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BACKGROUND OF THE INVENTION
The invention is in the field of image display composition, and more
particularly is in the field of systems which combine graphics and video
images for display on a single display device.
In systems which utilize a display to represent and explain services to
interested persons, it is often desirable to display a scene including
video and graphics imagery. For example, the display of program material
with spoken narrative explanation will be incomprehensible to a deaf
person. However, the provision of written narrative in a section of the
program display will permit a deaf person to comprehend both the visual
and verbal content of the program. Manifestly, the written portion must be
presented on the same display as the visual program if the deal viewer is
to appreciate the verbal and visual segments simultaneously.
One way of providing the written verbal narrative on the same display is to
utilize a conventional graphics generator to generate common alphanumeric
characters. Normally, the operation of the generator is directed by a
program controller which would insure that the written verbal content
output by the generator is synchronized with the visual presentation.
In other applications, it is useful to provide a display system which can
display not only written program narration, but a board set of graphics
images and symbols which can be displayed in any combination with video
images. Such a system would be flexible and adaptable to a wide variety of
uses.
Therefore, it is evident that there exists a need for a display apparatus
having the capability of enabling the display of both graphics and video
images in a variety of combinations.
SUMMARY OF THE INVENTION
The present invention is an apparatus which, under the control of a format
selection processor, combines video and graphics image signals from
respective sources to produce a display signal suitable for causing a
display device to show the images in a variety of selectable scene
formats.
The apparatus of the invention includes a video signal generator which
provides a signal representative of a video image, a graphics generator
which provides a graphics signal representative of a graphics image, and a
control device which selects one of a plurality of scene formats in which
one or more of the images is to be displayed and provides a signal
representative of the selected format. A format control and composition
circuit responds to the format signal by selectively processing the video
and graphics signals to produce a display signal which causes the display
to present the selected scene format containing the image to be displayed.
The format control composition circuit processes image signals by
selecting, in response to the format signal, and in synchronism with the
video signal, a portion of an image signal representative of a portion of
an image to be displayed. The circuit then produces a display signal
consisting of a sequence of selected image signal portions. The display
signal is provided by the format control and composition circuit in
synchronism with the video signal.
The invention also contemplates a method of combining video and graphics
signals to produce a display signal which causes a display device to
display one or more of the images in multiple, selectable formats. The
method includes the steps of selecting a display format, selecting, in
response to the selected format, and in synchronism with the video signal,
a portion of an image signal representative of a portion of an image to be
displayed, and synchronously providing a sequence of selected image signal
portions as the display signal.
Therefore it is an object of the present invention to provide an improved
apparatus for providing a display signal which causes a display device to
combine video and graphics images and to display the combined images in
multiple, selectable formats.
A further objective of the present invention is to provide an apparatus
which combines video and graphics signals in selectable ways which permit
the display of the combined images in multiple, selectable formats.
A further object of the present invention is to provide a method for
combining video and graphics image signals to produce a display signal
which causes a display device to display one or more of the images in
multiple, selectable formats.
Other objects and further advantages of the disclosed invention will become
more apparent when the following detailed description is taken together
with the described drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating the use of the apparatus of the
invention in a display system.
FIG. 2 illustrates a portion of a system routine for operating the FIG. 1
system to display video and graphics images in multiple, selectable scene
formats.
FIG. 3 illustrates a segment of a selected scene format wherein a graphics
image is displayed against a predetermined background.
FIG. 4 is a magnified portion of the selected scene illustrated in FIG. 1.
FIG. 5 is a magnified portion of the scene segment illustrated in FIG. 3.
FIG. 6 is a conceptual drawing illustrating the concept of the invention.
FIG. 7 is a partial schematic diagraph illustrating the format control and
composition circuit of the invention and its interconnection with video
and graphics image signal generators.
FIG. 8 is a detailed schematic diagram of select logic which is included in
the format control and composition circuit.
