U.S. patent application number 12/409379 was filed with the patent office on 2009-10-22 for soft aperture correction for lenticular screens.
This patent application is currently assigned to Real D. Invention is credited to Lenny Lipton, Michael G. Robinson.
Application Number | 20090262419 12/409379 |
Document ID | / |
Family ID | 39674379 |
Filed Date | 2009-10-22 |
United States Patent
Application |
20090262419 |
Kind Code |
A1 |
Robinson; Michael G. ; et
al. |
October 22, 2009 |
Soft aperture correction for lenticular screens
Abstract
An apparatus including an autostereoscopic image selection
device having a plurality of lenticules is provided. The
autostereoscopic image selection device has an opaque material
applied thereto in gaps between the plurality of lenticules. The
opaque material is applied to the autostereoscopic image selection
device in a soft aperturing manner, the soft aperturing manner
comprising applying the opaque material such that the opaque
material is tapered from the gaps over the plurality of lenticules.
The opaque material can be applied in accordance with a windowing
function.
Inventors: |
Robinson; Michael G.;
(Boulder, CO) ; Lipton; Lenny; (Beverly Hills,
CA) |
Correspondence
Address: |
REAL D - Patent Department
by Baker & McKenzie LLP, 2001 Ross Avenue, Suite 2300
Dallas
TX
75201
US
|
Assignee: |
Real D
Beverly Hills
CA
|
Family ID: |
39674379 |
Appl. No.: |
12/409379 |
Filed: |
March 23, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11880828 |
Jul 23, 2007 |
7508589 |
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12409379 |
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11701995 |
Feb 1, 2007 |
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11880828 |
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Current U.S.
Class: |
359/463 |
Current CPC
Class: |
G02B 3/0056 20130101;
G02B 3/0012 20130101; G02B 3/005 20130101; G02B 30/27 20200101 |
Class at
Publication: |
359/463 |
International
Class: |
G02B 27/22 20060101
G02B027/22 |
Claims
1. An apparatus comprising: an autostereoscopic image selection
device comprising a plurality of lenticules; and an opaque material
applied to the autostereoscopic image selection device in gaps
between the plurality of lenticules; wherein the opaque material is
applied to the autostereoscopic image selection device in a soft
aperturing manner, said soft aperturing manner comprising applying
the opaque material such that the opaque material is tapered from
the gaps over the plurality of lenticules.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/880,828, entitled "Soft Aperture Correction
for Lenticular Screens," filed Jul. 23, 2007, which is a
continuation-in-part of U.S. patent application Ser. No.
11/701,995, entitled "Aperture Correction for Lenticular Screens,"
inventor Lenny Lipton, filed Feb. 1, 2007, the entirety of which is
incorporated herein by reference.
BACKGROUND
[0002] 1. Technical Field
[0003] The present design relates generally to the art of
autostereoscopic displays, and more specifically to enhanced
techniques for flat panel monitor devices that improve optical
quality, and increase the depth of the image and the number and
quality of the viewing zones.
[0004] 2. Description of the Related Art
[0005] Today's stereoscopic display manufacturers seek to
continually improve the image quality associated with the
presentation of three-dimensional (3-D) content. One current
autostereoscopic flat panel monitor device that exhibits improved
image quality uses refractive optic techniques for image selection.
Refractive optic designs typically include lenticular screens and
Winnek slanted lenses. Another current flat panel monitor design
relies on raster barrier techniques for image selection. In both
designs, columns of images consisting of stripes made up of
perspective views form a repeating pattern on the autostereoscopic
display. Refractive optic techniques involve associating each
column of images with a cylindrical lenticule. Raster barrier
techniques associate each column of images with an aperture slit of
a raster barrier.
[0006] Autostereoscopic display designs have been the subject of
several prior disclosures. Reference is made to the work of, for
example, Okoshi in "Three-Dimensional Imaging Techniques", Academic
Press, New York, 1976.
[0007] An alternate technology currently available for use in flat
panel monitor device designs employs a "fly eye lens" technique for
image selection. This technique involves a number of related
miniature spherical lenses refracting light rays in both the
vertical and the horizontal direction.
[0008] As noted, refractive optic autostereoscopic display
techniques employ parallel rows of cylindrical lenticules, while
raster barrier autostereoscopic display techniques employ parallel
rows of slits. Both techniques produce a parallax effect only in
the horizontal direction, unlike the "fly's eye lens" that produces
parallax effects in both the vertical and horizontal directions.
Accordingly, the refractive and raster barrier techniques involve
horizontal parallax exclusively. Refractive and raster barrier
designs can produce images with lower resolution requirements since
they selectively use image information in the horizontal direction
only, rather than in both the vertical and the horizontal
directions.
