Autostereoscopic display and method

An autostereoscopic display includes a projection system which generates a plurality of real images that represent different spatial views of an object and further includes a plurality of contiguous field lenses. From the real images, the field lenses form a plurality of exit pupils which are separated by one interpupillary distance. An observer can "walk around" the display and observe different stereoscopic views of the object by positioning his eyes at an adjacent pair of exit pupils.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to optical displays and more 
particularly to stereoscopic displays. 
2. Description of the Related Art 
The ability to stereoscopically observe different spatial views of an 
object is of considerable value in many fields. For example, different 
spatial stereoscopic views of a body element, e.g., a heart, can be useful 
in medical training, diagnosis and evaluation. Similar views of a proposed 
automobile design could be helpful in design evaluation. Other exemplary 
fields of use include air traffic control, CAD/CAM design and military 
training and tactical/situational awareness displays. Preferably, such 
stereoscopic views are presented so that an observer can "walk around" the 
display and see views similar to those which would be seen if walking 
around the object or objects displayed. 
FIG. 1 illustrates a conventional holographic autostereoscopic display 
system 20 which includes a plurality of image sources in the form of 
cathode ray tubes 22A, 22B, 22C - - - 22N and a plurality of relay lenses 
24A, 24B, 24C - - - 24N (in which N represents a selectable number). Each 
of the relay lenses 24A, 24B, 24C - - - 24N (relay lenses are also 
referred to as projection lenses) is positioned with a respective one of 
the cathode ray tubes 22A, 22B, 22C - - - 22N to form a real image (not 
shown). The display 20 also incudes a transmissive, planar holographic 
member 26 which is formed with a plurality of holographic optical elements 
(HOE) 28 that are arranged in a layered relationship. 
A first one of the layered HOEs 28 is configured to process image 
information from the image source 22A and form an exit pupil 30A. A second 
one of the layered HOEs 28 is configured to process image information from 
the image source 22B and form an exit pupil 30B (the processing associated 
with image sources 22A and 22B is schematically indicated by projection 
lines 29). The remaining HOEs similarly process image information from 
image sources 22C - - - 22N to form exit pupils 30C - - - 30N. The display 
system 20 is arranged to space each of the exit pupils 30A, 30B, 30C - - - 
30N one interpupillary distance (IPD) from any adjacent exit pupil. 
When the image sources 22A, 22B, 22C - - - 22N form N real images of an 
object, a viewer can observe a stereoscopic view of the object by 
positioning his eyes at an adjacent pair of the viewing pupils 30A, 30B, 
30C - - - 30N. Although the stereoscopic display system 20 provides 
stereoscopic views of an object, the displayed visual information is 
limited because the planar holographic member 26 requires the exit pupils 
30A, 30B, 30C - - - 30N to be linearly arranged. 
In addition, all of the visual data is processed through the same 
processing aperture, i.e., the planar holographic member 26. For example, 
even though visual data from the image source 22A need only be processed 
by its respective one of the HOEs 28, this data passes through all of the 
other HOEs 28 along with visual data from image sources 22B - - - 22N. 
Passing all of the visual data through the same processing aperture 
typically increases optical degradation effects, e.g., crosstalk, 
absorption loss and color shift, in the observed view at the exit pupils 
30A, 30B, 30C - - - 30N. Excessive absorption loss is also introduced 
because the visual data must past through all of the layers of a common 
processing aperture. Data processing problems which are associated with a 
common processing aperture typically increase as the number of processed 
images increases. 
SUMMARY OF THE INVENTION 
The present invention is directed to displays which present high-quality, 
stereoscopic images of an object in which each image represents a 
different spatial view of the object. Preferably, multiple viewers can 
"walk around" the displays and simultaneously view different spatial 
aspects of the object, e.g., front, side, back and top. These images are 
viewed without the need for viewing aids, i.e., the displays are 
autostereoscopic displays. 
These goals are achieved with the realization that autostereoscopic views 
of an object can be formed by generating a plurality of real images which 
each represent a different spatial view of the object and processing each 
of these real images through a different processing aperture to form a 
different one of a plurality of exit pupils. Each exit pupil is the 
position at which the radiant energy density of its respective real image 
is maximized. 
