Composite video image device and related method

A composite video imaging device and related method are provided wherein a first and a second video signal, each of which respresents a plurality of lines of video data, are received and converted into corresponding first and second pixel data signals. The first and second pixel data signals are stored by a first and second storage means at a first and a second frequency, respectively, the loading of the first and second pixel data signals occurring independent of one another to permit the first and second pixel data signals to correspond to first and second video signals with different line and/or frame frequenices. Control means are provided for selecting the first or the second pixel data signal for each pixel to be displayed on a monitor and for delivering each selected pixel data signal to the monitor for display of a resultant composite video image.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates generally to a method and apparatus for providing a 
composite video image for display on a monitor, and specifically to a 
method and apparatus which permit first and second video signals having 
different line and/or frame frequencies to be selectively displayed on the 
monitor. 
2. Background Information 
In previously known systems, in order for a video signal having a first 
frequency to be delivered to a monitor for display at a second frequency 
of the first frequency, it is necessary to use two different memory units. 
While the video signal is being written into the first memory unit at the 
first frequency, the video signal is being read from the second memory 
unit at the second frequency. Similarly, while the video signal is being 
written into the second memory unit at the first frequency, the video 
signal is being read from the first memory unit at the second frequency. 
An example of such a device is given below. 
These known systems, however, require that the second or output frequency 
be equal to, or a multiple of, first or input frequency so that the 
frequency of the output video signal will be synchronized to the frequency 
of the input video signal. As a result, such previously known systems 
could not be used to display a composite video image of two or more 
asynchronous video signals on a monitor. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a video 
device which permits the simultaneous display of a composite video image 
of two or more asynchronous video signals. 
It is a further object of the present invention to provide a video device 
for displaying a composite video image on a monitor which requires a 
minimum amount of memory. 
Additional objects and advantages of the invention will be set forth in 
part in the description which follows, and in part will be obvious from 
the description, or may be learned by practice of the invention. 
To achieve the objects and in accordance with the purpose of the invention, 
as embodied and broadly described herein, there is provided, for display 
on a monitor, a composite video image formed from first and second video 
signals. The video device comprises means for receiving the first and 
second video signals, each representing a plurality of lines of video 
data; means for converting the first video signal into first pixel data 
signals and a control signal, and for converting the second video signal 
into second pixel data signals; first and second storage means for storing 
the first and second pixel data signals, respectively; first and second 
loading means for independently loading the first and second pixel data 
signals, respectively, into the first and second storage means, 
respectively, at first and second frequencies corresponding respectively 
to the first and second pixel data signals; output means, coupled to the 
first and second storage means, for forming an output signal representing 
the composite video image from portions of the first and second pixel data 
signals selected according to the control signal; and control means, 
coupled to the output means, for causing the output means to form the 
output signal by selecting the first and second pixel data signal for each 
pixel to be displayed as the composite video image on the monitor and for 
generating the timing control signal. The first loading means operates 
independently of the second loading means, and the output signal has an 
output frequency set according to a timing control signal which is 
independent of at least one of the first and second frequencies. 
The accompanying drawings, which are incorporated in and constitute a part 
of the specification, illustrate one embodiment of the invention and, 
together with the description, serve to explain the principles of the 
invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference will now be made to the present preferred embodiment of the 
invention, an example of which is illustrated in the accompanying 
drawings. 
FIG. 1 is a block diagram of a known video image display system of the type 
described above. Display system 10 includes a central processing unit 
(CPU) 28, a video device 18 and a monitor 32. Video device 18 includes a 
first switch 20, a first memory unit 22, a second memory unit 24, a second 
switch 26, and a timing control unit 30. First and second memory units 22, 
24 are coupled to one another and to first and second switches 20, 26. 
Timing control unit 30 is coupled to each of first and second switches 20, 
26 and supplies control signals thereto. A first video signal is input 
into first switch 20, in response to the control signal from timing 
control unit 30, alternately directs that video signal to first memory 
unit 22 and second memory unit 24. The stored first video signal is 
subsequently read from first memory unit 22 and second memory unit 24 via 
second switch 26 and output to monitor 32. Also applied to second memory 
unit 24 is a control signal from CPU 28. 