[0009] In practice, designs employing lenticular autostereoscopic
screens have drawbacks because they reduce the overall effective
display sharpness. In particular, autostereoscopic displays that
employ a lenticular screen for image selection tend to have
shortcomings with regard to the sharpness of the image having high
parallax values. Such shortcomings are particularly apparent with
regard to images including objects appearing off the plane of the
screen or very deep into the screen. Further issues with lenticular
screens can occur when a multiplicity of non-primary viewing zones
exist, particularly with respect to the sharpness of those
non-primary viewing zones.
[0010] In practice, designs employing raster barrier displays
reduce the overall display brightness and introduce undesirable
visible pattern noise. In fact, raster barrier autostereoscopic
screens turn out to be so dim, typically losing 80 or 90 percent of
the light when rendering multi-perspective images, that they may
not be commercially viable when used with currently available flat
panel displays.
[0011] Refractive screens employing "fly eye lens" designs have not
been deployed into the marketplace to any extent but have been
shown experimentally in laboratories. They have low resolution when
employed in connection with a flat panel monitor device.
[0012] Autostereoscopic displays using either lenticular screen,
raster barrier, or "fly eye lens" techniques are difficult to
manufacture due to the tight dimensional and alignment tolerances
required when used with the underlying flat panel monitor device
electronic display.
[0013] Further, it has been noted that certain performance issues,
particularly crosstalk due to diffraction of signals transmitted
through lenticules and perceived by a viewer, can occur when
lenticular arrays are employed.
[0014] Based on the foregoing, it would be advantageous to provide
a flat panel display device for use in viewing stereoscopic image
content that overcomes the foregoing drawbacks present in
previously known designs.
SUMMARY
[0015] According to one aspect of the present design, there is
provided an apparatus comprising an autostereoscopic image
selection device having a plurality of lenticules is provided. The
autostereoscopic image selection device has an opaque material
applied thereto in gaps between the plurality of lenticules. The
opaque material is applied to the autostereoscopic image selection
device in a soft aperturing manner, the soft aperturing manner
comprising applying the opaque material such that the opaque
material is tapered from the gaps over the plurality of lenticules.
The opaque material can be applied in accordance with a windowing
function.
[0016] These and other advantages of the present disclosure will
become apparent to those skilled in the art from the following
detailed description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The present disclosure is illustrated by way of example, and
not by way of limitation, in the figures of the accompanying
drawings in which:
[0018] FIGS. 1A, 1B, and 1C are diagrammatic representations of
refractive autostereoscopic lens sheets;
[0019] FIG. 2 is a ray diagram illustrating the optics of an
individual lenticule and consequent spherical aberration;
[0020] FIG. 3 show the optics of a lenticular screen, and the
curvature of field resultant from the simple optics employed;
[0021] FIG. 4 illustrates a ray tracing of a cross-section of a
lenticular screen, highlighting the issue of adjacent viewing
zones.
[0022] FIG. 5 is a lenticular screen with the over coating as
applied in the present design as a manufacturing step in the
embodiment described;
[0023] FIG. 6 shows a lenticular screen in the final stage of
manufacturing in that the overcoat has been buffed to produce the
aperture-corrected lenticular screen in accordance with the present
design;
[0024] FIG. 7 illustrates a lenticular screen with a ray diagram
showing the improvement of aperture correction with regard to
spherical aberration;
[0025] FIG. 8 illustrates a lenticular screen whose lenticules
exhibit curvature of field, showing aperture correction;
[0026] FIG. 9 is a ray trace diagram of the cross-section of a
lenticular screen, illustrating how the aperture correction
produces an improvement in the optical quality of off-axis viewing
zones;
[0027] FIG. 10a is the normalized diffracted intensity from a point
source in the viewing region of an autostereoscopic system imaged
through a 200 .mu.m cylindrical lens;
[0028] FIG. 10b shows the normalized diffracted intensity from a
point source in the viewing region of an autostereoscopic system
imaged through a 200 .mu.m cylindrical lens with soft
aperturing;
[0029] FIG. 11a illustrates a cross section of an unaltered
cylindrical lenticular array; and
[0030] FIG. 11b is a cross section of a soft apertured cylindrical
lenticular array.
DETAILED DESCRIPTION
[0031] The following description and the drawings illustrate
specific embodiments sufficiently to enable those skilled in the
art to practice the system and method described. Other embodiments
may incorporate structural, logical, process and other changes.
Examples merely typify possible variations. Individual components
and functions are generally optional unless explicitly required,
and the sequence of operations may vary. Portions and features of
some embodiments may be included in or substituted for those of
others.
[0032] The present design combines the virtues of both refractive
or lenticular autostereoscopic displays and raster barrier
displays. The technique described herein vastly improves the image
quality of an autostereoscopic display using refractive lenticular
optics, with only a minor reduction in light output.
Lenticular Screens
[0033] Autostereoscopic display technology has been applied to flat
panel displays with some success. There are two major variants--one
using refractive optics for image selection and the other using
raster barriers. In both cases, columns of images consisting of
stripes made up of perspective views form a repeating pattern on
the display. Each column is associated with a cylindrical lenticule
or with an aperture slit of a raster barrier. In addition to the
refractive and raster barrier techniques, which are essentially
optically interchangeable, another technique--the "fly's eye
lens"--has also been employed. The fly's eye lens includes a number
of miniature spherical lenses that refract in both the vertical and
the horizontal direction.
