Note: Descriptions are shown in the official language in which they were submitted.
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SEAMLE88 DISPLAY FOR MULTIPLE VIDEO IMAGES
Field of the Invention
The present invention pertains to the field of
video image displays and more particularly to a method
and apparatus for projecting a seamless video display
from multiple video signals.
Baokqround of the Invention
Theater audiences continuously seek out larger
displays with greater resolution. In the motion
picture industry this has resulted in a gradual
increase in the size of the film format from l6mm to
35mm to 70mm to "IMAX". In the television industry,
screens have increased in size so much that projection
TVs can now fill an entire wall of an average sized
living room.
However, while the larger film formats have
brought high resolution, commercial television
resolution is limited by the commercial industry
broadcast standards, The broadcast standards define
both the aspect ratio and the resolution of the image.
The broadcast standards limit resolution by defining
the number of horizontal lines per frame and the number
of picture elements in each line. An increase in the
size or horizontal scope of a commercial television
image necessarily brings no increase in the number of
lines or the number of picture elements in that image. ..
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1 Therefore, a very large picture will not be as sharp
and clear as a smaller image. Several commercial-type
video signals may be combined to form a single image
with a different aspect ratio, with more picture
elements, or with more lines per frame. However, this
requires either combining several projectors to farm
that single image, or developing a whole new format
different from the commercial standards.
In the film industry there have been several
experiments with multiple projector systems. One such
experiment was the "CINERAMA" systems of the 1950's.
In "CINERAMA," three films, shown through three
projectors, were combined to form a single panoramic
image. Disneyland and its affiliate parks continue to
use a °'CIRCLE VISION" multiple projector system. At
Disneyland, a circle of projectors shine onto a circle
of screens that circle the wall of a round room.
In the video field, multiple projector systems
have been suggested for flight simulators, see e.g.
U.S. Patent No. 4,103,435 to Herndon, arid U.S. Patent
No. 3,833,764 to Taylor. In addition, it is known to
place several video screens next to each other to form
a large image display from multiple projectors.
However, the difficulty with all video based multiple
projector display systems is making the multiple images
appear to be one single continuous image on the display
screen.
When two images are projected side by side on a
single screen, there will normally be a seam between
3o the two images. The final display image will either
appear to be two images placed side by side with a gap
in between or, if the images axe made to overlap on a
single screen, there will be a bright line where the
two images overlap. Because of the inconsistencies in
conventional cameras and projectors, it is exceedingly
difficult to perfectly match video images with no gap
and no overlap between the images. If the images are
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1 brought very close together on the same screen, there
will likely be both gaps and overlaps at the seam.
Summary of the Invention
The present invention includes a method and
apparatus for producing a seamless video display from
multiple images. The invention comprises a method for
producing a seamless image from at least two discrete
images where each image overlaps with at least one
other image by ramping the projected brightness of the
overlapping portions of each image.
The invention also comprises an apparatus
including at least two video signal generators where
each generator produces a video signal that corresponds
to a discrete image and each image overlaps at least
one other image. The video signals axe sent to at
least two ramp generators. At least one ramp generator
is coupled to each video signal generator. The ramp
generators ramp the parts of the video signals that
correspond to the overlaps between the images. At
least one projector is coupled to each ramp generator.
The images produced by the projectors, corresponding to
the ramped video signals, are projected onto a screen.
A synchronizer is coupled to the video signal
generators for synchronizing the images.
The present invention produces a seamless apparent
image by overlapping the separate images and then
s
ramping the brightness of the images at the seams
between the separate images.
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1 Brief Description of the Drawings
FIG. 1 is a block diagram of a preferred
embodiment of the present invention;
FIG. 2 is a graphical illustration of a video
signal;
FIG. 3 is a diagram of a screen incorporating the
present invention and its corresponding ramp functions;
and
FIG. 4 is a block diagram of an alternative
l0 embodiment of the present invention in which the video
signals are romped before being stored in the video
signal generators.
