclusively on software algorithms to
stretch contrast. By using, for example, a design such as shown in
FIG. 1, with the algorithmic elements described above, contrast
stretching without tone mapping or other contrast synthesis may be
achieved.
[0096] The present invention also may be utilized for maintaining
constant gamut over a wide range of luminance values. An expected
representation of the chromaticity (x,y) for different luminance
values follows a surface outlined the first drawing. However, the
measured luminance of a standard display at the maximum codewords
for the primaries creates an inclined top triangle as outlined in
the first drawing.
[0097] However, some display systems demonstrate a gamut limiting
effect as described by the bottom figure. The projection of the
color gamut onto the chromaticity axes (x,y) is reduced in area for
higher luminance values until it reduces to a single point at
maximum drive values for the individual color primaries (R=G=B=1.0
in normalized drive values). This point is usually the white point
of the system.
[0098] By using a non-uniform current drive for the 3 primaries,
the maximum input codewords for the individual primaries can give
us a flat-topped triangle at the higher luminance levels there by
increasing the color gamut and making the system demonstrate a more
uniform projection on the chromaticity plane at higher luminance
values (See FIG. 6, comparison of current system 610 and "ideal"
system 620).
[0099] The present invention includes the use of RGB individually
controlled tristimulus based backlights (e.g., LEDs, arranged in,
for example, an edge lit configuration, direct lit array, or other
arrangement). By scaling the current drives to the RGB individually
controlled tristimulus LED backlight, the 3D surface of the
luminance vs chromaticity of colors that represented may be
adjusted. Luminance control is primarily from the dimming plane and
the combination of the LED backlight and the dimming plane, scaling
the color drives to the LEDs allows for wider color gamut at higher
luminance values. For a target display luminance, the luminance vs
current characterization curves may be used to determine/create the
right scaling parameters for a current drive designed for better
control of color gamut at that target luminance. This forms a basis
for a global backlight controller embodiment.
[0100] The global backlight controller embodiment can be used, for
example, on a plurality of LEDs which are closely spaced to create
an edge lit zonal dimming backlight on conjunction with the color
LCD and the dimming plane. By working on a plurality of LEDs at a
time, the global backlight controller embodiment can also be used
for correcting drifts in the output wavelength of light from a zone
with luminance and maintain more accurate color properties at
higher wavelengths.
[0101] The present invention includes computation of a color
primary rotation matrix from a sparse data set. Given a sparse set
of tristimulus primaries (R, G, B) as input images to the display
system and their corresponding luminance (Y) and chromaticity
coordinates (x, y), we could arrive at the optimum color rotation
matrix for converting the RGB values to their corresponding XYZ
values on the concerned display in the following manner:
A=[P1P2P3 . . . Pn]T [0102] where Px=[R G B]x for the x input
sample primaries
[0102] B=[M1M2M3 . . . Mn]T [0103] where Mx=[X Y Z]x for the x
output luminance/chromaticity For example, let the color rotation
matrix be:
[0103] x=EMBED Equation.3
This could be expressed as a linear system of equations of the
form:
Ax=B
and compute the rotation matrix x using the pseudo-inverse as:
x=(A.sup.TA).sup.-1A.sup.TB
[0104] This computed color rotation matrix would be optimized for
minimum least square color distorting in the XYZ space given the
number of sample data points that we have captured. Given more
uniformly spaced data points, the computed color rotation matrix
would be a more accurate representation of the true rotation
operation by the display.
[0105] The present invention includes extending viewing angles in
multi-modulated display systems. The use of existing LCD panels
without red, green or blue color filters allows for much greater
resolution of contrast enhancement as used as a background or
foreground panel with another panel. This extra resolution becomes
even more important when these dimming panels are coupled with
different resolution color LCD panels or with similar scaled color
LCD panels, as it allows for adjustable viewing angles across the
display with minimized visual artifacts.