[0034] A lenticular screen that includes parallel rows of
cylindrical lenticules, or the raster barrier having parallel rows
of slits, produce their effect only in the horizontal direction,
unlike the fly's eye lens that works in both the vertical and
horizontal directions. Accordingly, these techniques involve the
use of horizontal parallax exclusively. Because of this
restriction, there is the ability to produce a sharper image
because the image information is used selectively only in the
horizontal direction, rather than in both the vertical and the
horizontal.
Standard Lenticular Screens
[0035] In FIG. 1A, a typical lenticular screen 101 is shown with a
subject lenticule 102, and the pitch of the screen P is given at
point 103. Display surface 104 is shown. The display surface 104
can be any type of display, including but not limited to hard copy
or electronic. For the most part the display surface 104 can be
either a self-illuminated or rear-illuminated display. The design
presented herein results in a reduction in brightness, and thus
self-illuminated or rear-illuminated displays can benefit from the
present design. Even though the technique can be applied to a hard
copy that is not rear-illuminated, the present technique can be
applied to rear-illuminated hard copy or electronic displays such
as plasma panels, liquid crystal displays, light-emitting diodes,
or similar displays that either modulate or emit light.
[0036] FIG. 1B is a Winnek slanted lens sheet is shown that is
highly similar to the screen of FIG. 1A. The difference here is
that the lenticules are slanted to the horizontal. Instead of the
boundary between lenticules being parallel to the vertical edge of
the display, the lenticules are slanted at some angle. The lens
sheet 105 is shown with individual lenticule 106 having pitch P
107, with display 108 as shown. The advantage to this type of
display has been discussed in, for example, U.S. Pat. No.
3,409,351. The major advantage to the Winnek tipping of the lens
sheet is to eliminate pattern noise and color banding or moire, and
to also equalize the resolution in the vertical and the horizontal
direction.
Fly's Eye
[0037] FIG. 1C shows a fly's eye lens sheet 109 with an individual
circular lens element 110. The fly's eye lens sheet 109 has a pitch
P 111 equal in both the vertical and the horizontal directions,
with the display surface 112 oriented as shown. Fly's eye
lenticular screens have not been widely accepted in the marketplace
but laboratory experiments have demonstrated their performance.
Fly's eye lenticular screens are generally difficult to manufacture
and also have low resolution when used with a flat panel display.
However, they do have interesting properties insofar as they
closely resemble holography in terms of their physics and end
effect for the viewer.
Raster Barriers
[0038] Other designs attempted include the raster barrier display,
consisting of a series of zebra-like slits or Ronchi-grating-like
slits, with the slits going in the vertical direction. These raster
barriers produce an autostereoscopic display having a greater
parallax budget before image breakdown occurs.
[0039] "Parallax budget" is defined as the useful range of parallax
within the display. In-screen parallax is assigned positive values
and off-screen parallax is assigned negative values. The greater
the absolute value of the parallax, the deeper the appearance of
image points associated with those values. Image points with large
values of parallax, such as in the autostereoscopic displays
discussed herein, tend to lose sharpness or take on unfortunate
artifacts such as image doubling. The range of parallax values, or
the parallax budget, that can be well represented by the display
before image breakdown is a principal quantitative measurement that
directly relates to stereoscopic image depth.
[0040] Raster barrier designs also have increased and sharper
viewing zones. The increased parallax budget is important because
parallax information is important in a stereoscopic display.
Because raster barrier displays can have a larger parallax budget,
the image can appear to be deeper, because parallax is the
principal stereoscopic depth cue.
[0041] In addition, raster barrier displays can also have a greater
number of viewing zones. The reason for the greater number of
viewing zones, optically, is that raster barrier displays use slit
optics rather than refractive optics and have, in effect, a great
deal of depth of focus because the image-forming rays are more
nearly parallel as a result of the tiny aperture involved.
[0042] The disadvantage of the raster barrier is the dimness, or
lack of brightness. In fact, raster barriers are so extremely dim
that they may not be commercially viable. Raster barriers require
an extremely bright underlying display, and both the commonly used
plasma panels and liquid crystal displays lack sufficient
brightness to make a satisfactory raster barrier autostereoscopic
display. One of the hallmarks of a good display, and one of the
most important things about an electronic display, is brightness,
and display manufacturers have had a challenge to meet the
brightness requirements for a flat panel display. Given the
additional brightness limitations of a raster barrier, the quest
for a display that meets illumination specifications becomes nearly
hopeless, because raster barrier displays for multi-view or
stereoscopic imaging typically waste 80 or 90 percent of the light
originally transmitted.
