JPH0937234A - Character signal superimposing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid mis-display of characters when no video signal input is in existence in a system where video signals from plural monitor cameras are selected and characters are superimposed and outputted. SOLUTION: A video signal 4 from plural monitor cameras is given to a video unit 1, a matrix switch or the like is selected by a signal from a changeover control section 3 and the selected signal is given to a character unit 2 and corresponding characters are superimposingly outputted. The character unit sends a control signal from an MPU to an on-screen driver with a switching timing pulse received via a changeover control section from the video unit, character data are transferred from a CGROM to a built-n VRAM and superimposed on a video signal 5. However, when no VD (vertical synchronizing signal) is not detected from the video signal 5, transfer of character data to the VRAM is inhibited and superimposition of characters when no video signal is received is stopped to avoid mis-display of characters.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a character signal superimposing device for displaying characters on a screen of a surveillance camera on a screen, and more particularly to a device for preventing erroneous display of characters when no video signal is input.

[0002]

2. Description of the Related Art A video unit for switching video signals from a plurality of surveillance cameras or the like to a plurality of output destinations by a matrix switch, and a character unit for superimposing characters representing a video signal source on each video signal from the video unit. There is a surveillance camera system configured from. The character unit reads corresponding character data from a CGROM (character data read-only memory) in response to switching of the video signal of the video unit and superimposes it on the video signal via the on-screen driver. By the way, the video unit internally generates a synchronizing signal when a video signal is not input and outputs a video / character switching timing pulse at its own timing, but the character unit is a VRAM built in the on-screen driver.
The transfer of the character data is started from the start to the second VD (vertical synchronization signal), and the transfer of the character is performed by this second VD, and the video signal is input. If the character data is not transferred, that is, if the character data is transferred to the VRAM without VD, the character display may not be displayed correctly due to the timing of the character switching. For example, "Fujitsu General" is displayed at the required position on the screen. There is a problem that what should be displayed, such as "General", which is a part of the character to be displayed, at a position other than the predetermined position.

[0003]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention takes into consideration such a point, and when a video signal is not input due to a video signal input switching or the like, the VRA built in the on-screen driver is used.
The transfer of the character data to M is prohibited, the character display is stopped so that the characters are not erroneously displayed on the monitor screen, and when the VD is input, the character data is transferred to the VRAM again and superimposed on the video signal. The point is to display the correct characters on the monitor screen.

[0004]

In order to solve the above-mentioned problems, the present invention inputs video signals from a plurality of video signal sources to a video unit and switches them in a required order / time interval by designating automatic switching. , A CGR that stores character data in the character unit, in which characters corresponding to respective video signals are superimposed and output.
OM, a sync separation circuit for separating a vertical sync signal of a video signal input from the video unit, and data read from a CGROM for a video signal input from the video unit in synchronization with a signal from the sync separation circuit. An MP that monitors a signal from the on-screen driver for superimposing a character based on the above, and a signal from the sync separation circuit, and controls the superimposition of a character by the on-screen driver by inputting a vertical synchronization signal
(EN) A character signal superimposing device composed of U and U.

[0005]

With the above construction, in the character signal superimposing device according to the present invention, when the video signal is not input from the switching destination by switching the video signal source, the input of the video signal is monitored to When the signal (vertical synchronization signal) is discriminated, the on-screen driver transfers the character data from the CGROM to the VRAM, superimposes it on the video signal, and outputs it.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a character signal superimposing device according to the present invention will be described in detail below with reference to the drawings. 1 is a block diagram of a main part of an embodiment of a character signal superimposing device according to the present invention, FIG.
FIG. 3 is a block diagram of a main part of an embodiment of a character unit. In FIG. 1, 1 is a video unit and 2 is a character unit. A switching control unit 3 controls the automatic switching between the video unit 1 and the character unit 2. Reference numeral 4 is a plurality of video signal sources, for example, a video signal from a surveillance camera, 5 is a video signal switched by a matrix switch or the like of the video unit 1, and 6 is a video signal in which characters are superposed by the character unit 2.

In the character unit of FIG. 2, 11 is an on-screen driver, which superimposes characters on the video signal 5 input from the video unit 1 based on the data from the CGROM 12. Reference numeral 13 is a VD (vertical synchronization signal) separation circuit that separates the vertical synchronization signal of the input video signal 5. 14 is M
The PU monitors the signal from the VD separation circuit 13, and when VD is detected, the on-screen driver 11 superimposes characters on the basis of the switching timing pulse 15 input from the video unit 1 via the switching control unit 3. Control to do.
Since the VD separated from the video signal 5 by the MPU 14 is monitored, the determination of VD has the same meaning as the determination of the presence of the video signal.

