Optical: systems and elements – Stereoscopic – With right and left channel discriminator
Reexamination Certificate
1996-01-26
2002-09-10
Henry, Jon (Department: 2872)
Optical: systems and elements
Stereoscopic
With right and left channel discriminator
C359S464000, C348S051000, C348S058000
Reexamination Certificate
active
06449090
ABSTRACT:
The present invention relates to three dimensional displays.
The term “autostereoscopic” as used herein is defined to mean providing parallax information without requiring the use of a viewing aid. The term “stereoscopic” as used herein is defined to mean providing parallax information with a viewing aid.
FIG. 1
of the accompanying drawings shows an autostereoscopic display of the type disclosed in EP-A-0 602 934. Light from an illuminator
1
is equally divided by a beam splitter
2
, for instance comprising a partially silvered mirror, between transmitted and reflected beams. The transmitted beam is reflected by a mirror
3
via a lens
4
and through a spatial light modulator (SLM) in the form of a liquid crystal display (LCD) panel
5
. The reflected beam is similarly reflected by a mirror
6
through a lens
7
and an SLM
8
in the form of an LCD panel. A beam combiner
9
, for instance comprising a partially silvered mirror, reflects light from the LCD panel
5
and transmits light from the LCD panel
8
. The lenses
4
and
7
form images of the illuminator
1
at respective viewing zones where the eyes of an observer
10
are located. Thus, the left eye of the observer
10
sees an image formed on the LCD panel
8
whereas the right eye sees an image formed on the LCD panel
5
. By displaying suitable two dimensional images on the panels
5
and
8
representing views of an object taken from different directions corresponding to the eyes of an observer, the observer
10
sees a three dimensional image which is autostereoscopic i.e. no viewing aids are required.
The display shown in
FIG. 1
makes good use of the light provided by the illuminator
1
so as to provide a relatively bright three dimensional image to the observer
10
. However, because the autostereoscopic imaging is based on imaging of the illuminator
1
at positions corresponding to the eyes of the observer
10
, the autostereoscopic three dimensional image is viewable in a relatively limited region of space so that the observer
10
has a limited freedom of location.
FIG. 2
of the accompanying drawings shows another autostereoscopic three dimensional (3D) display of the type disclosed in EP 0 656 555. The display shown in
FIG. 2
is of the same general type as that shown in
FIG. 1
in that it uses a beam combiner
9
to combine two dimensional images and effectively a single illuminator whose light is divided by a beam splitter
2
. However, the display of
FIG. 2
differs from that shown in
FIG. 1
in that the fixed relatively small illuminator
1
is replaced by a programmable illuminator
11
which provides or simulates a movable light source. The illuminator
11
is controlled by an observer tracking system
12
which determines the location of an observer and controls the illuminator
11
so that the images of the illuminator are formed at the current locations of the eyes of the observer. As illustrated in
FIG. 2
, the illuminator
11
comprises a plurality of light emitting areas which are controlled so as to simulate a moving light source. When the observer is at the location indicated at
10
a
, the portion
11
a
of the illuminator
11
is illuminated whereas, when the observer is at the position indicated at
10
b
, the portion
11
b
of the illuminator
11
is illuminated.
It is thus possible to provide an autostereoscopic display in which the observer can be tracked within a more extended region within which the 3D image is viewable. By tracking more than one observer and controlling the illuminator
11
such that more than one corresponding region is illuminated, it is possible to arrange for the 3D image to be viewable by more than one observer. However, the viewing region may still be undesirably limited and only a limited number of observers can be accommodated. Further, the complexity and cost of the display are increased by the provision of the observer tracking system
12
.
U.S. Pat. No. 5,264,964 discloses an imaging system which is capable of operating in both stereoscopic and autostereoscopic modes, which are illustrated in
FIGS. 3 and 4
, respectively, of the accompanying drawings. A spatially multiplexed stereoscopic image formed of alternating left eye view strips L and right eye view strips R is disposed below micropolarising arrays PA
1
, PA
2
and PA
3
. Polarisers having a first linear polarisation direction are denoted by P
1
whereas polarisers having a second linear polarisation direction orthogonal to the first linear polarisation direction are denoted by P
2
. Transparent non-polarising regions are denoted by T. Polarisers P
1
of the array PA
1
are disposed on the strips L whereas polarisers P
2
of the array PA
1
are disposed on the strips R.
The arrays PA
2
and PA
3
are spaced from the array PA
1
and each comprises a repeating pattern of regions P
1
, P, P
2
. In the stereoscopic mode illustrated in
FIG. 3
, regions of the same type of the arrays PA
2
and PA
3
are aligned with each other. In the autostereoscopic mode illustrated in
FIG. 4
, polarising regions of different types of the arrays PA
2
and PA
3
are aligned with each other to provide opaque regions which alternate with the transparent regions T to form a parallax barrier.
The arrays PA
2
and PA
3
are moved relative to each other to change between the stereoscopic and autostereoscopic modes.
As shown in
FIG. 3
; light is transmitted in regions A from the strips R via the transparent regions T to the right eye of an observer. In regions B, light is transmitted from the strips R via regions P
2
of the arrays PA
2
and PA
3
to the right eye. Because of differences in transmissivity between the regions T and P
2
, the image portions viewed via the regions B will be darker than the image portions viewed via the regions A. In region C, light from the strip R
2
towards the right eye is absorbed by the orthogonal polarisers P
1
and P
2
so that a dark band with be visible in the image. In regions D, light from the strips L towards the right eye is absorbed by the orthogonal polarisers so that the left eye view strips are not visible to the right eye.
Light from the strip R
1
is mostly transmitted to the right eye whereas light from the strip R
2
is mostly blocked from the right eye. Similar effects occur for the left eye of the observer. Thus, different parts of the same view have different intensities when seen by the observer. Further, the pars of the views at least partially obscured by orthogonal polarisers change for different positions of the observer so that intensity fluctuations are seen across the display as the observer moves.
In the autostereoscopic mode illustrated in
FIG. 4
, there is a problem with the size of the slit width of the parallax barrier. For a slit width equal to the barrier width and for a typical position of the observer as shown, the right eye sees a right eye view strip R
3
via a region E but also sees part of a left eye view strip L
1
via a region F. The left eye sees only part of the strip L
1
via a region G but sees the right eye view strip R
4
via a region H. A substantial amount of cross-talk is therefore visible in the image.
The amount of cross-talk varies with the angle between the display and the eyes of the observer so that, for each position of the observer, different parts of the display exhibit different levels of cross-talk. Also, as the observer moves, the amount of cross-talk seen by each eye varies.
In order to reduce the cross-talk, the slit width may be made narrow. However, this results in a deterioration of image quality in the stereoscopic mode. Thus, for the display to operate in both the autostereoscopic and stereoscopic modes, conflicting demands on the slit width result in poor image quality in both modes or in the image quality in one mode being sacrificed for the image quality in the other mode.
A further disadvantage with the system disclosed in U.S. Pat. No. 5,264,964 is the tight alignment tolerances required of the micropolariser arrays. Substantial cost and difficulty of manufacture are necessary in order to provide th
Ezra David
Omar Basil Arthur
Woodgate Graham John
Henry Jon
Renner Otto Boisselle & Sklar
Sharp Kabushiki Kaisha
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