[0043] Although raster barrier displays may appear easier to
manufacture, in point of fact they are not necessarily easier to
manufacture than lenticular displays. Both displays have challenges
with regard to dimensional tolerances and alignment with regard to
the underlying electronic display.
Parallax Issues
[0044] Autostereoscopic displays, especially those using lens
sheets for image selection, tend to have shortcomings with regard
to the sharpness of images having high parallax values, especially
with regard to images with objects appearing off the plane of the
screen or that go very deep into the plane of the screen. In other
words, the parallax budget is limited. Such displays also have
issues with both a multiplicity of non-primary viewing zones and
the sharpness of those non-primary viewing zones.
[0045] Lenticular displays have associated with them, behind each
vertical-going lenticule, a column of image information broken up
into stripes of perspective views. When viewing an autostereoscopic
image image selection takes place at the plane of the screen. The
functioning of lenticular screens and their optical characteristics
are described in detail in the Okoshi publication. One publication
discussing the aberrational correction of photographic optics is
Photographic Optics by Arthur Cox, 1974, Focal Press, London, 15th
edition.
[0046] The accompanying figures showing ray diagrams work to serve
as explanation for what is happening optically in FIGS. 1A, 1B, and
1C. In the case of FIGS. 1A and 1B, cylindrical lenticules are
employed, so the cross-section surface is assumed to be
perpendicular to the intersection of the lenticule boundaries. In
the case of FIG. 1A, the cross section is a horizontal plane passed
through the lenticules. In the case of FIG. 1B, the cross section
is a plane passing through the lenticules, but at an angle to
account for the Winnek tip angle--so that the plane that passes
through the lenticules is perpendicular to the boundary of
intersection of the lenticules, as shown in FIG. 1B. In the case of
FIG. 1C, the cross-section could be made at any angle, because the
fly's eye lenses at point 109 are sections of a sphere rather than
a cylinder.
[0047] From FIG. 2, a cross-section of a lens sheet 201 is shown
and an individual lenticule 202 is called out. Pitch P 203
represents the width of a lenticule. Display surface 204 is shown,
representing a flat panel display that could be a plasma display
screen, a liquid crystal display screen, a light-emitting diode
display screen, or any other suitable flat panel display. Curved
surface of the lenticule 205 is shown, and rays 206A and 206B are
emitted from the display screen 204 after having been refracted by
the individual lenticule 202. The arrows are pointing toward the
eyes of the observer because the surface produces pixels
illuminated in various ways depending upon the display type. Rays
207A and 207B are parallel, but these rays come from the central
area of the lens rather than from the boundary edges, and the
double-headed arrows indicate the rays. Point 208 is the location
where the outermost or boundary rays cross or are in sharp focus,
and point 209 is where the central rays 207A and 207B
cross--namely, behind the plane of the display surface. Point 208,
representing boundary or outermost rays crossing, is in front of
the plane of the display surface.
[0048] The drawings assume that the rays are monochromatic--that
is, the rays are for a single wavelength. Illustrated here is a
non-ideal lens having spherical aberration. With reference to FIG.
2, several of the classical aberrations will be described. Those
aberrations can be improved by stopping down the lens or by adding
an aperture. The present design reduces the numerical aperture (and
hence the area of the available lens surface) to improve correction
of the aberrations. The present design also can improve the depth
of field.
[0049] Multiple perspective views required for viewing the image
are included within the column P. When looking at a normal display
there is no refractive lens sheet, forcing each eye to see
individual image points, which produces the stereoscopic effect. In
the case of a normal display, there is but a single image point on
the display where the eyes converge and focus. However, because of
the autostereoscopic display's selection device--the lens
sheet--the perspective views incorporated within pitch P 203 are
refracted to different locations and seen by the eyes, and the
combination of these separate perspectives forms the stereoscopic
image.
[0050] In the case of lens sheets used for autostereoscopic
displays, such lens sheets are single-element devices. In order to
achieve good correction (namely, a significant reduction in
aberration), lens systems require a complex system of lens
elements. These elements have different dispersions and different
indices of refraction to compensate for the dispersive properties
of light and to produce a decently corrected image.
[0051] Simple lens sheets represent an optical system that cannot
possibly provide high-quality correction and reduction of
aberration. Aberration correction would be a departure from the
lenses' ability to produce single, small, clean image points of
objects in space. A good overall optical design must produce an
image that is sharp and has as high a contrast as possible coming
from the display surface. So, in a sense, the optics for this
design more nearly resemble the optics of a projector than a
camera. The entity or measurement of interest is termed "depth of
focus." Depth of focus is the range of acceptable focus that can be
sharply resolved with respect to the display plane 204 in the case
of FIG. 2.
[0052] Note that in the case of lens sheet 201, parallel rays that
emerge from the display, namely rays 206A and 206B, have a point of
sharp focus at point 209. Rays emerging not from the boundary edges
of the lenticules but from the center come to sharp focus at 208.
Accordingly, this condition, which has been described as "spherical
aberration," cannot produce perfectly sharp images.
