U.S. patent application number 08/985163 was filed with the patent office on 2001-05-24 for directional display for a directional display having an angular intensity profile compensator.
Invention is credited to EZRA, DAVID, MOSELEY, RICHARD ROBERT, WOODGATE, GRAHAM JOHN.
Application Number | 20010001566 08/985163 |
Document ID | / |
Family ID | 10804132 |
Filed Date | 2001-05-24 |
United States Patent
Application |
20010001566 |
Kind Code |
A1 |
MOSELEY, RICHARD ROBERT ; et
al. |
May 24, 2001 |
DIRECTIONAL DISPLAY FOR A DIRECTIONAL DISPLAY HAVING AN ANGULAR
INTENSITY PROFILE COMPENSATOR
Abstract
A directional display comprises a display arrangement such as a
spatial light modulator and a rear parallax barrier illuminated by
a suitable backlight. The spatial light modulator and the parallax
barrier cooperate to produce Fresnel diffraction which results in
spatially non-uniform brightness across viewing windows of the
display. Also, where the spatial light modulator has pixels of
non-constant vertical aperture, further variations in the intensity
profile at the windows occurs. In order to compensate for this, a
mask is provided, for instance between the parallax barrier and the
backlight. The mask cooperates with the parallax barrier to produce
an intensity pattern having variations which are the inverse of the
variations in intensity pattern produced by the parallax barrier
and the spatial light modulator. The variations are superimposed
and substantially cancel each other out so as to result in viewing
windows which have substantially uniform light intensities.
Inventors: |
MOSELEY, RICHARD ROBERT;
(WEST SUSSEX, GB) ; WOODGATE, GRAHAM JOHN;
(OXFORDSHIRE, GB) ; EZRA, DAVID; (OXFORDSHIRE,
GB) |
Correspondence
Address: |
NEIL A DUCHEZ
RENNER OTTO BOISSELLE & SKLAR
1621 EUCLID AVENUE
NINETEENTH FLOOR
CLEVELAND
OH
44115
|
Family ID: |
10804132 |
Appl. No.: |
08/985163 |
Filed: |
December 4, 1997 |
Current U.S.
Class: |
349/15 ;
348/E13.029; 348/E13.03; 348/E13.043; 348/E13.044; 348/E13.05;
349/61; 349/86 |
Current CPC
Class: |
H04N 13/31 20180501;
H04N 13/305 20180501; G02F 1/133512 20130101; G02F 1/133526
20130101; G02F 1/133606 20130101; G02B 30/30 20200101; G02F
1/133607 20210101; H04N 13/351 20180501; G03H 2270/54 20130101;
G02B 30/27 20200101; H04N 13/376 20180501; H04N 13/32 20180501;
H04N 13/359 20180501; G03H 2001/0439 20130101; H04N 13/312
20180501; G02B 5/32 20130101; G02F 1/133524 20130101; G03H 2210/22
20130101; G02F 1/1336 20130101 |
Class at
Publication: |
349/15 ; 349/61;
349/86 |
International
Class: |
G02F 001/1335; G02F
001/1333 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 12, 1996 |
GB |
9625497.4 |
Claims
What is claimed is:
1. A directional display comprising a display arrangement for
producing a plurality of viewing zones, each of which has a
non-uniform first angular intensity profile with a first angularly
varying component, the display further comprising a compensator for
superimposing in the viewing zones a second angular intensity
profile having a second angularly varying component which is
substantially the inverse of the first angularly varying
component.
2. A display as claimed in claim 1, wherein the display arrangement
comprises a spatial light modulator having a plurality of the
picture elements and array of discrete light sources.
3. A display as claimed in claim 2, wherein the picture elements
are arranged as columns and the light sources comprise parallel
evenly spaced line sources.
4. A display as claimed in claim 2, wherein the light sources
comprise a diffuse backlight and a parallax barrier.
5. A display as claimed in claim 4, wherein the picture elements
are of substantially constant vertical aperture, the spatial light
modulator and the parallax barrier cooperate to produce Fresnel
diffraction, and the compensator is arranged to compensate for the
non-uniform first angular intensity profile caused by the Fresnel
diffraction.
6. A display as claimed in claim 4, wherein the picture elements
are of non-constant vertical aperture, the spatial light modulator
and the parallax barrier cooperate to produce Fresnel diffraction,
and the compensator is arranged to compensate for the non-uniform
first angular intensity profile caused by the non-constant vertical
aperture and the Fresnel diffraction.
7. A display as claimed in claim 3, wherein the light sources
comprise a diffuse backlight and a parallax barrier, and wherein
the parallax barrier comprises a plurality of slits, each of which
cooperates with a respective group of the picture element columns
to form the viewing zones of a zeroth order lobe.
8. A display as claimed in claim 7, wherein the picture elements
are of substantially constant vertical aperture, the spatial light
modulator and the parallax barrier cooperate to produce Fresnel
diffraction, and the compensator is arranged to compensate for the
non-uniform first angular intensity profile caused by the Fresnel
diffraction.
9. A display as claimed in claim 7, wherein the picture elements
are of non-constant vertical aperture, the spatial light modulator
and the parallax barrier cooperate to produce Fresnel diffraction,
and the compensator is arranged to compensate for the non-uniform
first angular intensity profile caused by the non-constant vertical
aperture and the Fresnel diffraction.
10. A display as claimed in claim 7, wherein the compensator
comprises a mask disposed between the parallax barrier and the
backlight, the mask comprising a plurality of strips of varying
light transmissivity which cooperate with the slits of the parallax
barrier to form the second angularly varying intensity profile.
11. A display as claimed in claim 10, wherein the strips are of
substantially the same width as the picture element columns.
12. A display as claimed in claim 10, wherein the ratio of the
lateral pitches of the strips and the slits is substantially equal
to the ratio of the lateral pitches of the slits and the groups of
the picture element columns.
13. A display as claimed in claim 10, wherein the parallax barrier
and the mask are formed on opposite faces of a common transparent
substrate.
14. A display as claimed in claim 10, wherein
n.sub.1t.sub.1=n.sub.2t.sub.- 2, where n.sub.1 is the effective
refractive index between a picture element plans of the spatial
light modulator and the parallax barrier, t.sub.1 is the thickness
between the picture element plane of the spatial light modulator
and the parallax barrier, n.sub.2 is the effective refractive index
between the parallax barrier and the mask, and t.sub.2 is the
thickness between the parallax barrier and the mask.
15. A display as claimed in claim 10, wherein a lenticular screen
is disposed between the mask and the parallax barrier.
16. A display as claimed in claim 15, wherein the lenticular screen
comprises a plurality of lenticules, each of which is aligned with
a respective strip of the mask.
17. A display as claimed in claim 2, wherein a switchable diffuser
is disposed between the spatial light modulator and the array of
light sources and is switchable between a diffusing mode and a
substantially non-diffusing mode.
18. A display as claimed in claim 17, wherein the switchable
diffuser comprises a polymer dispersed liquid crystal layer.
19. A display as claimed in claim 1, wherein the display
arrangement comprises a diffuse backlight, parallax barrier and a
spatial light modulator disposed between the backlight and parallax
barrier.
20. A display as claimed in claim 19, wherein the spatial light
modulator comprises a plurality of picture element columns and the
parallax barrier comprises a plurality of parallel evenly spaced
slits, each of which cooperates with a respective group of the
picture element columns to form the viewing zones of a zeroth order
lobe.
21. A display as claimed in claim 20, wherein the compensator
comprises a mask comprising a plurality of strips of varying light
transmissivity, the parallax barrier is disposed between the
spatial light modulator and the mask, and each strip cooperates
with a respective slit to form the second angularly varying
intensity pattern.
