JP2003018430A - Video signal processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To faithfully reproduce a DC component of a video signal even when the original video signal has large sag. SOLUTION: A VCR 30 receives video signals outputted from a plurality of monitoring cameras 1, 1, etc., while being sequentially selected by a changeover device 2. When there is a large luminance level difference among the video signals from the monitoring cameras 1, 1, etc., a rapid level change is caused in the video signals received by the VCR 30 thereby producing large sag in the video signals after its DC component is cut off by a capacitor 50. However, a pre-processing circuit 20 can suppress the level change in the video signals due to the sag to a degree of being responded by a clamp circuit 60. Then the clamp circuit 60 receives the video signals after the suppression.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing device, and more particularly to a video signal processing device for clamping a video signal to reproduce a direct current component.

[0002]

2. Description of the Related Art A video signal processing device of this type is a VCR (Vi
deoCassette Recorder) and television receivers are essential. That is, in the video signal, the direct current component is usually cut during the transmission process,
Clamping is required to regenerate such a DC component. The details of the clamp circuit for realizing the clamp process are disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-53983 [H04N5 / 18].

[0003]

However, in the conventional clamp circuit, since the video signal is directly clamped, when the video signal has a large sag, the clamp processing can be performed in response to a sudden level change of the video signal due to the sag. However, there is a problem in that the DC component of the video signal cannot be faithfully reproduced. For example, as shown in FIG. 5, while monitoring video images captured by a plurality of surveillance camera devices 1, 1, ...
This problem occurs when a surveillance camera system that records in R3 is constructed.

That is, the video signal input from the switch 2 into the VCR 3 via the video input terminal 4 is DC-cut by the DC cut capacitor 5, and then the clamp circuit 6 is passed through an amplifier circuit, a filter circuit, etc. not shown. Entered in. In addition, the video input terminal 4 and the ground potential (GND)
A resistor 7 of 75 [Ω] for impedance matching is provided between and. The clamp circuit 6 reproduces the DC component of the video signal by performing a clamping process so that the DC voltage level of the pedestal portion or the sync signal tip portion of the input video signal is held constant. The video signal processed by the clamp circuit 6 is recorded on the video tape 9 by the recording circuit 8.

Here, each surveillance camera device 1,
There is a large difference in the brightness levels of the video signals output from 1, ..., For example, the brightness level of the surveillance camera device 1 called [B] is very large (almost white level),
Other surveillance camera devices 1, 1, such as [A] and [C]
The luminance level of ... is extremely low (almost black level). Under such a situation, the switching device 2 causes the respective surveillance camera devices 1, 1, ... to be [A] → [B] → [C] →
When switching is selected in the order of ...
A rapid level change (strictly speaking, an average picture level (APL: Average Picture Level) is exaggerated as shown in (a).
The video signal accompanied by the change (1)) is output. The figure shows a state in which the monitoring cameras 1, 1, ... Are switched and selected for each frame. Then, this video signal is, so to speak, differentiated by passing through the DC cut capacitor 5 in the VCR 3, whereby the video signal having a large sag as shown in FIG. 6B is input to the clamp circuit 6. If the slope of the sag (the degree of change in the level of the video signal) is steeper than the response characteristic (time constant) of the clamp circuit 6, the clamp circuit 6 can appropriately clamp the video signal of the sag portion. Not possible, and as a result,
The video signal after being clamped is accompanied by distortion as shown in FIG. 6 (c). When a large distortion occurs in the video signal in this way, the video signal can be recorded on a video tape, but when the recorded video signal is reproduced, the sync signal of the distorted portion cannot be normally captured, This causes inconvenience such as the reproduced image being greatly disturbed.

Therefore, a main object of the present invention is to provide a video signal processing device capable of faithfully reproducing the DC component of a video signal even if the video signal has a large sag.

[0007]

According to the present invention, in a video signal processing device for clamping a video signal to reproduce a direct current component, a suppressing means for suppressing a rapid level change of the video signal prior to the clamp processing is provided. Characterized by that
This is a video signal processing device.

