JPH0748850B2 - Camera switching device - Google Patents

Description

The present invention relates to a camera switching device used in a centralized monitoring device or the like.

[Conventional technology]

2. Description of the Related Art Conventionally, for example, a centralized monitoring device in a station yard, for example, selects video signals of a plurality of video cameras for imaging each platform, sequentially at regular intervals to display a monitor television receiver, a video tape recorder, etc. A camera switching device is provided for switching output to the recording device.

In order to prevent the synchronization disturbance of the input video signal of the display and recording device at the time of switching, the conventional camera switching device uses the reference synchronization signal or the power supply frequency signal of the reference synchronization signal generation circuit as the external synchronization signal or the synchronization control signal. Is supplied to each camera, and external synchronization or power supply synchronization is applied to each camera.

However, when external synchronization is applied as described above, it is necessary to provide each video camera with an output terminal for the video signal and an input terminal for the external synchronization signal, and moreover, since the number of tables of each video camera increases, The configuration is significantly complicated and expensive.

Also, when power supply synchronization is applied, it is necessary to provide each video camera with a complicated synchronization signal generation circuit that is PLL-controlled by the power supply frequency signal. Become more expensive.

Therefore, in Japanese Patent Laid-Open No. 186477/1984, a signal obtained by superimposing a DC signal for identification on the video signal of the video camera being switched and output is supplied to the video input / output terminals of the remaining video cameras, and , Each video camera separates and extracts the sync signal of the video signal input to the input / output terminal based on the detection of the DC signal, and resets the internal sync signal generation circuit by the sync signal. It is described that external synchronization is applied and external synchronization is applied without increasing the number of terminals and cables of each camera to simplify the configuration.

[Problems to be solved by the invention]

By the way, in the case of the device described in the above publication, it is necessary to include a circuit for generating a DC signal, and a buffer amplifier for prohibiting the output of the video signal by the input of the DC signal to each video camera, and a detection circuit for the DC signal. , And a sync separation circuit that operates according to the output of the detection circuit.

Also, as the number of video cameras increases, the number of contacts of each video camera in the switch circuit for selectively outputting the video signal of each video camera also increases.

Therefore, there is a problem in that it is necessary to provide a large number of complicated circuits in the device, which complicates the configuration and increases the cost.

[Means for solving problems]

The present invention has been made with the above points in mind,
A plurality of video cameras and a switching control circuit for sequentially switching and outputting the video signals of the video cameras, the control circuit having a plurality of video input terminals to which the video signals are respectively input, A control signal generation circuit for outputting a switching control signal for selecting each of the video signals at regular intervals synchronized with the video vertical frequency based on a vertical sync signal included in the video signal of the video camera or an internally formed vertical sync signal. And a switch circuit that operates according to the switching control signal and sequentially connects the input terminals to a common video output terminal, and outputs at least to each video camera other than the reference video camera. Connection detection circuit for detecting whether or not the input terminal of the video camera is connected to the output terminal according to a change in the video signal of Based on this, the camera switching device is provided with a synchronization signal generating circuit that is reset instantly when the connection is released.

[Work]

Therefore, based on the detection of the change of the video signal of each video camera, the video signal of each video camera is included in the video signal of the reference video camera or the vertical synchronization signal internally formed by the switching control circuit. It is controlled in synchronization with the signal, and the switching output of the video signal of each video camera is also
Synchronizing with the vertical synchronizing signal included in the video signal of the reference video camera or the vertical synchronizing signal internally formed by the switching control circuit, without increasing the number of terminals and cables of each video camera, and each video camera Also, without providing a complicated circuit for synchronizing the switching control circuit, the video signal of each video camera is sequentially selected and switched and output at regular intervals without disturbing synchronization.

〔Example〕

Next, the present invention will be described in detail with reference to FIGS. 1 to 3 showing one embodiment thereof.

FIG. 1 shows a case where N video cameras are provided. In FIG. 1, (1a), (1b), ..., (1n) are N video cameras, and (2) is a camera (1a) to ((a). N video input terminals (3a), (3b), to which each 1n) video signal is input.
, (3n) and a video output terminal (4) common to the switching control circuit.

(5) is N analog switches (6a), (6b), ...,
(6n) switch circuit, each switch (6a)
One end of ~ (6n) is connected to each input terminal (3a) ~ (3n), and the other end of each switch (6a) ~ (6n) is grounded via a common terminating resistor (7) of 75Ω. .

Reference numeral (8) is an output buffer amplifier provided between the other end of each of the switches (6a) to (6n) and the output terminal (4).

(9) is a vertical sync separation circuit connected to the input terminal (3a), which is included in the video signal of the input terminal (3a), that is, the video signal of the camera (1a) forming the reference video camera. The signals are separated and extracted, and one video vertical scanning period (1
A sync pulse is output for each field.

Reference numeral (10) is a pulse generation circuit for generating a reference pulse having a pulse width of about one field for each reference period T of camera switching which is sufficiently longer than one field.