[0106] In the case where the base panel has the pixels (e.g.,
sub-pixels compared to other modulators in the same image chain) in
clusters of four in a square configuration (2.times.2), even
greater control is possible as this doubles the pixel/sub-pixel
resolution in both horizontal and vertical directions. Existing
image processing techniques for image scaling can be applied to
these sub-pixel dimming regions if treated as individual control
points, allowing for variable viewing angles and distances. To
widen viewing angles as to accommodate multiple simultaneous
viewers, a Gaussian or similar low pass filter can be applied as
indicated by the spatial and range filtering embodiment in FIG.
4D.
[0107] The present invention includes controlling backlights for
constant color. Traditional methods for setting display backlight
light levels and color involve selecting from a set of voltage or
current levels that drive the light. These do not factor in the
changes to the color or luminance due to component or environmental
temperatures, component age, or other factors. Our method of
backlight control involves sending to the display a target color
and luminance (usually with a scaled RGB target value), which is
then compared with the values coming from a calibrated light and
color sensor that is directly coupled with the backlight, with
corrections made using a feedback loop. This eliminates the warm-up
time for the display to settle to a particular color, and any color
or brightness drift over time. This feedback process can be
accelerated by using a feed-forward feedback hybrid driver (for the
purpose of real-time backlight changes). This allows the backlight
to instantly respond to control changes while still maintaining the
precision maintained by the color and light sensors.
[0108] The present invention may be implemented in a number of
forms including combinations of hardware and processes described
here and above. Another exemplary embodiment of a display device
according to an embodiment of the invention is illustrated in FIG.
7A. A backlight 705 includes a reflective polarizer 710 that
produces backlight 715. The reflective polarizer reflects and
polarizes light that is directed toward the backlight's reflective
polarizing surface(s). Such reflections include light that has been
bounced back to the backlight from a reflective polarizer 725
because it was not of the desired orientation for further
downstream processing by the display. Further reflection by the
reflective polarizer changes the reflected lights polarization
providing it another opportunity to pass the reflective polarizer
725 and be utilized in production of a desired image.
[0109] A diffuser stack 720 smoothes and diffuses the backlight
715, and the reflective or other type of polarizer passes light of
a desired initial polarization for further downstream processing. A
contrast-improving panel 730 (e.g., controllable "sub-pixel"
polarizer--again "sub-pixel" because the pixels of the
contrast-improving panel may be of higher resolution than its
corresponding (e.g., downstream) image-generating panel) either
locally dims or further locally dims (further locally dims cases
where the light is already locally dimmed at some level, e.g.,
dimmed by another upstream panel (not shown) or backlight 710 is
itself locally dimmed) light in the image/light chain from
backlight to viewer. The backlight itself may be an array
(2-dimensional or linear) or other light source/sources that
illuminate the image chain either directly, from an edge, or
another perspective.
[0110] A diffuser stack 735 diffuses the locally dimmed light, and
a image-generating panel 740 (e.g., LCD panel) imparts final
modulation (e.g., color, brightness, and spatial resolution) into
the light, which is then emitted for display to a viewer. A
polarizer (usually absorptive) is included in front of the
image-generating panel to realize the modulation imparted by the
color panel. Additional anti-glare or other light processing layers
may be present in front of the image-generating panel.
[0111] The discussion on pixels is now elaborated with reference to
FIG. 7B which provides a diagram illustrating a possible
relationship between pixels of an image-generating panel and pixels
of a contrast-improving panel. An image-generating panel 750
includes sets of Red, Green and Blue (RGB) controllable elements
each comprising a pixel of the color panel. For example, one pixel
is defined as colorLCD(i,j), where I and j identify, for example, a
row and column position of the pixel or RGB triad comprising the
pixel. In this case, a similar location may be identified in the
contrast-improving panel 780, where a set of three pixels
corresponding to the RGB triad of colorLCD(i,j), P1, P2, and P3 of
a group of local dimming pixels identified as polarizer(i,j)
(however, P1, P2, and P3 may also be appropriately referred to as
sub-pixels as they optically correspond to (or modulate) sub-pixel
regions of the colorLCD pixels).