Each of the exit pupils is spaced substantially one interpupillary distance 
(IPD) from at least one other of the exit pupils so that a viewer can 
observe a view of the object by positioning his eyes at a pair of adjacent 
exit pupils. Another viewer can simultaneously observe a different spatial 
view of the object by positioning his eyes at a different pair of adjacent 
exit pupils. The quality of the stereoscopic images is improved by 
processing each of the real images through a different processing aperture 
and thereby avoiding the optical degradation, e.g., crosstalk, absorption 
loss and color shift, that would result if the images were processed 
through a common processing aperture. 
In one display embodiment, a plurality of optical field elements is 
combined with a projection system that is configured to form a plurality 
of real images. Each optical field element is spaced no further than its 
focal length from a different one of the real images to process that real 
image into one of a plurality of exit pupils at which the radiant energy 
density of that real image is maximized. Preferably, each optical field 
element is positioned coincident with its respective real image or is 
spaced from its respective real image by a few thicknesses of the optical 
field element. 
The optical field elements and the projection system are arranged to space 
each of the exit pupils substantially one interpupillary distance (IPD) 
from at least one other of the exit pupils. Preferably, the optical field 
elements are arranged in a contiguous relationship and are further 
arranged to form a geometric shape, e.g., a hemisphere, which is selected 
to enhance the stereoscopic views for the intended application. 
One projection system embodiment includes a plurality of conventional image 
sources (e.g., active matrix liquid crystal displays or cathode ray tubes) 
and a plurality of relay lenses (relay lenses are also referred to as 
projection lenses). In another projection system embodiment, the plurality 
of image sources is replaced by a single time-multiplexed image source 
which is configured to display a plurality of successive images. In this 
embodiment, an optical transmission system routes each successive image to 
a respective optical field element. 
The teachings of the invention are equally applicable to the display of 
monochrome and color images of single or multiple objects. 
The novel features of the invention are set forth with particularity in the 
appended claims. The invention will be best understood from the following 
description when read in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 2 illustrates a stereoscopic display system 40 in accordance with the 
present invention. In the system 40, a projection system 42 directs visual 
data to a plurality of field lenses 44A, 44B, 44C, 44D - - - 44N-1, 44N 
which are arranged in a contiguous relationship 46 and are further 
arranged so that, together, they form a display member 47 that has the 
geometric shape of a hemisphere 48 (although the field lenses contiguously 
form the display member 47, only exemplary field lenses are shown for 
clarity of illustration). The contiguous relationship 46 and the 
hemispheric shape 48 are facilitated because each of the field lenses has 
the shape of a hexagon 50. 
The projection system 42 includes a plurality of image sources 52A, 52B, 
52C, 52D - - - 52N-1, 52N and associated relay lenses 54A, 54B, 54C, 54D - 
- - 54N-1, 54N (in which N represents a selectable number). Imagery 
generated by the image source 52A and its respective relay lens 54A is 
processed through the field lens 44A to form an exit pupil 56A (this 
processing is indicated by projection lines 57). Imagery generated by the 
image source 52B and its respective relay lens 54B is processed through 
the field lens 44B to form another exit pupil 56B. 
In a similar manner, the imagery from each of the image sources 52C, 52D - 
- - 52N-1, 52N and its respective one of the relay lenses 54C, 54D - - 
-54N-1, 54N is processed through a respective one of the field lenses 44C, 
44D - - - 44N-1, 44N to form exit pupils 56C, 56D - - - 56N-1, 56N. The 
projection system 42 and the relay lenses 54A, 54B, 54C, 54D - - - 54N-1, 
54N are arranged to position each of the exit pupils 56A, 56B, 56C, 56D- - 
-56N-1, 56N an IPD space from at least one other of the exit pupils (e.g, 
as shown by the IPD space 60 between exit pupils 56C and 56D). 
Because the field lenses 44A, 44B, 44C, 44D - - - 44N-1, 44N are 
contiguously arranged in the shape of the hemisphere 48, the exit pupils 
56A, 56B, 56C, 56D - - - 56N-1, 56N lie in a three-dimensional viewing 
space 62 which has the shape of a hemisphere 64 that is larger than the 
hemisphere 48 and is concentric with that hemisphere. 
