Note: Descriptions are shown in the official language in which they were submitted.
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` Ri~AL TII`5E l~IGITAL VIDEO POSITIO~IEE~ SYSTEM
Field of the Invention
The present invention relates to video image
display systems, and more particularly to systems for
positioning a raster scan video image on a display screen
to provide real time apparent motion of a video scene.
In some applications requiring positioning of a
raster scan video image, it is necessary to provide video
scene n,otion in response ~o control inputs. Tnis would be
applicable to any visual simulation system wherein ~he
viewer's line of SigLIt changes in relation to changes in
control inputs. Here, the total video scene is re~ositioned
in response to these inputs. A portion of the screen (visible
window) is to be viewed, so tihat when the total scene is re-
positioned, apparent motion of the scene through the visible
window resulted. It is thus necessary to reposition tne
video each frame time. The repositioner must be stable,
accurate, and flexible to enable correlation of the display
witn respect to a particular simulation problem.
Known systeMs for repositioning tne raster scan
video image employed analog techniques and requires modification
of ~he horizontal and/or vertical position circuitry o~ the
monitor to perform this task. Other digital methods employed
to accomplish this task utilize D/A converters, image storage
memory, complex timing circuitry, and A/D converters. These
systems furtller require specially designed and complex display
moni~ors having specially designed horizontal and vertical
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position circuitry.
Sum~ary of the Invention
It is an object of the present invention to provide
a system for positioning a raster scan video image anywhere on
a display screen. It is another object to provide a sys~em
for positioning a raster scan video image anywhere on a screen
using a standard display monitor having separate sync input
ter~inals. It is another objct to position the video image
appearing on a display monitor with respect to changes in a
line of sight by r.leans external to the display monitor, in
order to simulate physical movement of tile line of sight
relative to a real world ~rame of reference. It is another
object to provi~e video positioning of a raster scan video
image using a minimum of hardware. It is a further object
to provide a system capable of positioning of the displayed
video image appearing on a display monitor for each video
frame, so as to generate real time apparent motion of the
video scene.
These and otller objects are achieved by t~le present
invention which provides a video positioning system for
a raster scan video image being generated on a display monitor
for generating real time apparent motion of a video scene.
The video positioning system includes a horizontal delay
circuit for receiving the video source horizontal sync signal
and generating a delayed horizontal sync pulse, for horizontal
sync positioning of the video image in accordance with the
horizontal`position data from a computer or control interface,
for shifting the picture. Similarly, a vertical delay circuit
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receives tle video source vertical sync signal and generates
a delayed vertical sync pulse, for vertical positioning of tne
video image in accordance with the vertical position data from
the computer or control interface, for vertically shifting the
picture. Sync generation logic circuits receive the delayed
horizontal and vertical sync pulses and generate standard
width horizontal and vertical sync and blanking pulses required
by the display monitor and R/G/B blan~ing circuitry therefor.
By delaying the blanking signals such that the image is lined
up with t'ne line of sight, the framing of the wider display
is shifted, per each frame. The blanking circuitry, therefore,
blanks the video during the delayed sync blanking perio~ to
enable the display to maintain a constant black reference level
during beam retrace time.
In this fashion, the video positioning system o~ ~he
present invention enables the positioning of a raster scan video
image, being generated in the red/green/blue/sync mode, anywhere
on tne display screen. The system permits a monitor independent
process in that any standard display monitor designed for R/G/B
sync video signals with independent horizontal and vertical
sync input terminals may be employed.
The video positioning system of the present invention
positions the di~played image each video frame by means
external to the display monitor and thereby simulates real
2~ time apparent motion of the video scene and raster scan image.
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Brief Description of the Drawin~s
Figure 1 is a circuit block diagram of the video
display system including the di~ital vid~o positioner system,
illustrative of the present invention:
Figure 2 shows the viewin~ area containing an
image and located behind a mask;
Figure 3.1 is a signal diagram of the video source
horizontal sync pulse,
Figure 3.2 is a signal diagram of a source video
si~nal;
Figure 3.3 shows the viewin~ area and mask
occurring with ~he standard sync signal;
Figure 4.1 is a signal diagram of the horizontal
sync signal,
lS Figure 4,2 is a si~,nal dia~ram of the delayed
- horizontal sync pulse;
Figure 4.3 is a si~nal diagram o~ the source
video si~nal;
~igure 4.4 shows the viewin~ area and mask
occurrin~ with ~he delayed sync pulse; and
Figure 4.5 shows the monitor viewing area with
the video image lined up with the line of sight.
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Description of_the Preferred ~mbodiments
Figure l is a functional block diagram of ~he video
display system including the digital video positioner of the
presen~ invention. A video iG.a~e is provided from a video
source 10 as a Red/Green/Blue (~/G/~) video signal on line
12 to a video display monitor 14 via a blanking logic circuit
16. ~he source video horizontal sync and vertical syn~ on
lines 20 and 22 from video source 10 are applied to a horizontal
delay circuit 24 znd a vertical delay circuit 26, respectively.
