U.S. patent application number 08/843558 was filed with the patent office on 2001-11-22 for image transformation and synthesis methods.
Invention is credited to MACINTOSH, DAVID, ROGINA, PETER R..
Application Number | 20010043737 08/843558 |
Document ID | / |
Family ID | 23440193 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043737 |
Kind Code |
A1 |
ROGINA, PETER R. ; et
al. |
November 22, 2001 |
IMAGE TRANSFORMATION AND SYNTHESIS METHODS
Abstract
A system for generating images of a scene as the scene would be
observed from an arbitrary location. A plurality of discrete
images, typically video images, taken at different viewpoints, as,
for example, by a plurality of cameras pointing outwardly on a
curving locus are converted to an offset epipolar image. The offset
epipolar image includes a plurality of linesets, each such lineset
incorporating one scanning line from each of the discrete video
images. Each line in the virtual image is reconstructed from a
lineset of the epipolar image. The reconstruction may include
interpolation between pixel data representing lines from adjacent
discrete images and mapping of pixels from one or more lines
representing one or more adjacent discrete images onto the pixel
line of the virtual image. The nature of the mapping depends upon
the viewpoint selected for the virtual image. The system can
provide real time stereoscopic telepresence, i.e., a virtual
viewpoint images for each eye as the observer moves his or her
head.
Inventors: |
ROGINA, PETER R.;
(MARTINSVILLE, NJ) ; MACINTOSH, DAVID;
(INVERKEITHING, GB) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,
KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Family ID: |
23440193 |
Appl. No.: |
08/843558 |
Filed: |
April 18, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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08843558 |
Apr 18, 1997 |
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08365750 |
Dec 29, 1994 |
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5703961 |
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Current U.S.
Class: |
382/154 ;
348/E13.014; 348/E13.015; 348/E13.041; 348/E13.045; 348/E13.059;
348/E13.062; 348/E13.066; 348/E13.071; 348/E13.073 |
Current CPC
Class: |
G06T 7/97 20170101; G06V
10/16 20220101; H04N 19/597 20141101; G06T 15/10 20130101; H04N
13/366 20180501; H04N 13/398 20180501; H04N 13/344 20180501; H04N
13/243 20180501; G06T 2207/20228 20130101; G06V 10/147 20220101;
H04N 13/167 20180501; H04N 13/117 20180501; H04N 13/189 20180501;
H04N 13/194 20180501; H04N 13/239 20180501 |
Class at
Publication: |
382/154 |
International
Class: |
G06K 009/00 |
Claims
What is claimed is:
1. A method of synthesizing an image of a scene corresponding to
the image of said scene which would be observed from a virtual
viewpoint comprising the steps of: (a) providing a plurality of
discrete images corresponding to the images of the scene observed
from a plurality of discrete viewpoints, each said discrete image
including an array of pixel data in first and second image
dimensions; (b) constructing a first epipolar image for said first
dimension from said discrete images, said first epipolar image
including a plurality of linesets, each said lineset including one
line of pixel data in said first dimension from each said discrete
image, all of the lines in each said line set corresponding to the
same location in said second dimension, said lines of pixel data
within each lineset being ordered in an order corresponding to the
order of said discrete viewpoints; (c) providing pixel data for
said synthetic image as a plurality of virtual viewpoint pixel
lines extending in said first image dimension and offset from one
another in said second image dimension by (i) associating each
virtual viewpoint line with a line set in said first epipolar image
corresponding to the location of such line in said second dimension
and (ii) for each pixel within each virtual viewpoint line,
deriving synthetic pixel data from pixel data in the associated
line set.
2. A method as claimed in claim 1 wherein said step of deriving
synthetic pixel data includes the steps of selecting a plurality of
lines within the associated line set corresponding to discrete
viewpoints in the vicinity of said virtual viewpoint and deriving
the synthetic pixel data from the pixel data in the so-selected
lines.
3. A method as claimed in claim 2 wherein said step of deriving
synthetic pixel data for each synthetic pixel includes the step of
choosing a plurality of pixels in the selected lines adjacent to
the position of the synthetic pixel in said first dimension and
deriving the synthetic pixel data from the pixel data in said
chosen pixels of said selected lines.
4. A method as claimed in claim 3 wherein said selected lines in
the line set include lines corresponding to discrete viewpoints
bracketing the virtual viewpoint.
5. A method as claimed in claim 4 wherein said step of deriving
pixel data for each synthetic pixel includes the step of
interpolating the pixel data of the chosen pixels in said selected
lines.
6. A method as claimed in claim 3 wherein for each synthetic pixel
in the virtual viewpoint image line, said step of selecting said
pixels in said selected lines includes the steps of, (i) setting an
offset distance, (ii) pixels in the bracketing lines offset from
one another in said first direction by said offset distance and
bracketing the first direction location of the synthetic image
pixel, and (iii) testing said chosen pixels of said bracketing
lines to determine if the pixel data in said chosen pixels of said
bracketing lines match one another within a preselected limit and,
if not, repeating steps (i) through (iii) with a different offset
distance on each repetition until such pixel data matches in step
(iii).
7. A method as claimed in claim 6 further comprising the step of
providing initial offset information for said offset epipolar image
specifying an initial offset in said first dimension between each
pair of adjacent lines in each line set, said step of setting said
offset distance including the step of initially setting said offset
distance to equal said initial offset.
8. A method as claimed in claim 7 wherein said initial offset
corresponds to the theoretical offset between pixels in adjacent
lines of the line set representing a feature in said scene
positioned at infinite distance from said viewpoints.
9. A method as claimed in claim 8 wherein said step of adjusting
said offset distance is performed so as to increase said offset,
distance on each repetition.
10. A method as claimed in claim 1 wherein said step of deriving
pixel data from the pixel data in other pixels of the associated
line set includes the step of processing the pixel data in such
line set to derive boundaries between regions of the line set
having different pixel data corresponding to different objects,
each such boundary defining a curve in an epipolar plane having a
first epipolar coordinate corresponding to pixel location in said
first dimension and a second epipolar coordinate corresponding to
viewpoint location, assigning each synthetic pixel to an object
based upon the location of such pixel relative to said boundaries
within said epipolar plane, and deriving the synthetic pixel data
for each synthetic pixel from discrete image pixel data in said
line set representing the same object.
11. A method of synthesizing an image of a scene corresponding to
the image of said scene which would be observed from a virtual
viewpoint location and viewing direction and having a predetermined
field of view, the method comprising the steps of: (a) providing a
plurality of discrete images corresponding to the images of the
scene observed from a plurality of discrete view directions from a
plurality of discrete viewpoints on a predetermined viewpoint
locus, said viewing directions being disposed at different angles
relative to a reference line in said first dimension, each said
discrete image including an array of pixel data in said first image
dimension and in a second image dimension orthogonal thereto,
whereby position of each pixel in said first image dimension within
each image will represent the angle between the viewing direction
of the image and a ray direction from said pixel to a point in the
scene; (b) constructing a first epipolar image from said discrete
images, said first epipolar image including a plurality of line
sets, each said line set including one line of pixel data in said
first image dimension from each said discrete image, all of the
lines in each said line set corresponding to the same location in
said second image dimension, said lines of pixel data within each
line set being ordered in an order corresponding to the order of
said viewing directions relative to said first dimension, whereby
each said line set defines an epipolar plane having a first
epipolar coordinate corresponding to viewing direction and having a
second epipolar coordinate corresponding to ray azimuth relative to
an index line; (c) selecting a base viewpoint on said viewpoint
locus; and (d) forming a line of the virtual viewpoint image from
each said line set by (i) providing a base line within the line set
corresponding to the base viewpoint; (ii) mapping pixel data of the
base line into the virtual viewpoint image line; (iii) selecting
supplementary pixels from one or more additional lines of the line
set, said supplementary pixels being adjacent to one or both ends
of the base line in said epipolar coordinates and (iv)
incorporating data from said supplementary pixels at one or both
ends of the virtual viewpoint image line so that the virtual
viewpoint image line includes pixel data for said predetermined
field of view.
12. A method as claimed in claim 11 wherein said viewpoint locus is
curvilinear, said discrete viewing directions pointing across said
locus from a camera side towards an object side thereof.
13. A method as claimed in claim 12 wherein the view direction for
each said discrete viewpoint is substantially orthogonal with
respect to said locus.
14. A method as claimed in claim 12 wherein said camera side is the
interior of the locus, adjacent the center of curvature thereof,
and said viewing directions for said discrete viewpoints point
outwardly, away from the center of curvature.
15. A method as claimed in claim 14 wherein said virtual viewpoint
is recessed inwardly toward the center of curvature of the locus,
said step of selecting supplementary pixels being performed so that
at least some of the supplementary pixels correspond to ray
directions substantially parallel to the ray azimuth of the end
pixel of the base line at one or both ends thereof.
16. A method as claimed in claim 15 wherein said step of mapping
said pixels from said base line to said virtual viewpoint line
includes the step of compressing the pixel data in said base line
into a smaller number of pixels and mapping said smaller number of
pixels onto only a portion of said virtual viewpoint line.
17. A method as claimed in claim 14 wherein said virtual viewpoint
has a view direction skewed from the base view direction, said step
of selecting supplementary pixels so that the ray azimuths of the
supplementary pixels added at an end of the base line vary
progressively in the direction of skew.
18. A method as claimed in claim 14 wherein said step of selecting
supplementary pixels is performed by selecting the pixel having
each ray azimuth from the additional line which has the view
direction closest to the base view direction of all lines
incorporating pixels at such ray direction.
19. A method as claimed in claim 11 further comprising the step of
providing a lookup table setting forth a plurality of viewpoints
and view directions and pixel location data specifying
supplementary pixels for each such viewpoint and view direction,
said step of selecting said supplementary pixels including the
steps of retrieving the pixel virtual viewpoint and virtual view
direction from said lookup table and selecting the supplementary
pixels in accordance with said location data.
20. A method as claimed in claim 19 wherein said step of retrieving
location data includes the step of interpolating between location
data for adjacent viewpoints and view directions.
21. A method as claimed in claim 11 wherein said base viewpoint is
located between two of said discrete viewpoints and wherein said
step of providing said base line in each said line set includes the
step of deriving pixel data for pixels constituting said base line
from pixel data in lines of said line set corresponding to discrete
viewpoints in the vicinity of said base viewpoint.
22. A method of synthesizing an image of a scene corresponding to
the image of said scene which would be observed from a virtual
viewpoint location and viewing direction, the method comprising the
steps of: (a) providing a plurality of discrete images
corresponding to the images of the scene observed from a plurality
of discrete viewing directions from a plurality of discrete
viewpoint locations on a predetermined viewpoint locus, said
viewing directions being disposed at different angles relative to a
reference line in a first dimension, each said discrete image
including an array of pixel data in a first image dimension and in
a second image dimension orthogonal thereto, whereby position of
each pixel in said first image dimension within each image will
represent the angle between the viewing direction of the image and
a ray direction from said pixel to a point in the scene; (b)
constructing a first epipolar image from said discrete images, said
first epipolar image including a plurality of line sets, each said
line set including one line of pixel data in said first image
dimension from each said discrete image, all of the lines in each
said line set corresponding to the same location in said second
image dimension, said lines of pixel data within each line set
being ordered in an order corresponding to the order of said
viewing directions relative to said first dimension, whereby each
said line set defines an epipolar plane having a first epipolar
coordinate corresponding to viewing direction and having a second
epipolar coordinate corresponding to ray azimuth in said first
dimension relative to said reference line; (c) forming a line of
the virtual viewpoint image from each said line set, each such line
including a plurality of pixels each having a view azimuth in said
first dimension, by selecting a plurality of pixel sets in the
virtual viewpoint line, each such pixel set including one pixel or
a plurality of mutually adjacent pixels, each such pixel set
defining a principal ray line extending from the virtual viewpoint
location at a principal view azimuth close to the view azimuths of
the pixels in such pixel set and, for each said pixel set: (i)
providing a viewpoint on said locus as a base viewpoint such that
an intercept of the principal ray line of the pixel set on the
viewpoint locus is adjacent the base viewpoint; (ii) selecting a
base line within the line set corresponding to the base viewpoint;
and (iii) for each pixel in the set, selecting one or more pixels
of the base line having ray azimuths close to the view azimuth of
the pixel in the set and mapping pixel data of the selected pixels
of the base line into such pixel of the set.
23. A method as claimed in claim 22 wherein each said pixel set
includes only one pixel of the virtual viewpoint image line, and
wherein the principal view azimuth of each set is the view azimuth
of the pixel constituting such set.
24. A method as claimed in claim 23 further comprising the step of
providing a lookup table setting forth a plurality of virtual
viewpoint location and view azimuths, and location data specifying
one or more pixels within a base line for each such virtual
viewpoint location and view azimuth, said step of selecting said
base line and said pixels in said base line for each pixel set
including the steps of selecting the pixels in accordance with said
location data for the virtual viewpoint and view azimuth of each
pixel.