Timing control unit 30 generates control signals so that as the first video 
signal is being written to first memory unit 22, a previously stored 
portion of the first video signal is read from second memory unit 21. 
Similarly, while the first video signal is being written to second memory 
unit 24, another previously stored portion of the first video signal is 
read from first memory unit 22. The timing of the writing to and reading 
from first and second memory units 22, 24 is controlled by timing control 
unit 30 via the application of control signals to first switch 20 and 
second switch 26. The video signal selected from memory units 22 and 24 by 
second switch 26 is passed to monitor 32. CPU 28 passes a control signal 
to second memory unit 24 which, in turn, may pass the control signal to 
first memory unit 22. 
Because the video image display system illustrated in FIG. 1 requires both 
first and second memory units 22, 24, the amount of memory required by 
such a configuration is generally twice that required in systems using 
only a single memory unit to receive, store, and output a video signal. 
Moreover, the video image display system illustrated in FIG. 1 requires 
that the frequencies of the video signal, control signal, and selected 
video signal be synchronous because of the complementary use of the first 
and second memory units. This requirement of synchronicity severely 
restricts operation of the system in the manner described above. 
FIG. 2 illustrates a block diagram of a video image display system 
incorporating the teachings of the present invention. As illustrated in 
FIG. 2, video image display system 12 includes a keyboard 34, a first 
signal generator 36, a second signal generator 37, a video device 38, a 
mouse 40, and a monitor 42. Keyboard 34 is coupled to first signal 
generator 36 and passes user inputs thereto. First signal generator 36 is 
also coupled to a printer (not shown) and to video device 38. 
Communication signals are passed from first signal generator 36 to video 
device 38 and from video device 38 to first signal generator 36. Also 
passed from first signal generator 36 to video device 38 is a first video 
signal. A second video signal is passed to video device 38 from second 
signal generator 37. Video device 38 is also coupled to mouse 40 from 
which user inputs may be received, to a host computer (not shown) to which 
communication signals may be sent and received, and to monitor 42 which 
receives selected pixel data signals from video device 38. The function of 
video device 38 will now be described in connection with FIGS. 3-5. 
FIG. 3 illustrates a block diagram of video device 38. As shown therein, 
video device 38 includes a receiver 44, a converter 46, a first loading 
unit 48, a second loading unit 50, a first storage unit 52, a second 
storage unit 54, an output unit 56, and a controller 58. 
Receiver 44 receives a first video signal from first signal generator 36 
(shown in FIG. 2) and a second video signal from second signal generator 
37 (shown in FIG. 2) . The first video signal and second video signal are 
output from receiver 44 to converter 46 which covers the first and second 
video signals to corresponding first and second pixel data signals, 
respectively. The first and second pixel data signals are inputs to first 
loading unit 48 and second loading unit 50, respectively. The first and 
second pixel data signals are output from first and second loading units 
48 and 50, respectively, to first and second storage units 52, 54 
respectively. The first and second pixel data signals, respectively are 
stored in first storage unit 52 and second storage unit 54, respectively, 
are output to output unit 56. Also connected to output unit 56 is 
controller 58 which also monitors the first and second video signals. 
Output unit 56 outputs selected pixel data signals to monitor 42. 
The first and second video signals each represent a plurality of lines of 
video data. The first and second video signals may have asynchronous 
frequencies, which means that the line and/or frame frequencies of the 
first and second video signals need not be multiples of each other, but 
rather may be independent of one another. The first and second video 
signals are passed from receiver 44 to converter 46 where they are 
converted to digital signals. The conversion is preferably accomplished by 
sampling the first and second video signals at frequencies corresponding 
to the first and second video signals respectively, to enable generation 
of first and second pixel data signals having different line and/or frame 
frequencies. 
The first and second pixel data signals are then passed through first 
loading unit 48 and second loading unit 50, respectively. Each of the 
loading units 48,50 preferably comprises a plurality of input shift 
registers for loading the first and second pixel data signals into first 
storage unit 52 and second storage unit 54, respectively at first and 
second frequencies, respectively. First loading unit 48 and second loading 
unit 50 operate independently of one another to permit the first and 
second pixel data signals, corresponding to the first and second video 
signals, respectively, and have independent line and/or frame frequencies. 