(11) is a synchronizing pulse of the separation circuit (9) and a generation circuit (10)
Of the reference pulse and the output of only the synchronizing pulse when the reference pulse is input.

Reference numeral (12) is a counter connected to the AND gate (11), which is composed of a ring counter and counts the synchronizing pulse output from the AND gate (11) and outputs a count value signal.

(13) is a decoder connected to the counter (12),
The count value signal of the counter (12) is decoded, an N-bit switching control signal for sequentially turning on each switch (6a) to (6n) for a fixed period is formed, and output to each switch (6a) to (6n). To do.

Reference numeral (14) is a control signal generation circuit including a separation circuit (9), a generation circuit (10), an AND gate (11), a counter (12), and a decoder (13).

By the way, each camera (1
b) to (1n) are the second parts showing the internal configuration of the camera (2a).
In the figure, (15) is an image sensor, and (16) is a signal processing circuit connected to the image sensor (15). , A vertical synchronizing signal is added and combined to form a video signal, and the video signal is input via the video output terminal (17) to the input terminal (3b)-
Output to (3n).

Reference numeral (18) is a connection detection circuit connected to the output terminal (17), and switches (3b) to (3n) of the input terminals (3b) to (3n) of the camera are changed by the amplitude change of the video signal output from the output terminal (17). 6b) to (6n) are connected to the output terminal (4) to detect whether or not the switches (6b) to (6n) are inverted from on to off and the amplitude becomes large. Output.

Reference numeral (19) is a synchronizing signal generating circuit which is instantly reset by the reset pulse of the detecting circuit (18) and outputs horizontal and vertical synchronizing signals to the processing circuit (16).

The camera (1a) may be formed by a video camera in which the detection circuit (18) is omitted from FIG. 2 or a video camera having the same configuration as each of the cameras (1b) to (1n). In this embodiment, The camera (1a) is a video camera having the same configuration as each of the cameras (1b) to (1n).

Then, when the power source of the apparatus is turned on, a reference pulse having a pulse width of about 1 field is output from the generating circuit (10) to the AND gate (11) every reference period T as shown in FIG. 3 (a). It

On the other hand, the separation circuit (9) to which the video signal of the input terminal (3a) is input separates and extracts the vertical synchronizing signal of the input video signal, and as shown in FIG. 3 (b), the input terminal (3a) A positive sync pulse is output to the AND gate (11) for each field of the video signal of (1), that is, for each field of the video signal of the camera (1a).

Therefore, as shown in FIG. 3 (c) from the AND gate (11), the synchronization pulse while the reference pulse is input,
That is, a synchronization pulse is output for each fixed period T in synchronization with the vertical synchronization of the video signal of the camera (1a).

Then, since the synchronizing pulse output from the AND gate (11) is input to the counter (12) as a clock pulse, the content of the count value signal output from the counter (12) to the decoder (13) is fixed every T. It changes from 1 to N in order.

Further, based on the decoding of the count value signal of the counter (12), each bit of the switching signal output from the decoder (13) sequentially becomes high level for a certain period of time T. 3 bits are shown in Fig. 3 (d),
It changes as shown in each of (e) and (f).

Then, each switch (6a) to (6n) is turned on by the high level of each bit of the switching signal of the decoder (13), so that each switch (6a) to (6n) is connected to the camera (1a).
The signal is turned on sequentially for a certain period T in synchronization with the video signal of.

Therefore, the input terminals (6a) to (6n) are connected to the camera (1a).
The video signals of the cameras (1a) to (1n) are sequentially switched and output in synchronism with the video signal of (1) to the output terminal (4) for a predetermined period T.

By the way, when each switch (6a) to (6n) is turned on, each input terminal (3a) to (3n) is terminated by the resistor (7), so that the images from each camera (1a) to (1n) While the signal is selected and output from the output terminal (4), the amplitude becomes smaller than that during the time when each of the switches (6a) to (6n) is turned off.

Since the amplifier (8) is provided in front of the output terminal (4), the terminating impedance of the output terminal (4) depending on the presence or absence of connection of a monitor television receiver, a video tape recorder, etc. ) To (1n) video signals are not affected.

The detection circuit (18) of each camera (1a) to (1n)
Depending on the change (difference) in the amplitude of the video signal, each camera (6a)
It is detected whether or not each of the (6n) video signals is selected and output, that is, whether or not each of the input terminals (3a) to (3n) is connected to the output terminal (4), and each switch (6a) is detected. ~ (6n) outputs a reset pulse when each of them is inverted from ON to OFF, that is, when the amplitude of the video signal changes from small to large and switches to the output of the video signal of the next video camera.

Further, since the generating circuit (19) is reset by the reset pulse of the detecting circuit (18), the generating circuit (19) outputs horizontal and vertical synchronizing signals with reference to the reset pulse of the detecting circuit (18). .

