JPH0728413B2 - Signal processing circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a video signal processing circuit used in a video tape recorder (VTR) or the like.

2. Description of the Related Art In recent years, a lot of comb filters have been used in signal processing circuits that handle video signals.

For example, in the case of an NTSC signal, the color signal (abbreviated as C signal) is set to a frequency that interleaves every horizontal period (abbreviated as 1H), so a Y-shaped signal that adds an input signal and an input signal delayed by 1H is added. The luminance signal (abbreviated as Y signal) is separated by the comb filter, and the chrominance signal is separated by the C-shaped comb filter that subtracts the signal delayed by 1H from the input signal. In other words, comb filters are often used in Y / C separation circuits. Also, in the color S / N improvement circuit of the VTR, the C-shaped comb filter is used.

However, these comb filters assume that the vertical correlation of the color signals is strong, and Y / C
Separation was not performed normally, and adverse effects such as color sag and dot interference occurred. Therefore, various methods have been proposed as means for detecting the presence or absence of the vertical correlation of the conventional colors. First
The above method uses the strong correlation between the Y signal and the C signal to detect and use the vertical correlation of the Y signal, but this will malfunction in a signal in which there is no correlation between the Y signal and the C signal.

As a second method, set the signal level of the color signal frequency component to 1H.
A method for detecting the correlation by comparing with the previous signal level has been proposed by the present inventor in Japanese Patent Application No. 59-168251.
According to this method, the presence or absence of vertical correlation is detected by the change in the saturation of the color in the vertical direction.

A simple block diagram of this conventional example is shown in FIG. In order to compare the amplitude direction of the color signal with that before 1H, the delay circuit 21,
It is composed of detectors 22 and 23 and a comparison circuit 24. According to this configuration, when a color signal as shown in FIG. 5A is input, a period in which the color signal has no vertical correlation is detected, and a signal as shown in d is output. Here, b and c show the waveforms of each part.

However, when signals having different phases as shown in a ₁ are input, the output signal becomes d ₁ and there is a disadvantage that the presence or absence of vertical color correlation is not detected.

Problems to be Solved by the Invention In the above configuration, there is no correlation between the C signal and the Y signal,
Moreover, it is not possible to detect that there is no vertical correlation of the color signal for a signal that has no change in the vertical amplitude of the color signal and only a change in hue, that is, the signal causes color sag and dot interference due to the comb filter. I could not avoid doing it.

In view of the above problems, the present invention is a signal processing circuit that surely detects the presence or absence of color vertical correlation by comparing the amplitude level and phase vertical correlation of color signals.

Means for Solving the Problems In order to solve the above problems, the signal processing circuit of the present invention obtains a color signal by subtracting an input video signal and a delayed signal obtained by delaying the input video signal for a predetermined time. A detection output of the color signal and a detection output of a delayed color signal obtained by delaying the color signal for a predetermined time are input to a comparator, and the comparator outputs a comparison signal by detecting a level difference between two inputs, A luminance signal is obtained by adding the input video signal and the delay signal, and the signal is output when the level of the luminance signal is equal to or higher than a predetermined level and the comparison signal is equal to or higher than the predetermined level. It is a thing.

Effect The present invention can detect the change in the amplitude level and the phase of the color signal in the vertical direction by the above-described configuration, and can reliably detect the presence or absence of the vertical correlation of the color signal.

Embodiment A signal processing circuit according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of the first embodiment of the present invention. The signal input from the input terminal 1 passes through the bandpass filter 2, and a color signal is obtained by the C-shaped comb filter including the 1H delay circuit 3 and the synthesizer 4. The color signal is sent to the delay circuit 6 and the detector 7, and the output of the delay circuit 6 is sent to the detector 8. The comparator 10 compares the respective detection outputs from the detectors 7 and 8, and outputs a high level signal to the arithmetic circuit 11 when the level difference becomes large. on the other hand,
A luminance signal is obtained by the Y-shaped comb filter composed of the 1H delay circuit 3 and the synthesizer 5. The luminance signal is sent to the detector 9, and the output of the detector 9 is sent to the arithmetic circuit 11.
The arithmetic circuit 11 is, for example, an AND circuit, and two inputs are Hi.
1 is output at the gh level.

With respect to the present invention having such a configuration, the operation of each unit will be described with reference to the waveform chart of FIG.