[0053] Looking at FIG. 3, note lens sheet 301 has an individual
lenticule 302 and pitch P 303. The display surface is shown as
surface 304. In this case curvature of field is illustrated. Once
again, the subject light is monochromatic light. The on-axial
parallel rays that enter the lens at its very boundary are denoted
as rays 306A and 306B. Rays 306A and 306B come to sharp focus at
point 308. Rays 307A and 307B enter at the same points of the lens,
but are viewed off-axially, and these are denoted by double-headed
arrows (whereas 306A and 306B are denoted by single-headed arrows)
and come to a sharp focal point 309. Focal point 309 lies on
surface 310 that, in the case of a lenticular sheet, is a
cylindrical surface with a curvature of fixed radius. If a fly's
eye lens is employed rather than a cylindrical surface, the
depiction would be a section of a sphere, as denoted by surface
310. And as noted above, the present drawings can serve for either
cylindrical lenticules or for a fly's eye lens.
[0054] In the case of FIG. 3, the aberration curvature of field
limits the effective depth of focus at the image plane 304, because
points 308 and 309 are at different distances. This is a condition
that is difficult to cure using a single element. The cure
advocated herein and that will be described below is one of
aperture correction, in which the lenticules are actually stopped
down to have a numerically higher aperture and less available
area.
[0055] In FIG. 4, lens sheet 401 is shown with individual lenticule
402 having pitch P 403, with a display surface 404. The curvature
405 of the lenticule is shown. The concern is with the observer
seeing the adjacent perspective views. When viewing a lenticular
autostereoscopic display, the progression or continuum of views can
be seen within a viewing zone. In space, some reasonable distance
from the display, the eyes of the observer can see a stereoscopic
image over a relatively limited angle of view. The angle of view
may be as narrow as a few degrees, or as great as several tens of
degrees. Once the observer moves to the side, a so-called "flip"
occurs, and the rays that heretofore had been associated with the
central viewing zone move to adjacent viewing zones.
[0056] An individual viewing an autostereoscopic display sees a
primary viewing zone, secondary viewing zone, tertiary viewing
zone, and so forth. The primary viewing zone--if the display has
been properly set up--is on-axis, and is of a certain specifiable
angular extent. When the observer moves laterally, he or she sees
the columns refracted by the lenticules. These columns are now not
directly under the lenticules and on-axis, but instead are the
secondary, tertiary, and so forth, columns (which in fact are image
columns under other lenticules). The images of the secondary,
tertiary, and so forth, columns should be sharp and well corrected.
The present design addresses making this improvement using aperture
correction.
[0057] Regarding raster barriers, autostereoscopic displays using
raster barriers tend to have sharper images and more image "pop."
That means that the image can apparently emerge further from the
screen, and actually go deeper into the screen, without the image
breaking down because of aberration defects. In addition, these
raster barrier displays have sharper secondary, tertiary, and so
forth, viewing zones--and indeed have more of these auxiliary
viewing zones, which is an advantage of some significance.
[0058] Raster barriers and lenticular screens are optically
interchangeable so one can be swapped for the other for a given
underlying display. A raster barrier display has narrow openings,
or slits. A raster barrier looks like a zebra-stripe grating or a
Ronchi grating, and despite the fact that these displays have
certain virtues, they have very low brightness for a
panoramagram-type display with a multiplicity of perspective views,
and also a noticeable pattern noise. Viewing images using a raster
barrier resembles looking through a grating, which indeed one
is.
[0059] With regard to FIG. 4, the familiar elements are shown. Lens
sheet 401 is shown, the individual lenticule 402 is presented,
width 403 is the width of the lenticule given by pitch P, display
surface 404 is shown, and curvature 405 is the curvature of the
individual lenticule. Of interest is how the image is formed by the
adjacent column. Rays 406A and 406B are seen, and once again only
monochromatic rays are assumed and are indicated with single-headed
arrows, forming sharp focus at point 408. This case assumes the
lens is a perfect lens, and aberration is not a consideration. The
concern is with depth of field. When viewing a secondary viewing
zone, rays 407A and 407B illustrate what is happening. These rays
have double-headed arrows. The rays cross at 409 in lenticule 402,
which is a secondary lenticule with regard to the specific rays. In
this case sharp focus is not maintained. With regard to tertiary
and lenticules that are even further away, focus will be even
worse.
Aperture Corrected Design
[0060] In the present design, a material is coated on top of the
lenticules and then is removed by buffing. FIG. 5 shows a section
of a lens sheet 501, with individual lenticule 502. The lenticule
pitch P 503, where display surface 504 is shown. Curve 505
represents the curved surface of a lenticule. Opaque material 506
is applied to the surface. The opaque material can be a waxy
material, or another appropriate masking material, including but
not limited to INX pigments or other waxy materials.