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1 Detailed Description of the Invention
Referring to FIG. 1, three video signal generators
10A, 10B, lOC operate in parallel. They generate video
signals which correspond to discrete images as
explained below. In the present embodiment, the signal
generators are video disc players. Pioneer Model LDZ
6000A is suitable. Each video disc player transmits a
unique frame number for each discrete image to a
synchronizer 8. The synchronizer compares the frame
numbers received from the video disc players and then
regulates the video disc players so they produce like
numbered images at the same time. In this way, the
synchronizer maintains synchronous parallel operation
for the whole system. An APh Model VDU-1 is a suitable
25 synchronizer. The video signal generators each
transmit their video signals, in parallel, to the
corresponding one of three ramp generators 12A, 12B,
12C. The ramp generators ramp the signal, as will be
described in more detail below. Commercially available
special effects generators, such as the Vidicraft Model
SEG-200, may be used for ramp generators.
Each of the ramp generators sends the ramped
signal to the corresponding one of three video image
projectors 14A, 14B, 14C. Commercially available
projectors, such as the Panasonic Model PT-101N, are
suitable. In the present embodiment, the projectors
convert the electrical signals to light beams. The
three beams are projected onto a single screen 16, in
parallel.
The screen displays three discrete images 18A,
18B, 18C which correspond to the three ramped video
signals. Where the images come together there are
overlaps 20A, 20B. The left overlap 20A occurs where
the left image 18A and the center image 18B are both
projected onto the same part of the screen. The right
overlap 20B occurs where the center image 18B and the
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Z right image 18C are both projected onto the same part
of the screen.
The information in the video signals corresponding
to the overlaps 20A, 20B is duplicated in the video
signals for the three images 18A, IBB, 18C. That is,
for the left overlap 20A, the right portion of the left
image 18A that is projected onto the left overlap 20A,
must be virtually identical to the left portion of the
center image 18B that is projected onto the left
overlap 20A. Otherwise, neither of the overlapping
portions of the two images 18A, 18B will appear clearly
on the screen. The same thing applies for the right
overlap 20B.
Because the images are duplicated within the
overlaps and because the video signals are romped, the
three images displayed on the screen appear to be one
continuous, seamless image almost three times as wide
as a single video image but with the same clarity and
sharpness as a single video image. This composite
larger image which appears on the screen will be
referred to as the apparent image.
The nature of the video signal emitted by the
video signal generators is illustrated in FIG. 2. The
video signal 28 has a sequence of horizontal
synchronization signals 30A, 3oB each followed by
amplitude signals 32A, 32B. The video signal includes
other components as well, but they are not important to
this discussion and are not shown in FIG. 2. Each
synchronization and amplitude signal pair, e.g. 30A and
32A, corresponds to a single scan line traced across
the screen. The synchronization signal indicates the
start of each scan line. The amplitude signal
indicates the brightness of the projector beam as the
line is traced.
In operation, the projector begins to trace a scan
line when it receives a synchronization signal. For
conventional direct viewing cathode ray tubes and for
1 projection televisions, this means that a beam of
electrons from an electron gun is aimed at the top left
corner of a phosphorous screen. The electron beam is
then deflected to the right across the top of the
screen. The number of electrons emitted by the gun is
regulated by the amplitude signal. When a new
synchronization signal is received, the electron beam
moves back to the left of the screen and traces a
second scan line immediately below the first. This is
repeated with each synchronization signal and each
amplitude signal, until the electron beam reaches the
bottom right hand corner of the screen. The beam has
then drawn one complete image and, upon receiving a
vertical synchronization signal, returns to the top
left of the screen to draw the next image. The lines
are drawn so quickly that there appears to be a single
moving image rather than a series of line tracings.
The number of lines and picture elements per image as
well as a host of other details are determined by the
standards for the particular format arid are intrinsic
to the video signal.
