JP2536405B2 - Video signal switching circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for processing a signal for displaying an image on a CRT, and in particular, it has two video signal inputs and detects a specific state of one of the video signals and detects the state. The present invention relates to a video signal switching circuit that selects and outputs one of two video inputs according to the above.

[0002]

2. Description of the Related Art When a CRT image signal output from a computer and an image signal of an image from, for example, a video camera, a video tape recorder, a laser disk, etc. are to be displayed at the same time, the system is the image of the video camera or the like. Analog-to-digital conversion, and then importing it into a computer, combining it with the original computer image with software and outputting as a video signal, and the image output from the computer and the image output from the video camera etc. with hardware. A method in which the two images are apparently combined and displayed is considered to be switched.

[0003]

Among the above-mentioned two methods, the former method is a method mainly performed by software, and processing such as display priority control, image data accumulation, and processing is easy. However, it requires a large amount of memory to store video images, requires a long time for display processing, and when the amount of image data is large, the movement may be slow and real-time display may not be possible, so dedicated software is required. There are some features.

On the other hand, the latter method requires no dedicated software, can display a video image or the like regardless of the application software of the computer, and can always display in real time regardless of the image data amount. It is characterized in that the priority order cannot be easily controlled, and that image data cannot be stored and processed.

An object of the present invention is to solve the problem of the control of the display priority order when adopting this method, paying attention to the advantage of the latter method in real-time display and the fact that it can be displayed regardless of application software. The present invention provides a video signal switching circuit.

[0006]

The present invention provides a video signal switching circuit which receives a first video signal and a second video signal as input and selects and outputs one of the two video signals. An addition circuit that outputs a signal of the sum of the amplitudes of the respective color components of the video signal of No. 1 and whether the value of the signal of the sum of the amplitudes output from the addition circuit is within a preset range or not is determined. A determination circuit that outputs a signal indicating the result, and a video signal selection circuit that selects and outputs one of the first video signal and the second video signal based on the signal output from the determination circuit. It is characterized by having.

[0007]

When the CRT video signal output from the computer and the video signal from, for example, a video camera, a video tape recorder, a laser disk, etc. are displayed simultaneously, R (red), G (green), output from the computer,
Only when each of the B (blue) video signals is in a specific state, by switching the video signal of the computer to a video signal such as a video signal and outputting the video signal, the computer screen is given priority over the video camera screen. And display it.

[0008]

EXAMPLES Next, examples of the present invention will be described.

FIG. 2 shows a personal computer (hereinafter referred to as P
It is a figure which shows the example which implemented this invention in the video conference apparatus which synthesize | combines and displays the image input from a video camera etc. (henceforth an external image) in the screen of C). In the video conference apparatus as in the present embodiment, it is necessary to display the external image on the original screen of the PC. When displaying a small image on a part of the CRT as shown in FIG. 2, there is no problem in most cases by simply displaying the external image on the PC screen, but as shown in FIG. 3, the external image is displayed on the CRT. When the PC screen is displayed on almost the entire screen with priority, the PC screen is almost hidden and it becomes difficult to operate the PC.

Therefore, when the RGB signal output from the PC has a specific color, this problem can be solved by providing a function of displaying the PC screen with priority over the external image. That is,
If you set icons, pull-down menus, etc. necessary for PC operation to this color, they will be given priority over external video (see Fig. 4), so even if the external video is displayed full screen Operation becomes possible.

In the case of this embodiment, R indicating the screen of the PC is displayed.
Only when the signal level of (red), G (green), and B (blue) is white or black, the external image is preferentially displayed, and in other cases, the PC screen is preferentially displayed. I am configuring.

Next, an embodiment of the present invention will be described with reference to the block diagram of FIG.