22. A display as claimed in claim 2, wherein the compensator
comprises means for defining aperture transmission properties of
the picture elements.
23. A display as claimed in claim 2, wherein the defining means
comprises a spatial light modulator black mask defining the shape
of picture element apertures.
24. A display as claimed in claim 22, wherein the defining means
spatially varies the transmissivity of picture element
apertures.
25. A display as claimed in claim 4, wherein the parallax barrier
comprises: a first polariser; a second polariser; and a
polarisation modifying layer disposed between the first and second
polarisers and having slit regions and barrier regions for
supplying light of orthogonal polarisations.
26. A display as claimed in claim 25, wherein the second polariser
comprises part of the spatial light modulator.
27. A display as claimed in claim 25, wherein the first polariser
is removable to provide a non-directional mode of operation.
28. A method of making a mask for a display as claimed in claim 10,
the method comprising steps of: disposing a photosensitive material
in a plane substantially parallel to the spatial light modulator
and intersected by the viewing zones; operating the display with
the picture elements being transmissive so as to expose the
photosensitive material; and reducing and repeating the image
recorded by the photosensitive material.
29. A method as claimed in claim 28, wherein the parallax barrier
is replaced with by a further parallax barrier of reduced slit
width during exposure of the photosensitive material.
30. A method as claimed in claim 28, wherein the display is
viewpoint corrected to form viewing windows in a preferred viewing
plane and the photosensitive material is disposed at the viewing
windows.
31. A method as claimed in claim 28, wherein the mask is formed on
a transparent substrate of the parallax barrier.
32. A method of making a holographic mask for a display of the type
claimed in claim 10 and of the viewpoint corrected type forming
viewing windows in a preferred viewing plane, the method comprising
steps of: disposing a photosensitive material at a parallax barrier
plane with respect to the spatial light modulator; and exposing the
photosensitive material by uniformly illuminating the viewing
windows and supplying a front reference beam.
33. A method of making a holographic mask for a display of the type
claimed in claim 10 and of the viewpoint corrected type forming
viewing windows in a preferred viewing plane, the method comprising
steps of: disposing a photosensitive material in a parallax barrier
position with respect to the viewing windows; and exposing the
photosensitive material by illuminating the viewing windows with a
first intensity profile having a first spatially varying component
which is substantially the inverse of a second spatially varying
component of a second intensity profile produced by the display
without the compensator and by supplying a front reference beam.
Description
[0001] The present invention relates to a directional display, for
instance of the autostereoscopic three dimensional (3D) type. Such
displays may be used in office environment equipment, laptop and
personal computers, personal entertainment systems such as computer
games, 3D television, medical imaging, virtual reality, videophones
and arcade video games. The present invention also relates to a,
method of making a mask for a directional display.
[0002] FIG. 1(a) is a horizontal cross-sectional diagrammatic view
of a known type of autostereoscopic 3D display, for instance as
disclosed in EP 0 625 861, EP 0 726,482 and EP 0 721 131. The
display comprises a diffuse or Lambertian backlight 1 disposed
behind a spatial light modulator (SLM) 2 in the form of a liquid
crystal device (LCD). The SLM 2 comprises a plurality of picture
elements (pixels) such as 3 and the pixels are arranged in groups
of columns. In the example illustrated, there are three columns in
each group to provide a three window display. The columns are
laterally contiguous as disclosed in EP 0 625 861 and as
illustrated in FIG. 3, where the pixels 3 have apertures defined by
an opaque black mask 11. The edge 12 of each column of pixels is
contiguous with the edge of the adjacent column. A lenticular
screen 4 is disposed in front of the SLM 2 with each lenticule
being aligned with a corresponding group of three columns of
pixels.
[0003] In use, the columns of each group display vertical slices of
three different two dimensional (2D) images taken from different
view points so that the 2D images are spatially multiplexed. Each
lenticule such as 5 images light passing through the associated
group of three pixel columns into wedge-shaped regions which form
three viewing zones of a zeroth order lobe. Each lenticule 5 also
images the groups of pixel columns aligned with an adjacent
lenticule into repeated viewing zones of higher lobe order. The
viewing zones are angularly contiguous.
[0004] In order to provide viewpoint correction so that each eye of
the observer sees the same 2D view across the whole of the display,
the pitch of the lenticules 5 of the lenticular screen 4 is
slightly less than the pitch of the groups of pixel columns of the
SLM 2. As illustrated in FIG. 2, the viewing zones thus define
viewing windows 7 and 8 at the designed viewing distance of the
display such that these windows lie in a plane parallel to the
display and have the widest lateral extent at the window plane
within the viewing zones. Provided the eyes 9 and 10 of the
observer are located in adjacent viewing zones, for instance in
adjacent windows 7 and 8, a 3D image is perceived without the need
for the observer to wear viewing aids.
[0005] FIG. 1(b) shows another 3D autostereoscopic display which
differs from that shown in FIG. 1 in that the lenticular screen 4
is replaced by a parallax barrier 6. Each of the lenticules 5 is
thus replaced by a vertical slit which cooperates with the adjacent
group of three pixel columns to define the viewing zones and the
viewing windows of the zeroth order.
[0006] FIG. 1(c) discloses a display which differs from that shown
in FIG. 1(b) in that the parallax barrier 6 is disposed between the
SLM 2 and the backlight 1. The parallax barrier 6 is shown as being
formed on a substrate of the SLM 2.
[0007] GB 9616281.3 and EP97305757.3 disclose an SLM which is
particularly suitable for use in rear-illuminated autostereoscopic
displays. Diffraction of light caused by transmission through
pixels of the SLM causes degradation of the viewing zones. In order
to reduce the diffraction spreading of the transmitted light, a
complex transmission profile is imposed on the pixel apertures to
modify the aperture profile and reduce the higher angular orders of
diffractive spreading,
[0008] U.S. Pat. No. 4,717,949 discloses an autostreoscopic display
which differs from that shown in FIG. 1(c) in that the backlight 1
and the parallax barrier 6 are replaced by an arrangement for
forming a plurality of emissive light lines such as 13 as shown in
FIG. 4. U.S. Pat. No. 5,457,574 discloses a specific arrangement
for producing such lightlines as shown in FIG. 5. Light from a
backlight 1 passes through a diffuser 14 and is collected by a
Fresnel lens 15. The Fresnel lens 15 collimates the light from the
backlight 1 and the diffuser 14 and supplies the collimated light
to a lenticular screen 16. The lenticular screen 16 forms images of
the diffuser 14 on a weak diffuser 17 so as to form the lightlines.
Light from these lightlines is modulated by a spatial light
modulator 2 and light efficiency is improved by another Fresnel
lens 18 which restricts the illumination from the display to the
region in space where an observer will be located.
[0009] Other known front lenticular screen and front parallax
barrier autostereoscopic displays are disclosed in: G. R,
Chamberlin, D. E. Sheat, D. J. McCartney, "Three Dimensional
Imaging for Video Telephony", TAO First International Symposium,
(December 1993); M. R. Jewell, G. R. Chamberlain, D. E. Sheat, P.
Cochrane, D. J. McCartney, "3-D Imaging Systems for Video
Communication Applications", SPIE Vol. 2409 pp 4-10 (1995); M.
Sakata, C. Hamagishi, A. Yamasjita, K. Mashitani, E. Nakayama, "3-D
Displays without Special Glasses by Image-Splitter Method", 3D
Image Conference '95; and JP 7-287198.