[0112] The present invention includes the use of modulators having
different resolutions. In such cases it may not be possible to
align pixels of the color and dimming panels as illustrated in FIG.
7B (however, alignment is not necessarily the case even when there
is a direct correspondence between the size and arrangement between
pixels of the local dimming panel and pixels of the color panel).
Still, the pixels of the contrast-improving panel may be referenced
as pixels of the contrast-improving panel or as sub-pixels of the
color panel when they are of smaller size or greater resolution
than the color panel pixels, which they jointly modulate to produce
an image.
[0113] The invention may be further extended to displays with
additional modulators. For example, a display with 3 modulating
panels and techniques for driving the panels. By placing an
additional controllable polarizer in front of the design discussed
and illustrated in FIG. 7, light at an output of the display could
be steered at different polarization angles, ether in a linear or
circular manner. By using this system in conjunction with 3D
polarized glasses, we could steer the objects on the display to
either left or right eyes based on the modulation drive for the 3rd
polarization panel. This stereoscopic-driving layer can be driven
in various means using spatial, temporal, or color based
stereoscopic methods along side traditional two-dimensional
content, alone or simultaneously.
[0114] In FIG. 8, a display 800 includes all of the proposed parts
associated with the FIG. 7 embodiment, with an additional
controllable panel 810. The additional controllable panel may be,
for example, a controllable polarizer similar in construction to
the exemplary controllable polarizer described with respect to
local dimming panel 730. However, here the panel is controlled to
output images for respective channels. The channels may be, for
example, a left eye viewing channel or a right eye viewing channel
that may be separated for viewing by viewing glasses 815 that
include different filters for the left eye and right eye.
[0115] For example, display 800 could be energized to alternately
display a left view and a right view of a 3D image. The images
would then be separated into different corresponding viewing
channels by energizing the additional controllable polarizer to
polarize each of the images consistent with its viewing channel.
For example, in a left and right polarization viewing system, the
glasses 815 could be constructed to include a P polarization filter
on the left eye lens and an S polarization filter on the right eye
lens. In such a case, controllable panel 810 is energized to
pass/convert light modulated with left image data to a P
polarization and pass/convert light modulated with right image data
to S polarization. In another example, the light may modulated with
left or right image data in sections (e.g., light being emitted
from the display at any given time contains parts of both a left
and right channel image), and the controllable polarizer panel is
also energized in sections and synchronized with the displayed
image sections to convert those sectional images to the appropriate
polarization and subsequent viewing through polarized filters by
the left and right viewing channels.
[0116] Beyond 3D, the configuration of FIG. 8 allows the design to
be extended to either more color accurate HDR or a 3D HDR display
system. In conjunction with a method to drive the accurate
compensate for color performance in 2D and 3D modes, a passive 3D
display results. In addition, a hybrid 2D/3D display may be
implemented (either driving the additional modulator for 3D channel
separation, or to further refine a 2D image).
[0117] To create a quality image, color and brightness correction
may be performed over the total image areas. The display can be
switchable between 2D and 3D operations, and can be configured to
simultaneously drive 3D and 2D on the same screen. As 3D images are
split between two eyes, they tend to be less bright. Additional
color filters can be applied to the 2D image areas so that both 3D
and 2D areas appear as the same brightness. Possible color
correction can be applied as well.
[0118] In one embodiment, the additional controllable panel 810 is
utilized for both 2D and 3D displays, and for providing a
completely black border around the simultaneously displayed 2D and
3D images. As shown in FIG. 9, a display 900 is energized to
provide a 2D display area 902 and 3D display area 903. In the 2D
display area 902, the additional controllable panel 810 is utilized
to enhance the dynamic range and black levels of the 2D display.
Simultaneously, in the 3D display area 903, the additional
controllable panel 810 is utilized to steer polarization of the
left or right channel image being displayed to a polarization
consistent with the corresponding left or right viewing channel.