Then, the reset pulse of the detection circuit (18) is transferred to the camera (1
Since it is output in synchronization with the video signal of a), each camera (1
The video signals of a) to (1n) are the same as the video signals of the camera (1a).

For example, the first to third bits of the switching signal output from the decoder (13) fall to a low level at t ₁ , t ₂ and t _3, respectively, as shown in FIGS. 3 (d) to (f). And the vertical sync signals of the cameras (1a) and (1b) are (g) and (h) in FIG.
As shown in each of the figures, instant reset is performed at each timing of t ₁ and t ₂ , and the vertical synchronizing signal of the third video camera (not shown) next to the camera (1b) is t ₃ as shown in FIG. At that timing, an instant reset is performed, and the vertical sync signals of the cameras after reset are the same.

Therefore, when the switches (6a) to (6n) are turned on for the second time and thereafter, the video signals of the cameras (1a) to (1n) are synchronized with the video signals of the camera (1a). Since the switches (6a) to (6n) switch in synchronism with the video signal of the camera (1a), the output terminal (4) outputs a video signal without synchronization disturbance.

Since the generation circuit (19) is reset when the connection is released, the video signal at the output terminal (4) is not disturbed by the reset.

The detection circuit (1) inside each camera (1a) to (1n)
8), each input terminal (3a) to (3n) based on the change of the video signal amplitude of each camera (1a) to (1n)
Detects whether or not each is connected to the output terminal (4) and instantly resets the internal generation circuit (19) of each camera (1a) to (1n) to synchronize with each camera (1a) to (1n) Therefore, the number of terminals of each camera (1a) to (1n) and the number of cables do not increase, and a DC signal generation circuit and detection circuit required when a DC signal is superimposed on a video signal for synchronization. Also, it is not necessary to provide a buffer circuit for prohibiting the output of the video signal, and even if the number of video cameras is large, the number of contacts of the switch circuit (5) is increased only by the number of cameras. Become cheaper.

In addition, regardless of the switching of each switch (6a) to (6n), each input terminal (3a) to (3n) is connected to each camera (1a) to (3a).
Since the video signal of (1n) is continuously input, for example, if the control circuit (2) is provided with N auxiliary video output terminals connected to the respective input terminals (3a) to (3n), regardless of switching. It is also possible to monitor the video signals of the cameras (1a) to (1n).

By the way, in the above embodiment, the camera (1a) was used as a reference video camera, and the video signals of the remaining cameras (1b) to (1n) were synchronized with the video signal of the camera (1a). A video camera other than the above may be used as the reference video camera.

Further, the detection circuit (18) may detect whether or not the connection has been made based on a change in the frequency or the like other than the amplitude, and the switch circuit (5) may be formed by a multiplexer or the like.

Further, without setting the reference video camera, a vertical synchronizing signal generating circuit is provided in the generating circuit (14) instead of the separating circuit (9), the generating circuit (10), and the AND gate (11), and the synchronizing of the generating circuit is performed. The signals of the switches (6a) to (6n) and the video signals of the cameras (1a) to (1n) may be synchronized with the signal, and in this case, the configuration is further simplified.

〔The invention's effect〕

As described above, according to the camera switching device of the present invention, whether or not each video input terminal is connected to the video output terminal is detected from the change in the video signal of each video camera, and based on the detection, each connection is released at the time of disconnection. Since the sync signal generation circuit of the video camera is instantly reset and synchronized with each video camera, the video signal of each video camera can be sequentially selected and output at regular time intervals with a simple and inexpensive configuration. is there.

[Brief description of drawings]

1 to 3 show an embodiment of a camera switching device of the present invention. FIG. 1 is a block diagram, FIG. 2 is a detailed block diagram of a video camera, and FIGS. 3 (a) to (i). Is a timing chart for explaining the operation. (1a) ~ (1n) ... video camera, (2) ... switching control circuit, (3a) ~ (3n) ... video input terminal, (4) ... video output terminal, (5) ... switch circuit , (14) …… Control signal generation circuit, (18) …… Connection detection circuit, (19) …… Synchronization signal generation circuit.

Claims (1)

[Claims] 1. A plurality of video cameras, and a switching control circuit for sequentially switching and outputting video signals of the respective video cameras, and a plurality of video inputs to which each of the video signals is input to the control circuit. Outputs a switching control signal for selecting each video signal at fixed intervals synchronized with the video vertical frequency based on the terminal and the vertical sync signal included in the video signal of the reference video camera or the internally generated vertical sync signal. And a switch circuit that operates according to the switching control signal and sequentially connects the input terminals to a common video output terminal, and at least each video camera other than the reference video camera. A connection detection circuit for detecting whether or not the input terminal of the video camera is connected to the output terminal based on a change in a video signal being output, A camera switching device characterized in that it is provided with a synchronizing signal generating circuit which is instantly reset when the connection is released based on the detection of the output circuit.