FIG. 9 is a state diagram of the programmed logic array which forms a part
of the select logic of the format control and composition circuit.
FIG. 10 is a table illustrating how the output states of the FIG. 9 state
table control the selection of image signal portions which are provided as
a display signal to the red gun of a color display device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The system of the invention is illustrated in a typical operational
environment in FIG. 1. In FIG. 1 a conventional three-gun, color CRT
display 10 is included in a system which interacts with a user to perform,
for example, an automobile leasing transaction. In order to inform the
customer of the automobiles which are available to be leased, moving video
images of the automobiles are displayed on the screen of the display 10.
One or more graphics images can be displayed together with the images of
the automobile to indicate the customer's acceptance or non-acceptance of
a pictured automobile. For example, the graphics images may consist of the
words YES and NO which are enclosed in respective boxes on the lower part
of the display screen.
A customer indicates his response to touching one of the boxes and a
conventional touch screen apparatus 11 provides an indication of the box
which has been touched.
Depending upon the customer's decision, another image of an automobile may
be projected together with the decision boxes should the customer decide
not to accept the initially displayed automobile. Alternatively, if the
customer decides to accept the automobile, another image may be shown, for
example, a scene comprising a listing in alphanumeric graphic images of
the different rental plans available for the selected automobile.
Displays such as that indicated by 10 and touch screen systems which
perform the functions required of the touch screen apparatus 11 are
well-known in the art. In the arrangement just described, the display is
required to display scenes which comprise both video and graphics images
separately or in combination. The touch screen apparatus 11 provides a
signal indicating when a particular display is to be changed. In this
operational application, the apparatus of the invention (indicated by 12
in FIG. 1) can respond to the signals provided by the touch screen
apparatus 11 by selecting a scene format in which one or more video or
graphics images are to be displayed. The apparatus 12 further selects one
or more images to be displayed in the selected format and composes a
display signal which is effective to cause the display 10 to display the
selected images in the selected format.
The apparatus 12 includes a control processor 13 which is connected
conventionally to a typical bus interface 14 comprising address, data, and
control lines. The bus 14 interconnects the processor 13 with the touch
screen 11. The bus 14 also interconnects the processor 13 with a graphics
generator 16 and a display format control and composition circuit 18. The
processor accesses a laser disc player 20 through the control and
composition circuit 18, and the disc player 20 is connected to a
conventional NTSC decoder 22.
The processor 13 can comprise, for example, a microprocessor which is
conventionally programmed to execute a format and image selection routine,
described in greater detail below. In the preferred embodiment, the
control processor 13 includes a microprocessor available from Zylog, Inc.,
under the tradename Z-80.
The graphics generator 16 is connected to be controlled over the bus
interconnection 14 by the processor 13. Both FORMAT SELECT and GRAPHICS
SELECT signals are provided by the processor to the graphics generators.
The FORMAT SELECT signal indicates the scene format which has been
selected for display. If the selected scene is to contain a graphics
image, the image is indicated by the GRAPHICS SELECT signal. In response
to the FORMAT and GRAPHICS SELECT signals, the generator generates and
provides a graphics image signal representative of a graphics image
selected by the processor 13, The operation of the graphics generator 16
is synchronized to the video image signal and to the operation of the
display 10 by the provision of an SYNCHRONIZATION signal from the control
and composition circuit 18.
Selection of video images is made by the processor 13 which passes a VIDEO
SELECT signal to the control and composition circuit 18. The VIDEO SELECT
signal is indicative of a storage location on a laser disc, not shown,
which is conventionally used by the laser disc player 20. Video images are
extracted from the indicated laser disc locations and provided by the
player 20 as video image data to the NTSC decoder 22 which processes the
video image data into conventional NTSC composite video format and
provides the formatted video image signal to the control and composition
circuit 18.
As is typical, the NTSC decoder also provides a composite NTSC
synchronization signal. The NTSC synchronization signal is fed to the
display 10 which responds to it and to the DISPLAY signal to display the
selected images in the selected format according to the well-known, two
dimensional scanning technique.
