JPH0898207A - Chroma signal processing circuit for video tape recorder - Google Patents

Abstract

PURPOSE: To obtain a chroma signal processing circuit which improves dullness of the waveform in the vicinity of a noncorrelation part of a chroma signal and has a high S/N improvement effect by subjecting the non-correlation part of the reproduced chroma signal to amplitude limiting processing and feeding it back. CONSTITUTION: When the reproduced chroma signal outputted from a first comb line filter 10 is inputted to an adder 22 of a second comb line filter 20 through a 18 delay line 23, this adder 22 extracts and outputs the non-correlation part and the noise component of the signal from the output of an adder 21. A limiter 24 subjects the non-correlation part or the output of the adder 22 to amplitude limiting processing, and an attenuator 25 attenuates the output of the limiter 24 and feeds it back. By this constitution, the noise component of the reproduced chroma signal is attenuated to the original amplitude by the attenuator 25, and the non-correlation part has the same small amplitude as the noise component by the limiter 24. Consequently, dullness of the waveform in the vicinity of the non-correlation part is improved to prevent color slurring and color blot, and a high S/N improvement effect is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chroma signal processing circuit for a video tape recorder for reducing noise components.

[0002]

2. Description of the Related Art Conventionally, for example, as disclosed in Japanese Patent Laid-Open No. 57-160288, a helical scan type video tape recorder for reproducing a video signal from a magnetic tape by a rotary magnetic head has adjacent tracks. Crosstalk component removal by AM and PM, S /
A chroma signal processing circuit for improving N or the like is provided. For the chroma signal processing circuit, for example, a comb filter using a delay line is used, and a cyclic type or a non-cyclic type is known.

As an example, a chroma signal processing circuit used in a reproducing system of an NTSC system video tape recorder will be described with reference to FIG.

A reproduction chroma signal containing a crosstalk component is supplied to the input terminal 101. The output from the adder 102 is sent to the adders 103 and 104, respectively, and the 1H delay line 10 having a delay amount of 1H (horizontal period) is supplied.
It is sent to the adders 103 and 104 via 5, respectively. The output from the adder 103, that is, the crosstalk component, is transmitted via the attenuator 106 to the adder 10
Feedback to 2. The correlation and non-correlation of the chroma signal are detected with the correlation and non-correlation of the luminance signal, and the constant (feedback constant) k of the feedback loop defined by the attenuator 106 is set to k = 0 to 1.
In the reproduced chroma signal supplied to the terminal 101, the noise component is reduced by this feedback loop, the crosstalk component is removed by the configuration of the adder 104 and the 1H delay line 105, and the chroma signal is output from the output terminal 107. Is output.

[0005]

In the chroma signal processing circuit described above, even if the feedback constant k is set to k = 0, the adder 104 and the 1H delay line 105 are used.
The comb signal causes the chroma signal to deviate by 1H (2H in the PAL system) in the vertical direction in the uncorrelated portion. The vertical deviation of the chroma signal with respect to the luminance signal (so-called misregistration) does not cause much problem when the feedback constant k is set to a small value, but the noise reduction amount, that is, S / N. The improvement effect will be low. Therefore, if the feedback constant k is increased, that is, if the feedback amount is increased, the S / N improving effect is enhanced, but the uncorrelated portion of the chroma signal circulating in the feedback loop is not easily attenuated, and the waveform has a step difference. For example, so-called waveform drooping occurs over several H. As a result, color misregistration and color fringing occur in the reproduced image.

The present invention has been proposed in view of the above-mentioned conventional problems, and is a video capable of improving the drooping of the waveform near the non-correlation part of the chroma signal and having a high S / N improving effect. An object of the present invention is to provide a chroma signal processing circuit for a tape recorder.

[0007]

In order to achieve the above-mentioned object, the present invention is a chroma signal processing circuit of a video tape recorder for reproducing a video signal from a magnetic tape by a rotary magnetic head, wherein A chroma signal of a video signal is input, first delay means for delaying the chroma signal by a predetermined horizontal period corresponding to the horizontal period of the video signal, an output signal from the first delay means and a polarity of the chroma signal A first comb-type filter, which is composed of a first signal adding means for adding an inverted signal, and is mainly intended to remove a crosstalk component in the chroma signal by the reproduction, and a crossing by the first comb-type filter. Second adding means to which the chroma signal from which the talk component has been removed is supplied, and a non-correlation part and a noise component of the signal are extracted from the output of the second adding means. Extraction means for extracting from the input side the chroma signal from which the crosstalk component has been removed by the first comb filter, and output from this extraction means is subjected to amplitude limiting processing on the non-correlation part and the second addition means. And an amplitude limiting means having a predetermined gain for returning to
And a comb filter.