First, FIG. 3 shows a case where the color signal amplitude changes in the vertical direction. Here, a to h indicate waveforms corresponding to the respective parts of a to h in FIG.

The input signal a becomes a color signal b obtained by the C-shaped comb filter, becomes d and e when detected by the detectors 7 and 8, and a signal f is output from the comparator 10 and sent to the arithmetic circuit 11. To be On the other hand, the input signal a is a luminance signal obtained by the Y-shaped comb filter and becomes c, and when it is detected by the detector 9, it becomes g and is sent to the arithmetic circuit 11. And the signal f,
A signal h is output by calculating g in the arithmetic circuit 11. Here, it can be seen that the signal h indicates the period z in which there is no vertical color correlation.

Next, FIG. 4 shows the case where the hue changes in the vertical direction.

The input signal a becomes a color signal b obtained by the C-shaped comb filter, becomes d and e when detected by the detectors 7 and 8, and a signal f is output from the comparator 10 and sent to the arithmetic circuit 11. To be On the other hand, the input signal a is a luminance signal obtained by the Y-shaped comb filter and becomes c, and when it is detected by the detector 9, it becomes g and is sent to the arithmetic circuit 11. And the signal f,
A signal h is output by calculating g in the arithmetic circuit 11. Here, it can be seen that the signal h indicates the period z in which there is no vertical color correlation.

That is, it is possible to detect a change in hue in the vertical direction.

Here, the bandpass filter BPF2 may be inserted in the input stage as in the embodiment, may be positioned in front of the detectors 7, 8 and 9, or may be omitted.

Further, when the present invention is applied to a recording / reproducing system such as a VTR, the BPF2 and the comb filters 3, 4 and 5 in FIG. 1 of the embodiment are inserted into the recording system, and the subsequent blocks are inserted into the reproducing system for recording. The present invention can be realized by passing it through a reproduction system. This has the advantage that only one delay circuit is required.

Further, when the present invention is applied to the PAL system, some modification such as setting the delay time of the delay circuit to 2H is necessary.

Further, the comparator 10 and the arithmetic circuit 11 may be either an analog circuit whose output changes in an analog manner or a digital circuit whose output changes digitally.

Although the present invention can be realized by a digital circuit by replacing the delay circuit with a memory or the like, it does not fall outside the scope of the present invention.

As is apparent from the above description, according to the present invention, a color signal is obtained by calculating an input video signal and a delay signal obtained by delaying the input video signal by a predetermined time, and a detection output of the color signal and the color The detection output of the delayed color signal obtained by delaying the signal by a predetermined time is input to the comparator, and the comparator outputs the comparison signal by detecting the level difference between the two inputs. Further, the input video signal and the delay signal are output. A luminance signal is obtained by calculation, and a signal is output when the level of the luminance signal is equal to or higher than a predetermined level and the comparison signal is equal to or higher than a predetermined level, thereby reliably detecting the presence or absence of vertical correlation of color signals. The effect is great for a signal processing circuit using a comb filter.

[Brief description of drawings]

FIG. 1 is a block diagram of a signal processing circuit according to an embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams showing signal waveforms of respective portions of FIG. 1, and FIG. 4 is a conventional signal processing circuit. FIG. 5 is a waveform diagram thereof. 2 ... Band pass filter, 3,6 ... 1H delay circuit, 4,5 ...
… Synthesizer, 7,8,9 …… Detector, 10 …… Comparator, 11 …… Arithmetic circuit.

Claims (4)

[Claims] 1. A color signal is obtained by calculating an input video signal and a delay signal obtained by delaying the input video signal for a predetermined time, and a detection output of the color signal and a delayed color signal obtained by delaying the color signal for a predetermined time. The detected output is input to a comparator, the comparator outputs a comparison signal by detecting the level difference between the two inputs, and the luminance signal is obtained by calculating the input video signal and the delay signal. A signal processing circuit, which outputs a signal when a level of a luminance signal is a predetermined level or higher and the comparison signal is a predetermined level or higher. 2. The signal processing circuit according to claim 1, wherein the predetermined time period is one horizontal cycle period. 3. The signal processing circuit according to claim 1, wherein the predetermined time period is two horizontal cycle periods. 4. A band pass filter for passing a frequency band including a color signal is provided at an input stage of a signal processing circuit or at a stage before detection, wherein a band pass filter is provided. Signal processing circuit.