In operation, each of the image sources 52A, 52B, 52C, 52D - - - 52N-1, 52N 
generates an image which represents a different spatial view of an object, 
e.g., an automobile. These images are allocated to the image sources 52A, 
52B, 52C, 52D - - - 52N-1, 52N so that the views presented at the exit 
pupils 56A, 56B, 56C, 56D - - - 56N-1, 56N spatially correspond to the 
spatial origins of those views. 
For example, the images presented at exit pupils 56A and 56B represent 
views of an automobile which have the same angular separation as the 
angular separation of the exit pupils themselves. Continuing with this 
example, if the images presented at exit pupils 56A and 56B represent 
views of one side of the automobile, then the images presented at exit 
pupils 56N-1 and 56N represent views of another side of the automobile and 
images presented at exit pupils 56C and 56D represent views of the top of 
the automobile. 
If an observer positions his eyes at the exit pupils 56A and 56B, he sees a 
stereoscopic view of one side of the automobile and if he moves his eyes 
to exit pupils 56C and 56D and then to exit pupils 56N-1 and 56N he 
successively sees a stereoscopic view of the top of the automobile and a 
stereoscopic view of another side of the automobile. Alternatively, three 
observers can place their eyes at these pairs of exit pupils and 
simultaneously see different stereoscopic views of the automobile. Because 
of its hemispheric form, the display system 40 presents stereoscopic views 
over a solid angle of substantially 2.pi. steradians. 
In the stereoscopic display system 40, the image data which corresponds to 
each view of the displayed object is processed through a different 
processing aperture, i.e., through a different one of the field lenses 
44A, 44B, 44C, 44D - - - 44N-1, 44N. Accordingly, crosstalk between sets 
of visual data is reduced. In addition, each data set only incurs the 
absorption loss of a single processing aperture. Because the field lenses 
44A, 44B, 44C, 44D - - - 44N-1, 44N are discrete optical elements, they 
can be arranged in a geometric shape, e.g., the hemisphere 48 of FIG. 2, 
that spatially corresponds to the object which is imaged. 
The image processing of FIG. 2 is shown in more detail in FIG. 3 with 
reference to an exemplary set of the image sources, relay lenses and field 
lenses of FIG. 2. In FIG. 3, the relay lens 54A has focal points 70 which 
are spaced from it by a focal length 72. The relay lens 54A is spaced from 
the image source 52A by a space greater than the focal length 72 so that a 
real image 74 is formed. The image source 52A can be any conventional 
image source, e.g., a cathode ray tube, an active matrix liquid crystal 
display 77 (which is shown adjacent the image source 52A) or any other 
flat-panel display. 
The field lens 44A has a thickness 79 and a focal point 80 which is spaced 
from it by a focal length 82. The field lens 44A is spaced no more than 
its focal length 82 from either side of the real image 74. As shown in 
FIG. 3, it is preferably spaced less than a few, e.g., one or two, lens 
thicknesses 79 from the real image 74 and, more preferably, it is 
positioned coincident with the real image 74 as indicated by the broken 
line position 84. Spherical aberration, coma and astigmatism are reduced 
by positioning the field lens 44A coincident with the real image 74. 
However, negative visual artifacts (caused by dust and other particulate 
matter) may be objectionable at this position. The visibility of these 
artifacts is reduced by slightly spacing the lens from coincidence. 
The field lens 44A forms an image of the relay lens 54A (more particularly, 
the aperture stop of the relay lens 54A) at a point in space represented 
by the exit pupil 56A. The exit pupil 56A is the position at which the 
radiant energy density of the image is maximized. Therefore, it is the 
optimum position for placement of an observer's eye when viewing the image 
formed by the field lens 44A and the relay lens 54A. The image data from 
the image source 52A is processed through the processing aperture 
represented by the field lens 44A. As shown in FIG. 2, the image data from 
others of the image sources 52B, 52C - - - 52N-1, 52N are similarly 
processed through their respective field lenses, i.e., processing 
apertures. 
FIG. 4 is similar to FIG. 3, with like elements represented by like 
reference numbers. FIG. 4 shows that the processing function of the field 
lens 44A can be performed by a holographic optical element (HOE) 87. 
Basically, in the arrangement of FIG. 4, refraction processes of the field 
lens 44A are replaced by diffraction processes of the HOE 87. Similar to 
the field lens 44A, the HOE 87 is preferably positioned less than a few of 
its thicknesses 88 from the real image 74 and, more ideally, is positioned 
coincident with the real image 74 as indicated by the broken line position 
89. 