[0010] FIG. 6 illustrates the principle of operation of the rear
parallax barrier display shown in FIG. 1(c). The parallax barrier
is a flat opaque screen with a series of thin transmitting slits 19
having a regular lateral pitch .sigma. and forming vertical
illumination lines behind the LCD 2 when the backlight 1 is
activated. The LCD 2 comprises pixel columns having a regular
lateral pitch p. A number N of images are interlaced in adjacent
vertical columns of pixels on the LCD and the parallax barrier
pitch is approximately given by:
.sigma.=Np (1)
[0011] Therefore, for each column of pixels, there is a defined
range of angles of illumination as shown at .theta. due to the
associated light line In the rear parallax barrier.
[0012] So that an observer's eye located in the optimum viewing
plane can only see one of the interlaced images displayed on the
LCD 2, the pitch of the rear parallax barrier is designed to be
slightly greater than that given by equation (1) so that the range
of angles of view for each pixel column converge on the optimum
viewing position. This is shown by the rays traced in FIG. 7 for a
display showing two images. This pitch correction is known as
"viewpoint correction" and ensures that, at any given point on the
viewing plane containing the viewing windows 7, 8, the parallax
barrier slit 19 is visible at the same horizontal position within
each pixel of one view. Moving laterally in the viewing plane
causes the slit position to move within the pixels and ultimately
be visible behind the adjacent columns of pixels. At this position
the observer is in the next viewing zone. Hence the interlaced
images and the parallax barrier 6 give rise to the viewing windows
7, 8, in the viewing plane within which only one view is visible
across the whole of the display. The viewpoint corrected pitch of a
rear parallax barrier may be calculated from
.sigma.=Np(1t/nL)
[0013] where t is the separation of the pixel plane and the barrier
slits, n is the composite refractive index of the medium in this
spacing and L is the optimum viewing distance of the display.
[0014] The front parallax barrier display operates in a
substantially similar way. In this case the pixels are occluded by
opaque parts of the mask outside of the viewing zones and visible
through the slits in the viewing zones. FIG. 8 shows the viewing
geometry of such a system.
[0015] Geometrical arguments lead to a first approximation of the
viewing window intensity profile. If the LCD 2 has rectangular
pixels, the viewing windows have uniform illumination across their
central region. The illumination profile at the edges is sloped
linearly due to the partial occlusion of the rear slit as the
lateral position in the viewing plane causes the parallax barrier
slit to move under the pixel edge. Therefore a wide rear slit gives
a gentle slope to the edge of the viewing window and a narrow rear
slit gives sharp edged viewing regions. A compromise between window
edge function and light throughput decides the optimum parallax
barrier slit width. FIG. 9 shows the ideal geometrical viewing
window intensity profile as given by the dimensions shown in FIG.
7.
[0016] If the pixel apertures as defined by the black mask in the
LCD are not rectangular, then the viewing window profile is not
this simple trapezoidal or "tent" shape. At different lateral
positions within the viewing plane, the observer will see the light
lines through different vertical aperture sizes within the pixel.
Thus the viewing window Intensity follows the vertical extent of
the pixel apertures blurred by the finite rear slit width. FIG. 10
shows an example of this. Gaps between adjacent columns of pixels
will lead to dark areas in the viewing plane due to total occlusion
of the parallax barrier light lines.
[0017] The geometrical performance of such displays is modified by
diffraction effects. Fresnel diffraction effects are observed in
the near-fields at apertures or obstacles in an optical path. This
either means that the observer is very close to the
aperture/obstacle or the light source is close behind the
aperture/obstacle. Both cases are analogous in that they take into
account the curvature of the wavefront. Fraunhofer diffraction is a
simplified theory of the far-field case of diffraction and can be
obtained by various simplifications in the Fresnel analysis
including neglecting wavefront curvature effects and assuming a
plane wave approach. Rear and front parallax barrier displays
generally cause very different diffraction effects. The effect of
diffraction in rear parallax barrier displays will be described in
detail hereinafter.
[0018] To give a typical example, in the rear parallax barrier
display of FIG. 1(c), the observer is looking at pixel apertures of
90 .mu.m width from 600 mllimetres away. Therefore Fraunhofer
diffraction would seem to be applicable for the light distribution
caused by these. However, the action of the rear parallax barrier
is to provide a defined source of light very close (1.3 mm) behind
the pixel apertures.
[0019] Each point in the rear silt acts like a point source
emitting spherical wavefronts due the diffuse rear illumination. As
the slit is relatively narrow, these wavefronts do not combine to
generate a plane wave across the pixel aperture width. Hence the
illumination wavefront is not plane at the pixel aperture and
Fresnel diffraction results. FIG. 11 shows this. If the rear silt
was larger than the pixel aperture, then the wavefront across the
pixel aperture would be essentially plane and Fraunhofer treatment
would be appropriate.
[0020] The theory of Fresnel diffraction is covered in many
appropriate textbooks, such as E. Hecht, "Optics", 2nd Ed.
(Addison-Wesley, 1987).
[0021] The basic geometry is shown in FIG. 12 and consists of a
point source at a distance .rho..sub.o behind an aperture of width
w. A straight line connects the point to an observer P through the
aperture (at 0) and defines an origin line. The observer is at a
distance r.sub.o from the aperture. The contributions to the
amplitude received by the observer are summed over the aperture
taking into account the phase of the curved wavefront within the
aperture.
[0022] To calculate the intensity pattern received on the
observation plane, the SOP line is considered fixed and the
aperture is offset relative to this to give the effect of the
observer's motion. Thus the limits of integration for the aperture
width are changed to follow the movement of the origin point 0
within the aperture. Full details are given in the textbooks but
the final result for an infinitely long slit is as follows, The
intensity I(x) received at the lateral position x in the
observation plane is given by:
I(x)=.vertline.B(u1 (x),u2(x)).vertline..sup.2
[0023] where u1 and u2 are the limits of integration for the
Fresnel integrals and are defined as:
u1(x)=(x+w/2)[2(.rho..sub.o+r.sub.o)/(.delta.r.sub.o.rho..sub.o)].sup.1/2
u2(x)=(x-w/2)[2(.rho..sub.o+r.sub.o)/(.delta.r.sub.o.rho..sub.o)].sup.1/2
[0024] The Fresnel integrals themselves are given by:
B(u1(x),u2(x))=FR1(u2(x),u1(x))+IFR2(u2(x),u1(x))
[0025] where 1 FR1 ( b , a ) = a b cos ( w 2 / 2 ) w FR2 ( b , a )
= a b sin ( w 2 / 2 ) w
[0026] An example diffraction pattern from a 90 .mu.m slit with a
point source 1.3 mm behind viewed from 600 mm is given in FIG. 13.
These parameters are typical for a current display system. The back
working distance (1.3 mm) defines the wavefront curvature
(.rho..sub.o) of the incident light at the aperture. The pattern is
complex with many sub-fringes.
[0027] The complete model for the viewing window intensity profile
relies on the viewpoint correction between the rear parallax
barrier 6 and the pixel layout as described hereinbefore. This
pitch correction between the two components assures that, from the
viewing plane, each pixel associated with a viewing window has a
parallax barrier slit 19 behind it located in the same horizontal
position relative to the pixel aperture 20. This horizontal offset
changes as the observer moves laterally in the viewing plane as
described above. The intensity received at a point in the viewing
plane is the sum of the contributions from the Fresnel diffraction
patterns produced by the pixels and, due to the viewpoint
correction, every pixel gives the same contribution as the point
source is located in the same position behind each pixel.