As the first and second video signals are stored in the first storage unit 
52 and second storage unit 54, respectively, output unit 50 removes the 
first and second pixel data signals from first storage unit 52 and second 
storage unit 54 at an output frequency is; set independent of at least one 
of the first and second frequencies of the first and second pixel data 
signals. 
As the first and second pixel data signals are removed from storage units 
52,54, they form an output signal labelled "Selected Pixel Data Signals"in 
Fig. 3. The output is used for display of a resultant composite video 
image on monitor 42. To generate the output signal, controller 58 passes 
control signals to output unit 56 to select the first or the second pixel 
data signal from output unit 56 for each pixel to be displayed on monitor 
42. Controller 58 generates the control signals using the first and second 
video signals. 
FIG. 4 is a more detailed block diagram of the present preferred embodiment 
of video device 38. Certain specific areas of correspondence between FIGS. 
3 and 4 will be set forth in the following description. As shown therein, 
video device 38 includes receiver 44, converter 46, and controller 58, as 
shown in FIG. 3. Device 38 also preferably includes a frame buffer memory 
unit 64, having load units 48, 60 as well as unloading units 52, 54 shown 
in FIG. 3. In addition, video device 30 in FIG. 4 includes a red, a green, 
and a blue look-up table 78, 80, 82, respectively, and a triple 
digital-to-analog (D/A) converter 84 coupled to tables 78, 80, 82. 
Preferably output unit 56 in FIG. 3 includes unloading units 55, 57, 
tables 78, 80, 82, and D/A converter 84 in FIG. 4. 
As shown in FIG. 4, converter 46 includes a first analog-to-digital (A/D) 
converter 60, a first sampler 61, a second A/D converter 62, and a second 
sampler 63. Frame buffer memory unit 64 includes first, second, and third 
loading units 48, 60, 66 respectively, first second and third storage 
units 52, 54, 70, respectively, and first, second, and third unloading 
units, 55, 57, 68, respectively. Controller 58 includes a row operation 
sequencer 72, a direct memory access (DMA) sequencer 74, and a central 
processing unit (CPU) 76. 
The first and second video signals from receiver 44 are passed to first and 
second A/D converters 60, 62, respectively, in converter 46. A/D 
converters 60, 62 digitize the respective video signals which are passed 
to first and second sampler 61, 63, respectively. Samplers 61, 63 sample 
the respective digitized video signal at independent sampling rates. 
Preferably, the rates of samplers 61 and 63 are set so that the same 
number of samples is obtained for each line of video of both the first and 
second video signals. Thus, the sampling rates are preferably determined 
in accordance with the frequency of the respective first and second video 
signals. 
The sampled signals are passed to first and second loading units 48 and 50, 
respectively of frame buffer memory unit 64. First and second loading 
units 48 and 50 pass the pixel data signals to first and second storage 
units 52 and 54, respectively which in turn pass the pixel data signals to 
first and second unloading units 55 and 57, respectively. 
The first video signal, like the second video signal, normally contains 
video data representative of an image to be displayed However, on occasion 
the first video signal comprises pixel control data. Pixel control data 
includes specifying mask data for each pixel location, whether the 
displayed pixel for that location will come from the first video signal or 
the second video signal. When control video data is received, the output 
of sampler 61 is directed to loading unit 66 instead of loading unit 48. 
Loading unit 66, storage unit 70 and unloading unit 68 operate on the 
control video data of the first video signal in the same manner that 
loading unit 48, storage unit 52 and unloading unit 68 operate on the 
normal video data of the first video signal. 
Preferably, the frame buffer is constructed as a plurality of planes of 
integrated circuits. The first loading unit 48, first storage unit 52, and 
first unloading unit 55, together comprise a first set of planes 86. 
Similarly, second loading unit 50, second storage means 54, and second 
unloading unit 57 together comprise a second set of planes 88 and third 
loading unit 66, third storage unit 70, and third unloading unit 68 
together comprise a third set of planes 90. 