The projection system 42 of FIG. 2 can be simplified by the use of a single 
time-multiplexed image source 90 as shown in FIG. 5. FIG. 5 is similar to 
FIG. 3 with like elements represented by like reference numbers. The 
time-multiplexed image source 90 displays successive images in response to 
a timing signal 92. These successive images are then transmitted to their 
respective field lens by a conventional optical transmission system 94. 
The optical transmission system 94 routes the successive images along 
image paths as indicated by ray sets 95A, 95B and 95N. 
Each of these successive ray sets is sent by the optical transmission 
system 94 to a respective relay lens as exemplified by the connection 
between the ray set 95B and the relay lens 54A. The optical transmission 
systems can be formed with various conventional transmission elements, 
e.g., mirrors and switched optical fibers. A completely solid state 
projection system can be obtained by using a solid state display, e.g., an 
active matrix liquid crystal display, for the image source 90. 
The formation of the exit pupil 56A in FIG. 3 can be performed by any 
optical field element which can process a real image into an exit aperture 
from which an image of maximum radiant energy density can be viewed. 
Exemplary optical field elements include the classical field lens 44A of 
FIG. 3 (a positive refractive lens, e.g., a double convex lens), the HOE 
87 of FIG. 4 and a Fresnel lens such as the Fresnel lens 98 shown in FIG. 
5. Because of its stepped structure, the Fresnel lens 98 occupies less 
volume than the classical field lens 44A of FIG. 3. For clarity of 
illustration, the stepped Fresnel lens 98 is spaced a few of its 
thicknesses from the real image 74. 
The optical field elements of the invention, e.g., the field lenses 44A, 
44B, 44C, 44D - - - 44N-1, 44N of FIG. 1, are preferably positioned in a 
contiguous relationship to facilitate the formation of a display member 
(e.g., the display member 47 of FIG. 1). In addition, the contiguous 
relationship facilitates realization of the IPD spacing of the exit 
pupils. 
The hemispheric display member 47 of FIG. 2 can be realized with hexagonal 
optical field elements whose outer faces correspond with the hemispheric 
shape or with flat-faced hexagonal optical field elements, i.e., the outer 
surface of the display member 47 may be formed with a smooth or a faceted 
surface. 
Although a hexagonal shape is particularly useful in forming these 
contiguous relationships, other optical field element shapes, e.g., 
pentagonal, may be substituted. Preferably, the optical field elements are 
arranged to give the display member a geometric shape which enhances the 
objects being displayed. In addition to the three-dimensional hemispheric 
shape 48 of the display member 47, another exemplary geometric shape is 
illustrated by the display member 100 of FIG. 6. 
The display member 100 is formed with a plurality of contiguously arranged 
optical field elements 102 (for clarity of illustration, only exemplary 
field elements are shown) that are arranged in the shape of a 
two-dimensional plane 104. The hemispheric shape 48 of the display member 
47 could enhance the stereoscopic display of images of an object which is 
typically viewed from spatially opposed positions, e.g., a proposed 
automobile design. The planar shape 104 of the display member 100 requires 
less space than the hemispheric shape 48. If desired, various other views 
can be displayed with the display member 100 by causing the image sources 
(e.g., the image source 52A of FIG. 3) to sequentially generate spatially 
different views. 
Autostereoscopic display systems of the invention avoid a significant 
source of crosstalk between optical signals (a common processing aperture) 
because each source of image data is processed through its own processing 
aperture. Not only do these systems reduce the opportunity for crosstalk 
but they reduce absorption losses compared to conventional systems which 
use a common processing aperture. Display systems of the invention 
facilitate "walk around" viewing by a plurality of simultaneous viewers. 
They involve no moving parts, can be adapted to a completely solid state 
configuration and do not require viewing aids, e.g., polarizing glasses. 
The teachings of the invention are equally applicable to the display of 
monochrome and color images. 
While several illustrative embodiments of the invention have been shown and 
described, numerous variations and alternate embodiments will occur to 
those skilled in the art. Such variations and alternate embodiments are 
contemplated, and can be made without departing from the spirit and scope 
of the invention as defined in the appended claims.