FIG. 3 demonstrates how video signals are ramped
according to the present invention. In the exemplary
embodiment, the three parallel systems, each consisting
of a video signal generator, a ramp generator and a
video image projector are synchronized. For each
image, therefore, all three projectors 14A, 14B, 14C ..
begin to project a trace of their respective first scan
lines 40A, 4oB, 40C at the same time on different parts
of the same screen 16. Because of the speed at which
the lines are traced, this produces the appearance of
a continuous line across the screen. When all the
lines for the three images have been traced, it appears
as if a continuous image almost three times the width
of a standard image has been projected onto the screen.
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1 However, the overlaps 20A, 20B will be traced
twice. For the left overlap 20A, the top line of the
image will be traced first by the center scan line 40B
at the beginning of its travel and then by the left
scan line 40A at the end of its travel. A similar
thing happens at the right overlap 20B. Without
ramping, the apparent image would be substantially
brighter in the overlaps than in the rest of the
screen. The double tracing creates two bright seams
between the three images. The bright seams can be
eliminated by moving the projectors 14A, 14B, 14C apart
to eliminate the overlaps 20A, 20B. However, it is
virtually impossible to perfectly match the images and
there will either be thin bright seam overlaps or thin
dark line gaps between the three images or both.
The invention eliminates the seam by applying a
ramp function 42A 42B, 42C, depicted in FIG. 3, to the
amplitude signal 32. This is done by the ramp
generator 12 before the video signal is transmitted to
the projector 14. The synchronization signals 30 are
undisturbed. The first ramp function 42A is applied by
the left ramp generator 12A to the amplitude signal
generated by the left video signal generator 10A. The
second ramp function 42B is applied by the center ramp
generator 12B to the signal from the center signal
generator lOB, and the third ramp function 42C is
applied by the right ramp generator 12C to the signal
from the right signal generator lOC.
The ramp functions 42 affect the amplitude signals
only at the image seams. Each ramp function includes
a flat portion 44A, 44B, 44C which does not affect the
video signal, and one or two ramped portions 46A, 46B,
48A, 48B. The ramped portions are smooth curves which
affect the video signal. The negative slope curves
4.6A, 46B smoothly reduce the amplitude signal from full
strength to near zero strength. The positive slope
curves 48A and 48B smoothly increase the amplitude
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1 signal from near zero strength to full strength. The
curves are smooth because sudden transitions may show
up as apparent lines, image details, or visual
artifacts on the screen. However, in another
embodiment, it may be desirable to use square functions
or other differently shaped ramp functions instead of
the smooth curves depicted in FIG. 3.
The curves complement each other in that where a
negatively and a positively sloped curve, e.g., 46A and
48A, affect the apparent image at the same overlap,
e.g., 20A, the combination of the two curves across the
overlap is equivalent to the flat portion of the ramp
functions 44. In FIG. 3, the illustrations of the ramp
functions 42 are aligned with the corresponding
portions of the screen 16. Combining the three ramp
functions 42 together provides a flat line 50 equal in
amplitude to the flat portion 44 of the ramp functions.
Uniform image brightness is thereby maintained across
the entire screen 16. If square or otherwise shaped
ramp functions are used, the ramp functions must still
be complementary in order to maintain uniform
brightness.
In operation, the first projected scan line 40A
for the left image 18A is at first unaffected by the
ramp function 42A. The flat portion of the ramp
function 44A has no effect on the amplitude signal.
When the trace reaches the left edge of the left
overlap 20A, the ramp function 42A starts to smoothly
reduce the amplitude of the amplitude signal, By the
time the line is traced to the right edge of the left
image 18A, the amplitude signal is reduced to
approximately zero. As a result, the brightness of the
first line on the screen begins to fall off at the left '
edge of the center screen until it reaches zero at the
right edge of the left screen. The same ramp function
is applied to each successive amplitude signal
affecting each successive line the same way. The left
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1 image 18A accordingly darkens gradually at its right
edge.