First, second, and third set of planes 86, 88, 90 receive, store, and 
unload the pixel data and pixel control signals output from converter 46. 
Each plane comprises at least one integrated circuit chip on which the 
respective loading, storage and unloading units are provided. An example 
of a satisfactory integrated circuit chip may be found in U.S. patent 
application Ser. No. 06/571,991 filed Jan. 19, 1984, entitled "A Multiport 
Memory And Source Arrangement For Pixel Information," now abandoned in 
favor of Ser. No. 07/068,728, filed Jun. 29, 1987, the contents of which 
are incorporated herein by reference. The configuration of sets of planes 
86, 88, 90 will be discussed in detail below in connection with FIG. 5. 
In the preferred embodiment, the first and second video signals are also 
passed from the output of receiver 44 to controller 58 inputs of row 
operation sequencer 72. From the first and second video signals, row 
operation sequencer 72, DMA sequencer 74, and CPU 76 operate to output a 
first control signal to first, second and third storage units 52, 54 and 
70, respectively and a second control signal to red, green, and blue 
look-up tables 78, 80, 82. The first control signal controls the 
frequencies with which the first and second pixel data signals are 
unloaded by unloading units 55, 57, 68. Accordingly, the unloading of the 
pixel data and control signals can occur at a frequency set independently 
of the frequencies at which the first and second pixel data or control 
signals were loaded into storage units 52, 54 and 70. 
The pixel data or pixel control signals output from first, second, and 
third unloading units 55, 57, 68, respectively are passed to inputs of 
red, green, and blue look-up tables 78, 80, 82, respectively. The pixel 
data and control signals, controlled by the second control signal output 
from controller 58, are correlated with known color values stored in the 
look-up tables. The red, green and blue signals output from look-up tables 
78, 80, 82 respectively identify specific red, green, and blue color 
components to be displayed at each particular pixel location. The outputs 
from tables 78, 80, 82 are passed to inputs of triple D/A converter 84 
which outputs selected pixel data signals to monitor 32. The pixel control 
signals from third unloading unit 68 are used in tables 78, 80, 82 to 
select for each pixel location either the first or the second pixel data 
signal. 
FIG. 5 is a detailed illustration of frame buffer memory unit 64. As shown 
therein, memory unit 64 comprises first, second and third sets of planes 
86, 88, 90, respectively. Because the loading units and unloading units 
illustrated in FIG. 4 comprise a plurality of input and output shift 
registers, the loading units and unloading units are identified, where 
appropriate in FIG. 5, as a shift register unit. Each shift register unit 
and memory unit comprises at least one integrated circuit chip. Depending 
upon the storage contraints of the integrated circuit chip used, it may be 
necessary to configure a plurality of integrated circuit chips into a 
cascaded formation to achieve storage capabilities consistent with the 
display capabilities of monitor 32. For example, four integrated circuit 
chips connected in series may be used for a particular embodiment. 
FIG. 5 illustrates a configuration of frame buffer memory unit 64 wherein 
first set of planes 86 comprises a pair of integrated circuit chips. The 
first pixel data signal input to first plane 86 is received by the loading 
units of the shift register units of each integrated circuit chip and is 
stored by the respective memory units. Separate integrated circuit chips 
are provided to load, store, and unload separate bits of the first and 
second pixel data signals. For example, second set of planes 88 may 
comprise twelve planes of four integrated circuit chips cascaded in series 
to load, store, and unload the red, green and blue color components of the 
second pixel data signal. Third set of planes 90 preferably comprises a 
single plane of integrated circuit chips cascaded in series for storing 
mask data corresponding to each pixel to be displayed on monitor 32. 
It will be apparent to those skilled in the art that various modifications 
and variations can be made in the apparatus and method of the present 
invention without departing from the spirit or scope of the invention. 
Other embodiments of the invention will be apparent to those skilled in 
the art from consideration of the specification and practice of the 
invention. It is intended that the specification and examples described 
herein be considered as exemplary only, with a true scope and spirit of 
the invention being indicated by the following claims and their 
equivalents.