Furthermore, as the observer moves laterally, the intensity pattern
will follow the Fresnel diffraction pattern for a single slit. This
is because movement in the viewing plane causes the slit to move
behind every pixel by the same amount. This displacement of the
source changes the diffraction effects which follow the diffraction
profile calculated above. This is shown schematically in FIG. 14.
Therefore, the viewing window intensity profile is merely a
magnified version of the Fresnel diffraction pattern from a single
slit and can therefore be expected to be non-uniform if significant
diffraction is occurring.
[0028] The assumption of slit apertures in the theoretical
treatment (as opposed to rectangular apertures which are closer to
the actual pixel shape) is valid as the pixels add up in columns to
give a long vertical extent and any diffraction in the vertical
plane is washed out by this. For a non-rectangular aperture a more
complex treatment is appropriate which may be derived along the
same lines as this simplified treatment. The finite width of the
rear parallax barrier slits 19 needs to be taken into account
however. This is done by considering the slit width to be an
integration of point sources across itself and the final
diffraction pattern is generated as the sum of the patterns from
all the individual point sources.
[0029] Mathematically this integration is combined with the Fresnel
diffraction integration by a convolution defined as follows. The
Fresnel pattern I(x) is convolved with a top-hat function R(x)
which mirrors the rear slit transmission function to give the
viewing window profile V(x) in the usual manner: 2 V ( x ) = -
.infin. .infin. l ( t ) R ( t - x ) t
[0030] The window profile produced after convolution with the rear
slit width is shown in FIG. 15. This profile is generated from the
data used in FIG. 13 and a rear slit width of 25 .mu.m, again a
typical figure for a practical display.
[0031] Another complication is that the incident light is not
monochromatic but is white. The theory assumes monochromatic light
and a second convolution due to the range of wavelengths should
strictly be performed. This is not accounted for in the present
mathematics but would lead to a slight further blurring of the
pattern.
[0032] According to a first aspect of the invention, there is
provided a directional display comprising a display arrangement for
producing a plurality of viewing zones, each of which has a
non-uniform first angular intensity profile with a first angularly
varying component, characterised by a compensator for superimposing
in the viewing zones a second angular intensity profile having a
second angularly varying component which is substantially the
inverse of the first angularly varying component.
[0033] The display arrangement may comprise a spatial light
modulator having a plurality of picture elements and an array of
discrete light sources. The picture elements may be arranged as
columns and the light sources may comprise parallel evenly spaced
line sources.
[0034] The light sources may comprise a diffuse backlight and a
parallax barriers.
[0035] The parallax barrier may comprise a plurality of slits, each
of which cooperates with a respective group of the picture element
columns to form the viewing zones of a zeroth order lobe.
[0036] The picture elements may be of substantially constant
vertical aperture, the spatial light modulator and the parallax
barrier may cooperate to produce Fresnel diffraction and the
compensator may be arranged to compensate for the non-uniform first
angular intensity profile caused by the Fresnel diffraction.
[0037] The picture elements may be of non-constant vertical
aperture, the spatial light modulator and the parallax barrier may
cooperate to produce Fresnel diffraction, and the compensator may
be arranged to compensate for the non-uniform first angular
intensity profile caused by the non-constant vertical aperture and
the Fresnel diffraction.
[0038] The compensator may comprise a mask disposed between the
parallax barrier and the backlight and comprising a plurality of
strips of varying light transmissivity which cooperate with the
slits of the parallax barrier to form the second angularly varying
intensity profile.
[0039] The strips may be of substantially the same width as the
picture element columns.
[0040] The ratio of the lateral pitches of the strips and the slits
may be substantially equal to the ratio of the lateral pitches of
the slits and the groups of the picture element columns.
[0041] The parallax barrier and the mask may be formed on opposite
faces of a common transparent substrate.
[0042] n.sub.1t .sub.1 may be equal to n.sub.2t.sub.2, where
n.sub.1 is the effective refractive index between the spatial light
modulator and the parallax barrier, t.sub.1 is the thickness
between a picture element plane of the spatial light modulator and
the parallax barrier, n.sub.2 is the effective refractive index
between the parallax barrier and the mask, and t.sub.2 is the
thickness between the parallax barrier and the mask.
[0043] A lenticular screen may be disposed between the mask and the
parallax barrier. The lenticular screen may comprise a plurality of
lenticules, each of which is aligned with a respective strip of the
mask.
[0044] A switchable diffuser may be disposed between the spatial
light modulator and the array of light sources and may be
switchable between a diffusing mode and a substantially
non-diffusing mode. The switchable diffuser may comprise a polymer
dispersed liquid crystal layer.
[0045] The display arrangement may comprise a diffuse backlight a
parallax barrier, and a spatial light modulator disposed between
the backlight and the parallax barrier.
[0046] The spatial light modulator may comprise a plurality of
picture element columns and the parallax barrier may comprise a
plurality of parallel evenly spaced slit, each of which cooperates
with a respective group of the picture element columns to form the
viewing zones of a zeroth order lobe.
[0047] The compensator may comprise a mask comprising a plurality
of strips of varying light transmissivity, the parallax barrier may
be disposed between the spatial light modulator and the mask, and
each strip may cooperate with a respective slit to form the second
angularly varying intensity pattern.
[0048] The compensator may comprise means for defining the aperture
transmission properties of the picture elements.
[0049] The defining means may comprise a spatial light modulator
black mask defining the shape of picture element apertures.
[0050] The defining means may spatially vary the transmissivity of
picture element apertures.
[0051] The parallax barrier may comprise a first polariser, a
second polariser and a polarisation modifying layer disposed
between the first and second polarisers and having slit regions and
barrier regions for supplying light of orthogonal
polarisations.
[0052] The second polariser may comprise part of the spatial light
modulator.
[0053] The first polariser may be removable to provide a
non-directional mode of operation.
[0054] According to a second aspect of the invention, there is
provided a method of making a mask for an embodiment of the display
according to the first aspect of the invention, comprising
disposing a photosensitive material in a plane substantially
parallel to the spatial light modulator and intersected by the
viewing zones, operating the display with the picture elements
being transmissive so as to expose the photosensitive material, and
reducing and repeating the image recorded by the photosensitive
material.
[0055] The parallax barrier may be replaced by a further parallax
barrier of reduced slit width during exposure of the photosensitive
material.
[0056] The display may be viewpoint corrected to form viewing
windows in a preferred viewing plane and the photosensitive
material may be disposed at the viewing windows.
[0057] The mask may be formed on a transparent substrate of the
parallax barrier.
[0058] According to a third aspect of the invention, there is
provided a method of making a holographic mask for an embodiment of
the display according to the first aspect of the invention of the
viewpoint corrected type forming viewing windows in a preferred
viewing plane, comprising disposing a photosensitive material at a
parallax barrier plane with respect to the spatial light modulator,
and exposing the photosensitive material by uniformly illuminating
the viewing windows and supplying a front reference beam.
[0059] According to a fourth aspect of the invention, there is
provided a method of making a holographic mask for an embodiment of
the display according to the first aspect of the invention and of
the viewpoint corrected type forming viewing windows in a preferred
viewing plane, comprising disposing a photosensitive material in a
parallax barrier position with respect to the viewing windows and
exposing the photosensitive material by illuminating the viewing
windows with a first intensity profile having a first spatially
varying component which is substantially the inverse of a second
spatially varying component of a second intensity profile produced
by the display without the compensator and by supplying a front
reference beam.