The synchronized graphics image and composite video image signals are fed
to the display format control and composition circuit 18 which combines
them in a manner described hereinbelow to produce the DISPLAY signal. The
DISPLAY signal comprises components for operating the red, green and blue
(R, G, B) guns of the display device 10.
There are a variety of available equipments and devices which can be used
to perform after "certain" functions certain of the apparatus 12
illustrated in FIG. 1. For example, the graphics generator 16 can include
a high resolution color graphics generator available under the equipment
number STD-C-GDC-1024 from Antares Technology Associates, Inc., San Diego,
Calif. The laser disc player 18 can include a Pioneer LDV1000 layer disc
player which operates using a laser disc having a video track which is
divisible into separate, uniquely addressable sections, each of which can
conventionally store video image data.
When the apparatus of the invention operates in conjunction with a
user-interactive setup such as the touchscreen display 10, the control
processor 13 can be appropriately programmed to select various formats and
images for display on the display device 10 in response to touch
indications received from the touch screen apparatus 11. For example, the
processor may be programmed as illustrated by the flow chart of FIG. 2 to
output an initial screen showing a video image including a moving
automobile. This display can be obtained, for example, from an
appropriately addressed section of the laser disc included in the disc
player 20. The processor also controls the graphics generator 16 to
produce a graphics message directing a person to touch the screen if he
wishes to rent an automobile. Both the graphics image comprising the
message to the user and the video image comprising the scene of the moving
automobile are provided to the display control and composition circuit 18
which combines them to produce the DISPLAY signal.
The initial scene is displayed until a customer, desiring to rent a car,
touches the screen, which action is detected by the touch screen apparatus
11 which provides an appropriate touch response signal to the processor
13.
When the touch response signal is received by the processor 13, its
operational program selects a scene format which, for the purposes of
illustration, can be characterized as format 1, and selects images to be
displayed according to the selected format.
The processor 13 then sends appropriate FORMAT and graphics select signals
to the graphics generator 16 indicating a selected format and a graphics
image, if one is included in the format, and a VIDEO SELECTION signal
which is passed through the control and composition circuit 18 to the disc
player 20, indicating a selected video image if the scene includes one. At
the same time the FORMAT SELECT signal, indicating the format selected, is
also provided to the display format and composition circuit 18, which
causes the circuit to combine the selected graphics and video image
signals in a manner determined by the format control signal and to provide
the combined signals as the DISPLAY signal.
The selected format 1 can include the scene illustrated on the display of
FIG. 1. In this case, the selected video image would be of a moving
automobile while the selected graphics image would comprise the
alphanumeric characters enclosed in the respective rectangles. Now, the
selection of another scene format and another image or images to be
presented will depend upon which rectangle has been touched in the scene
illustrated on the display 10 of FIG. 1. In case the NO image is touched,
the touch screen apparatus 11 will provide an appropriate signal to the
processor 13 indicating the customer's rejection of the displayed
automobile. This may be characterized as TOUCH RESPONSE 1 in FIG. 2.
In the case of TOUCH RESPONSE 1 the processor 13 will select another video
image illustrating another automobile and will display that image together
with the previously-selected graphics image in format 1. This process can
be repeated until a YES response, characterized as TOUCH RESPONSE 2 in
FIG. 2 and indicating selection of the displayed automobile, is received.
When the YES response to received by the processor 13, it can select a new
scene format, different from format 1, and a new set of images to be
displayed according to the new format. A representative new format would
include a written verbal representation of leasing rate plans which would
be available to the customer for the selected automobile. This could
comprise, for example, a list of time periods for which the car could be
rented, each displayed with the current rental rate applying to that
period. The listing can be displayed as a solely graphics image including
the graphics symbols necessary to present the list. The display of a
graphics image according to format 2 is illustrated in FIG. 3.