Next, the operation of the character superposing device according to the present invention will be described. In this device, for example, surveillance cameras are installed at a plurality of locations, a video signal 4 output from each surveillance camera is input to a video unit 1, and switching is performed at an appropriate order and at an appropriate interval (5). Is a monitoring device that superimposes characters and the like indicating a video source generated corresponding to each surveillance camera, sends these signals 6 to one or more monitors, and displays them on the screen. These switching controls are performed based on the control data stored in the switching control unit 3, and the operation is performed by a signal from an operator console (not shown) or the like.

When the video signal 4 is input from the switching destination of the video unit 1, the switching timing input via the switching control unit 3 in the character unit 2 as shown in the time chart of FIG. M based on pulse 15 ()
The PU 14 causes the on-screen driver 11 to output an address to the CGROM 12, etc., serial transfer of character data is started from the CGROM 12 (), and the character data is written in the built-in VRAM or the like. The transfer of this character data is 2 after the transfer is started.
Since the process is completed by the second VD, the image and the character are simultaneously switched at the second VD ().

When a video signal is not input from the switching destination when the video unit 1 is switched, the video unit 1 is independently switched by a self-running synchronizing signal internally generated as shown in the time chart of FIG. Timing pulse 15
Outputs (). However, since the video signal 5 is not input to the character unit 2, VD is not separated by the VD separation circuit 13, and the MPU 14 cannot determine the VD. Therefore, the transfer of the character data from the CGROM 12 of the on-screen driver 11 is prohibited. Then, the signal from the VD separation circuit 13 is continuously monitored, and when VD is discriminated (1 vertical cycle = 16.7 mS
(VD is input during this period) (), the MPU 14 causes the on-screen driver 11 to output an address to the CGROM 12, etc., and the serial transfer of character data from the CGROM 12 is restarted (), and is written in the built-in VRAM or the like. And
Similarly to the above, the transfer is completed by the second VD and the characters are switched (). In this case, since the video switching is performed at the timing when the VD is input, the character display is 2
Although delayed by VD, the phenomenon that the characters to be displayed are erroneously displayed does not occur.

[0011]

As described above, according to the character signal superimposing device of the present invention, when the input destination is switched to the video signal source from which the video signal is not output, the character superposition is performed until the video signal is input. Since it is not performed, it is possible to prevent erroneous display of characters that would occur when there is no video signal.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an embodiment of a character signal superimposing device according to the present invention.

FIG. 2 is a block diagram of a main part of a character unit of an embodiment of a character signal superimposing device according to the present invention.

FIG. 3 is a time chart for explaining switching between video and characters.

[Explanation of symbols]

 1 video unit 2 character unit 3 switching control unit 4 video signal source (plural) 6 video signal output (plural) 11 on-screen driver 12 CGROM 13 vertical sync signal separation circuit 14 MPU

Claims (5)

[Claims] 1. A video signal from a plurality of video signal sources is input to a video unit, and a required sequence is specified by specifying automatic switching.
In the case of switching at time intervals, inputting to the character unit, and superimposing and outputting characters corresponding to each video signal, the character unit monitors the video signal input from the video unit and inputs the video signal. A character signal superimposing device that superimposes a character on a video signal in the case of an error. 2. The character signal superimposing device according to claim 1, wherein the monitoring of the video signal is to monitor a synchronizing signal separated from the video signal input from the video unit. 3. The character unit synchronizes with a CGROM that stores character data, a sync separation circuit that separates a vertical sync signal of a video signal input from the video unit, and a signal from the sync separation circuit. An on-screen driver for superimposing characters on a video signal input from a video unit based on data read from a CGROM,
2. The character signal superimposing device according to claim 1, which comprises an MPU which monitors a signal from the sync separation circuit and controls superimposition of characters by an on-screen driver when a vertical sync signal is input. 4. The on-screen driver is the M
Built-in V by the signal with vertical sync signal input from PU
4. The character signal superimposing device according to claim 3, wherein the character data read from the CGROM is transferred to the RAM and written. 5. The character unit, after starting the transfer of the character data read from the CGROM to a built-in VRAM, switches the character with a second vertical synchronization signal corresponding to the completion of the transfer of the character data. Claim 1 consisting of:
The character signal superimposing device according to claim 2, claim 3 or claim 4.