25. A method as claimed in claim 22 wherein said viewpoint locus is
curvilinear, said discrete viewing directions pointing across said
locus from a camera side towards an object side thereof.
26. A method as claimed in claim 25 wherein the view direction for
each said discrete viewpoint is substantially orthogonal to said
locus.
27. A method as claimed in claim 25 wherein said camera side is the
interior of the locus, adjacent the center of curvature thereof,
and said viewing directions for said discrete viewpoints point
outwardly, away from the center of the curvature.
28. A method as claimed in claim 22 further comprising the step of
providing a lookup table setting forth a plurality of viewpoint
location and principal view directions and base view location data
specifying base views for each such virtual viewpoint location and
principal view direction, said step of selecting said base view for
each pixel set including the step of selecting the base view from
said lookup table in accordance with said base view location
data.
29. A method as claimed in claim 22 wherein said base viewpoint for
at least some pixel sets is located between two of said discrete
viewpoints and wherein, for each said base viewpoint, said step of
providing said base line in each said line set includes the step of
deriving pixel data for pixels constituting such base line from
pixel data in lines of said line set corresponding to discrete
viewpoints in the vicinity of said base viewpoint.
30. A method as claimed in claim 22 wherein said step of providing
said base line for each pixel set includes selecting the line in
the associated line set corresponding to the discrete viewpoint
closest to the intercept of the principal ray line on the viewpoint
locus and providing the so-selected line as pixel data of the base
line.
31. A method of synthesizing an image of a scene corresponding to
the image of said scene which would be observed from a virtual
viewpoint location, the method comprising the steps of: (a)
providing a plurality of discrete images corresponding to the
images of the scene observed from a plurality of discrete view
directions from a plurality of discrete viewpoint locations on a
two-dimensional viewpoint locus, each said discrete view direction
defining a view direction vector, each said discrete image
including pixel data for pixels in an array extending in a first
image dimension and in a second image dimension orthogonal thereto,
whereby position of each pixel within each image will represent a
ray offset vector between the view direction vector of the discrete
image and a ray direction vector from said pixel through the
discrete viewpoint to a point in the scene; (b) assigning virtual
image pixel data for each pixel in a two-dimensional array of
virtual pixels by selecting a plurality of pixel sets in the
virtual array, each such pixel set including one pixel or a
plurality of mutually adjacent pixels, each said pixel set defining
a principal ray vector extending from the virtual viewpoint
location in a principal view direction close to the ray vector
directions of the pixels in such pixel set and, for each said pixel
set: (i) determining an intercept of the principal ray vector on
the viewpoint locus; (ii) providing an image on said locus close to
said intercept as a base image for the pixel set; and (iii) for
each virtual pixel in the set, selecting one or more pixels of the
base image having ray directions close to the view direction of the
virtual pixel and mapping pixel data of the selected pixels of the
base image into such pixel of the set
32. A method of synthesizing an image of a scene corresponding to
the image of said scene which would be observed from a virtual
viewpoint location, the method comprising the steps of: (a)
providing a plurality of discrete images corresponding to the
images of the scene observed from a plurality of discrete view
directions from a plurality of discrete viewpoints distributed in
two orthogonal directions on a viewpoint locus; (b) transforming
said plurality of discrete images into a plurality of
three-dimensional transform images each including some pixel data
from each of the discrete images; (c) selecting information from a
plurality of said three-dimensional transform images according to a
selection scheme based upon said selected view location and
combining the so-selected information; and (d) mapping the selected
information from the transform images into the virtual viewpoint
image.
33. A method of synthesizing an image of a scene corresponding to
the image of said scene which would be observed from a virtual
viewpoint location, the method comprising the steps of: (a)
providing a plurality of discrete images corresponding to the
images of the scene observed from a plurality of discrete view
directions from a plurality of discrete viewpoints distributed in
two orthogonal dimensions of said scene on a viewpoint locus, each
said discrete view defining a view location vector having a first
component in an azimuth dimension and a second component in an
elevation dimension orthogonal to the azimuth direction, each said
discrete image including pixel data for pixels in an array
extending in first and second image dimensions orthogonal to one
another and to the view location vector, whereby the position of
each pixel in the first and second image directions correspond to
the difference in azimuth and elevation, respectively, between the
view location vector of the discrete image and a ray direction
vector from said pixel through the discrete viewpoint to a point in
the scene depicted by said pixel; (b) constructing a first epipolar
image from said discrete images, said first epipolar image
including a plurality of line sets, each said line set including
one line of pixel data in said first image dimension from each said
discrete image, all of the lines in each said line set
corresponding to the same location in said second image dimension,
said lines of pixel data within each line set being ordered so that
each said line set defines an epipolar space having a first
epipolar coordinate corresponding to the azimuth component of the
view location vector, having a second epipolar coordinate
corresponding to the elevation component of the view location
vector and also corresponding to the elevations of the ray
direction vectors of the pixels, and having a third epipolar
coordinate corresponding to the azimuth of the ray direction
vectors of the pixels and; (c) assigning virtual image pixel data
for each pixel in a two-dimensional array of virtual pixels by
selecting a plurality of pixel sets in the virtual array, each such
pixel set including one pixel or a plurality of mutually adjacent
pixels, each said pixel in the set defining a ray direction vector
from the pixel through the virtual viewpoint location and having
azimuth and elevation, each said pixel set defining a principal ray
vector extending through the virtual viewpoint and having azimuth
and elevation close to the azimuths and elevations of the pixels in
such pixel set and, for each said pixel set: (i) determining an
intercept of the principal ray vector on the viewpoint locus; (ii)
providing a line of one said lineset having first and second
epipolar coordinates corresponding to a location close to said
intercept as a base line for the pixel set; (iii) for each virtual
pixel in the set, selecting one or more pixels of the base line
having a third epipolar coordinate close to the ray direction
azimuth of the virtual pixel; and (iv) mapping pixel data of the
selected pixels of the base image into such pixel of the pixel
set.
34. A method as claimed in claim 33 wherein each said pixel set
includes only one pixel of the virtual viewpoint image, and wherein
the principal ray vector of each pixel set is the ray direction
vector of the pixel constituting such set.
35. A method as claimed in claim 34 further comprising the step of
providing a lookup table setting forth a plurality of virtual
viewpoint locations pixel locations in said first and second image
dimensions, and location data specifying one or more pixels within
a base line for each such virtual viewpoint location and pixel
location, said step of selecting said base line and said pixels in
said base line for each pixel set including the steps of and
selecting the pixels in accordance with said location data for the
virtual viewpoint and pixel location of each pixel.
36. A method as claimed in claim 33 wherein said viewpoint locus is
a sphere or a portion of a sphere, said discrete viewpoint
directions being substantially radial with respect to said sphere
or portion of a sphere.
37. A method as claimed in claim 33 further comprising the step of
providing a lookup table setting forth a plurality of viewpoint
location and principal view directions and base view location data
specifying base views for each such virtual viewpoint location and
principal view direction, said step of selecting said base view for
each pixel set including the step of selecting the base view from
said lookup table in accordance with said base view location
data.
38. A method as claimed in claim 33 wherein said base viewpoint for
at least some pixel sets is located between a plurality of said
discrete viewpoints and wherein, for each such base viewpoint, said
step of providing said base line in each said line set includes the
step of deriving pixel data for pixels constituting such base line
from pixel data in lines of said line set corresponding to discrete
viewpoints in the vicinity of said base viewpoint.
39. A method as claimed in claim 33 wherein said step of providing
said base line for each pixel set includes selecting the line in
the associated line set corresponding to the discrete viewpoint
closest to the intercept of the principal ray line on the viewpoint
locus and providing the so-selected line as pixel data of the base
line.
40. A method as claimed in any one of claims 1, 11, 22, 31, 32 or
33 wherein said step of providing said discrete images includes the
steps of capturing images of a real scene by means of one or more
cameras and correcting each said captured image for distortion
introduced by the camera.
41. A method as claimed in claim 40 wherein said step of capturing
images by means of one or more cameras includes the steps of moving
said one or more cameras with respect to the scene and capturing
different discrete images at different positions of said one or
more cameras.
42. A method of providing telepresence comprising the step of
detecting the disposition of a real observer as the observer moves,
selecting at least one virtual viewpoint location and direction
corresponding to a viewpoint location and view direction of the
real observer, synthesizing a virtual viewpoint image by a method
as claimed in any one of claims 1, 11, 22, 31, 32 and 33 for each
selected virtual viewpoint location and direction and displaying
the virtual viewpoint image to the observer substantially in real
time, so that the observer sees the correct virtual viewpoint image
for a new disposition substantially immediately as he moves to the
new disposition.
43. A method as claimed in claim 42 wherein said step of selecting
at least one virtual viewpoint location and direction includes the
step of selecting a pair of virtual viewpoint locations offset from
one another by an interpupillary distance, said steps of
synthesizing and displaying being conducted so as to display a
binocular pair of images, one to each eye of the observer.
44. A method as claimed in claim 42 wherein said step of selecting
at least one virtual viewpoint image includes the step of selecting
a plurality of virtual viewpoints simultaneously corresponding to
the locations of a plurality of viewers, said synthesizing step
including the step of synthesizing a virtual viewpoint image for
each said virtual viewpoint and said displaying step including the
step of displaying each said virtual viewpoint image to the
associated observer so that each observer sees one or more virtual
viewpoint images associated with his position substantially in real
time as he moves.
45. A method of compressing a set of images of a scene including a
plurality of discrete images corresponding to the images of the
scene observed from a plurality of discrete viewpoints, each said
discrete image including an array of pixel data arranged in a first
image dimension corresponding to position of depicted objects in a
first dimension in real space and in a second image dimension
orthogonal thereto, the method including the steps of: (a)
constructing one or more epipolar images from said discrete images,
each said epipolar image including a plurality of line sets, each
said line set including one line of pixel data in said first image
dimension from each said discrete image, all of the lines in each
said line set corresponding to the same location in said second
image dimension, said lines of pixel data within each line set
being ordered in an order corresponding to an order of said
viewpoints in said first real dimension; and (b) compressing the
pixel data in said line sets to form one or more compressed
epipolar images.
46. A method as claimed in claim 45 further comprising the step of
transmitting or storing said compressed epipolar images.
47. A method as claimed in claim 46 further comprising the step of
decompressing said compressed epipolar images.
48. A method as claimed in claim 45 wherein said step of
compressing the pixel data in said line sets includes is performed
by compressing the data in each said line set independently of the
data in the other said line sets.
49. A method as claimed in claim 45 wherein said set of discrete
images of said scene includes a plurality of subsets of discrete
images representing the scene at different times, all of the images
in each said subset representing the scene at the same time, said
step of forming one or more epipolar images includes the step of
constructing an epipolar images from the discrete images in each
said subset, whereby each said epipolar image corresponds on one
said time, said compressing step including the step of comparing
data in a first said epipolar image with data in at least one other
said epipolar image from a different time to determine the
differences therebetween.
50. A method as claimed in claim 49 wherein said comparing step
includes the step of comparing each said line set in said first
epipolar image with a corresponding line set in one or more other
epipolar images.
51. A method of combining a first set of images of a first scene
and a second set of images of a second scene, each said set of
images including a plurality of discrete images corresponding to
the images of the scene observed from a plurality of discrete
viewpoints, each said discrete image including an array of pixel
data arranged in a first image dimension corresponding to position
of depicted objects in a first dimension in real space and in a
second image dimension orthogonal thereto, the method including the
steps of: (a) constructing a first epipolar image from said first
set of discrete images and a second epipolar image from said second
set of discrete images, each said epipolar image including a
plurality of line sets, each said line set including one line of
pixel data in said first image dimension from each said discrete
image, all of the lines in each said line set corresponding to the
same location in said second image dimension, said lines of pixel
data within each line set being ordered in an order corresponding
to an order of said viewpoints in said first real dimension; and
(b) combining the pixel data in said line sets of said first and
second epipolar images to form combined line sets constituting a
combined epipolar image.
52. A method as claimed in claim 51 wherein said step of combining
said pixel data includes the step of combining pixel data of each
line set in said first epipolar image with one line set in said
second epipolar image.
53. A method as claimed in claim 52 wherein said step of combining
said pixel data in said line sets includes the step of deriving new
pixel data for each pixel in each combined line set by combining
pixel data for the corresponding pixel in the line set of the first
epipolar image with pixel data for the corresponding pixel in the
line set of the second epipolar image according to a combining
formula which varies from pixel to pixel.
54. A method as claimed in claim 53 wherein said combining formula
is a function of the pixel data in said second line set.
55. A method of providing telepresence comprising the steps of: (a)
providing a plurality of discrete two-dimensional images
corresponding to the image of the scene observed from a plurality
of discrete viewpoints on a predetermined viewpoint locus; (b)
transforming said plurality of discrete images into two-dimensional
transform images each including some information from a plurality
of said discrete images; (c) displaying the virtual viewpoint image
to the observer substantially in real time, so that the observer
sees the correct virtual viewpoint image for a new disposition
substantially immediately as he or she moves to the new
disposition.