Returning to FIG. 2, after the format 2 list has been displayed for a
predetermined period of time, the processor 13 returns to its initial
state, reselects the initial state images and format, and the apparatus of
the invention operates the display 10 to provide the initial display.
The operation of the display format control and composition circuit 18,
which is central to the operation of the apparatus 12 of the invention,
can be understood with reference to FIGS. 4-6. As is conventional, a scene
is presented on the display 10 in composite, scanned NTSC video format
which is a time sequence of analog traces, each trace representing the
three-color RGB (red, green, blue) signal along a horizontal sweep line of
the scene. Each horizontal sweep line is composed of a sequential array of
individual picture elements or pixels, each representing a small portion
of the displayed scene which is scanned by the horizontal line.
Subdividing the scanned scene in this manner produces a set of pixels in a
two-dimensional array with each pixel individually identified by its
coordinates in the array.
FIG. 4 illustrates a 3.times.3 matrix of pixels from the location
indication by 30 in the scene presented by the display 10 in FIG. 1. The
pixels in the matrix of FIG. 4 are arbitrarily numbered for purposes of
illustration only. In the format of the FIG. 1 scene, a portion of the
graphics image generated and provided by the generator 16 and comprising a
portion of the right hand vertical side of the box containing the message
YES includes pixels P.sub.2, P.sub.5, and P.sub.8. The other pixels of the
matrix represents portions of the road included in the video image
extracted from the laser disc player 20. The control and compositions
circuit 18 controls the characteristics of the DISPLAY signal so that,
while it is tracing the segment of the horizontal line containing pixels
P.sub.1 -P.sub.3 those characteristics are determined by the composite
video image signal while the DISPLAY signal is tracing the portion of the
scene occupied by the pixels P.sub.1 and P.sub.3. Similarly, while the
DISPLAY signal is providing the park of the scene occupied by the pixel
P.sub.2, its characteristics are determined by the portion of the graphics
image signal supplied by the generator 16 which defines that portion of
the YES box.
A portion 32 of the FIG. 3 scene is magnified in FIG. 5 where the 3.times.3
pixel array now spans the symbol numeral 1 which is presented against a
uniform background. As with the scene portion illustrated in FIG. 4, that
part of the symbol including pixels P.sub.2, P.sub.5, and P.sub.8 are
drawn by portions of the DISPLAY signal whose characteristics are
determined by the graphics image signal from the generator 16. The
background portions including the other pixels are determined by the
FORMAT signal supplied to the control and composition circuit 18 in a
manner described hereinbelow.
The formats among which the processor selects to specify the general form
of the scene presented by the display 10 can be understood with reference
to FIG. 6. In FIG. 6 three planes are shown which are selectively
activated by the apparatus of the invention in order to establish a scene
format. When a video image is to be included in the format, it is
displayed on what may be considered a video plane. When a graphics image
is to be displayed embedded in a selected background, the video plane is
blocked by the activation of background/graphics plane, with the selected
image being presented on the background. In the case where a graphics
image is to be superimposed onto a video image, the background/graphics
plane is made transparent, everywhere except where the graphics image is
to be displayed. With this arrangement, the graphics image overlays the
video plane to produce the effect illustrated in the FIG. 1 scene.
In the case where the control processor 13 selects a large or complex
graphics image for display, it may be that the graphics generator 16
requires a measurable amount of time to reconfigure itself for generation
of the image. In this case it would be desirable to block the graphics
plane while the image is being generated until such time as the graphics
generator 16 has configured itself to generate the image. A foreground
format is provided for this purpose which essentially consists of
transferring the background/graphics plane from its position to a point in
front of where the graphics image is to be displayed so that it is placed
between the viewer and the asembling graphics image. Then, activation of
the foreground plane will block the display of any of the planes behind it
until such time as an image is ready for display on its respective plane.
When the image is ready for display, the foreground plane can be shifted
back to the position of the background plane. In this position it can
either be made transparent if video and graphics images are to be
displayed together or it can be activated with a selected background if
only graphics images are to be displayed.