[0008]

That is, the video signal is input to the suppressing means before being clamped. The suppressing unit suppresses a rapid level change of the video signal. Then, the video signal in which the rapid level change is suppressed is clamped.

In one embodiment of the present invention, the restraining means is
A filter means for extracting low frequency components of the video signal and a superposition means for superimposing the low frequency components on the video signal and outputting a superposition signal are included. By superimposing the video signal and the low frequency component thereof in this manner, it is possible to suppress a rapid level change of the video signal. Then, the superimposed superimposed signal is clamped.

Another embodiment of the present invention comprises a recording means for recording the video signal after the clamp processing on the recording medium.

[0011]

According to the present invention, the video signal is clamped after its abrupt level change is suppressed.
Therefore, even if the video signal has a large sag, the DC component of the video signal can be faithfully reproduced.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the detailed description of the embodiments below with reference to the drawings.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a surveillance camera system 10 of this embodiment uses a VCR 30 incorporating a preprocessing circuit 20 in place of the VCR 3 in the configuration of FIG. 5 described above.

That is, the VCR 30 is the above-mentioned VCR 3
Image input terminal 4, DC cut capacitor 5,
Similar to the clamp circuit 6, the impedance matching resistor 7 and the recording circuit 8, a video input terminal 40, a DC cut capacitor 50, a clamp circuit 60, a resistor 70 and a recording circuit 80 are provided. Then, the clamp circuit 60
The pre-processing circuit 20 is provided in the preceding stage of the
The video signal processed by is input to the clamp circuit 60. The video tape 90 is similar to the video tape 9 in FIG.

Referring to FIG. 2, the preprocessing circuit 20 comprises a center detection circuit 22, a low pass filter circuit 24, an amplification circuit 26 and an addition circuit 28. Of these, the center detection circuit 22 and the addition circuit 28 are respectively input with the video signal after the DC cut by the DC cut capacitor 50. Here, it is assumed that a signal similar to the video signal shown in FIG. 6A is input to the video input terminal 40, for example. Then, the center detection circuit 22 and the addition circuit 28 are respectively supplied with video signals having the sag shown in FIG. 3A similar to FIG. 6B.

The center detection circuit 22 detects the center level of the input video signal, as indicated by the alternate long and short dash line X in FIG. The detection of this center level can be realized by extracting the low frequency components of the video signal.
The center detection circuit 22 outputs a center level signal having a waveform as shown in FIG. Then, the center level signal is input to the low pass filter circuit 24.

The center level signal is further passed through a low pass filter circuit 24 to extract low frequency components,
As a result, as shown in FIG. 3 (c), the signal corresponding to the sag is blunted. And this low
The signal processed by the pass filter circuit 24 is appropriately level-adjusted by the amplifier circuit 26, and then added by the adder circuit 2.
8 is input.

The adder circuit 28 processes the signal processed by the low pass filter circuit 24 (strictly speaking, the signal obtained by amplifying this signal by the amplifier circuit 26) and the DC cut capacitor 50.
The video signal after the DC cut by is added to each other, that is, superposed. As a result, as shown in FIG. 3D, the adder circuit 28 outputs a signal in a state in which the abrupt level change of the video signal due to the above-described sag is suppressed.
Then, the video signal whose level change is suppressed is input to the clamp circuit 60.

Since the video signal input to the clamp circuit 60 is a signal whose level changes gently, the clamp circuit 60 can reliably clamp the video signal. Therefore, from the clamp circuit 60, as shown in FIG.
As shown in (e), a video signal faithfully reproducing the DC component is output. That is, the original video signal shown in FIG. 6A is reproduced.

In order to faithfully reproduce the original video signal in this way, the clamp circuit 60 can respond to the degree (gradient) of the level change due to the sag of the video signal input to the clamp circuit 60. It is necessary to sufficiently suppress it. The degree of this suppression is adjusted (determined) by the time constant of the low pass filter circuit 24.