The second ramp function 42B is applied to the
center image 18B. The second ramp function ramps the
right edge of the center image in the same way that the
first ramp function 42A ramps the right edge of the
left image 18A. However, the second ramp function also
ramps the left edge of the center image. Therefore,
when the first scan line for the center image 40B is
begun at the top left corner of the center image 188,
the line has near zero brightness. The brightness of
the line increases smoothly as it is traced to the
left. At the right edge of the left image 18A, the
line is at full brightness. It stays at full
brightness until it reaches the left edge of the right
image 18C where it is ramped back down to near zero in
the same way that the left image line 42A is ramped.
The ramp function is added to every line that makes up
the center image 18B so that the center image is ramped
at both ends.
The right image 18C is ramped at its left edge in
the same way that the center image 18B is ramped at its
left edge. The right edge of the right image is
unaffected by the ramping function, just as the left
edge of the left image 18A is unaffected.
When all three images are projected onto a single
screen, the portions of each image that lie in the
overlaps combine. Therefore, the brightness level
across the whole screen remains uniform and the
apparent image appears to be seamless.
In the present embodiment, the video projectors
are conventional devices using standard formats. As a
result, conventional cameras, editors, processors and
players may be used to create and process the parallel
images. The video signal generators may be tape
players, television receivers, cameras or any other
source of video signals. In addition, material
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1 prerecorded in conventional video formats can be easily
integrated into a display which exploits the benefits '
of the present invention. The projectors may be
conventional cathode ray tube, projection televisions,
LCD displays, or any other type of video display
device.
While the present embodiment uses three parallel
projectors coupled to three signal generators, any
plural number of parallel systems may be used. A still
wider apparent image may be obtained by using four or
more parallel projection systems in a row.
A tall apparent image may be produced by stacking
images vertically. Vertically stacked images are
ramped at the top and bottom edges corresponding to the
horizontal overlaps. The brightness of each scan line
is consistent throughout the line, but the brightness
of consecutive scan lines is varied. For the top
image, the bottom scan lines are successively ramped to
near zero at the overlap. For the bottom image, the
top scan line is at near zero brightness and successive
lines are brighter until full brightness is reached at .
the end of the overlap. Intermediate images are ramped
both at the top and the bottom. Vertical and
horizontal stacking may be combined to obtain an
apparent image with any desired aspect ratio and size.
The present invention may also be implemented
using specially dedicated equipment. For example,
instead of using three video disc players, a specially
constructed disc or tape and player system capable of
3o producing three or any other plural number of discrete
video signals, or a single camera capable of producing
multiple discrete video signals, may be used. Instead
of using three projectors that cast light on a single
wide screen, the projectors may comprise independent
electron beams within a cathode ray tube that sweep
across neighboring overlapping portions of a single
phosphor coated screen.
. -'".. , " .'; . : ,' , _ . ,.; v:;: .,.," ,.,. , . ,:., ,;:: ~ ; ~ ,. -;
.::~ : ..
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1 Instead of using separate special effects genera-
tors as ramp generators, the ramp generators may be
incorporated into the projectors or into the video
signal generators. The tamping rnay also be performed
between the projector and the screen with an optical or
electrical filter placed between the projector's light
or electron beam and the screen.
If the signal generator is reading a stored
signal, the tamping may also be applied to the signals
before they are stored. In FIG. 4, incoming signals
from a receiver, a camera, a tape or disc player, or
some other source or from several such sources are
tamped and then stored in video signal storage media
11A, 11B, 11C. The storage media can be tape or disc
drives or some other device. The tamping is then
incorporated into the output of the signal generators
which feed directly inta the projectors. This allows
a presentation to be edited completely before display.
At the display site, no ramp generators are therefore
required. Other modifications and adaptations of the
present invention may also be made without departing
from the scope of the present invention as defined in
the appended claims.
30
t