Finally, in border areas surrounding the 2D and 3D display areas,
the additional controllable panel 810 is utilized to increase
blackness (e.g., making a black boarder darker) or otherwise
enhance the border area.
[0119] Variances in any particular 3D implementation may include,
for example, a mix of shutter styles, per pixel steering, and
brightest area chroma-based techniques, alongside 2D images as
well. For example, for shutter style, one embodiment alternatively
displays left and right images with steering of entire image to
left or right eye with polarization layer (albeit at a reduced, or
1/2 frame rate). For a pixel steering embodiment, where left and
right images differ, steering may be performed at alternate pixels
to one eye or the other (albeit at a reduced, 1/2 resolution per
image). In a brightest area embodiment, each pixel from both eye's
images you find the highest luminance, then using the delta
luminance between the two images steer the right light proportion
to both eyes (albeit at a reduction of color resolution in the
dimmer channel).
[0120] FIG. 10 is an arrangement of controllable panels 1000
according to an embodiment of the present invention. A backlight
1005 provides polarized light 1010 used to illuminate downstream
panels. The backlight may be, for example, a polarized light
source, an unpolarized light source with polarization converting
layers, and/or various combinations of optics, sources, films, and
converters that ultimately produce the polarized light 1010.
Typically, the backlight preferably includes a reflective
polarization or a scattering layer for, for example, any of
recycling, re-polarizing, de-polarizing, and/or redirection of
stray lights or reflected lights toward (or back toward) the
downstream panels. Such functions of the panel may be selected on a
case-by-case basis depending on other factors of a particular
design.
[0121] The backlight may include, for example, optics, louvers,
light guides, or other devices (not shown) that are utilized to
help align the polarized light 1010 so that individual rays are
parallel. A backlight diffuser 1015 mixes and homogenizes the
polarized light removing, for example, local non-uniformities in
intensity.
[0122] A first biasing polarizer 1020 sets the polarization of
downstream light to a first reference polarization. The reference
polarization is used for downstream modulation provided by a first
modulating panel, e.g., LCD panel without color filters 1025.
[0123] An optional first analyzing polarizer 1030 is utilized, for
example, when the LCD panel without color filters only changes
polarization of light rays to be modulated, the first analyzing
polarizer then effects the modulation intended to be imparted by
those polarization changes. In other embodiments, the first
analyzing polarizer may act as more of a clean-up polarizer
removing unwanted stray polarizations or simply filter out light
intended to be removed by the preceding LCD panel (e.g., reflected
by a polarizer in the LCD panel).
[0124] A sub-pixel scaled diffuser 1035 mixes and diffuses light
passed by the first modulating layer (panel 1025 and optional
polarizer 1030). By making the diffuser sub-pixel scaled, diffusion
only occurs at the sub-pixel level or has minimal diffusion amongst
neighboring pixels (but significant diffusion between sub-pixels).
In lower resolution versions of the invention, the diffuser may be
designed to diffuse between a limited set of pixels (e.g., blocks
of pixels such as 4 or 9) pixels. The sub-pixel scaled diffuser
1035 maintains the specific modulation intended for each pixel, and
may be designed to maintain polarization.
[0125] A second biasing polarizer 1040 sets the polarization of
downstream light to a second reference polarization. The second
reference polarization is used for downstream modulation provided
by a second modulating panel 1045, e.g., 2.sup.nd LCD panel with
color filters removed. An optional second analyzing polarizer 1050
performs a similar function as analyzing polarizer 1030 and is a
final polarization/analysis device in the illustrated example.
[0126] Resolution of the modulating panels may be the same. In one
embodiment the first modulating panel is of lower resolution
compared to the second modulating panel. In one embodiment, the
first modulating panel has greater resolution than the second
modulating panel.