[0060] It is thus possible to provide a display which allows
viewing zones and viewing windows to be generated with
substantially improved uniformity of light intensity profile. For
instance, variations caused by Fresnel diffraction can be
substantially reduced, Further, for display arrangements having a
pixel shape of non-constant vertical extent or aperture, the
resulting illumination non-uniformity may also be substantially
reduced. This allows SLMs having pixels of arbitrary shapes, such
as existing SLMs, to be used, for instance in flat panel
directional displays, while still producing a substantially uniform
intensity of illumination within the viewing zones or viewing
windows. Such displays allow an observer to move laterally, for
instance within the optimum viewing plane, without perceiving
substantial variations in display brightness. For such displays
which track movements of an observer, undesirable flicker artefacts
are substantially reduced. Further, even if an observer is not
located in the optimum-viewing plane, improvements in uniformity of
display brightness over the whole display can be achieved. Also,
freedom of viewing is extended laterally and longitudinally.
[0061] By compensating for diffraction effects within a display
arrangement, the slit size of a rear parallax barrier may be
reduced, This provides sharper edged viewing windows and provides
greater viewing freedom.
[0062] It is also possible to provide a display which is switchable
between 2D and 3D modes of operation, for instance using a
switchable diffuser. Such a display has the advantages described
hereinbefore in the 2D mode as well as in the 3D mode.
[0063] The invention will be further described, by way of example,
with reference to the accompanying drawings, in which:
[0064] FIG. 1(a) illustrates a known flat panel autostereoscopic 3D
display having a front lenticular screen;
[0065] FIG. 1(b) illustrate a known flat panel autostereoscopic 3D
display having a front parallax barrier;
[0066] FIG. 1(c) illustrates a known flat panel autostereoscopic 3D
display having a rear parallax barrier;
[0067] FIG. 2 is a diagram illustrating the formation of viewing
regions in an autostereoscopic display;
[0068] FIG. 3 illustrates a known layout of pixels in an SLM,
[0069] FIG. 4 illustrates a known autostereoscopic 3D display;
[0070] FIG. 5 is a diagrammatic plan view of another; known
autostereoscopic 3D display;
[0071] FIG. 6 is a diagram illustrating an angle of illumination
produced by a rear parallax barrier slit;
[0072] FIG. 7 illustrates the generation of viewing zones by
viewpoint correction In a rear parallax barrier display.
[0073] FIG. 8 illustrates the generation of viewing zones by
viewpoint correction in a front parallax barrier display;
[0074] FIG. 9 is a graph illustrating light intensity against
lateral observer position for a rectangular pixel aperture and rear
parallax barrier slit without diffraction;
[0075] FIG. 10 is a graph similar to FIG. 9 illustrating viewing
window intensity profile for a non-rectangular pixel aperture;
[0076] FIG. 11 illustrates the origin of Fresnel diffraction at a
pixel aperture;
[0077] FIG. 12 is a diagram illustrating the geometry used in
Fresnel diffraction calculations;
[0078] FIG. 13 illustrates intensity against lateral direction of
an example of a Fresnel diffraction profile;
[0079] FIG. 14 is a diagrammatic plan view of an autostereoscopic
display illustrating relative positions of a rear parallax barrier
slit and a pixel aperture as seen from different lateral viewpoints
in viewing windows;
[0080] FIG. 15 is a graph of light intensity against lateral
direction illustrating an example of a viewing window light
intensity profile for an autostereoscopic 3D display;
[0081] FIG. 16 shows structures and resulting light intensity
profiles for illustrating an embodiment of the invention;
[0082] FIG. 17 is similar to FIG. 16 for another embodiment of the
invention;
[0083] FIG. 18a is a diagrammatic plan view of a display
constituting an embodiment of the invention;
[0084] FIG. 18b is a diagrammatic plan view of a modified display
of the type. shown in FIG. 18a;
[0085] FIG. 19 is a graph of transmission against lateral position
illustrating a transmission profile of a part of a mask;
[0086] FIG. 20 is similar to FIG. 19 for another mask
component:
[0087] FIG. 21 is a diagram illustrating a method of making a
mask;
[0088] FIG. 22a illustrates diagrammatically a method of making a
mask constituting an embodiment of the invention;
[0089] FIG. 22b illustrates a first type of master for use in the
method illustrated in FIG. 22a;
[0090] FIG. 22c illustrates a second type of master for use in the
method illustrated in FIG. 22a;
[0091] FIG. 23 illustrates diagrammatically a method of making a
mask constituting an embodiment of the invention;
[0092] FIG. 24 shows the display of FIG. 18a operated to perform
observer tracking;
[0093] FIG. 25 is a diagrammatic plan view of a switchable display
constituting an embodiment of the invention;
[0094] FIG. 26 is a diagrammatic plan view of a display
constituting an embodiment of the invention;
[0095] FIG. 27 is a diagrammatic plan view of a display
constituting an embodiment of the invention;
[0096] FIG. 28 illustrates a pixel shape suitable for balancing the
effects of diffraction;
[0097] FIG. 29 illustrates a pixel transmission profile for
balancing the effects of diffraction;
[0098] FIG. 30 is a diagrammatic plan view of a display
constituting an embodiment of the invention;
[0099] FIG. 31 is a diagrammatic plan view of a display
constituting an embodiment of the invention;
[0100] FIG. 32 illustrates diagrammatically a method of making a
mask constituting an embodiment of the invention;
[0101] FIG. 33 illustrates diagrammatically another method of
making a mask constituting an embodiment of the invention;
[0102] FIG. 34 illustrates diagrammatically an arrangement for
illuminating a mask made by the method of FIG. 32 or FIG. 33;
[0103] FIG. 35 is a diagrammatic plan view of a display
constituting an embodiment of the invention;
[0104] FIG. 36 is a diagrammatic plan view of a display
constituting an embodiment of the invention;
[0105] FIG. 37 is a diagrammatic plan view of a display
constituting an embodiment of the invention;
[0106] FIG. 38 is a diagrammatic plan view of a display
constituting an embodiment of the invention;
[0107] FIG. 39a is a diagrammatic plan view of part of a
display;
[0108] FIG. 39b illustrates the Illumination profile of the part of
the display shown in FIG. 39a;
[0109] FIG. 40a is a diagrammatic plan view of the remainder of a
display constituting an embodiment of the invention;
[0110] FIG. 40b illustrates the degree of visibility of pixels of
the part shown in FIG. 40a;
[0111] FIG. 41a is a plan view of a display comprising the parts
shown in FIG. 39a and 40a;
[0112] FIG. 41b illustrates the illumination profile of viewing
windows of the display of FIG. 41a;
[0113] FIG. 42a is a diagrammatic plan view of part of a
display;
[0114] FIG. 42b illustrates the illumination profile of the part of
the display show in FIG. 42a;
[0115] FIG. 43a is a diagrammatic plan view of the remainder of a
display constituting an embodiment of the invention;
[0116] FIG. 43b illustrates the degree of visibility of pixels of
the part shown in FIG. 43a;
[0117] FIG. 44a is a plan view of a display comprising the parts
shown in FIG. 42a and 43a; and
[0118] FIG. 44b illustrates the illumination profile of viewing
windows of the display of FIG. 44a.
[0119] Like reference numerals refer to like parts throughout the
drawings.
[0120] The upper row of FIG. 16 Illustrates a display arrangement
which comprises an SLM 2 and a rear parallax barrier 6 and which
forms part of an autostereoscopic 3D display. The corresponding
light intensity profile formed in a viewing window by the display
is illustrated to the right as light intensity against lateral
position of the observer. Thus, the intensity varies significantly
across the viewing window. Observers are sensitive to a change in
illumination of less than 2% across the whole display area if in
the viewing plane. Outside the viewing plane, where the variations
are seen across the display surface, observers can discern
illumination changes of less than 0.5%.