Rin1, Gin1, and Bin1 in FIG.
Video signals input from a PC, 1, 2 and 3 are direct current reproduction circuits for giving a direct current potential to these video signals, and 4 is an output of the direct current reproduction circuits 1, 2 and 3,
An adder circuit 5 that outputs a signal indicating the sum of these three signals outputs level 1 when the output voltage of the adder circuit 4 is higher than a preset value, and outputs level 0 when it is low.
A comparator circuit 6 which outputs a level 0 when the output voltage of the adder circuit 4 is larger than a preset value, and a level 1 when the output voltage of the adder circuit 4 is smaller than the preset value. An OR gate that outputs the logical sum of the outputs of 6 outputs level 1 when any one of the inputs is level 1, and outputs level 0 when both inputs are both level 0. R
in2, Gin2, and Bin2 are other external video signals, which are input in synchronization with a vertical synchronization signal and a horizontal synchronization signal (not shown) output from the PC. 8, 9, 10
Is a direct current reproduction circuit for giving a direct current level to these video signals, and 11, 12, 13, 15, 16, 17 are R
A delay line for compensating the propagation delay amount in the adder circuit 4, the comparator circuit 5 or 6 and the OR gate 7 in the video signal paths of in1, Gin1, and Bin1, and 14 is the OR gate 7.
When the output of is at level 1, Rin2, Gin2, Bin
When the video signal of 2 is selected and the level is 0, Rin1 and G
It is a selection circuit for selecting video signals of in1 and Bin1.

Next, the operation of the circuit of the embodiment shown in FIG. 1 will be described.

When only the PC screen is displayed on the CRT,
The screen of the PC may be drawn using a color other than white or black. When the output for the CRT of the PC is other than white or black, the output of the adder circuit 4 satisfies the condition of V _B <the output level of the adder circuit <V _W , so that the outputs of the comparison circuits 5 and 6 are both level 0. Then, the output of the OR gate 7 also becomes level 0, and Rin1, Gin1, Bin1 are output from the selection circuit 14.
The signal input from is output, and as a result, only the screen of the PC is output.

When an external image is displayed on the CRT, CR
The area on the T screen where the external image is to be displayed ((X1,
It suffices to fill Y1) and (the area surrounded by (X2, Y2)) with white or black before outputting. When the output for the CRT of the PC is white, the output of the adder circuit 4> V _W , and the output of the comparison circuit 5 becomes level 1. PC C
When the output for RT is black, the output of the adder circuit 4 becomes <V _B , and the output of the comparison circuit 6 becomes level 1.

In any case, the output of the OR gate 7 becomes level 1, and the external video signal R is output only in the area shown in FIG.
in2, Gin2, and Bin2 are output from the selection circuit 14.

[0018]

As described above, according to the present invention,
There is an effect that a device that can display a video image and a computer image at the same time is provided without requiring dedicated software for the computer, and that the computer image can be displayed prior to the video image as needed.

[Brief description of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing a CRT screen when video images are simultaneously displayed on a PC screen.

FIG. 3 is a diagram showing a CRT screen when a video image is displayed with priority over a PC screen.

FIG. 4 is a diagram showing a CRT screen when a video image is preferentially displayed on a PC screen.

FIG. 5 is a diagram showing how to provide a display position of an external image.

[Explanation of symbols]

 1, 2, 3, 8, 9, 10 DC regeneration circuit 4 Adder circuit 5,6 Comparison circuit 7 OR gate 11, 12, 13, 15, 16, 17 Delay line 14 Selection circuit

Claims (4)

(57) [Claims] 1. A video signal switching circuit for inputting a first video signal and a second video signal and selecting and outputting one of the two video signals, wherein each color of the first video signal An adder circuit that outputs a signal of the sum of the amplitudes of the components, and determines whether the value of the signal of the sum of the amplitudes output from the adder circuit is within a preset range, and outputs a signal indicating the result. And a video signal selection circuit that selects and outputs one of the first video signal and the second video signal according to the signal output from the determination circuit. Signal switching circuit. 2. The video signal switching circuit according to claim 1, wherein when the first video signal is only a white or black signal, the second video signal is preferentially output, and the first video signal is white. Alternatively, a video signal switching circuit which preferentially outputs the first video signal when a signal other than a black signal is output. 3. The video signal switching circuit according to claim 1, wherein the first video signal is output from the computer as C.
A video signal switching circuit, wherein the RT video signal is used, and the second video signal is a video signal output from a video camera, a video tape recorder, a laser disk, or the like. 4. A video conferencing apparatus comprising the video signal switching circuit according to claim 1.