[0127] A display according to the invention may further comprise an
optical stack including a reference polarizer (e.g., first biasing
polarizer 1020 or second biasing polarizer 1040) and a series of
films configured to enhance brightness and reduce loss of light
transmitted through the stack. The films may include, for example,
at least one brightness enhancing layer, and may be designed to
maintain polarization.
[0128] The optical stack may be positioned after a source of the
locally dimmed light and before a first of the downstream
modulators, or between downstream modulators, or both (e.g., an
embodiment having duplicate or similar optical stacks). In one
embodiment, the stack comprises a backlight resolution scale
diffuser where the backlight resolution comprises a resolution of a
local dimming capability of a source or sources of the locally
dimmed light (a stack that would be placed between the backlight
and first downstream modulator, for example). In another
embodiment, the stack comprises a sub-pixel scale diffuser where
the sub-pixel scale corresponds to sub-pixels of an upstream
modulator.
[0129] A sub-pixel scale diffuser may comprise, for example, a
diffuser that diffuses sub-pixels proportional to sub-pixels
generated by an LCD panel with color filters removed. In one
embodiment, subpixels of the modulator each comprise approximately
1/3 of a standard LCD pixel (which may be, for example, a "stripe"
or "row" of individually controllable liquid crystals across a
pixel).
[0130] A processing device 1055 receives a video or image signal
and produces energizing signals for the first and second modulating
panels and may also be produced to control local and/or global
dimming of the backlight. The energizing signals may be produced
exclusively from the image signal, or may incorporate one or more
of light field simulations based on the backlight (or energization
level of the backlight or portions of the backlight, or
colors/spectrum present in the backlight lights and/or other
optical properties of the display. The energizing signals may be
produced utilizing additional sensor information from any of
brightness, spectrum, polarization of light at various points in
the display (e.g., at the backlight or between panels of other
layers of the display), or ambient viewing conditions.
[0131] In various embodiments, a controller (e.g., processing
device 1055) according to the invention comprises a light field
simulation module configured to determine a light field incident on
one or more of the downstream modulators. The simulation takes into
account, for example, the scale of modulation and/or diffusion that
takes place prior to illumination of incidence on the downstream
modulators. Thus, in at least one embodiment, the simulation takes
into account two different scales of modulation and/or diffusion in
determining light incident on the modulators. This includes, for
example, consideration of local dimming and diffusion that occurs
prior to illumination of the first downstream modulator. The
simulation also takes into account any films (e.g., BEF,
polarization (reference, analyzing, or clean-up) prior to
illumination of the downstream modulating panels. Ultimately, the
simulation is used to determine modulation that should occur at the
one or more downstream panels and produce corresponding
energization signals.
[0132] Such a controller is useful in both profession and consumer
display equipment. In one embodiment, the controller is installed
in a medical device. The controller may be configured to control a
display of the medical device with regard to high resolution and
contrast. Such a display may be designed so that viewing angle is
traded for higher resolution and/or contrast. The display may be,
for example, a grayscale medical imaging device (e.g., configured
to replicate film based x-rays), or a high color high contrast
(e.g., CAT scan or other images). In another embodiment, the
controller is installed in a consumer display and is configured to
control the display in a manner that provides high contrast and
resolution with an industry standard viewing angle.
[0133] The invention includes enabling and/or disabling high
dynamic range features on a HDR display using software. For
example, the present invention includes packing a software system
that enables HDR video/display capability when enabling a plug-in
or activating a mode in a graphics driver. This would allow the
user to switch between LDR (low dynamic range) mode and HDR (high
dynamic range) mode at the click of a button the graphics driver UI
and that would enable and disable HDR capability on a display with
any of the hardware designs that have been described in this
disclosure. Similarly, enabling of 2D and 3D modes may be performed
through software or plug-ins installed on a system utilizing the
described displays.
[0134] In part, the present invention has been described using the
terms image-generating panel and contrast--enhancing panel.