56. A method as claimed in claim 55 wherein each said discrete
image includes pixel data for a plurality of pixels in a first
ordered array, and each said transform image pixel data for a
plurality of pixels in a second ordered array said step of
transforming said discrete images including the step of
incorporating pixel data for a set of pixels from each said
discrete image into each said transform image.
57. A method as claimed in claim 56 wherein said step of
synthesizing said virtual viewpoint image includes the step of
selecting pixel data for a set of pixels from each said transform
image and incorporating the so-selected pixel data into an ordered
array to form said virtual viewpoint image.
58. A method as claimed in claim 55 wherein said step of selecting
at least one virtual view location and direction includes the step
of selecting a pair of virtual view locations offset from one
another by an interpupillary distance, said steps of synthesizing
and displaying being conducted so as to display a binocular pair of
images, one to each eye of the observer.
59. A method as claimed in claim 55 wherein said step of detecting
the disposition of an observer includes the step of detecting the
dispositions of a plurality of observers simultaneously, said
synthesizing and displaying steps including the steps of
synthesizing and displaying a plurality of virtual viewpoint images
simultaneously so that a virtual viewpoint image corresponding to
the disposition of each observer is displayed to that observer.
Description
[0001] The present invention relates to methods of apparatus for
processing pictorial information to synthesize images from
arbitrary viewpoints.
[0002] Ordinary image display systems such as a common television
set or a computer screen with standard image display software
provide monocular images from a viewpoint which is independent of
the viewer's actual position. When the viewer turns his or her
head, the displayed image does not change. Rather, the image
continually reflects the viewpoint of the camera which originally
generated the video signal or an artificial viewpoint in the image
display software. Common systems for displaying stereoscopic images
suffer from the same problem. For example, some common stereoscopic
vision systems display a separate video image to each eye of the
viewer, each such image corresponding to a slightly different
camera position or slightly different artificial viewpoint in the
case of computer generated images. Here again, however, the
viewpoints do not change as the observer moves. Such systems
therefore do not provide a truly realistic viewing experience.
[0003] Holographic images inherently provide a more realistic
viewing experience. A viewer looking at a hologram sees the
depicted object from a new viewpoint if he or she moves his or her
head to a new location, or turns it to a new viewing angle. In this
respect, the experience of looking at a hologram resembles the
experience of looking at the depicted objects in reality. However,
it is generally impractical to display holographic images of
changing scenes. Although some holographic video systems have been
demonstrated, they are extremely expensive, require very large
bandwidth and suffer from other drawbacks.
[0004] So-called "virtual reality" systems can provide viewpoints
which move as the observer moves his or her head. Some of these
systems display computer generated images synthesized from
mathematical models of the scene to be depicted. Such an image
involves computation of the projection of the mathematically
modelled elements of the scene onto an arbitrary view plane. To
provide a stereoscopic view, two different viewing planes are used,
corresponding to the slightly different viewing planes of the
observers two eyes. Such systems can be provided with detectors for
monitoring the actual orientation of the viewer and can be arranged
to change the view planes used in the reconstruction as the
orientation of the viewer changes. Such an arrangement
theoretically can provide an illusion of presence in the scene.
However, such systems are limited only to displaying images of
mathematically generated scenes. Accordingly, they can only display
images of synthetic, computer-created scenes or of real scenes
which can be captured and modelled as mathematically tracktable
elements suitable for handling by computer graphics software. They
cannot normally display images of an arbitrary scene. Moreover,
such systems require substantial computational power to perform all
of the complex mathematical manipulations required. This problem is
aggravated where the scene includes moving elements.
[0005] An alternative arrangement has been to use an actual camera
or cameras directed at the real scene. For a stereoscopic view, two
cameras are employed, spaced apart from one another by distance
corresponding to the viewer's interpupillary distance. The cameras
are mounted on a platform which in turn is linked to a
servomechanism. The servomechanism is controlled by a sensor linked
to the user's head. As the user moves his or her head, the camera
platform duplicates such movement. Accordingly, the images captured
by the cameras and transmitted to the user's eyes realistically
duplicate the images which the user would see as he or she looks at
the scene from any viewpoint. The system can provide a realistic
experience of telepresence. The viewer sees essentially the same
images as he or she would see if he were at the scene, and these
images change in a realistic manner as the viewer's head moves.
These systems are expensive, in that a set of cameras and the
associated servo mechanisms must be provided for each user.
Moreover, these systems require that the scene be in existence and
available for viewing at the time the viewer wants to see the
scene. They cannot operate with recorded images of the scene.
Moreover, there must be continuous, two-way communication between
the viewer's location and the real location of the scene, where the
cameras are positioned. At least the communications channel from
the scene location to the viewer's location must be a high-band
width video channel. All of these drawbacks together limit
application of such servomechanism based systems to rare
situations.
[0006] As described in an article by Takahashi et al, Generation of
Intermediate Parallax-images For Holographic Stereograms,
Proceedings SPIE, Volume 1914, Practical Holography VII (1993) a
so-called "Holographic Stereogram" can be synthesized from numerous
individual monocular images of a scene, typically about 50 to 100
such images. To alleviate the need for actually capturing so many
real images, the authors propose to generate intermediate images by
projection back from three dimensional data defining the scene. The
three dimensional data, in turn, is calculated from the images
taken by real cameras at various locations on a linear camera
locus. In this manner, the system is able to create intermediate
images simulating the image which would be taken by a camera
positioned between positions of real cameras. This system depends
upon two-dimensional projection from three-dimensional data; i.e.,
calculation of the image which would appear in a viewing plane
based upon data defining the location of objects in the scene in
three dimensions. The system must determine the depth from the real
cameras of each point in the scene.
[0007] To facilitate this determination, the authors propose to use
certain characteristics of a so-called "epipolar image". As further
described below, an epipolar image combines data from multiple
cameras into partial images, each including part of the data from
each camera. With conventional raster-scan video cameras, each
portion of the epipolar image typically includes one scanning line
from each camera of the multiple camera set. In such epipolar
images, features appear as sloping strips or bands. The width and
slope of the bands are related to the depth or distance between the
actual feature and the camera locus. Moreover, it is possible to
determine from the epipolar image which features in the scene
occlude other features, i.e., which features lie to the front,
closer to the cameras and in which features lie to the back. The
authors thus propose to recover the depth of the various points in
the image by using the epipolar image. That depth information, in
turn, is used as part of three-dimensional data, which in turn is
used to project a two-dimensional image simulating the
two-dimensional image which would be captured by a camera at an
intermediate location. This system nonetheless involves all of the
computational complexity required to reconstruct two-dimensional
images from three-dimensional images. Moreover, Takahashi et al
characterize their system only as suitable for generation of the
sterographic holograms, and not for generation of images to be
viewed directly by a viewer.
[0008] Accordingly, despite all of this effort in the art, there
still remains a substantial, unmet need for improved methods of
synthesizing and displaying an image of a scene from an arbitrary,
synthesized viewpoint. In particular, there are substantial, unmet
needs for improved methods of providing telepresence, including
display of images from different viewpoints as the users head moves
in real time. In particular, there are needs for a telepresence
system which can provide images to multiple users
simultaneously.
SUMMARY OF THE INVENTION
[0009] The present invention addresses these needs.
[0010] One aspect of the present invention includes a method of
providing an image from an arbitrary virtual viewpoint. Methods
according to this aspect of this invention include the steps of
providing a plurality of discrete two-dimensional images
corresponding to the image of a scene observed from a plurality of
discrete viewpoints on a predetermined viewpoint locus. The methods
further include the step of transforming the plural discrete images
into a set of two-dimensional transform images, each including some
information from a plurality of the discrete images. In each
discrete image, all of the information is taken from a single
viewpoint. Thus, each discrete image has a first dimension
corresponding to a first real dimension of the actual scene (such
as the horizontal dimension) and a second real dimension
corresponding to the second real dimension of the scene (such as
the vertical dimension). Each transform image includes some
information from plural discrete images, and desirably from all of
the discrete images each representing a different viewpoint. In
each transform image, one dimension desirably, corresponds to a
real dimension of the scene, whereas the second dimension desirably
corresponds to viewpoint. That is, information from different
discrete images at different viewpoints is disposed at different
locations in the second dimension of the transform image. Stated
another way, information from selected parts of each discrete image
is mapped to selected portions of each transform image according to
a preselected mapping scene. For example, where the discrete images
include rows of pixels extending in a first image direction, these
rows being disposed one atop another in a second image direction,
the transform images may be epipolar images, each including a
plurality of line sets. Each line set may incorporate one scanning
line from each discrete image. All of the scanning lines in each
line set are taken from the same location in the second dimension
of their respective discrete images. The lines from the various
discrete images are disposed side-by-side in the second or
viewpoint dimension of the epipolar image in an order corresponding
to the viewpoints of the discrete images from which such lines were
taken. Thus, within each line set of the epipolar image, the first
dimension corresponds to the first real dimension of the scene and
the second dimension corresponds to viewpoint location.
[0011] The method further includes the step of selecting at least
one virtual viewpoint, typically including a virtual viewpoint
location and a virtual viewpoint direction. Once a virtual
viewpoint has been selected, a two dimensional virtual viewpoint
image, corresponding to the image which would be observed looking
from the virtual view location in the virtual view direction is
synthesized. This synthesis is accomplished by selecting
information from a plurality of the two-dimensional transform
images according to a selection scheme which varies with the
selected virtual viewpoint, i.e., with virtual view location,
virtual view direction or both and combining the so-selected
information, as by mapping the selected information to the new
image. Preferably, this mapping is performed directly from each
transform image to a part of the virtual viewpoint image. As
further discussed below, the selection desirably includes the step
of selecting a base viewpoint on the discrete viewpoint locus,
i.e., selecting a base viewpoint from among the discrete viewpoints
of the discrete images or a viewpoint interpolated between discrete
images. Desirably, the selected base viewpoint is a viewpoint close
to the virtual viewpoint. The base viewpoint may be used in mapping
from transform images into the virtual viewpoint image.
[0012] Where the transform images include an epipolar image, having
plural line sets as discussed above, the step of synthesizing the
virtual viewpoint image may be performed by forming each line of
the virtual viewpoint image independently, one such line being
formed from each line set of the epipolar image. Formation of each
line may include the steps of selecting or forming a base line
within the line set corresponding to the base viewpoint, selecting
pixel data in the base line, transforming this pixel data so that
the transformed data represent pixel data taken from the virtual
viewpoint. For example, the pixel data may be transform by
compressing them in the dimension along the line to compensate for
a different view direction. The selected transformed pixel data
from the base line is incorporated into the line of the virtual
viewpoint image. Ordinarily, the pixel data selected from the base
line does not include all of the information necessary to fill out
the line of the virtual viewpoint image. Thus, the step of forming
each virtual viewpoint image line further includes the step of
selecting supplementary pixels from one or more additional lines of
the same line set. These supplementary pixels are adjacent to one
or both ends of the base line. Data from the supplementary pixels
is incorporated at one or both ends of the virtual viewpoint image
line. All of the lines of the virtual viewpoint image may be formed
in the same way so as to provide a full image corresponding to the
image which would be seen from the selected virtual viewpoint.
[0013] These steps can be used in providing telepresence. In a
telepresence system, the step of selecting a virtual viewpoint
includes the step of detecting the disposition of an observer as
the observer moves and selecting the virtual viewpoint so as to
correspond to the viewpoint of the observer. Also, in a
telepresence system, the method further includes the step of
displaying the virtual viewpoint image to the observer
substantially in a real time. That is, the steps of detecting the
disposition of the observer, synthesizing a virtual viewpoint image
and displaying that image are performed substantially in real time,
as the observer moves, so that the observer sees the correct
virtual viewpoint image for a new observer disposition as
substantially immediately as the observer moves to the new
disposition. For stereoscopic images, two virtual viewpoint images
are generated for each observer disposition, these images being
taken from slightly different virtual viewpoints corresponding to
the dispositions of the observer's eyes.
[0014] In methods according to the foregoing aspects of the
invention, each virtual viewpoint image is derived from
two-dimensional images. There is no need to reconstruct the full or
there-dimensional scene, or to calculate a projection from full
three-dimensional scene-specifying data onto a two-dimensional
image plane. Indeed, as further discussed below, the manipulation
of pixel data required to construct the virtual viewpoint image
preferably include only simple mapping of pixel data and lines of
pixel data with some linear combinations or interpolations of pixel
data. These steps can be carried out rapidly even where the images
to be handled include large amounts of data as encountered in
common video images. The system does not require any mathematical
modelling or knowledge of the elements in the scene to be depicted.
The discrete images can be any images of a scene, whether
computer-generated or taken by a real cameras or some combination
of the two. The discrete images need not be captured in real time
during viewing. The discrete images or, the transform images, may
be prerecorded. Further, the discrete images need not be static.