[0061] The material is then buffed, as shown in FIG. 6. FIG. 6
shows the corresponding lens sheet identical to that shown as lens
sheet 501. Individual lenticule 602 is shown, with pitch P 603,
where display surface 604 is shown. Curvature 605 is the curvature
of the lens sheet, or the very top surface, while material 606
represents the remaining aperture material.
[0062] Once the material 506 has been applied as shown in FIG. 5,
depending upon the type of opaque material employed, after a
passage of time (which may be very rapid, or may take time for the
material to set), the material may be manually buffed or wiped way
with a polishing or wiping cloth, or the rubbing, buffing, or
polishing performed by a machine. By applying the proper pressure
the top surfaces are revealed, forming a reduced section of a
cylinder in the case of a lens sheet, or a circle in the case of a
fly's eye lens. The result is an aperture reduction.
[0063] Lens apertures can be placed at various points in a lens
system. They can be placed in front of a simple lens, or behind a
simple lens, or they can be placed--probably most
efficaciously--within a complex lens system at or near the optical
center of the lens. In this case, several issues exist with regard
to manufacturing a lens sheet of this type with aperture
correction. One is that the optical center of the lens, or the
radius of the lens, lies within the lens sheet, so it is difficult
or impossible to place an aperture there. An aperture could be
placed in other ways, but many of the other ways are difficult,
costly, and/or impractical. Placement of an aperture at the display
screen causes a loss of pixels and resolution and results in a poor
quality picture with pattern noise.
[0064] The best place to place the aperture is at the surface of
the lens, as described with the aid of FIGS. 5 and 6. This approach
is self-locating. Because there are frequently tens of thousands of
individual lenticules in such a display, it would be virtually
impossible to find a way to manufacture an aperture sheet that
could be located in intimate juxtaposition with the lenticules and
provide the advantages described herein. Various materials can be
used.
[0065] The benefits of the reduction are shown with respect to
FIGS. 7, 8, and 9. FIG. 7 shows lens sheet 701 with individual
lenticule 702 whose pitch P 703 is presented together with display
surface 704. The top surface 705 of the lens is shown. The
aperture-reducing material 710 is shown. In this case there is a
reduction of spherical aberration because the outer rays touch the
aperture. Rays 706A and 706B (single-headed arrows) form a point of
sharp focus at point 708. Rays 707A and 707B, indicated by
double-headed arrows, form a point of sharp focus 709. The rays
here are more nearly parallel, the focus spot is a tighter, smaller
spot, and focus is improved.
[0066] In FIG. 8 an improvement in curvature of field is shown,
because lens sheet 801 with individual lenticule 802, given pitch P
803 and display surface 804, now has a narrower angle at the focus
point. This can be illustrated by looking at the parallel rays 806A
and 806B that come to focus at point 808. The on-axial rays 806A
and 806B are indicated by single-headed arrows. Rays 807A and 807B,
which are indicated by double-headed arrows, come to a focal point
809 on curve 810. The rays are now more nearly parallel, or form a
focus point at a less steep angle. Accordingly, the curvature of
field becomes less of a problem because the image points are
tighter and smaller as they cross the image-forming surface
804.
[0067] FIG. 9 presents the operation of secondary and tertiary
viewing zones. Lens sheet 901 is shown, including individual
lenticule 902, where pitch P 903 is illustrated with display
surface 904. Curvature 905 is the curvature of the lenticule and
opaque material 910 has been applied to reduce the aperture. Rays
906A and 906B are on-axial parallel rays that are out at the edge
of the aperture, illustrated by single-headed arrows. Rays 906A and
906B come to focal point 908. Rays 907A and 907B are non-axial
points that are refracted and form image point 909 in lenticule
902. Rays 907A and 907B are illustrated with double-headed arrows.
An observer seeing the non-primary viewing zone sees a sharper
image because the rays are more nearly parallel and the focus spot
is a tighter, smaller point. Thus by using the opaque material, the
present design improves the depth of field (or the depth of focus,
more properly) of the lens elements. This improvement in depth of
focus helps both non-primary viewing zone viewing and correction of
both spherical aberration and curvature of field.
[0068] The result of this is a lens sheet that has one significant
reduction in quality, namely brightness. Such a design is typically
less bright than a normal lens sheet, but likely far brighter than
a raster barrier display. The modern flat panel displays can be
extremely bright, so a small sacrifice in brightness--even a loss
of half or a third of the brightness--still produces a reasonably
bright display. But the end result now is an image with much
greater "pop." Off-screen effects before any image breakdown are
noticeably improved, larger values of parallax can hold up, and the
parallax budget of the display has been greatly expanded. The
benefit is a highly enhanced stereoscopic effect.
[0069] In addition, the secondary and tertiary viewing zones have
vastly improved sharpness. And, indeed, there will be more of them
because the image-forming rays as shown in FIG. 9 are more nearly
parallel.