[0121] The middle row of FIG. 16 illustrates an angular intensity
corrector element 21 and the corresponding intensity profile
produced by the element 21 at the viewing window. The element 21
may, for instance, comprise a mask component and a parallax barrier
which cooperate together in the same way as the SLM 2 and the
parallax barrier 6 to generate the same viewing zones and windows.
The mask has a light transmissivity which is such that the
illustrated intensity profile is created at the viewing window.
[0122] The intensity profile created by the parallax barrier 6 and
the SLM 2 includes a component which varies spatially across the
viewing window Similarly, the element 21 produces a profile having
a spatially varying component which is substantially the inverse of
the spatially varying component produced by the SLM 2 and the
parallax barrier 6. As shown at the bottom of FIG. 16, the
intensity profiles are superimposed so as to reduce or
substantially cancel the spatially varying components within at
least the main part of the viewing window. Thus, the effects of
diffraction and of variations in the vertical aperture of pixels
are substantially reduced so that any residual light intensity
variations resulting from relative movement between an eye of an
observer and a viewing window can be made sufficiently small so as
not to result in undesirable visual artefacts.
[0123] As shown in FIG. 17, the corrector element 21 may be
embodied as a mask which cooperates with the rear parallax barrier
6 so as to compensate for the effects of diffraction and, when
present, of pixels of varying vertical aperture. Such an
arrangement is illustrated in more detail in FIG. 18a. The display
shown in FIG. 18a is of the rear parallax barrier type as shown in
FIG. 1(c). The mask 21 is disposed between the parallax barrier 6
and the backlight 1 and comprises a plurality of vertical strips
having light transitivities as illustrated in FIG. 19 for two
adjacent strips. The display is of the type producing two viewing
zones so that each slit of the parallax barrier 6 cooperates with
two columns of pixels of the SLM 2. Similarly, each slit of the
parallax barrier 6 cooperates with two strips of the mask 21. The
pixels of the SLM 2 are of rectangular cross-section and so have
constant vertical apertures. Pixel arrangements of the type shown
in FIG. 3 are suitable, The spatially varying transitivities of the
strips of the mask 21 are thus designed to compensate only for the
Fresnel diffraction produced by the parallax barrier slits and the
pixels of the SLM 2.
[0124] The width of each strip of the mask 21 is made substantially
equal to the width of the associated column of pixels of the SLM 2.
The pitches of the pixel columns of the SLM 2, the slits of the
parallax barrier 6 and the strips of the mask 21 are selected so as
to provide a viewpoint corrected display as described
hereinbefore.
[0125] In order for the effects of the mask and diffraction to
cancel over the whole of the viewing region, the windows formed by
the mask 21 and the parallax barrier 6 must have the same size and
optimum viewing plane as the windows formed by the parallax barrier
6 and the SLM 2. To achieve this, the optical path length between
the mask 21 and the parallax barrier 6 rust be the same as that
between the parallax barrier 6 and the SLM 2. Thus, if n.sub.1 and
n.sub.2 are the effective refractive indices of the regions between
the SLM 2 and the parallax barrier 6 and between the parallax
barrier 6 and the mask 21, respectively, and t.sub.1 and t.sub.2
denote the two thicknesses of the corresponding regions, then this
condition is satisfied when:
n.sub.1t.sub.1=n.sub.2t.sub.2
[0126] If the relative pitches are then viewpoint corrected for the
same optimum viewing plane, the combination of the mask 21 and the
parallax barrier 6 and the combination of the parallax barrier 6
and the SLM 2 interact correctly and the windows in all display
lobes are superimposed.
[0127] The addition of two imaging parallax systems is valid in
terms of diffractive effects. Diffraction in the mask 21 is
irrelevant because it is illuminated by a Lambertian backlight 1
which contains light travelling in all directions.
[0128] Because the mask strips are wider than the parallax barrier
slits, the input wavefront to the parallax barrier slits is
essentially plane and the narrowness of the slits ensures that
strong Fresnel diffraction does not occur until the apertures of
the SLM pixels. Thus, the imaging of the "balancing" windows from
the mask 21 will occur with good definition in balance with the
diffractive effects at the pixels of the SLM 2. The mask profile
can be altered slightly to take into account any diffraction at the
slits if necessary.
[0129] FIG. 18b shows a rear parallax barrier display of the type
shown in FIG. 18a. In this case, the parallax barrier 6 and the
mask 21 are formed on opposite faces of a common transparent
substrate 21a.
[0130] FIG. 20 illustrates a pixel shape 22 of nonconstant vertical
aperture and the resulting transmission profile of the mask strips
to compensate both for the effects of diffraction and the effects
of the non-constant vertical aperture of the pixel. Thus, the use
of the mask 21 can allow non-ideal pixel aperture shapes to be used
while providing a substantially uniform illumination profile within
the viewing windows. It is therefore possible to use conventional
LCDs whose pixel aperture shapes would otherwise render them
unsuitable for this type of display.
[0131] The spatial transmission profile of the mask may be decided
by the calculations given hereinbefore for the window intensity
profiles. Alternatively, empirical techniques may be used. The
finite width of the parallax barrier slits causes a blurring of the
profile generated by the mask 21 and the parallax barrier 6 alone
in the same way as the finite size of the parallax barrier slits
causes blurring in the Fresnel diffraction pattern.
[0132] Thus, the spatial profile of the mask 21 is the inverse of
the unconvolved diffraction pattern from the SLM pixels. Any
correction for SLM pixels of non-uniform vertical aperture is
imposed as necessary on top of this. The finite width of the
parallax barrier slits then blurs this to become the same as the
convolved diffraction pattern from the SLM pixels.
[0133] In the case of a colour display, each pixel may have a
colour filter associated with it. If the pixels are arranged in
columns of like colours, then the part of the mask which cooperates
with each column of pixels can be tuned to be most accurate for the
corresponding colour of light.
[0134] The mask 21 may be made by photographic or lithographic
techniques, for example, in a photosensitive layer on a transparent
substrate, which may comprise the substrate on which the parallax
barrier 6 is formed. One technique for forming such a mask is to
use a precision scanning system to move the substrate relative to a
tightly focused laser spot. Such an arrangement is illustrated in
FIG. 21. A laser 25 whose light output amplitude can be modulated
produces a light beam which is reflected by a mirror 26 to a
focusing lens 27. A substrate 28 carrying a photosensitive layer is
mounted on a scanning table 29 which can be scanned in X and Y
directions. As the XY scanning proceeds, the output of the laser 25
is modulated so as to modulate the exposure of the photosensitive
layer on the substrate 28 in order to form the desired spatial
transmission properties of the mask 21.
[0135] FIG. 22a illustrates another method of making the mask 21. A
mask substrate 28 of the same type as that shown in FIG. 21 is
moved in a direction 24 while being exposed to illumination through
a grey-scale master 23. The master 23 is in the form of a slit
having a light transmissivity which varies longitudinally of the
slit as illustrated in FIG. 22b. The grey-scale master 23 may be
made by any suitable technique, for instance as disclosed
herein.
[0136] The master 23 is illuminated with a constant even intensity
of illumination and the mask substrate 28 is moved at constant
speed in the direction 24. The grey-scale produced by the mask 23
and used to expose the substrate 28 is thus constant so that the
level of exposure of the substrate 28 at each point along the
length of the slit of the master is likewise constant. Following
development, the mask 21 having the appropriate transmissive
properties is produced.