Thus, the discrete images may be provided as sets, each such set
incorporating discrete images captured at a given instant as, for
example, frames or fields captured simultaneously by a plurality of
video cameras. New transform images may be created for each such
set. Here again, the step of creating the transform images from the
discrete images need not include any complex, three-dimensional
projection, but may instead may include simple concatenation of
pixel data. Thus, methods according to this aspect of the present
invention can be applied to provide telepresence in a dynamic
environment, i.e., the illusion that the observer is actually
present in a scene including moving objects. The observer sees both
motion of the objects and apparent motion caused by movement of his
or her viewpoint relative to the scene.
[0015] A further aspect of the present invention provides
additional methods of synthesizing an image of a scene
corresponding to the image which would be observed from a virtual
viewpoint. Methods according to this aspect of the invention also
include the step of providing a plurality of discrete images
corresponding to the images of the scene observed from plural
discrete viewpoints on a viewpoint locus, each such discrete image
including an array of pixel data in first and second dimensions.
Methods according to this aspect of the invention, also include the
step of deriving transform images from the discrete images. The
transform images desirably include a first epipolar image. Each
epipolar image desirably includes a plurality of line sets. Here
again, each line set includes one line of pixel data in the first
dimension from each discrete image. All of the lines in each line
set correspond to the same location in the second image direction.
The lines of pixel data within each such line set are ordered in an
order corresponding to the order of the discrete viewpoints from
which the discrete images were taken.
[0016] A method according to this aspect of the invention
preferably includes the step of providing virtual viewpoint image
pixel data for a plurality of virtual viewpoint image pixel lines
extending in the first image dimension and offset from one another
in the second image dimension. The pixel data for the synthetic
image lines is provided by associating each line of the virtual
viewpoint image with a lineset of the first epipolar image
corresponding to the location of the that line in the second image
dimension. For each pixel within each such virtual line, synthetic
pixel data is derived from other pixel data in the associated
lineset.
[0017] For example, where the first dimension is the horizontal
image dimension and the second image dimension is the vertical,
each lineset will include lines taken from each discrete image at
the same vertical location. Each line of the virtual viewpoint
image at a particular vertical location is associated with the
lineset at that vertical location and the pixel data in the virtual
viewpoint image line is derived from the pixel data of the
so-selected lineset. Preferably, the step of deriving the synthetic
pixel data for the virtual viewpoint image line includes the steps
of selecting a plurality of lines within the associated lineset
corresponding to discrete viewpoints in the vicinity of the
synthetic viewpoint and deriving the synthetic pixel data from the
pixel data in the so-selected lines of the lineset. The pixel data
for each synthetic pixel may be derived by choosing a plurality of
pixels in these selected lines adjacent the position of the
synthetic pixel in the first image dimension and deriving the
synthetic pixel data in the chosen pixels of the selective lines.
The selected lines in the lineset desirably include lines
corresponding to discrete viewpoints bracketing the virtual
viewpoint. For each synthetic pixel, the chosen pixels have first
dimension locations bracketing the locations of the synthetic pixel
in the first image dimensions Stated another way, the chosen pixels
of the selected lines are the pixels surrounding the location of
the synthetic pixel in question in the transform image, i.e., in
the lineset of the epipolar image. The step of deriving pixel data
from these chosen pixels of the selected lines may include the step
of interpolating the pixel data of these chosen pixels. Such
interpolation can be performed readily, using standard video
processing hardware and interpolation software commonly used for
other purposes. Methods according to this aspect of the present
invention constitute a special case of the more general methods
discussed above. That is, methods according to this aspect of the
invention are normally used only to provide images for virtual
viewpoints interpolated between the discrete viewpoints of the
discrete images on the discrete image. These interpolated
viewpoints can be displayed to a viewer or also can be used as base
images in the more general system discussed above.
[0018] A further aspect of the present invention incorporates the
realization that data arranged in the two-dimensional transform
images discussed above, such as the epipolar images, can be
compressed and stored or transmitted in compressed form, and then
subsequently decompressed for use in image synthesis steps as
described above. The degree of data compression achievable through
compression of the transform images is, in many cases, greater than
the degree of data compression achievable by compressing the
original, discrete images using comparable compression algorithms.
Thus, it is advantageous to store and transmit the images in the
form of compressed transform images, such as compressed epipolar
images, and then decompress the transform images. Because the
transform images are two-dimensional images and desirably images
consisting of data for plural pixels or lines, the transform images
can be compressed and decompressed using essentially the same
methods as used for ordinary video images as, for example,
run-length encoding, MPEG and JPEG compression techniques.
[0019] Still further aspects of the invention incorporate the
realization that the transform images, such as the epipolar images,
can be combined with one another. Thus, methods according to this
aspect of the invention can provide a first set of two-dimensional
transform images such as a first epipolar image derived from one
set of discrete images and transforming the plural discrete images
of the second set into a second transform image such as a second
epipolar image and then combining the two transform images with one
another to yield a combined transform image. The step of combining
the transform images may include the step of combining pixel data
of each lineset in the first epipolar image with a corresponding
lineset of the second epipolar image. Such combination can be
performed using essentially the same techniques as are used to
combine plural video images in conventional television equipment.
For example, the combining step may include the step of deriving
pixel data for each pixel in the combined lineset by combining
pixel data for the corresponding pixel data of the lineset from the
first image with the pixel data from the corresponding pixel in the
lineset from the second image according to a combining formula
which varies from pixel to pixel. The combining formula may be a
function of the pixel data in one or both linesets as, for example,
in so-called "chroma keying".
[0020] These and other objects, features and advantages of the
present invention will be more readily apparent from the detailed
description of the preferred embodiments set forth below, taken in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a diagrammatic, perspective view showing portions
of a system in accordance with embodiment of the invention in
conjunction with a real scene to be depicted.
[0022] FIG. 2 is a functional block diagram depicting further
portions of the system of FIG. 1.
[0023] FIG. 3 is a further functional block diagram depicting still
further portions of the same system in conjunction with
observers.
[0024] FIG. 4 is a schematic representation of several discrete
images as initially captured by the system.
[0025] FIGS. 5 and 6 are schematic representations of linesets
utilized in operation of the system.
[0026] FIG. 7 is a diagrammatic plan view depicting various real
and virtual viewpoints used in the system.
[0027] FIG. 8 is a view similar to FIG. 4 but depicting a virtual
viewpoint image as created by the system.
[0028] FIG. 9 is a chart depicting, on an enlarged scale, a portion
of the lineset depicted in FIG. 6.
[0029] FIG. 10 is a further diagrammatic view of the line set
depicted in FIG. 9, depicting a further operation.
[0030] FIG. 11 is a view similar to FIG. 7 but depicting a further
virtual viewpoint.
[0031] FIG. 12 is a further view similar to FIG. 10 but depicting
the operations required for the virtual viewpoint of FIG. 11.
[0032] FIG. 13 is a view similar to FIG. 11 but depicting a
different virtual viewpoint.
[0033] FIG. 14 is a view similar to FIG. 12 but depicting the
operations required for the virtual viewpoint of FIG. 13.
[0034] FIG. 15 is a diagrammatic view depicting a further
embodiment of the system.
[0035] FIG. 16 is a diagrammatic top view depicting certain
structures utilized in a practical test of certain aspects of the
invention.
[0036] FIGS. 17a, 17b and 17c are actual photographic images as
initially captured with the equipment of FIG. 14.
[0037] FIG. 18 is a depiction of lineset generated from the images
captured by the apparatus of FIG. 14.
[0038] FIG. 19 is a depicting of the lineset of FIG. 16 after
modification.
[0039] FIG. 20 is an actual image captured at one position of the
apparatus of FIG. 14.
[0040] FIG. 21 is a synthesized image, derived from other images
captured by the same apparatus, to depict the image which would be
captured from the same viewpoint as FIG. 20.
[0041] FIG. 22 is a view similar to FIG. 14 but depicting
operations in accordance with another embodiment of the
invention.
[0042] FIG. 23 is a view similar to FIG. 13 but depicting a virtual
viewpoint associated with the embodiment of FIG. 22.
[0043] FIG. 24 is a diagrammatic perspective view of a viewpoint
locus in accordance with yet another embodiment of the
invention.
[0044] FIG. 25 is a diagrammatic view of a lineset associated with
the viewpoint locus of FIG. 25.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] Apparatus in accordance with one embodiment of the present
invention includes a plurality of video cameras 100 arranged on a
horizontal curvilinear locus 102 which in this embodiment is a
circle having a center of curvature 104. The cameras are arranged
so that each camera 100 points substantially radially outwardly
away from center 104. That is, the optical axis 106 of each camera
is a radial line passing through the center 104, and so that the
lens of each camera is positioned at the same radial distance from
the center. Each of cameras 100 is positioned at a different
viewpoint. Each viewpoint may be denoted by a viewpoint location
from an index or zero degree reference line 108. As illustrated,
360 individual video cameras are provided, one per degree, around
the entire periphery of circle 102. Each camera 102 may be
essentially any type of video camera as, for example, a
conventional raster-scanning image tube type or a solid state type
such as a CCD. As further discussed below, the images captured by
the cameras will ultimately be converted to pixel data representing
pixels in horizontally, oriented lines. For that reason, it is
preferred to provide the cameras so that the real elements
constituting the raster lines of the camera are already aligned in
the horizontal direction, i.e., parallel to the plane of locus 102.
Alternatively, each image can be rotated about the axis of the
camera using conventional, well-known video processing techniques,
to provide the image restated in a series of horizontal lines. All
of cameras 100 are synchronized, so that each camera captures a
frame at the same time. As illustrated in FIG. 1, the camera set is
capturing a real scene, including objects such as a flag pole and
flag 110, utility poles 112, 114 and 116 and sign post 118. These
and other objects may entirely surround the camera array, and
include moving objects as well as still objects.
[0046] Cameras 100 are connected to a precorrection and epipolar
image formation unit 120 (FIG. 2), so that each camera 100 feeds an
individual image into this unit. Unit 120 is arranged to correct
each of the individual images and then to transform the group of
images into an epipolar image comprising a series of linesets as
discussed below. Each including some of the information from each
one of the incoming images.
[0047] Unit 120 is connected to a compression unit 124. Unit 120
feeds each of the linesets to the compression unit. Compression
unit 124 incorporates apparatus for compressing two-dimensional
images using standard techniques commonly applied to standard video
images. Such techniques can be applied directly to the linesets
produced by units 120. The compression unit 124 is connected to
storage, reproduction and transmission unit 126. This unit may
incorporate any available form of equipment for storing,
reproducing or transmitting data such as, for example, equipment
for modulating the data onto a suitable carrier and broadcasting it
or transmitting it through wire or fiber optic links, or equipment
for recording the data on conventional media such as magnetic or
optical storage media. Unit 126 treats each of the compressed
linesets received from compression unit 124 independently.
[0048] Unit 126 is linked via a one-way communications channel 128
to reception and playback unit 130 (FIG. 3) adjacent the location
of observers who will view the images produced by the equipment.
Communications channel 128 need only provide one-way communication
of the compressed aligned sets; it need not provide instantaneous
communications. For example, where the compressed linesets are
recorded by unit 126 on media such as tapes or disks,
communications channel 128 may include distribution of the physical
media by conventional channels as, for example, sale of the same in
stores. Alternatively, communications channel 128 can be arranged
for substantially instantaneous, real time transmission of the
compressed linesets as, for example, in a conventional broadcast,
cable or fiber channel. Also, although only one playback and
reception unit 130, and only one group of associated equipment is
illustrated in FIG. 3, it should be appreciated that any number of
such playback and reception units, and the associated components
discussed below, can use the same data from unit 126 either
simultaneously (where the communication channel operates
instantaneously), or at different times (where the channel provides
delay, such as distribution of recorded media).
[0049] Playback and reception unit 130 is arranged to recover data
from communications channel 128 as, for example, by demodulating
broadcast or cable signals or playing back recorded media, so as to
provide the linesets in compressed form substantially as provided
by compression unit 124. Here again, each lineset is handled
independently. Decompression unit 132 is arranged to reverse the
compression applied by compression unit 124 to each lineset. Here
again, the conventional techniques used to process ordinary
two-dimensional video images can be employed. Compression unit 132
provides the decompressed data representing the linesets to a
virtual image synthesis unit 134.
[0050] The system further includes display devices 138, 140, 142
and 144. As illustrated, display devices 138 and 140 are
incorporated in a helmet or goggles unit 145 which can be used by
an observer 146, the display devices 138 and 140 being arranged to
display their respective images to the two eyes of the observer
146. Likewise, display devices 142 and 144 are mounted to a helmet
unit 148 which is worn by an observer 150. Devices 142 and 144 are
arranged to display their respective images to the right and left
eyes of the observer, respectively. The display devices and helmets
may be conventional units of the type employed for so-called
"virtual reality" displays. Typically, these include small cathode
ray tubes or active matrix displays mounted to the helmet, with
appropriate eye pieces linking each such display to the eye of the
observer.