[0070] The present design lens sheet configuration may reduce
overall brightness. This method will be less bright than a normal
lens sheet, but may be far brighter than current raster barrier
display designs. Today's flat panel monitor devices can be
extremely bright, so the reduction in brightness associated with
the present design may still display a reasonably bright image. In
contrast, the present design can render images with a very much
greater "pop" or a more pleasing overall effect. In addition, the
present design can improve the off-screen effects before any image
breakdown occurs and allow larger values of parallax to be
realized. The parallax budget of an autostereoscopic display
according to the present design can be greatly expanded and produce
what is known as a deep stereoscopic effect. The secondary and
tertiary viewing zones may yield images with improved sharpness and
may provide additional off-axis viewing zones resulting from the
image-forming rays as illustrated in FIG. 9 become nearly
parallel.
Enhanced Correction--Soft Aperturing
[0071] Another aspect of aperturing lenticular arrays is the
suppression of optical diffraction effects. Lenses can only image
within a diffraction limit determined by their physical size. With
autostereoscopic displays, lenticular elements determine the pixel
size of the viewed image, and thus smaller elements are generally
preferred. The eye resolves down to one minute of arc, a
physiological phenomenon dictating the maximum size of lens
elements.
[0072] For a display positioned two meters from a viewer, one
minute of arc translates into a minimal resolvable pixel size of
0.6 mm and implies a desired RGB color sub-pixel size of 0.2 mm;
the size of a desired lens element. Simple diffraction estimation
gives the angular spread of light through an aperture of size d as
.lamda./d, where .lamda. is the wavelength of visible light,
approximately 0.5 .mu.m. At a two meter viewing distance (D), this
corresponds to a "smearing" of 5 mm from a desired 0.2 mm (d) lens.
Compared with the average inter-ocular separation of 65 mm (the
maximum size of an autostereoscopic viewing region), such smearing
appears to be sufficiently small to be ignored.
[0073] Smearing is not confined to the angular spread given by the
simple formula, but determined by the one dimensional Fourier
transform of the lens aperture written analytically as:
sin.sup.2(.pi.dx/.lamda.D)/(.pi.dx/.lamda.D).sup.2 (1)
where x is the side-to-side distance of the aperture in the plane
of the viewer.
[0074] FIGS. 10a and 10b plot the normalized diffracted intensity
from a point source in the viewing region of an autostereoscopic
system imaged through a 200 .mu.m cylindrical lens with and without
soft aperturing, respectively. The first zero plotted in FIG. 10a
corresponds to the first estimation of the spread above in Equation
(1). In actuality, the intensity of the diffraction peaks fade
gradually, described by (.lamda./.pi.dx).sup.2. Crosstalk at the
center of a viewing region from both neighboring views (at a
maximum distance of approximately 30 mm away) is significant,
greater than 0.3 percent, further increasing toward the edges.
[0075] FIGS. 11a and 11b show the structure of bare and
soft-apertured lenses, respectively. To reduce diffraction
conventional windowing techniques can be employed, where windowing
techniques are signal processing techniques employed to create a
specific signal profile where the function employed has a value of
zero outside a specific boundary.
[0076] Windowing is most commonly used to filter temporally varying
signals to reduce temporal side-lobes or `ringing` which would
otherwise act to reduce signal bandwidth. Windowing and side-lobes
are relevant here since the relationship between the time and
frequency domains are mathematically analogous to those that relate
angle scattering to spatial constriction, i.e. diffraction.
[0077] The most common windowing techniques are cosine and Hamming
windows. Windowing softens the edges of the aperture and can reduce
diffraction side-lobes. A simple cosine amplitude variation over
the lens can reduce side lobes to an inconsequential level such as
is shown in FIG. 10b. In practice any softening of the edges can
dramatically reduce diffraction and improve autostereoscopic
crosstalk.
[0078] Application of material in soft aperturing comprises
applying material to the lens array such that the signal
transmitted to the lens array is partially obscured by the material
resulting in a transmitted signal profile having properties similar
to the profile of FIG. 10b. In other words, without material
applied, the signal transmitted from the lenticular screen is
similar to the profile of FIG. 10a. Material is applied such that
the resultant signal has properties similar to FIG. 10b, and thus
the lenticular screen acts as a filter for the received signal and
application of material through the soft aperturing described
herein performs the function of further filtering the signal such
as by a Hamming or cosine window. Thus the soft aperturing
described herein may be applied to any type of lenticular screen,
including one having lenticules slanted at an angle such as the
Winnek angle or in a fly eye lens arrangement. The result is the
filtering described being applied to the uncompensated lenticular
screen by application of material in a soft aperturing manner as
described.
[0079] Cosine windowing equations and parameters are generally
known in the art or easily accessible from signal processing
literature and resources. In the present application of windowing,
it is to be noted that precise conformance to classic windowing
definitions is not required. Rather, soft aperturing can be
effective in this optic/lensing design when material is applied in
a manner generally similar to the aforementioned windowing
techniques, but the application of material does not need to result
in a precise windowing function result or match precise equations
of windowing known in the art. Application of material in a manner
approximating a windowing function is generally sufficient for the
present design.