The apparatus of the invention therefore has the ability to select one from
a plurality of display formats. In one format a video image extracted from
the disc player 20 is displayed alone. In the second format, a graphics
image generated by the graphics generator 16 is superimposed on a video
image from the disc player. Another format presents a graphics image
against a selected background. Finally, in the foreground format, the
display of any image is curtained by a uniform foreground.
With reference now to FIGS. 7 and 8, the detailed structure and operation
of the apparatus of the invention can be more fully appreciated. The
format control and composition circuit 18 includes an information staging
and synchronization section 40. This section 40 includes a subaddressable
section SUBADDR1 for selection of a video image in the laser disc player
20. A second subaddressable section SUBADDR2 stages format selection data
from the control processor 13.
For the selection of video imagery, the control processor 13 address
SUBADDR1 on the address portion of the bus 14. At the same time it
provides data on the data section of the bus which indicates the storage
section of the laser disc containing the desired video image. The data is
forwarded as a VIDEO SELECT signal by section SUBADDR1 to the laser disc
player 20. The disc player then accesses the selected section on the disc
and forwards the stored information to the decoder 22 which renders it
into a conventional composite video format including red, green and blue
(R, G, B) signals. The composite signals are forwarded as the VIDEO IMAGE
signal. As stated above, the decoder 22 also provides a standard composite
SYNCHRONIZATION signal comprising horizontal and vertical synchronization
segments which are used to synchronize the operation of the display 10 in
a conventional manner.
The SYNCHRONIZATION signal is also provided to a synchronization strip
circuit 42 which operates in a well-known manner to strip the horizontal
synchronization (HSYNCH) signal. As is known, the HSYNCH signal defines
the beginning of the application of a horizontal sweep of the DISPLAY
signal to the display 10 is displaying a line of a presented scene. The
HSYNCH signal is fed to a standard phase comparator 44 which compares it
with an oscillating signal having the same frequency as HSYNCH. The
comparator circuit 44 develops an error signal indicative of the phase
error between HSYNCH and the oscillatory signal which is provided to a
pixel clock circuit 46. The pixel clock circuit provides a clock signal
which oscillates at the frequency with which the pixels are swept in a
horizontal sweep of the DISPLAY signal. The error signal from the
comparator circuit 44 therefore synchronizes the phase of the PIXEL CLOCK
signal with the occurrence of pixels during the sweep of a horizontal line
on the display 10.
The PIXEL CLOCK signal is provided to a synchronization section 50 of the
graphics generator 16. The synchronization section 50 responds to the
PIXEL CLOCK signal by clocking the operations of an image generation
section 52 of the graphics generator 16. The STD-C-GDC-1024 device which
forms the graphics generator 16 comprises a preprogrammed microprocessor
which responds to high level commands from the control processor 13 to
generate the selected graphics image and provide it pixel-by-pixel at the
rate of the PIXEL CLOCK signal. The microprocessor of the generator 16
receives the GRAPHICS SELECT signal from the control processor 13 which
indicates which image has been selected, the color the image is to be
displayed in, and the location in pixel coordinates which the image is to
occupy on the screen. The microprocessor of the generator 16 then employs
conventional graphics generation algorithms to generate the graphics image
at the PIXEL CLOCK rate and to synchronize its output with the operation
of the display 10 so that the image is provided at the time the DISPLAY
signal is sweeping the display locations which the image is to occupy.
When the graphics generator 16 has responded to the GRAPHICS SELECT signal
provided by the control processor 13, and configured itself for provision
of the graphics image signal, it sends a signal GDONE back to the control
processor 13 indicating that the graphics image selected can now be
generated. The signal GDONE is used by the control processor 13 to shift a
foreground plane curtain to its normal background position so that the
graphics image can be displayed.