[0051] Helmet unit 145 includes a magnetic locating transmitter
152, whereas unit 158 includes a similar magnetic locating
transmitter 154. The system further includes an observer viewpoint
detection unit 156. The observer viewpoint detection unit detects
the magnetic fields from transmitters 152 and 154 and determines
the positions and orientations of each of the helmet units 145 and
148. Magnetic location and orientation detection systems per se are
well-known, and are used, for example, in virtual reality systems
and in systems for detecting the position and orientation of a
pilot's helmet in military aircraft applications. Examples of such
detection systems include those described in U.S. Pat. Nos.
4,613,866; 5,109,194 and 4,054,881. Any other operable location and
orientation detection system, such as an optical, mechanical or
electromechanical system can be used instead of the magnetic
system. Viewpoint detection unit 156 provides a signal to virtual
image synthesis unit 134 representing the viewpoint of each of
display devices 138, 140, 142 and 144. This viewpoint signal is
derived from the location and orientation of the associated helmet
145 or 148, and from information concerning the position and
orientation of each display device with respect to the associated
helmet. Thus, the viewpoint for display device 140 will differ from
that for display device 138, this difference corresponding to the
difference in viewpoints of the observer's two eyes. However, these
two viewpoints will change in unison as observer 146 moves or
turns. Likewise, the viewpoint for display device 142 and 144 will
differ from one another, but viewpoints 142 and 144 will change in
unison as observer 150 moves and turns.
[0052] The observer viewpoint signals provided by unit 156 denote
each viewpoint as position and orientation of the observer
associated with each display device, i.e., the position of the
observer's eye, in terms of an observer locus 158 corresponding to
the real locus 102 that was originally used for cameras 100. Thus,
each viewpoint is provided in terms of observer viewpoint radius
from an observer center point 160, to the eye of the observer and
an observer viewpoint angle 166 from an observer index line 164
corresponding to the index line 108 of the real camera locus. Also,
the observer viewpoint detection unit determines an observer step
angle 168 between the optical axis of the observer's eye and the
radius from center point 160 to the eye. This angle is determined
based upon the position of the observer's head, from the movements
of helmet 145 as reported by magnetic transmitter 152. If desired,
the system can also incorporate devices for detecting movements of
the eye relative to the head, also called "pupillary tracking"
devices, to provide an even more accurate eye position.
[0053] As further described below, virtual image synthesis unit 134
converts the linesets received from compression unit 132 into
virtual images for display by each of the display devices. Thus, a
first virtual image will be fed to display device 140 whereas the
second, different virtual image will be fed to display device 130
and still other virtual images will be passed to display devices
142 and 144.
[0054] In operation, each camera 100 captures a conventional,
two-dimensional video image of the scene. As indicated in FIG. 4,
each video image includes pixels in a two-dimensional array,
including a first or horizontal image direction H and a second or
vertical image direction V. As best appreciated with reference to
FIG. 7, the position of each pixel in the first or horizontal
direction H represents the offset angle B between the optical or
view axis 106 of the image (the viewing axis of the camera which
captured the image) and a ray 180 from an object in real space to
the particular pixel. Stated another way, the horizontal or first
image dimension represents a real dimension of the viewed scene,
namely, the offset angle or angular displacement of the object
represented in a particular pixel from the optical axis 106 of the
camera. Similarly, the location of any pixel in the image
represents the vertically directed offset angle (not shown) between
the optical axis 106 and the ray from the real object represented
by the pixel. Thus, as shown in FIG. 4, image 182.sub.1, from
camera 100.sub.1 includes conventional representations of light and
dark objects on a two-dimensional field, representing a projection
of the real, three-dimensional image onto an image plane
perpendicular to optical axis 106.sub.1 of camera 100.sub.1.
[0055] In FIG. 4, and in the succeeding figures, the images are
shown as pictorial images, i.e., relatively dark areas in the real
scene being shown as dark areas in the image and so on. This
representation is used solely for ease of understanding. In fact,
the video images produced by the cameras incorporate electronic
signals representing the optical qualities of the various pixels in
the standard manner of video signals. The particular optical
qualities will vary with the type of video images. In a monochrome
system, each pixel may have associated with it only a single analog
signal level or digital number representing brightness. In a color
system the data for each pixel may include analog or digital values
for several parameters, such as luminance and a pair of chrominence
parameters, or else may include separate primary color brightness
signals such as red, green and blue. In the conventional fashion,
the pixels constituting each image are arranged in lines, the lines
extending in the first image direction. For example, image
182.sub.1 includes 625 pixel lines extending in the first image
direction, the first such pixel line 184.sub.1,1 representing the
top of the image and the last such pixel line 184.sub.1,625
representing the bottom of the image. Likewise, the image from
viewpoint or camera 100.sub.2 includes a similar array of pixel
lines starting with top pixel line 184.sub.2,1 and ending with
bottom pixel line 184.sub.2,625 and so on, through the image from
360th camera or viewpoint 182.sub.360, which include pixel lines
184.sub.360,1 through 184.sub.360,625.
[0056] The real physical components utilized to provide images
182.sub.1 through 182.sub.360 ordinarily suffer from some
distortion. That is, the first image dimension or horizontal image
dimension H may not exactly represent the offset angle B (FIG. 7)
ray and the optic axis 106 and the vertical dimension may not
exactly represent the vertical rear angle. Unit 120 (FIG. 2) is
arranged to apply standard distortion correcting techniques to
substantially remove these effects. As is well known in the video
processing arts, a distorted image can be corrected by applying an
appropriate mathematical mapping based upon prior knowledge of the
distortion, the data from the various pixels is remapped so that
the data originally included in a particular pixel of the distorted
image is transposed into a different pixel in the corrected image.
Image correction techniques of this nature are well-known in the
standard video arts, and hence are not further described herein.
Unless otherwise indicated, references hereinbelow to images 182,
or to the pixels from such images, should be understood as
referring to the corrected versions.
[0057] After distortion-correcting each of images 182 captured by
cameras 100 at a particular time, epipolar image unit 120 reorders
the data in all of these images 182 into an epipolar image
incorporating a number of linesets. One such lineset 186 is
depicted schematically in FIG. 5. The number of linesets 186 in the
epipolar image is equal to the number of lines in each of the
starting images. Thus, using the starting images shown in FIG. 4,
each of which contains 625 lines, each epipolar image will include
625 such linesets. Each lineset includes pixel data from all of the
original images 182 at the same location in the vertical or second
image dimension. That is, the Nth lineset includes the Nth line of
pixels from each image. For example, lineset 186.sub.27 in FIG. 5,
includes the 27th line from image 182.sub.1 (line 184.sub.1,27);
the 27th line from image 184.sub.2 (line 184.sub.2,27) and so on
through the 27th line from image 184.sub.360. These lines are
ordered in an order corresponding to the order of the viewpoints of
the various images, i.e., line 184.sub.1,27, 184.sub.2,27 . . . ,
184.sub.360, 27. Each of the other linesets, from 186.sub.1 through
186.sub.625 has the lines arranged in the same order.
[0058] Within each lineset, as initially provided and as seen in
FIG. 5, the lines of pixels extend in a first epipolar direction F
and the lines are ordered in a second epipolar direction S. Unit
120 modifies each lineset to the form shown in FIG. 6. Thus, unit
120 applies an initial offset of M pixels between each pair of
adjacent lines in the image;
M=(R/B*).times.P
[0059] where: R is the difference in the viewpoint angle A between
the viewpoints of two successive images, i.e., the difference in
angle A between camera 100.sub.n and camera 100.sub.n+1; B is the
horizontal field view of each camera, i.e., the difference between
the maximum and minimum values of the horizontal offset angle B
between ray 180 and the axis of the image and P is the number of
pixels per line in the image. In effect, the offsetting process
removes the effect of the differing camera angles and hence the
differing images axis angles 106 from the epipolar image linesets.
The relative positions of the pixels in the offset epipolar image
are the same as if all of the cameras were pointed in the same
direction from the different viewpoints. In the modified lineset
188 (FIG. 6) the first dimension F corresponds to direction of the
ray to the depicted feature relative to the line 108. That is, in
the modified lineset, the coordinate for the first dimension F to
any pixel corresponds to the azimuth angle Z, i.e., the angle
between the index line 108 and the ray 180 from the pixel in
question to the real object imaged. For pixels taken from any
particular image 182n from camera 100n, the azimuth angle will be
the sum of the viewpoint location A.sub.n from the reference line
to the axis of the image and the offset angle D from the image 106
to the rear.
[0060] The second dimension S of each modified lineset 188
corresponds to the viewpoint, i.e., the particular image from which
the lines were derived. As seen in FIG. 6, the various features in
real space, depicted found in the individual discrete images 182
form linear features in the epipolar linesets. The flag on flagpole
110 forms linear feature 110' whereas telephone pole 114 forms
stripe 114'. Stripe 110' is substantially vertical. This indicates
that the ray azimuth does not change appreciably with viewpoint,
i.e., that the flag is far away. The stripe representing an object
at infinite distance has a substantially constant ray azimuth and
hence substantially zero change in a first direction F throughout
its entire extent within the epipolar image lineset. By contrast,
stripe 114' representing a portion of utility pole 114 has a
substantial slope or change in the first dimension or ray azimuth
with viewpoint or second dimension S. The physical meaning of this
change is that there is a large degree of parallax causing the
apparent position of the telephone pole to shift as the viewpoint
from which the image is taken shifts. The initial linesets 186
(FIG. 5) share the same properties. That is, stripe 110' as seen in
the initial lineset has a slope substantially less than that of
stripe 114'. However, the slopes of both stripes are exaggerated
substantially in FIG. 5 by the effect of camera rotation, which is
removed in FIG. 6.
[0061] Although only two stripes are illustrated in FIGS. 5 and 6,
every feature of the images captured by cameras 100 will be
reproduced as a strip-like feature in the linesets of the epipolar
images. Thus, each lineset would include far more features than are
illustrated. Also, only one lineset is illustrated in each of FIGS.
5 and 6. The actual epipolar images again includes a lineset for
every horizontal scanning line in the original images. The epipolar
image in this arrangement includes all of the information captured
by the original cameras. Once again, the linesets are depicted in
graphical form in FIGS. 5 and 6, and indeed can be displayed like
any other two-dimensional image. However, it should be appreciated
that manipulation of the data to form the linesets normally will be
accomplished in digital form. Thus, the data for each pixel in each
image may be stored at an address representing the location of the
pixel within the original image 182 (FIG. 4). The data can be
reformulated into the epipolar image linesets merely by reassigning
addresses to the data constituting each lineset from memory in a
new order, so that the pixels from one line of a first image will
read out followed by the pixels from the same line in the next
image and so on. Stated another way, it is not essential that the
physical storage units used to store the data have structures
corresponding to the original lines of the image or to the epipolar
image; the image structure may be specified entirely by data and
address values stored in memory. However, memory structure such as
those commonly referred to as VRAM or Video Random Access Memory,
adapted to receive and pass data in the form of a two-dimensional
raster can be utilized advantageously in handling and processing
the epipolar image linesets.
[0062] The foregoing description refers to formation of a single
epipolar image, including only one series of 625 linesets. This
process is repeated continually as new images are captured by
cameras 100. Preferably, all of the cameras 100 operate in
synchronism, so that each camera captures a new frame or a new
field simultaneously with the other cameras. In this regard, unit
120 may form the epipolar images in real time, so that each
epipolar image is formed at substantially the same time as the
initial images captured. Alternatively, the epipolar image
formation unit may operate on previously stored images captured by
cameras 100. Thus, the original discrete images captured by the
individual camera may be stored on conventional tape, disks or
other media, preferably along with timing signals so that the
various stored images can be synchronized, and the stored images
can be played back and converted to epipolar images.
[0063] The epipolar images are then passed to compression unit 124.
As aforementioned, compression unit 124 includes conventional video
compression hardware and software. The linesets may be compressed
using essentially the same algorithms and techniques as employed
compression of standard video images. Each lineset can be treated
essentially as the equivalent of a field of video information. Each
such lineset may be compressed by techniques involving only
manipulation of the data within the individual lineset as, for
example, run length encoding to compress lines of constant-value
data into individual data words denoting the length of the constant
value line. Alternatively or additionally, corresponding linesets
in successive epipolar images may be compared with one another to
detect changes, and a compressed signal incorporating only the
change data may be provided. Examples of the former system include
the Joint Photographic Experts Group or JPEG standard for still
images, whereas an example of the latter includes the Motion
Picture Experts Group or MPEG standard.
[0064] The compressed information from compression unit 124 is
passed to the reproduction and transmission unit 126. Here again,
the various linesets of each epipolar image are maintained separate
from one another. Thus, the data relating to lineset 186.sub.27 are
handled separately from the data relating to lineset 186.sub.28 and
so on. Again, the data is in essentially the same form as standard,
compressed two-dimensional fields, one such compressed field
corresponding to each lineset, and thus conventional techniques may
be used. As mentioned above, the data transmission may include
either instantaneous transmission or recordation of the data onto
conventional media.