[0137] FIG. 22c illustrates at 23' a half-tone master which may be
used in place of the grey-scale master 23 in FIG. 22a. The halftone
master 23' has a binary transmission pattern such that the exposure
of the substrate 28 at each point along the slit is proportional to
the length of the clear part of the slit transverse to its
longitudinal axis. Such a half-tone master 23' may be easier to
manufacture, for instance by conventional printing techniques. For
instance, such masters may be used to expose very large sheets of
the substrate 28 on an industrial web. The substrates may then be
cut to the required size and the manufacturing cost may therefore
be reduced.
[0138] FIG. 23 illustrates another method of making the mask 21.
The display in which the mask is to be provided, or a display of
the same type for use only in manufacturing the masks, is provided
with the parallax barrier 6 being replaced by a parallax barrier 6'
having slits of the same pitch but of smaller width. The SLM 2 is
controlled so as to be fully transmissive and a photographic plate
30 is disposed in the window plane of the display. The backlight 1
is then switched on so as to expose the plate 30. The resulting
diffraction pattern is thus recorded, as seen magnified by the
Moire effect, at the window plane.
[0139] In step 2, the exposed and processed plate 30 from step 1 is
illuminated by an illumination source 31 and the image is reduced
by an optical system shown as a lens 32. The reduced image is
formed on a suitable substrate 33. The illumination source 31 is
switched off and the substrate 33 stepped forward for this process
to be repeated. By means of this step and repeat process, the
required pattern is photographically reduced and replicated across
the mask. Alternatively, a lenticular screen may be used in place
of the lens 32 to perform the optical imaging and repetition across
the mask allowing a single exposure to record the mask strips
across the whole of the substrate 33.
[0140] The brightness and contrast levels in the photographic
processes should be appropriately adjusted to give the desired
grey-scale levels in the final mask 21. The spot sizes used for
illumination in the first step are significantly smaller than the
slit size of the parallax barrier 6 in the final display so as to
avoid blurring the recorded pattern.
[0141] As mentioned hereinbefore, the mask 21 may be manufactured
on a separate substrate or on an existing substrate. For instance,
the mask may be formed on one side of a transparent substrate and
the parallax barrier on the other side as shown in FIG. 18b. This
arrangement provides a rugged design by eliminating any possible
relative movement of the two components.
[0142] Displays of this type may be used in observer tracking
displays. For instance, the arrangement shown in FIG. 18a need only
be modified to provide three viewing windows in each lobe of the
display in order for it to be suitable for the tracking techniques
disclosed in EP 0 726 482 and EP 0 721 131. FIG. 24 illustrates a
modification of the display to permit mechanical tracking of an
observer in association with an observer tracker (not shown). In
order to track an observer moving in the direction of arrow 35, the
parallax barrier 6 is required to move in the direction of arrow 36
and the mask 21 is required to move in the direction of arrow 37.
However, the mask 21 is required to undergo an amplified movement
(twice as far in the case of equal spacing and equal refractive
index between the mask 21 and the parallax barrier 6 and between
the parallax barrier 6 and the SLM 2) in comparison with the
parallax barrier 6 so as to maintain the correct parallax
throughout the display. Longitudinal observer tracking may also be
provided by displacing the parallax barrier 6 longitudinally with
respect to the SLM 2 and by displacing the mask 21 longitudinally
by twice that displacement.
[0143] The presence of the mask 21 restricts the transmission of
light through the display and so reduces the overall brightness of
the windows. However, if the variations in the window intensity
profiles to be corrected are approximately five to ten percent, the
reduction in window brightness which may be expected will be
substantially of this order of magnitude. Thus, the improvement in
display quality will far outweigh the relatively small reduction in
display brightness or the increased power consumption to maintain
display brightness. Some of the reduction in brightness may be
regained by making the rear surface of mask 21 reflective rather
than absorptive. Light blocked from the display output by the mask
21 is returned to the backlight 1 where it may be reflected back
towards the display.
[0144] FIG. 25 shows a display which differs from that shown, for
instance, in FIG. 18a in that a switchable diffuser 38 is disposed
between the parallax barrier 6 and the SLM 2. The diffuser 38,
which may comprise a polymer dispersed liquid crystal layer, is
switchable between highly and lowly scattering states by means of a
suitable applied electric field. When the diffuser 38 is in the
lowly scattering mode, the display operates as an autostereoscopic
display as described hereinbefore. When the diffuser 38 is switched
to the highly scattering state, the parallax within the display is
lost so that all of the SLM pixels are visible over a wide range of
angles in front of the display as in a standard image SLM. Thus,
the full resolution of the SLM 2 may be used in the 2D mode.
[0145] The display shown in FIG. 26 differs from that shown in FIG.
18a in that the SLM 2 is disposed between the backlight 1 and the
parallax barrier 6 and the parallax barrier 6 is disposed between
the SLM 2 and the mask 21. This display is thus of the front
parallax barrier type illustrated in FIG. 1(b), Operation of the
display of FIG. 26 differs from that of FIG. 18a in that the
spatial transmission profile of the mask 21 balances diffraction
caused in the mask slits and the SLM. The design process for the
spatial transmission profile of the mask 21 may have to be
iterative, taking diffractive effects of the mask profile itself
into account and attempting a convergence on a pattern which
balances its own diffraction.
[0146] The mask 21 is used mainly to correct for non-uniform
intensity profiles generated by SLM pixels of non-uniform vertical
aperture but also has a role in compensating for the Fresnel
diffraction effects produced in front parallax barrier displays.
These effects are not as significant in front parallax barrier
displays as in rear parallax barrier displays but still exist to
some extent.
[0147] FIG. 27 illustrates a display of the rear parallax barrier
type shown in FIG. 18a but in which the mask 21 is integral with
the SLM 2. In particular, the SLM pixel apertures contain the
spatial transmission profile necessary to balance diffractive or
non-uniform vertical aperture effects.
[0148] In one form of the display shown in FIG. 27, the black mask
39 of the SLM 2 which defines the pixel apertures is modified so
that the vertical aperture of the pixels as illustrated in FIG. 28
varies in order to generate the appropriate intensity profile
within the viewing windows. This arrangement does not require any
grey-scaling so that the black mask remains as one or more layers
having transparent and opaque regions.
[0149] FIG. 29 illustrates an alternative black mask 39 in which
the pixel apertures are provided with spatially varying
transitivities by applying a grey-scale mask over the whole of each
pixel aperture. In this arrangement, the transmission profiles
balance distribution of light intensities and do not reduce
diffractive spreading of light.
[0150] The display shown in FIG. 30 differs from that shown in FIG.
18a in that a lenticular screen 40 is disposed between the mask 21
and the parallax barrier 6. The lenticular screen 40 images the
mask onto the viewing windows and is disposed directly behind the
slits of the parallax barrier 6 so as to avoid Moire effects. Thus,
each slit acts as an aperture stop for the associated lenticule.
The lenticular screen provides improved resolution in imaging of
the mask element so that there is less blurring of the mask. This
in turn permits low resolution in fabrication of the mask 21.
However, the small lens apertures limit the resolution increase
because lens performance is dominated by diffraction in the small
slit aperture. The lenticular lens elements need not be associated
with respective slits of the parallax barrier 6 and may have a
different pitch which may be larger to ease manufacturing
tolerances.
[0151] FIG. 31 shows a display which differs from that shown in
FIG. 18a in that the mask 21 is combined with the parallax barrier
6. In this embodiment, the mask 21 comprises holograms for
generating the balancing window intensities. The holograms 41 may
be disposed in the slit apertures of the parallax barrier 6 as
shown in FIG. 31 or may be disposed immediately behind the slit
apertures on a separate substrate. The backlight is replaced by a
light source providing a suitable replay beam 42 for the holograms.