The format selected by the control processor 13 is provided s the FORMAT
SELECT signal to both the generator 16 and the subaddressable format
section SUBADDR2 of the circuit 40, which forwards the signal as a FORMAT
signal.
A select logic circuit 60 receives the GRAPHICS IMAGE signal from the
generator 16, the FORMAT signal from the subaddressable section SUBADDR2,
and the VIDEO IMAGE signal from the NTSC decoder 22. The select logic
circuit 60 responds to the FORMAT signal by processing the GRAPHICS IMAGE
and VIDEO IMAGE signals to produce a DISPLAY signal which presents a
selected image or selected images in the selected format. The control
logic circuit 60 also responds to the FORMAT signal by selectively
activating the foreground and background planes and implementing the
selected background or foreground. The select logic circuit 60 further
responds to the FORMAT signal by making the background/graphics plane
transparent when the video display format is selected.
As shown in FIG. 8, the select logic circuit 60 comprises a conventional
programmable logic array (PLA) which, in the preferred embodiment,
comprises an 82S153 device. An array of three decoders 64-68 are connected
to the outputs of the PLA 62. In turn, the outputs of the decoders 64-68
are fed through a bank of standard buffer circuits, one of which is
indicated by 70, to the inputs of three bilateral switches 80, 82, and 84.
Preferably, the decoder circuits comprise 7445 devices, and the switches,
4066 circuits.
The inputs to the PLA 62 include the GRAPHICS IMAGE signal which is a
four-bit digital word representative of a current pixel portion of a
graphics image and output by the graphics generator 16. The GRAPHICS IMAGE
word is updated at the PIXEL CLOCK rate. The four bits of the GRAPHICS
IMAGE signal are provided by the graphics generator on separate, parallel
lines G.sub.0 -G.sub.3. The FORMAT signal forwarded from the control
processor 13 also comprises four separate, parallel bits F.sub.0 -F.sub.3.
The FORMAT and GRAPHICS IMAGE signals are connected to respective input
nodes of the PLA 62 as shown in FIG. 8.
The output nodes of the PLA 62 comprise three groups of two nodes A.sub.i
and B.sub.i. Each group of two nodes is assigned to be determinative of
the characteristics of a respective portion of the display signal which
controls one of the guns on the display 10. Thus, for example, the output
nodes A.sub.0 and B.sub.0 are assigned to control the red gun, and the
signals which they provide are denoted as A.sub.R and B.sub.R,
respectively.
In the explanation which follows, control of the portion of the DISPLAY
signal which is fed to the red gun of the display 10 is described, with
the understanding that the description also characterizes the respective
portions of the DISPLAY signal controlling the green and blue guns as
well. Thus, the A.sub.R and B.sub.R signals are fed to the decoder 64
which decodes them by activating a respective one of its output ports. The
output ports of the decoder 64 are connected through their respective
buffering circuits to the control nodes C.sub.0 -C.sub.3 of the switch 80.
The switch 80 also receives, as illustrated, at its input nodes I.sub.0
-I.sub.3 three input voltages V.sub.1 -V.sub.3 and the red portion R of
the composite video signal from the NTSC decoder 22. The output nodes of
the switch 80, O.sub.0 -O.sub.3, are connected together with the common
connection being fed as the red R display portion of the DISPLAY signal.
The R portion of the DISPLAY signal is conventionally connected to drive
the red gun of the display 10.
Returning to the switches 80-84, the voltages V.sub.1 -V.sub.3 are set at
levels corresponding to white (WH), gray (G) and black (B) voltage levels
respectively. Thus, if, for example, voltage V.sub.1 were passed by the
switches 80-84 and connected therethrough to the red, green and blue guns
of the display 10, the composite display would be white.
The operation of the select logic circuit, illustrated in FIG. 8, is
determined by the combination of the instantaneous states of the GRAPHICS
IMAGE and FORMAT signals input to the PLA 62. The input signal
combinations define the output states of the PLA 62 according to the table
illustrated in FIG. 9. The output of the PLA 62 establishes the scene
format, determines the pattern of the background and foreground, maps the
GRAPHICS IMAGE signal to a color contained on a color look-up table, and
implements the display of the images represented by the VIDEO and GRAPHICS
IMAGE signals, if required.