[0065] The data is received by playback and reception unit 130,
either simultaneously with its processing by unit 126 or later in
the case of recorded data. Unit 130, in conjunction with
decompression unit 132, recovers or plays back the data to provide
a series of epipolar images, effectively reversing the effects of
compression and storage units 124 and 126. The internal structure
and algorithms used by decompression unit 132 and playback and
reception 130 will be determined by the precise structure of units
124 and 126. Here again, conventional algorithms, such as those
used to process conventional two-dimensional raster images can be
employed. Decompression unit 132 thus provides the series of
epipolar images, each including 625 modified linesets 188 as
discussed above with reference to FIG. 6. These epipolar images are
provided as a series in time so that the timing between epipolar
images corresponds to the timing between capture of the original
image sets by cameras 100.
[0066] Virtual image synthesis unit 134 transforms the epipolar
images into a series of visual images for the display devices
associated with each observer, based upon the viewpoint information
for that display device provided by observer viewpoint detection
unit 156. As noted above, this information includes the radial
distance from center point 160 of the observer frame of reference
to the observer's eye associated with the display device; the
observer viewpoint angle 166 between observer index line 164 and
the radial line 162 from center 160 to the observer's eye; and the
observer skew angle 168 between the central axis of the observer's
eye and the radial line 162. This viewpoint data, taken in the
observer frame of reference, defines a virtual viewpoint in the
camera frame of reference. That is, for each viewpoint detected,
the system forms a virtual image corresponding to the image which
would have been captured by a camera at a virtual viewpoint in the
camera frame of reference at a virtual viewpoint 190 (FIG. 7)
having a radial distance 193 from center 104 equal to the radial
distance from center 160 of the observer's eye; having a virtual
viewpoint location angle 191 from index line 108 (FIG. 7) equal to
the observer viewpoint location angle 166 from index line 164 (FIG.
3) and having a viewing axis 195 at a virtual viewpoint skew angle
192 to the radial line 193 corresponding to the observer viewpoint
skew angle 168. The system synthesizes a virtual image 200 (FIG. 8)
which would have been captured by a camera disposed at the virtual
viewpoint 190. In each case, the system constructs each line of the
virtual image from the corresponding lineset in the epipolar image.
Each virtual image, like each real image captured by each one of
the cameras 100, has a first or horizontal dimension corresponding
to the angle B between the axis of the image and the ray to the
object represented by the pixel and again has a vertical dimension
corresponding to the vertical angle (not shown) between the image
axis and the ray. Here again, each virtual image 200 includes lines
202 of pixels 204, the lines 202 being ordered in the same manner
as the lines 184 of the original images 182. Image synthesis image
134 forms each line 202 in virtual image 200 from the corresponding
lineset 188 in the epipolar image. That is, line 202.sub.n is
reconstituted from lineset 188.sub.n, incorporating information
from the Nth line of each original image 182.
[0067] In a first step of the reconstruction process, the system
selects a base image, and hence base lines of pixels 184s, for
which the viewpoint location angle A corresponds to the viewpoint
location angle 191 of the virtual viewpoint 190. That is, the
system uses the second dimension information S to locate the
desired line of pixels for use in the synthesis. Where the
viewpoint location angle 191 is intermediate between the viewpoint
location angles A.sub.n and A.sub.n+1 of the discrete images 182,
the system synthesizes an intermediate line of pixels by
interpolation between the pixel values for corresponding pixels in
adjacent lines. Thus, the viewpoint location angle 191 for the
virtual viewpoint may lie between the viewpoint location angles A
for images 182.sub.n and 182.sub.n+1 (FIG. 7). In this case, the
values constituting the pixel data in line 184s are derived by
interpolation between the corresponding values in lines 184.sub.n
and 184.sub.n+1. Such interpolation can be performed using standard
techniques used in resolution enhancement of two-dimensional video
raster images. One simple technique involves direct linear
interpolation between the values of the pixel data in the adjacent
lines such that D.sub.s=D.sub.n+K(D.sub.n+1-D.- sub.n) where:
[0068] D.sub.n is the data in a pixel in line 184.sub.n;
[0069] D.sub.n+1 is the data in the pixel at the same position F in
line 184.sub.n+1;
[0070] D.sub.s is the data of the pixel in line 184.sub.s at the
same position F
[0071] K is defined by:
K=(la.sub.191-A.sub.n)/(A.sub.n+1-A.sub.n)
[0072] That is, pixels directly above and below one another as seen
in the offset epipolar image are combined. For a few pixels at each
end of line of line 184.sub.s, the pixel value in one of lines
184.sub.n and 184.sub.n+1, will be missing. In this case, the pixel
value present in the other line can be used directly in line
184.sub.s. The values in each pixel of base view line 184.sub.s
will be closer to the values in line 184n if the location angle 191
of the virtual viewpoint is close to the location angle A.sub.n of
camera loon. This interpolation step in effect generates the pixel
lines for a base image or virtual viewpoint image 190a at the
correct location angle 191 but still disposed on the camera locus
102 (FIG. 7) and still having a directly radial view direction,
i.e., a skew angle 192 of zero.
[0073] The original pixel lines 184 of image 188 represent zero
skew angle. All of the images used to form the epipolar image were
images taken with radially directed view axes. Each line 184s,
derived by interpolation between pixel lines of the epipolar image,
also represents a zero degree skew angle.
[0074] Image synthesis unit 134 further modifies interpolated line
184s to show the effect of a non-zero skew angle. To create a new
line of pixels 210 representing the desired virtual image or
non-zero skew angle image, the system shifts the pixel data in
interpolated line 184s by a preselected number J pixel positions
where;
K=(F/SA.sub.192).times.P
[0075] B is the field view of the original camera which captured
the pixel line, i.e., the difference between the maximum and
minimum values of image angle B;
[0076] SA.sub.192 is the skew angle 192; and
[0077] P is the number of pixels in the line. Thus, where the skew
angle is such that the new line 210 is shifted to the right, the
system begins to create the new line 210 by copying the Jth pixel
in line 184 (J pixels from the left-hand end of the line as seen in
FIG. 10) into the first pixel position of line 210, the J+Ith pixel
of line 184s into the second pixel position of line 210 and so on.
This process continues until the system reaches the (P-J)th pixel
of line 184s, which is the last pixel in that line. To provide the
last J pixels in line 210, the system copies the pixel data from
the closest pixels in adjacent lines of the offset epipolar image
188.sub.27. Thus, the system selects supplementary pixels 212 so
that the ray azimuth or first dimension F increase progressively
from the end of base view line 184.sub.s. Each supplementary pixel
212 is selected from the line 184 in the epipolar image closest to
base view line 184.sub.s in the second dimension and pixels at the
required ray azimuth. Thus, as illustrated in FIG. 10, the first
few supplementary pixels 212 are copied from line 184.sub.n+1, next
adjacent to the base view line 184s. The next pixels are copied
from line 184.sub.n+2 and so on. Thus, after reaching the last
pixel in the base view line 184s, the system selects new
supplementary pixels by incrementing the ray azimuth or first
dimension F, finding the closest line 184 having a pixel at the
incremented ray azimuth and copying the pixel data from that pixel
into a pixel of virtual viewpoint line 210, and continuing in this
fashion until line 210 has been filled in with P pixels.
[0078] Alternatively, where the skew angle 192 has the opposite
sign, line 210 is shifted in the opposite direction relative to the
base view line 184. That is, line 184 is shifted to the left as
seen in FIG. 10, to the position indicated at 210' in the drawing.
In this instance, the system derives the first J pixels of line
210', adjacent the left-hand end of the base view line 182s from
the closest lines 184 in the image. Thus, the system starts at a
ray azimuth or first-dimension value F equal to the ray azimuth of
the first pixel in base view line 184s minus the skew angle 192.
The system selects the line with the viewpoint location angle S
closest to the virtual viewpoint location angle of 191 base view
line 184s having a pixel at that ray azimuth as, for example, the
line at 184.sub.n-4 having pixel 214 at the required ray azimuth.
The system copies pixels from this line into virtual viewpoint line
210' until it reaches a ray azimuth at which line 184.sub.n-3 has
its first pixel 216, whereupon the system begins copying pixel data
from line 184.sub.n-3, and so on until the system reaches the
beginning of base view line 184.sub.s. Thus, the system maps pixels
from lines 184.sub.n-4 through line 184n and 184s on to virtual
view image line 210'. That line may be displayed as the appropriate
line of the virtual view image 200 (FIG. 8). Thus, where the
lineset used to derive the line was image 188.sub.27, constructed
from the 27th line of each discrete image, the resulting line 210'
will be displayed as the 27th line 202.sub.27 of the virtual view
image 200. The other lines of the virtual view image are
constructed similarly from the other linesets. For any given
virtual view point, the mapping of pixels is the same for every
lineset in the epipolar image and every line of the virtual view
image. Moreover, because this pixel mapping is a one-to-one mapping
wherein the pixel data in one pixel of the epipolar image lineset
is mapped into one pixel of the virtual view image line, the
mapping can be accomplished simply by rearrangement of address
pointers denoting the pixel data in the memory of a computer. There
is no need to manipulate the pixel data values themselves in this
stage.
[0079] As best illustrated in FIG. 11, the virtual viewpoint
190.sub.c may be disposed inside the locus 102 of the discrete
viewpoints, i.e., closer to the center of curvature 104 than the
locus. In physical terms, this means that the observer 146 is
disposed inside the observer viewpoint locus 158. In FIG. 11, the
virtual viewpoint has a skew angle of zero. That is, the virtual
viewpoint 190.sub.c is disposed radially inwardly of locus 102 on a
particular radial line, and the view direction is outwardly, along
the radial line. Stated another way, virtual viewpoint 192
represents the viewpoint which a virtual camera would have if it
were disposed initially at viewpoint 190a and then moved radially
inwardly while maintaining the same orientation. To maintain the
same apparent field of view, the system must incorporate
information from beyond the base image representing viewpoint 190a
on locus 102. Thus, the base image has a preselected field of view
2B, maximum negative ray offset B- to maximum positive ray offset
B+. The end pixels of the interpolated line 184s (FIG. 6)
representing this line in the image at location 190a contain
information only to edge rays 220 and 222. To provide a line
representing the virtual view image at 190.sub.c, with the same
apparent angular field of view from B- to B+, the image must
incorporate pixel data from ray 224 to ray 226. Accordingly, the
system derives each line of the virtual viewpoint image for
viewpoint 190.sub.c by processing the corresponding lineset 188 to
derive the interpolated base pixel line 184s having the appropriate
viewpoint location angle 191 for viewpoint 190a, as above. The
system then forms a virtual view image line 230 from the base pixel
line 184s and from other lines in the lineset 188. One step in this
formation process is to map the pixel data in the entire
interpolated line 184s into a central region 228 of line 230. Line
180s and line 330 as a whole each include P pixel. The central
region 228 includes C pixels where C/P is the proportion of the
final field of view (from edge ray 224 to edge ray 226) encompassed
by the original view (from line 220 to line 222).
[0080] Mapping of the P pixels in line 184s into the C pixels of
central portion 228 may be performed by many standard algorithms.
One simple algorithm is to map pixels 121 from line 184s onto line
228, but to skip one pixel in line 184s after each [P/(P-C)] pixels
have been mapped. A higher-quality algorithm is to calculate the
pixel data for each pixel within central portion 228 by calculating
a spot in the first dimension of line 184 corresponding to the
center point of the pixel in central region 228. Thus, each pixel
of region 228 is treated as including [P/C] pixel positions on line
184s. The Nth pixel of central portion 228 thus is positioned at
N(P/C) pixel positions on line 184s. Where this pixel position is
not an integer, the value for pixel data is calculated by merging
the pixel data from pixel centered on either side of the calculated
position in line 184s, depending upon the proportionate distance
between the calculated position and the center of each pixel in
base line 184.sub.s. For example, a pixel in central region 228
having calculated position 137.7 on line 184.sub.s has a distance
of 0.7 from pixel 137 and a distance of 0.3 from pixel 138 on line
184.sub.s will have pixel data equal to the sum of 0.7 times the
pixel data of pixel 138 and 0.3 times the pixel data of pixel
137.
[0081] In addition to forming the pixels in central region 228, the
system maps pixel data from adjacent lines of the lineset 118 into
end regions 232. In this instance, the system selects (P--C)/2
supplementary pixels for each end region 232. The pixels are
selected at a constant ray azimuth in each end region. That is, all
of the pixels mapped into end regions 232 have ray azimuth equal to
the ray azimuth for the last pixel in the baseline 184s. Thus, the
supplemental pixels mapped into end zone 232a of line 230 have ray
azimuth equal to the ray azimuth of the right-hand end pixel of
line 184s. This corresponds to the azimuth of right-hand edge ray
222. Conversely, the pixels- mapped into end zone 232b of line 230
have ray azimuth equal to that of the left end pixel in baseline
184s, i.e., ray azimuth equal to the azimuth of left edge ray 220.
In effect, the image from the base viewpoint 190a is expanded by
filling in its edges with additional pixel data derived by looking
parallel to the edges. This pixel data of course comes from the
adjacent lines 184 through 184. Typically, one pixel is mapped from
each adjacent line.