In FIG. 4, the center detection circuit 22 and the low pass
A specific configuration with the filter circuit 24 is shown. As shown in the figure, the center detection circuit 22 is connected between a resistor 80 provided in series in the transmission path of the video signal and between the output side of the resistor 80 (right side in the figure) and the ground potential. It is constituted by an RC filter in which the combined capacitor 82 is combined. In the experiment, the resistance value of the resistor 80 is 1 [k
Ω], and the capacitance value of the capacitor 82 is 0.
01 [μF] was used.

Further, with respect to the capacitor 82 described above,
The low-pass filter circuit 24 is configured by providing another capacitor 84 in parallel. The capacitor 84 has a larger capacity than that of the above-described capacitor 82.
The one of about [μF] is used. Also, the amplification circuit 2 in the latter stage
In order to achieve impedance matching with 6, a resistor 86 of 1 [kΩ] is provided between the output side of the resistor 80 and the ground potential. As described above, the center detection circuit 22 and the low pass filter circuit 24 can be configured by an extremely simple circuit called an RC filter.

As described above, according to this embodiment, the above-mentioned problems of the prior art can be solved with a simple structure in which the preprocessing circuit 20 is provided for the conventional VCR 3. Moreover, since the center detection circuit 22 and the low-pass filter circuit 24 that form the preprocessing circuit 20 can be configured by a simple RC filter circuit, even if the preprocessing circuit 20 is provided, the cost does not increase so much. .

The technique described in this embodiment is based on VC
The invention is not limited to R30, and can be applied to other devices that require a clamp circuit such as a television receiver.

However, the technique of this embodiment is based on the VCR 30
It is particularly effective when applied to a recording device such as. That is, in the recording apparatus, even if the video signal to be recorded is accompanied by the distortion as shown in FIG. 6C, the video signal can be recorded on the recording medium such as the video tape 90. . However, the recorded video signal is distorted until it gets tired, and cannot be reproduced normally. When reproducing a video signal with such distortion, the synchronization signal cannot be captured normally,
Playback video is greatly disturbed. For example, there arises inconvenience that the image is skipped in units of several frames, or the image cannot be reproduced at all. Therefore, the technique of this embodiment is extremely effective in eliminating such inconvenience.

Further, in this embodiment, the center detection circuit 2
2 and the low-pass filter circuit 24 have a circuit configuration as shown in FIG. 4, but the invention is not limited to this. Moreover, the CPU is not limited to the pure hardware configuration as shown in FIG.
(Central Processing Unit) and DSP (Digital S
The center detection circuit 22 and the low-pass filter circuit 24 are configured by software processing using an ignal processor), and further the pre-processing circuit 20 including these components.
May be configured. Further, the center detection circuit 20 and the low pass filter circuit 24 may be configured by one low pass filter.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a detailed configuration of a preprocessing circuit in the embodiment of FIG.

FIG. 3 is a timing chart showing signal waveforms of respective main parts in the embodiment of FIG.

4 is a center detection circuit and a low pass
It is an electric circuit diagram which shows the more detailed structure of a filter circuit.

FIG. 5 is a block diagram showing a schematic configuration of an entire surveillance camera system using a conventional VCR.

FIG. 6 is a timing chart showing signal waveforms of respective main parts in FIG.

[Explanation of symbols]

10 ... Surveillance camera system 20 ... Preprocessing circuit 30 ... Clamp circuit 50 ... DC cut capacitor

Claims (3)

[Claims] 1. A video signal processing apparatus for clamping a video signal to reproduce a direct current component, comprising a suppressing means for suppressing an abrupt level change of the video signal prior to the clamping processing.
Video signal processing device. 2. The suppressing means includes a filter means for extracting a low-frequency component of the video signal, and a superimposing means for superimposing the low-frequency component on the video signal to output a superimposed signal. The video signal processing device according to claim 1, which clamps a signal. 3. The video signal processing device according to claim 1, further comprising recording means for recording the video signal after the clamp processing on a recording medium.