If composite video is available, rather than separate R/G/B/Sync
and video, then a video decoder, not shown, shall be used to
convert the composite video into the required R/G/B/Sync and
video signals. Both tne horizontal and vertical delay circuits
24 and 26 receive clock pulses from a pixel clock 28 via line
30 or from another suitable internal clock generator, not shown.
A computer or control interface 32 provldes the
communication and interface either directly with the user's
scene viewing controls 34, or with a computer 35 performing
the scene positionin~ computations frorn such controls.
The interface 32 receives the timing and control data
provided on line 36 from con~rol circuit 37, loads a horizontal
(h) delay count into ~i (horizontal) delay co~mt buffer 38 and
a vertical (v) delay count into V (vertical) delay count buffer
40 with the required nurnber of pulse counts calculated for
providing the corl~anded snift of the video image. The H and V
delay counts are loaded via lines 42 and 44, respectively, into
the horiz~ontal delay circuitry 24 and vertical delay circuitry
26 upnn receiving a load signal command on line 46 from computer35.
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The horizontal delay circuit 24 generates a delayed
horizontal sync pulse ~or horizontal posi.ioning of ~he video
i~age. Circuit 24 has a digi~al counter, count decode logic,
and delay lines. The counter is loaded upon command by the load
signal on line 46. The counter then counts until overflow or
underflow is reached, at wilich time the counter initiates a
series of subcycle (subpixel) pulses generated by a set of delay
lines and a selection logic in delay circuit 24. The subcycle
logic is controlled by the least significant bits (LSB'S) of the
delay count on line 42 and ~I delay count buf~er 38. The subcycle
pulses were generated to achieve a video position resolution
greater than that of the clock. The total horizontal delay is
the sum of the horizontal counter delay and the subpixel clock
delay.
The vertical delay circuit 26 provides a similar
function as the norizontal delay circuit 24 except that there is
generated a delay vertical sync pulse rather than a delayed
horizontal sync pulse.
The llorizontal and v~rtical delay circuits 24 and 26
provides the delayed pulses to horizontal and vertical pulse gen-
erators 48 and 50, respectively, which generate pulses of fixed
duration and polarity for utilization by the logic circuits in
a sync generator 52. The sync generator 52 receives the delaye~
horizontal and vertical sync pulses and generates standard width,
delayed, 'norizontal and vertical sync and blanking signals. More
particularly, the sync generator 52 provides the delayed sync
pulses on line 54 to the video display 14 and on line 56 provides
blanking pulses to the blanking logic circuit 16 corresponding to
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the delayed blanking period. This enables the display to
maintain a constant black reference level during bea~ retrace
time. If desired, a video amplifier can be incorporated in
this section, following the video blanking circuits 16, to
provide impedance matching and gain control of the individual
R/G/B signals.
According ~o the present inventio~, and as shown in
Figure 2, the total image is repositioned each frame time, with
only a portion of the total image, for example, 65 per cent,
visible througn the window 62 cut in mask 64. Thus, only a
portion of the monitor is visible due to the mask 64. As long
as the video image is not shifted beyond the mask limits, ~he
source video blanking interval will not be visible, and the
image 60 will appear to move with respect to the line of sight
61. ~ere, the object is to shift the framing of tne visual
display, per frame, by delaying the blanking signals such that
the image is lined up with the line of sight. This is accomplished
via manual positioning of the user's controls 34.
Figure 3.1 shows the unshifted video source horizontal
sync pulse 76 present on line 20, Figure 3.2 shows the corres-
ponding unshif~ed red source video signal for a typical raster
line, which includes an active portion 78 and a blanking portion
80. The blanking portion 80 is shown to occur after the active
line and corresponds to the beam retrace period. Figure 3.3
shows the corresponding image.
Figure 4.1 ShOWS the source horizontal sync signal
76, as shown in ~igure 3.1, while the delayed horizontal sync
pulse 82 is shown in Figure 4.2. The red source video signal
is shown in Figure 4.3 and includes the normal source video
blanking portion 84, an active line 86 and a reblanking portion
88 which occurs during the delayed sync portion 82 when retracing
actually occurs~
By delaying the sync signal 82, there is caused a
spatial shift in the position of the video on the monitor,
as well as a shift in the blanking period 84 as indicated in
Figure 4.4. Thus the image 60 appears to move within the window
62 proportional to the amount that the sync signal is delayed.
Figure 4.5 shows the video image 60 lined up with
the line of sight 61. Again, it is noted that the mask 64 causes
only a portion of the monitor to be visible since such mask
64 covers the peripheral portions of the monitor screen.
Thus, there has been provided, in a system having
a video monitor for displaying an image, a system external to
the video monitor, for reposltloning such video image corresponding
to changes in the viewers defined line of sight with respect ~o
a real-world reference, by shifting the sync signal to thereby
shift the video image.
While the invention has been described above with
respect to its preferred embodiments, it should be understood
that other forms and embodiments may be made without departing
from the spirit and scope of the invention.
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