[0082] As seen in FIG. 13, a virtual view image can be formed for a
completely arbitrary virtual viewpoint 190 inside discrete
viewpoint locus 102 having any orientation and placement, i.e., any
viewpoint location angle 191 and any skew angle 192, whether zero
or non-zero. For a non-zero skew angle, the system first calculates
the intercept of the virtual viewpoint centerline 195 on the
discrete viewpoint locus 102. That intercept lies at a viewpoint
location angle A* which is readily calculable from the geometry of
the system. The radially directed (zero skew angle) viewpoint 190a
at viewpoint location angle A* is used as a base view for synthesis
of the virtual view at viewpoint 190. Where angle A* is exactly
equal to the location angle of one of the original, discrete views
182, that view will serve as the base view. In the general case
however, angle A* falls between the view point angles of two
discrete views. In this situation, the base view is an interpolated
view. Thus, within each lineset 188 of the epipolar image, the
system forms an interpolated base viewpoint line 184s in the same
manner as described above with reference to FIG. 6 and FIG. 9.
Within each lineset 188, the system then forms a skewed viewpoint
pixel line 210, representing a line from a virtual viewpoint 190b
disposed on locus 102 at the same viewpoint location angle A* but
having a skew angle 192' so that the center line of the view is
directed along the same center line 195 as the desired virtual
view.
[0083] Skewed viewpoint line 210 is formed in exactly the same way
as the skewed viewpoint line 210 as discussed above with reference
to FIG. 10, i.e., by starting at the Jth pixel of base viewpoint
line 184.sub.s and mapping the pixels one for one into line 210
(FIG. 14) until reaching the end of line 184s, then mapping pixels
one for one from the closest available lines 184 until a line of P
pixels is produced. Here again, the mapping operation need not
involve physical movement of the pixel data for the various pixels,
but instead may incorporate mere modification of the addresses for
data in a list of data included in the line. In effect, by the
image skewing process, the system moves from an image having a
field of view bounded by edge rays 220 and 222 to a new image
having a field of view bounded by edge lines 220' and 222' (FIG.
13).
[0084] In the next stage of the operation, the system maps the
pixel data constituting the P pixels in skewed image line 210 into
C pixels constituting a central region 228 (FIG. 14) on a composite
line 240. This mapping procedure is performed in the same way as
described above with reference to FIGS. 11 and 12. The system fills
in the end zones 232a and 232b of composite line 240 by mapping
pixels from other lines having the same ray azimuth angles as the
end pixels of skewed image line 210. That is, the system selects
pixels from other lines having the same ray azimuth as edge lines
220' and 222' of the skewed image. In the same manner as discussed
above, the system starts at the right-hand end of line 210, as seen
in FIG. 14, and selects supplementary pixels having the same
azimuth angle, i.e., on a vertical line 242 extending upwardly from
the end pixel of line 210. The same process at the opposite end of
line 210 proceeds along a vertical line 242', i.e., at the same
azimuth angle as the left end of skewed image line 210 and hence at
the same azimuth angle as edge line 220'.
[0085] In this arrangement as well, the same mapping procedure is
used for each lineset in the epipolar image 188. Thus, depending
upon the position and orientation of each observer, the virtual
viewpoint image 200 displayed to that observer may include pixel
line 202 formed by any of the procedures discussed above. However,
in each case, every pixel line 202 in the virtual viewpoint image
will be formed by the same procedure. Different images are required
for each of the different observer viewpoints as, for example, for
the two displays 138 and 140 associated with observer 146, and for
the two display 142 and 142 associated with the other observer 150.
Image synthesis unit 134 forms all of these different images
substantially simultaneously. The nature of the image-formation
process lends itself to this simultaneous operation. All of the
images are formed by operations performed on the same linesets.
ordinarily, the data in the original, discrete images used to form
the virtual viewpoint images include progressively changing, full
motion video data. An epipolar image formed from each such new set
of frames or fields and new epipolar images are continually
supplied to the virtual image synthesis unit 134. Thus, changes in
the discrete images with time are reflected in the virtual
viewpoint images formed by unit 134 so that the observer sees the
scene in full motion video. Moreover, detection unit 156 and a
synthesis 134 operate in real time with respect to the movements of
the observer. Thus, as each observer moves, the virtual viewpoint
images presented to his or her eyes change in essentially the same
manner as they would if the observer were actually present and
moving about within the real scene.
[0086] In a method according to a further embodiment of the
invention, the system constructs each line of the virtual image for
a virtual viewpoint 590 disposed at arbitrary radial distance 593
from the center of a circular locus in a viewpoint plane and at
arbitrary virtual viewpoint location angle 591 from the index line
508 (FIG. 2) using a plurality of different base images on locus
502. For each line in the virtual image, the system treats the
pixels of the line in many small sets, each such pixel set
encompassing less than all of the pixels in the line. Pixels 510,
511 and 512 constitute one such set. As in the embodiments
discussed above, the horizontal or first dimension location of each
pixel corresponds to the angle B between the central axis 595 of
the virtual image and a ray direction vector 561 extending from the
pixel through the virtual viewpoint 590 to the object imaged by the
particular pixel. Here again, there is an arbitrary skew angle or
horizontal first dimension angle between the central axis 555 of
the virtual image and the viewpoint location vector 593 from the
center 504 of the locus. Accordingly, the difference between angle
B and the skew angle represents a ray offset angle 596 between ray
direction vector 561 and virtual viewpoint location vector 593.
Stated another way, for a given virtual viewpoint location 590 and
skew angle 595, the horizontal or first dimension location of a
pixel specifies the ray azimuth Z' or angle between the ray
direction vector 561 and the index line 508.
[0087] The mutually adjacent pixels 510, 511 and 512 define ray
direction vectors 561a, 561b and 561c at ray azimuth angles close
to one another. The system selects a principal ray direction vector
563 extending from virtual viewpoint 590 and having azimuth close
to the ray azimuths of the ray direction vectors 561a, 561b and
561c of the pixels constituting the set. In this instance,
principal ray direction vector 563 is coincident with the ray
direction vector 561b from the center pixel 511 of the set.
[0088] The system then computes the intercept of principal ray
direction vector 563 on the discrete viewpoint locus 502 and
selects a viewpoint on that locus having a view location 589a at or
close to the intercept, i.e., the discrete view having viewpoint
location closest to the intercept of vector 563 and the locus of
502,. The System thus selects the corresponding line 584a in the
lineset of the epipolar image (FIG. 22). If the intercept of the
principal ray direction vector on the locus falls between two
adjacent discrete view locations, then the system picks the
discrete view location closest to the intercept. In an alternative
version of this embodiment, the system can respond to an intercept
falling between discrete view locations by preparing an
interpolated line 584' in each lineset corresponding to a view
location on the discrete view locus at the intercept.
[0089] Whether discrete line 584a or interpolated line 584' is
used, in the next step of the method the system selects a pixel
within the selected line having ray azimuth closest to the ray
azimuth of each virtual pixel. Stated another way, the system
selects the pixel in the selected line having first epipolar
coordinate F closest to the ray azimuth of the individual pixel.
For Example, pixel 571a has a ray direction vector at an azimuth
close to the ray azimuth of virtual pixel 512 and hence pixel 571a
of the discrete image is selected for pixel 512. Pixel 571b has a
ray azimuth close to that of pixel 511 and so on. The data from
each pixel in line 584a is mapped to the virtual view image line by
copying such data to the corresponding pixel in the virtual view
image line.
[0090] This process is repeated using additional pixel sets. A
different discrete or interpolated image on locus 502 is selected
for each pixel set. For example, the set of pixels 513, 514, 515 of
the virtual view line has a principal ray direction vector 563'
extending through the view location of discrete image 589b. Line
584b corresponding to image 589b is used as the source of pixel
data copied to pixels 513, 514, 515. Other pixel sets take pixel
data from other image and hence from other lines of the epipolar
image lineset.
[0091] This approach may be implemented with larger pixel sets or,
preferably, with smaller pixel sets. In a particularly preferred
variant, each pixel set used in the process consists of only a
single pixel, defining only a single ray direction vector. In this
case, the principal ray direction vector is the ray direction
vector of the single pixel. With a single-pixel set, the line of
the epipolar image used to provide the pixel data may be a
discrete-image line or an interpolated line, corresponding directly
to the intercept of the ray direction vector of the pixel on the
view locus 502. The pixel data is provided substantially without
parallax error. The use of small pixel groups, such as the
three-pixel groups illustrated in FIG. 22 and 22 approximates this
zero-parallax condition.
[0092] The virtual view image line can be of essentially any
length, corresponding to essentially any range of ray offset angles
B and any field of view in the virtual image. In a further variant
of this approach, the pixel data is not directly copied
pixel-for-pixel from each selected line 584 (FIG. 22) into the
virtual view image line. Rather, where the virtual view pixel has a
ray azimuth or first-direction epipolar coordinate F falling
between the ray azimuths of the adjacent pixels in a selected
discrete line 584 or interpolated line 584', data from the two
closest pixels can be combined and mapped onto one pixel. For
example, in FIG. 22, virtual view image line pixel line 511 has a
ray azimuth between those of pixels 571c and 571b on line 584a. The
data from pixels 571b and 571c can be combined, as by a weighted
average lending more weight to the pixel data in pixel 571b, closer
to the desired ray azimuth and the combined data may be mapped into
pixel 511. This arrangement provides even more exact pixel data for
the pixels of the virtual view image line. As in the arrangements
discussed above, lookup tables may be employed. That is, the system
may store tables of data denoting the epipolar coordinates of a
discrete or interpolated image to select for each combination of
virtual view location and pixel location within the virtual view
line.
[0093] As illustrated in FIG. 24, a generally similar approach may
be applied using a set of discrete images distributed in two
orthogonal directions on a multi-dimensional image locus such as
the surface 602 of a sphere or sector of a sphere having a center
604. In this embodiment, the location of a discrete view is
specified by the azimuth angle A and elevation angle E of the
viewpoint location vector 605 extending from center 604 to the
viewpoint 692. The azimuth and elevation are specified with
reference to an index line 603 passing through the surface at a
location of zero azimuth and zero elevation. Each viewpoint has a
central principal view direction vector coincident with the view
location vector 605. That is, each view is directed substantially
radially with respect to the spherical view locus.
[0094] The azimuth and elevation of the discrete views correspond
to azimuth and elevation in the frame of reference of the scene.
For example, where the discrete views are views captured by real
cameras looking at a real scene, the camera which captures discrete
view 692a would be disposed at a relatively high elevation and
pointing upwardly in the scene, whereas the camera which captures
discrete view 692b would be mounted at a lower elevation and
pointing downwardly in the real scene. Here again, each view has
first and second image dimensions, desirably vertical and
horizontal dimensions V and H parallel to the elevation and azimuth
directions respectively. Here again, the first horizontal image
dimension H represents the difference in azimuth B" between (1) the
ray direction vector 661 from the pixel 671 through discrete image
location 692 and (2) the principal view direction vector which is
coincident with the view location vector 605. Correspondingly, the
location of the pixel 671 in the vertical image dimension V
represents the difference BB" in elevation between the ray
direction vector 661 and the viewing axis and view location vector
605. Thus, the vertical horizontal image dimensions of each pixel
671, the discrete image define the azimuth Z" and elevation ZZ" of
the ray direction vector 661 relative to an index line 603'
parallel to the index line.
[0095] A two-dimensional virtual viewpoint image for a virtual
viewpoint 694 specified by a virtual viewpoint location vector 693
having radius different than the radius of the spherical surface
602 and at a arbitrary azimuth and elevation can be derived as a
two-dimensional array of virtual image pixels 611. A set of
mutually adjacent pixels 611a, 611b . . . 611n is selected from
within the array. Here again, each pixel defines a ray direction
vector 695 from the virtual pixel through the virtual viewpoint
690. Each such ray direction vector defines a ray azimuth Z'
relative to the index line 603 or relative to an index line 603'
parallel to index line 603. Similarly, each ray direction vector
defines an elevation angle ZZ' relative to the index line. The
various pixels 611 within each small set of mutually adjacent
pixels define a principal ray direction vector 663 which has
similar azimuth and elevation. Here again, in the limiting case,
each small group of adjacent pixels includes only one pixel 611 and
the principal ray direction vector 663 is simply the ray direction
vector 695 of that pixel.
[0096] For each set of virtual pixels, the intercept of the
principal ray direction vector 663 on the discrete view locus 602
is determined, and the discrete image at viewpoint 692 closest to
that intercept is selected. Within the selected discrete image, the
System selects the pixel or pixels 671 having ray direction vectors
661 with azimuth and elevation closest to the azimuth and elevation
of the ray direction vector 695 of the particular pixel. Data from
that pixel is then copied directly into the pixel 611 of the
virtual image. Different pixel sets defining different principal
ray direction vectors 663 will take data from different discrete
images 682. For example, the pixel set including virtual pixel 611z
will define a principal ray direction vector passing through
discrete viewpoint 692c.