The holograms are designed to create a uniform viewing window
intensity profile in replay with the SLM 2 and the parallax barrier
6 in place.
[0152] FIG. 32 illustrates a method of recording the holograms 41
for the display of FIG. 31. A hologram recording plane 43 is
disposed behind the SLM 2, or an SLM of the same type, which is
controlled so as to be fully transmissive. The surface of the
hologram recording plane 43 facing the SLM 2 is illuminated with a
reference beam 44 whereas a recording beam of uniform intensity
profile is supplied from the desired window regions 45. The
reference and recording beams interfere to create the desired
hologram structure on the hologram recording plane 43.
[0153] FIG. 33 illustrates a modification of the method shown in
FIG. 32 to allow the SLM 2 to be removed during recording of the
hologram. This arrangement avoids problems with areas on the
hologram not being exposed because of occlusion by the black mask
of the SLM 2. The recording beam from the windows 45 differs in
that the window regions are illuminated with the desired
anti-diffraction profile.
[0154] FIG. 34 illustrates replaying of the recorded hologram plane
43 by means of a replay beam 46. The replay beam 46 is a beam of
collimated light of limited spectral bandwidth and at a defined
reference angle as decided during recording of the holograms. The
replay beam is diffracted so as to recreate the uniformly
illuminated windows.
[0155] Because of the monochromatic nature of holograms, each slit
of the parallax barrier 6 may be associated with one colour of a
filter of the SLM 2 so as to be tuned for optimum performance at
that colour.
[0156] FIG. 35 shows a display of the front parallax barrier type
in which the mask 21 formed on a transparent substrate is disposed
between the backlight 1 and the SLM 2. However, the parallax
barrier 6 as described hereinbefore is replaced by a parallax
barrier arrangement of the type disclosed in British patent
application No: 9713985.1 and European patent application No:
97307085.7. This arrangement comprises a patterned polarisation
modifying parallax barrier 6a cooperating with a removable
polariser 6b.
[0157] When operating in the 3D autostereoscopic mode, the
removable polariser 6b is in place as shown in FIG. 35. The
polarisation modifying parallax barrier 6a comprises slit regions
such as 6c separated by barrier regions such as 6d. The SLM 2
includes an output polariser so that light supplied to the
polarisation modifying parallax barrier 6a is linearly polarised.
In one arrangement, the slit regions 6c have no effect on
polarisation whereas the barrier regions 6d rotate the polarisation
by 90.degree.. The polarising axis of the removable polariser 6b is
parallel to the polarization axis of the output polariser of the
SLM 2 so that light passing through the slit region 6c passes
through the polariser 6b whereas light passing through the barrier
regions 6d is extinguished by the polariser 6b. In another
arrangement, the silt regions 6c rotate the polarisation of light
by 90.degree. whereas the barrier regions 6d have no effect on
polarisation. The polarisation axis of the polariser 6b is
perpendicular to the polarisation axis of the output polariser of
the SLM 2 so that, again, light from the slit regions 6c passes
through the polariser 6b whereas light the from the barrier regions
6d is extinguished by the polariser 6b. As described hereinbefore,
the mask 21 corrects for non-uniformities in the display viewing
zones.
[0158] In the 2D mode of operation, the polariser 6b is removed so
that polarised light passing through the regions 6c and 6d is
output from the display without attenuation or extinction, However,
because of the different polarisations of light from the regions 6c
and 6d, the polarisation modifying parallax barrier 6a may cause
diffraction and unevenness of illumination of the viewing zones.
The mask 21 reduces such variations in illumination as described
hereinbefore.
[0159] FIG. 36 illustrates a display which differs from that of
FIG. 35 in that it is of the rear parallax barrier type. The
removable polariser 6b is disposed between the backlight 1 and the
mask 21 whereas the polarisation modifying parallax barrier 6a is
disposed between the mask 21 and the SLM 2. The polariser 6b thus
acts as the input polariser for the parallax barrier in the 31 mode
and an input polariser of the SLM 2 acts as the output polariser of
the parallax barrier, which therefore functions in the same way as
described with reference to FIG. 35. FIG. 36 also shows the
presence of an optional switchable diffuser 38 of the type
described hereinbefore with reference to FIG. 25.
[0160] As shown in FIG. 9, the combination of a parallax barrier
and rectangular SLM pixels results in an illumination profile which
is characterised by a flat centre region which is useful for
viewing the display because of the uniform illumination level. The
width of this region is determined by the ratio of the pixel size
to the slit width of the parallax barrier. Wider slits produce
narrower uniform centre regions but also improve the light
throughout and hence brightness of the display. It is therefore
desirable to provide wider uniform central regions while retaining
wide parallax barrier slits in order to produce a bright display
with wider useful viewing windows.
[0161] A technique for achieving this is illustrated in FIG. 37,
which illustrates a display of a type similar to that shown in FIG.
30 but of the front parallax barrier type. In particular, a
lenticular screen 40 is disposed on the mask 21 and, in combination
with the backlight 1, alters the illumination profile of the SLM 2
and the parallax barrier 6 so as to widen the uniform central
region of the illumination profile while permitting the use of
wider parallax barrier slits to increase display brightness. FIG.
38 shows a similar display but of the rear parallax barrier
type.
[0162] FIG. 39a illustrates the illumination profile produced by
the combination of the backlight 1, the mask 21 and the lenticular
screen 40. The profile has a uniform centre region which then rises
linearly towards the edge as shown in FIG. 39b. FIG. 40a shows the
combination of the SLM 2 and the parallax barrier 6 and FIG. 40b
illustrates the illumination profile at the viewing windows which
would be achieved if the combination shown in FIG. 40a were
illuminated in the conventional manner as described hereinbefore
with the SLM pixels fully transmissive. This profile corresponds to
the degree of visibility of the pixels of the SLM 2 as determined
by the slits of the parallax barrier 6.
[0163] FIG. 41a illustrates diagrammatically the combination of
elements shown in FIG. 37. FIG. 41b illustrates the illumination
profile of FIG. 39b in chain dot lines, the illumination profile of
FIG. 40b in broken lines and the resultant illumination profile in
unbroken lines. The resultant profile has a wider uniform central
region so as to reduce undesirable visual artefacts caused by
intensity variations as an observer moves laterally. The quality
and viewing freedom of the viewing windows are therefore
substantially improved.
[0164] As compared with the conventional illumination profile shown
in FIG. 40b, the profile shown in FIG. 41b exhibits higher levels
of crosstalk between adjacent windows because the individual window
illumination profiles overlap and the overlapping regions are
brighter with respect to the centre region. A compromise between
increased width of uniform intensity centre regions and increased
crosstalk has to be found and this may be achieved as illustrated
in FIGS. 42a to 44b. FIG. 42a, 43a and 44a illustrate the same
general arrangements as shown in FIG. 39a, 40a and 41a,
respectively, but the lenticular screen 40 and the mask 21 are
arranged to produce the illumination profile shown in FIG. 42b. The
conventional illumination profile shown in FIG. 43b is the same as
that shown in FIG. 40b and, when combined with the illumination
profile of FIG. 42b, gives rise to the resultant profile shown in
FIG. 44b. In this case, the resultant profile has wider uniform
centre regions than the profile shown in FIG. 43b but reduced
crosstalk as compared with the resultant profile shown in FIG. 41b.
Thus, in this case, the width of the uniform centre regions has
been somewhat sacrificed in favour of reduced crosstalk.
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