In the table of FIG. 9, the input combinations of the FORMAT and GRAPHICS
IMAGE signals are listed vertically. Since these signals are provided on a
conventional tri-state databus, each can have one of three possible
states. Thus, for example, the F.sub.0 bit of the FORMAT signal can assume
a high voltage state indicated by H, a low voltage state indicated by L,
or an intermediate state indicated by no entry, which is essentially
equivalent to placing the F.sub.0 line driver in a high input impedance
condition. As is conventional, a dash - in the input portion of the table
represents a don't-care input condition. In the output portion of the
table, the designations H and L refer to high and lower states,
respectively.
In the table of FIG. 9 the possible combinations of the GRAPHICS IMAGE and
FORMAT signals input to the PLA62 are numbered in the column 90 labelled
"Input Signal Combination" and specified in the eight columns to the right
of the column 90. Each input signal combination determines a respective
combination of the outputs A.sub.i B.sub.i of the PLA; this is shown in
the columns labelled "Display Selection Outputs". In turn, the outputs
A.sub.i B.sub.i, which are input to the decoders 64-68, determine the
outputs of the decoders according to the table of FIG. 10. Thus, for
example, when A.sub.R B.sub.R are both low, the 0 output of the decoder 64
is selected which causes the switch 80 to provide voltage V.sub.1 as the R
portion of the DISPLAY signal. Similarly, when A.sub.R is high and B.sub.R
is low, the red portion of the VIDEO IMAGE signal is provided as the R
portion of the DISPLAY signal.
It should be evident, then, that each input signal combination of FIG. 9
selects either a respective signal combination of three voltages, or the
red, green and blue portions of the VIDEO IMAGE signal, with the selected
signals provided through the switches 80-84 as the DISPLAY signal. This is
shown in the three righthand columns of FIG. 9.
When an input combination causes a respective associated combination of
voltages to be selected by the switches 80-84, the voltage combination
causes the display to assume a respective color. The colors associated
with the input and voltage signal combinations are in the column of FIG. 9
to the left of column 90.
Finally, FIG. 9 illustrates how the selected scene m and image displays are
implemented. When the F.sub.0 bit of the FORMAT signal is high, the
display 10 is caused to operate in either the video only or foreground
formats. In the video only format, the F.sub.0 bit is high, and the
F.sub.1 -F.sub.3 drivers are in their switched-off or high-impedance
states. This causes the A.sub.R signal to be high and the B.sub.R to be
low, which selects output node 1 of the decoder 64 as illustrated in FIG.
10. When the output node 1 of the decoder 64 is selected, it assumes a low
voltage state which is inverted by the buffer circuit connected between
decoder node 1 and input C.sub.1 of the switch 80. This activates the
switch S.sub.1 of the switch circuit 80, connecting the input node I.sub.1
to the output node O.sub.1. Since node I.sub.1 is connected to the R
portion of the VIDEO IMAGE signal, the switch S.sub.1 connects the R
portion to the red gun of the display 10. As illustrated in FIG. 9, the
video only state similarly configures the decoders 66 and 68 as well as
the switches 82 and 84 so that the DISPLAY signal comprises the composite
VIDEO IMAGE signal from the decoder 22.
When a foreground format is selected, the F.sub.0 bit is set high together
with one or more of the other FORMAT signal bits F.sub.1 -F.sub.3. When
this occurs, the outputs of the PLA 62 cause the switch circuits 80-84 to
be set to select some predetermined combination of the voltages V.sub.1
-V.sub.3. The voltage combination is passed through the switch circuits
80-84 as the DISPLAY signal. In the preferred embodiment, a foreground
configuration causes the display to present an unbroken, monochromatic
scene which cannot be affected by either the GRAPHIC IMAGE or the VIDEO
IMAGE signal. The unbroken, monochromatic scene will be displayed until
the FORMAT signal is changed by the control processor 13.