[0080] The present design employs these functions in the design of
the individual lenticules and covering portions of the lenses with
a material according to equations such as the foregoing, a
procedure referred to as soft aperturing. Soft aperturing is
therefore covering portions of the lenticules, and as noted herein,
use of signal processing windowing techniques such as cosine or
Hamming or other windowing techniques may be helpful in producing
the signal shown in FIG. 10b. Thus the present design entails
taking the lenticule profile into consideration and applying soft
aperturing such as according to Equations (2) or (3) or similar
windowing equation to establish regions of the lenticules for
blocking or obscuring.
[0081] Note that one aspect of soft aperturing is the gradual
tapering of material at the edges of the material being filled into
the joints of the lenticular screen. This soft aperturing is in
contrast to hard aperturing, or application of material to a
lenticular screen where a hard edge or clear line is formed from
the material. Soft aperturing can be employed in the manner
suggested, such as forming a Hamming or cosine window, or may
simply entail the gradual tapering of material toward the
lenticule, and may be employed with any type of lenticular screen
(angled lenticules, fly eye lens, etc.) without the specific
windowing described herein.
[0082] FIGS. 11a and 11b show cross sections of a bare cylindrical
lenticular array and a soft apertured cylindrical lenticular array,
respectively. The present aspect of the current design thus
apertures lenticular elements in such a way to soften edges and
reduce diffraction using the structure of the lens to control
optical density. In the bare case of FIG. 11a, lens apertures 1101
are defined by the physical size of the individual lenses, each
lens defined by an undesirable abrupt edge line such as line 1102.
FIG. 11a also shows the tapered profile of the lens height in the
region on either side of this line.
[0083] Depositing an absorbing material in the valley region
between lenses such as is shown in FIG. 1b provides a material
whose thickness (and hence absorption) varies as a function of
distance from the lens edge. Such absorption variance provides a
convenient amplitude modulation and can reduce harsh diffraction
effects. Methods of depositing material can include application of
solvents whereby a dye material contained within a solvent could be
first applied to the surface of the lenses at a controlled
thickness, using for example the established `doctor-blade`
technique, wherein a metal strip or other blade-like surface is
used to wipe solvent off desired areas of the lenses, leaving
solvent inside the desired lens areas. The solvent can then be
allowed to evaporate leaving the remaining material in the gaps
between the lenses as desired.
[0084] An alternative approach uses a UV-curing material containing
dye material and deposits this material on the surface of the
lenses. Exposure occurs through the UV-absorbing lenses such that
those regions with less lens material (the so-called valleys) cure,
allowing those regions above the lenses to remain uncured for
removal at a later process stage.
[0085] In summary, soft aperturing cuts light from the joints
between the cylindrical lenses. This helps in the first instance by
cutting light from `bad` regions of the lens. Additionally, soft
aperturing suppresses unwanted diffraction effects with very narrow
lenses (.about.300 um) by the black stripes formed by the material
gradually becoming transparent at their edges. Striping in this
manner looks to the eye (under a microscope) as if the stripes have
fuzzy, non-sharp edges. The precise tapering of the optical
attenuation is optional to the designer, although certain optimal
profiles (cosine, Hamming windowing, etc.) optimize high angle
scattering beyond any practical relevance. Any tapering, or any
soft aperturing is helpful in this lenticular screen environment.
To fabricate, dye is placed into an encapsulating material of a
known refractive index which works with that of the lens to provide
an appropriate focal length.
[0086] What has been shown will be appreciated by a worker with
ordinary skill in the art as having produced an aperture reduction
that produces a consequential improvement in image quality. This
aperture reduction has been achieved without requiring precision
location of a multiplicity of apertures, because it is essentially
self-locating in terms of its manufacturing process. In addition,
there is a vast improvement in image quality for certain viewing
zones. And, indeed, additional viewing zones are now possible that
can be viewed and enjoyed, and that have enhanced quality. In other
words, the overall stereoscopic effect is vastly extended and
improved. Further, using the soft aperturing technique can improve
crosstalk due to diffraction without introducing significant
manufacturing cost.
[0087] The design presented herein and the specific aspects
illustrated are meant not to be limiting, but may include alternate
components while still incorporating the teachings and benefits of
the disclosure. While the invention(s) have thus been described in
connection with specific embodiments thereof, it will be understood
that the disclosed embodiments are capable of further
modifications. This application is intended to cover any
variations, uses or adaptations of the invention following, in
general, the principles of the invention, and including such
departures from the present disclosure as come within known and
customary practice within the art to which the disclosure
pertains.
[0088] The foregoing description of specific embodiments reveals
the general nature of the disclosure sufficiently that others can,
by applying current knowledge, readily modify and/or adapt the
system and method for various applications without departing from
the general concept. Therefore, such adaptations and modifications
are within the meaning and range of equivalents of the disclosed
embodiments. The phraseology or terminology employed herein is for
the purpose of description and not of limitation.
* * * * *