Liquid crystal cells – elements and systems – Liquid crystal system – Stereoscopic
Reexamination Certificate
2001-06-05
2002-10-29
Sikes, William L. (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Stereoscopic
C349S187000, C348S051000, C359S462000
Reexamination Certificate
active
06473141
ABSTRACT:
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.
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.
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.
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.
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.
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
.
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.
U.S. Pat. No. 4,717,949 discloses an autostereoscopic 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.
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, (Dec. 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.
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 &sgr; 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:
&sgr;=
Np
(1)
Therefore, for each column of pixels, there is a defined range of angles of illumination as shown at &thgr; due to the associated light line in the rear parallax barrier.
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
&sgr;=
Np
(1
+t
L
)
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.
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.
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 occ
Ezra David
Moseley Richard Robert
Woodgate Graham John
Chowdhury Tarifur R.
Renner Otto Boisselle & Sklar
Sharp Kabushiki Kaisha
Sikes William L.
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