When a graphics image is to be presented against either a selected
background or a video image, the F.sub.0 bit of the FORMAT signal is set
to a low L state. When the format combining a video and a graphics image
is selected, all of the bits F.sub.0 -F.sub.3 are set low. This is
detected by the graphics generator and causes it to set its tri-state
logic drivers to provide bits G.sub.0 -G.sub.3 low when the display is
sweeping pixels which do not contain portions of the graphics image. Thus,
referring again to FIG. 4, when pixels P.sub.1 and P.sub.3 are being swept
by the DISPLAY signal, the graphics generator 16 sets each of its output
drivers providing bits G.sub.0 -G.sub.3 to a low state. As illustrated in
FIGS. 9 and 10, when this occurs, the outputs of the PLA 62 assume states
which cause the switch circuit 80-84 to pass the R, G, and B portions of
the composite VIDEO IMAGE signal to the display 10. However, when pixel
P.sub.2 in the same horizontal line is being swept, the graphics generator
16 will set its GRAPHICS IMAGE signal drivers to produce one of the
combinations of high voltage and high impedance signals which are
specified in combinations 1-15 of the table in FIG. 9. For example, if the
graphics image portion displayed at P.sub.2 in FIG. 4 is to be orange,
bits G.sub.0 and G.sub.3 will be set to a high voltage level, while bits
G.sub.1 and G.sub.2 will be set to the high impedance level. This
corresponds to input combination 9, which will produce the combination of
output signals necessary to cause the switching circuits 80-84 to provide
the voltages V.sub.1, V.sub.2, and V.sub.3 to be red, green, and blue
guns, respectively, of the display device 10. When the guns are activated
by this combination of voltages, the resulting portion of the graphics
image occupying the space defined by pixel P.sub.2 will be orange. As
another example, if the portion of the graphics image occupying the pixel
P.sub.5 area is to be black, then G.sub.0 is set high while bits G.sub.1
-G.sub.3 are set to their high impedance levels. This corresponds to the
graphic signal input at state 8 of the PLA table which will result in
V.sub.3, the black level voltage, being fed to each of the color guns.
When the background format is selected, the graphics generator 16 sets each
of the bits G.sub.0 -G.sub.3 to the high impedance level when the display
signal is sweeping horizontal line portions which do not contain portions
of the graphics image being displayed. This permits the output of the PLA
62 to be determined by the FORMAT signal bits F.sub.1 -F.sub.3. Thus, for
example, if, in FIG. 5, the graphics image is to be displayed in a black
background and the line containing the pixels P.sub.1 -P.sub.3 is being
swept, the input signal bits for the PLA will assume the levels defined
for them in input state 16. As the FIG. 9 table shows, input state 16 will
cause the switch circuits 80-84 to provide V.sub.3, the black voltage
level, to the red, green, and blue guns of the display 10. When the
display signal is deflected to the pixel P.sub.2 location, the bits
G.sub.0 -G.sub.3 will assume one of the input combinations 1-15, resulting
in the display of the graphics image portion occupying that pixel
location.
In view of the operation of the select logic circuit 60, one can regard the
DISPLAY signal which it produces as consisting of three parallel data
streams, one for each gun of the display device 10. Each data stream
consists of a succession of pixel-defining voltages which are synchronized
by the GRAPHICS IMAGE signal inputs to the PIXEL CLOCK signal rate. Since
PIXEL CLOCK is phased to the NTSC SYNCHRONIZATION signal, the data
streams, and thereby the DISPLAY signal, are synchronized with the
operation of the display 10 which receives the SYNCHRONIZATION signal from
the decoder 22.
Each pixel-defining voltage of a DISPLAY signal color stream is determined
by a respective input state of the FIG. 9 table. Thus, the scene-producing
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