[0097] The foregoing method permits construction of a virtual view
image, but does not provide for interpolation between discrete
images. That is, where a principal ray direction vector falls
between discrete view locations 692, the system must accept the
closest discrete view location. In an alternative method, using the
same discrete view locations and geometry as depicted in FIG. 25,
the data from the discrete images is converted into a
three-dimensional epipolar or transform image including a plurality
of line sets as illustrated in FIG. 25. Each such line set includes
one line of pixel data 784 from each discrete image. Each such line
in the entire line set has the same second or vertical image
dimension coordinate V (FIG. 24). Each lineset has a first epipolar
coordinate F' corresponding to azimuth of the discrete view and a
second epipolar coordinate S' corresponding to elevation of the
discrete view. Because all of the pixels in the line set have the
same second image dimension or difference in elevation from the
view location vector of the view itself, the second image dimension
S'of each pixel also represents the elevation Z" of the ray
direction vector from the pixel. That is, for every pixel in a
given lineset, the elevation of the ray direction vector is equal
to the elevation of the image location vector 605 plus a constant,
this constant being different for different linesets but uniform
throughout any given lineset. Each lineset also has a third
epipolar coordinate corresponding to the azimuth Z" of the ray
direction vector 661 of the particular pixels. Thus, each lineset
as depicted in FIG. 26 includes lines from numerous discrete
images. The lines from images on any circular locus 605 of constant
elevation fall in a single plane 783 of the epipolar image having
constant second epipolar coordinate whereas lines from images on
the same line of longitude 607 or circular locus of constant
azimuth fall in a plane 785 of constant first dimension F'. As in
the epipolar images discussed above, the number of line sets in the
epipolar image equals the number of horizontal lines within each
discrete image. The line sets are formed by processes similar to
those used in formation of the two-dimensional linesets discussed
above.
[0098] The epipolar image is used to create a virtual view image by
a process similar to that discussed above with reference to FIGS.
22 and 23. Thus, for each set of pixels 611 the system selects an
image location on locus 602 close to the intercept of principal ray
direction vector 663 on the locus. That is, the system provides a
line of pixel 784 having first and second epipolar coordinates
close to the intercept for use as a base line. Where the intercept
does not coincide exactly with a discrete image location, the
system can form an interpolated line 784' by interpolation between
the pixel data in the for surrounding discrete image lines 784 at
the same ray azimuth or third epipolar coordinate T. Here again,
the pixel data from the selected line 784 or 784' of the epipolar
image may be mapped into the pixels of the virtual view image line
being synthesized by simple copying from one pixel of the selected
line to the pixel having the closet azimuth in the virtual view
image. Alternatively, a more complex mapping scheme involving
interpolation between adjacent pixels can be employed.
[0099] Line sets involving three-dimensional epipolar images can be
compressed, stored and combined by methods corresponding to
handling of the two-dimensional epipolar line sets discussed above.
For example, each plane 783 or 785 of such an epipolar line set can
be handled or combined by the same methods as applied to the
individual two-dimensional epipolar line sets described above.
[0100] In this regard, it should be noted that the image
reproduction achieved by a system as discussed above normally is
not perfect. For example, substitution of the supplementary pixels
at the ends of the pixel lines necessarily introduces some parallax
error. The substituted pixels have been taken from viewpoints
differing from the base viewpoint. They may not have exactly the
same information as a hypothetical pixel taken from the base
viewpoint at the same ray azimuth. However, in normal operation
these errors are relatively small and affect only the edges of the
virtual viewpoint image. The center of the image, where the
observer's vision is most acute, remains substantially unaffected.
To suppress these errors still further, the system may be arranged
to capture images having a field of view wider than the virtual
viewpoint images to be displayed. Thus, as illustrated in FIG. 10,
each line 184 may incorporate P pixels, representing the full field
of view, whereas the image to be displayed may require only a
smaller number of pixels indicated by image line 250, representing
a smaller field of view. This leaves M' excess pixels at each end
of the line 184. For a normal, unskewed image, line 250 contains
the pixels from the central portion of line 184. However, for a
skewed image, line 250 can be reconstituted to start closer to one
end or the other end of line 184. In this instance, the pixels at
the ends of the line are taken from the same line 184, i.e., from
an image with the correct viewpoint. If the degree of skew exceeds
that which can be accommodated by M' pixels, then supplementary
pixels from adjacent lines are used.
[0101] Numerous variations and combinations of the features
discussed above can be utilized. The interpolation scheme used to
derive an interpolated line in the epipolar image (FIGS. 6 and 9)
can differ from the pixel-by-pixel interpolation scheme described.
Various schemes for detecting edges and boundaries of objects in
video images are well-known in the processing of conventional,
two-dimensional video images. Any of these schemes can be applied
to each lineset of the epipolar image. For example, in FIG. 6 the
edges of strip 110' can be detected directly. Once such edges have
been detected, the same can be used to assign pixel values in the
interpolated line; the pixel values can be calculated from the
closest pixel values on the same side of the edge, while
disregarding pixel values on the opposite side of the edge.
[0102] The systems described above can introduce certain occlusion
and disocclusion errors. That is, where the virtual viewpoint image
represents a substantial skewing or displacement of the base image,
the virtual viewpoint image may not accurately reflect occlusions
of distant objects by close objects. This problem is substantially
minimized by using a base image reasonably close to the virtual
viewpoint image as discussed above. Provided that the locus of the
observer is reasonably close to the locus of the discrete images,
the system does not introduce close occlusion errors.
[0103] The system discussed above with reference to FIGS. 1-14
utilizes a planar, circular, discrete viewpoint locus. It assumes
that the observer is looking in a single horizontal plane. It does
not provide corrections for tilt of the observer's head. However,
the invention is not limited in this manner. In a further extension
of the system, the discrete images can be provided as a spherical
image array as discussed above with reference to FIGS. 24 and 25 or
as illustrated in FIG. 15. In that system, the discrete images may
be taken as radial images at intersections of meridians 301 and
latitude lines 305 of a sphere. The discrete images taken on any
latitude line 305 of the sphere can be treated in substantially the
same way as the images on the circular locus discussed above. Thus,
the system can derive a virtual image representing the image at
latitude line 305 and on an arbitrary longitude line 301'
intermediate between the longitude line 301 of the discrete images
using substantially the same methods as described above. In the
same manner, the system can derive virtual images for numerous
locations along longitude line 301' by independently treating the
data for the images on the various latitude lines as, for example,
the various discrete images on line 305a at its intersection with
line 301 and the discrete images on line 305c at its intersection
with the various latitude lines 301. Thus, the system derives a set
of virtual images which can be treated as a set of discrete images
at various locations on the virtual meridian 301'. The system can
then process these images to derive a virtual viewpoint image at
any arbitrary location 305', 301' or 301' in the same manner as the
system described above derive images on the circular locus.
Likewise, the system can derive a virtual viewpoint image for any
arbitrary point within the spherical locus, on the plane of virtual
meridian 301' in the same manner as the system described above
derives virtual viewpoint images for arbitrary locations within the
circular locus.
[0104] In all of the systems discussed above, the camera locus is
curvilinear, the discrete images represent viewpoints looking
outwardly from within the locus and the virtual viewpoints are
inside of the locus. However, the virtual viewpoints may be
disposed outside of the camera locus. For example, the system
discussed above can accommodate a virtual viewpoint location
outside of the locus, with the view axis pointing outwardly, away
from the locus. In this case, the base view would be taken as the
view immediately behind the outwardly looking virtual viewpoint,
and would be modified to map less than all of the pixels in the
base view line of the epipolar lineset into the entire virtual
image line. However, where the virtual viewpoints are far from the
discrete viewpoint locus, and where the same are substantially
skewed, the virtual viewpoints can require information which is
simply not present in the discrete images and therefore not present
in the epipolar image lines. For example, a viewpoint for outside
of the image locus, with the viewer looking inwardly toward the
locus, will require information as to the color and brightness of
the back sides of objects which have their front sides facing
towards the locus.
[0105] In the systems described above, the virtual image synthesis
apparatus determines the required mapping by calculations performed
in real time as the observer's position changes. However, operation
of the system can be considerably expedited by providing a look-up
table listing the pixel mappings to be performed for each position
of the observer. Moreover, in the systems discussed above, the
virtual image synthesis unit derives the two virtual images for
each observer independently. However, because the observer's
interpupillary distance is fixed, there is a fixed relationship
between the two points of view of the observer. Stated another way,
the view point of the virtual image to be presented through one
display unit 140 of a given observer bears a fixed relationship to
the viewpoint of the image to be presented through the other
display unit 138 for the same observer. Thus, the pixel mappings
required to form the image for display 140 will bear a determinable
relationship to the pixel mappings required for the display unit
138.
[0106] Various techniques can be employed to reduce the processing
load involved in generating the images. First, where the scene to
be portrayed includes static elements, the static and moving
elements can be segregated. For example, the contents of one frame
can be subtracted from the contents of the next succeeding frame to
form image including only the changed portions. The static elements
can be segregated from the moving elements by well-known image
processing techniques. An epipolar image including all of the
static elements can be captured once. Separate epipolar images
consisting only of the moving elements can be constructed from the
images by the real cameras. Each lineset of the epipolar image of
the moving objects can be overlaid onto the corresponding lineset
in the image of the static objects. The linesets can be overlaid by
determining the slope of each strip in the lineset to detect
distance from the camera. Where both linesets include data, the
pixels representing the closer object, whether moving or still, are
included in the final composite lineset. Alternatively, the static
environment can be captured in one lineset whereas a real moving
object as, for example, an actor in a scene, can be captured in
other epipolar images including real pixel data only for the
desired object and a artificial information, such as a deep blue
background color, for the remainder of the pixels. The epipolar
image including the changing data can be merged with the epipolar
image representing the static background by the conventional
technique of "chroma keying". In this technique, each lineset of
the background image is combined with the corresponding lineset of
or changing by checking the chroma or color reflected in the pixel
data of the changing image. Wherever the chroma indicates the
artificial background color such as dark blue, the second image is
disregarded and the pixel data is taken entirely from the first
image. Conversely, wherever the second image includes pixel data
indicating a different color, the pixel data is taken entirely from
the second image. This technique is applied routinely in processing
of ordinary video images, and can be applied to the epipolar image
linesets in the same manner.
[0107] Although the foregoing discussion has centered on images of
real scenes captured by real cameras, the same techniques can be
applied to mathematically generated images. For example, a computer
can be actuated to generate the various discrete images of a
mathematically constructed scene, and the resulting pixel data can
be processed in exactly the same way as the real image pixel data
discussed above. Also, an epipolar image representing a real scene
can be merged with an epipolar image representing a computer
generated object or objects.
EXAMPLE 1
[0108] Certain aspects of the present invention are illustrated by
the following non-limiting example. As illustrated in FIG. 16, a
video camera 400 is positioned on a turntable 402 so that the
camera points radially outwardly from the center of the turntable
and so that the lens of the camera lies at a radius of 250 mm from
the turntable center. The camera and turntable are positioned on a
flat horizontal surface. Several ordinary coat hangers 404 are
arranged vertically above the surface. A string 406 extends
vertically. All of these elements are positioned in front of a
dark, vertical backdrop 408 at a distance of 1750 mm from the
turntable center. The distance to each object from the turntable
center is indicated by the scale at the bottom in FIG. 16. Camera
400 has a field view of 27 degrees from edge-to-edge, or 13.5
degrees on either side of the view center line. The turntable is
actuated to turn in one degree steps. At each step of the
turntable, while the turntable is stopped, camera 400 captures a
video image. The camera thus captures discrete images at 1 degree
increment. FIG. 17a is the 31st discrete image; FIG. 17b is the
32nd discrete image and FIG. 17c is the 33rd discrete image. The
effect of camera rotation and parallax can be seen in these images.
See, for example, the image of hanger 404b [?] disappearing from
the left-hand edge in FIGS. 17b and 17c, and the change in the
apparent relative position between the two hangers at the top of
the image.
[0109] FIG. 18 illustrates one lineset from an initial epipolar
image reconstituted from the images captured by the camera. FIG. 19
shows the same lineset after application of an offset as discussed
above with reference to FIG. 6.
[0110] FIG. 20 is an enlarged version of the 32nd image as captured
and as also illustrate in FIG. 17b. FIG. 21 shows a virtual image
generated by interpolation between the discrete images of FIGS. 17a
and 17c. That is, each line in the image of FIG. 21 was derived by
interpolation in a lineset from the epipolar image, as if the
discrete 32nd image did not exist. The image is truncated at its
edges. Nonetheless, it is apparent from comparison of FIGS. 20 and
21 that the scene has been portrayed with good accuracy in the
virtual image.
[0111] As these and other variations and combinations of the
features discussed above can be utilized with departing from the
present invention, the foregoing description of the preferred
embodiment should be taken by way of illustration rather than by
way of limitation of the invention as defined by the claims.
* * * * *