However, it should be understood that both panels generate images,
and both panels impart contrast into a final image for display. The
image-generating panel, in most described embodiments, imparting
color and contrast through a combination of filtering and
brightness modulation, and the contrast-improving panel imparting
contrast, or enhancing contrast, via brightness modulation. And it
should also be understood that the contrast-improving panel could
also include color filtering or other variations of function in one
or more of the contrast-improving panel and/or the image-generating
panel.
[0135] In describing preferred embodiments of the present invention
illustrated in the drawings, specific terminology is employed for
the sake of clarity. However, the present invention is not intended
to be limited to the specific terminology so selected, and it is to
be understood that each specific element includes all technical
equivalents which operate in a similar manner. Furthermore, the
inventors recognize that newly developed technologies not now known
may also be substituted for the described parts and still not
depart from the scope of the present invention. All other described
items, including, but not limited to panels, LCDs, polarizers,
controllable panels, displays, filters, glasses, software, and/or
algorithms, etc. should also be considered in light of any and all
available equivalents.
Portions of the present invention may be conveniently implemented
using a conventional general purpose or a specialized digital
computer or microprocessor programmed according to the teachings of
the present disclosure, as will be apparent to those skilled in the
computer art.
[0136] Appropriate software coding can readily be prepared by
skilled programmers based on the teachings of the present
disclosure, as will be apparent to those skilled in the software
art. The invention may also be implemented by the preparation of
application specific integrated circuits or by interconnecting an
appropriate network of conventional component circuits, as will be
readily apparent to those skilled in the art based on the present
disclosure.
[0137] The present invention includes a computer program product
which is a storage medium (media) having instructions and/or data
stored thereon/in which can be used to control, or cause, a
computer to perform any of the processes of the present invention.
The storage medium can include, but is not limited to, any type of
disk including floppy disks, mini disks (MD's), optical discs, DVD,
HD-DVD, Blue-ray, CD-ROMS, CD or DVD RW+/-, micro-drive, and
magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, DRAMs, VRAMs,
flash memory devices (including flash cards, memory sticks),
magnetic or optical cards, SIM cards, MEMS, nanosystems (including
molecular memory ICs), RAID devices, remote data
storage/archive/warehousing, or any type of media or device
suitable for storing instructions and/or data (including remotely
stored or executed programs or data connected via Internet or other
networks such as wireless, cellular, etc., to a device performing
or using one or more results of the invention (e.g., cell phone,
PDA, computer display, HDTV, etc)). Such instructions may also be
divided between a network server and an end-user device, such as
processing performed by a cellular service provider and a cell
phone to produce a display on the cell phone according to any one
or more teachings of the present invention.
[0138] Stored on any one of the computer readable medium (media),
the present invention includes software for controlling both the
hardware of the general purpose/specialized computer or
microprocessor, and for enabling the computer or microprocessor to
interact with a human user or other mechanism utilizing the results
of the present invention. Such software may include, but is not
limited to, device drivers, operating systems, and user
applications. Ultimately, such computer readable media further
includes software for performing the present invention, as
described above.
[0139] Included in the programming (software) of the
general/specialized computer or microprocessor are software modules
for implementing the teachings of the present invention, including,
but not limited to, calculating pixel/sub-pixel blurring of a local
dimming panel, calculating color correction or characterizations,
preparing image signals and applying them to driver and/or other
electronics to energize backlights, panels, or other devices in a
display, calculating luminance values, interpolating, averaging, or
adjusting luminance based on any of the factors described herein,
including a desired luminance for a pixel or region of an image to
be displayed, and the display, storage, or communication of results
according to the processes of the present invention.
[0140] The present invention may suitably comprise, consist of, or
consist essentially of, any of element (the various parts or
features of the invention) and their equivalents as described
herein. Further, the present invention illustratively disclosed
herein may be practiced in the absence of any element, whether or
not specifically disclosed herein. Obviously, numerous
modifications and variations of the present invention are possible
in light of the above teachings. It is therefore to be understood
that within the scope of the appended claims, the invention may be
practiced otherwise than as specifically described herein.
* * * * *