[0008]

In the chroma signal processing circuit of the video tape recorder according to the present invention, the crosstalk component is removed from the reproduced chroma signal by the first comb filter, and the second reproduced chroma signal from which the crosstalk component has been removed is removed. The noise component is removed by the comb filter. The second comb filter is supplied with a reproduced chroma signal from which crosstalk components have been removed by the first comb filter.
From the output of the adding means, the uncorrelated portion and the noise component of the signal are extracted by the extracting means, and the output from this extracting means is subjected to the amplitude limiting processing on the uncorrelated portion by the amplitude limiting means and fed back to the second adding means By doing so, the reproduced chroma signal from which the noise component is removed is output from the second adding means.

[0009]

Embodiments of the present invention will be described in detail below with reference to the drawings. The examples described below are NTSC.
The present invention is applied to a chroma signal processing circuit of a video tape recorder for reproducing a video signal from a magnetic tape compatible with the system by a rotary magnetic head.

In the embodiment shown in FIG. 1, an input terminal 1 to which a reproduced chroma signal containing a crosstalk component due to an adjacent track is supplied is connected to an adder 11 and the addition is performed via a 1H delay line 12. Connected to the container 11. The adder 11 and the 1H delay line 12 form a first comb filter 10 whose main purpose is to remove the crosstalk component.

The adder 11 is connected to the adder 21. The adder 21 is connected to the adder 22 and is also connected to the adder 22 via the 1H delay line 23. The adder 22 and the 1H delay line 23 are
It constitutes an extracting means for extracting the non-correlated portion and the noise component of the signal from the output of the adder 21. The adder 22 is connected to a limiter 24 which is amplitude limiting means. The limiter 24 has a predetermined gain, and a noise component having a small amplitude is amplified to the extent that it does not reach the threshold value for amplitude limitation and output as it is, and a non-correlated portion of a signal having a large amplitude is amplified. As a result, the above threshold value is applied and a saturated state is reached, and the amplitude is limited and output. The limiter 2
4 is connected to the adder 21 via an attenuator 25. The adder 21 is connected to the output terminal 2.

The adders 21, 22, 1H delay line 23,
The limiter 24 and the attenuator 25 constitute a second comb filter 20 whose main purpose is to reduce noise components, that is, improve S / N. In addition, the feedback constant k of the feedback loop is k = k ₁ · by the product of the constant k ₁ by the limiter 24 and the constant k ₂ by the attenuator 25.
It is defined as k ₂ . Since the limiter 24 does not limit the amplitude of noise components having a small amplitude but limits the non-correlation part of a signal having a large amplitude, it is assumed that the constant k ₁ is automatically set according to the amplitude of the input. It is functioning.

In the chroma signal processing circuit having the above-mentioned configuration, when the reproduced chroma signal including the crosstalk component is supplied to the input terminal 1, the first comb filter 1
With 0, the crosstalk component is approximately removed. Here, the crosstalk component is removed in the second stage in the latter stage.
This is to prevent the limiter 24 of the comb filter 20 from being saturated by the crosstalk component and adversely affecting the noise reduction operation. The output from the first comb filter 10, that is, the reproduced chroma signal having a small amplitude of the included crosstalk component is sent to the adder 21 of the second comb filter 20. Then, adder 2
An uncorrelated portion of the signal and a noise component are output from 2 and sent to the limiter 24. In the limiter 24, the small-amplitude noise component is amplified with a predetermined gain and output as it is, and the non-correlation part of the first amplitude is amplified. As a result, the amplitude is limited and output. The limiter 24
The output from is attenuated by the attenuator 25. Here, the noise component is attenuated to about the original amplitude, and the non-correlation part is reduced in amplitude by the limiter 24, and thus has a small amplitude similar to the amplitude of the noise component. This is because the feedback constant k is k≈0 for the uncorrelated portion.
It means that Then, the output from the attenuator 25 is fed back to the adder 21, and the adder 21
The chroma signal output, which is the difference component from the reproduced chroma signal supplied to, is output from the output terminal 2.

That is, the amplitude of the small-amplitude noise component is not limited, and an appropriate feedback amount is obtained, and a good noise reduction operation is performed. Second comb filter 2
The S / N improvement logic value by 0 is 10 log (1 + 2k) [dB], and the S / N improvement logic value of the entire circuit is 3 + 10 log (1 + 2k) [dB], and a high S / N improvement effect is obtained. Further, at least 1H is generated in the vertical direction with respect to the luminance signal in the uncorrelated portion due to the first comb filter 10, but as described above, the feedback coefficient k≈0 due to the action of the limiter 24 in the uncorrelated portion. Since the amount of feedback is extremely small, there is almost no waveform dripping, and color misregistration or color bleeding does not occur.

Here, the transfer function of the second comb filter 20 is 1 / ((1 + k) + kZ-1), which is larger than the denominator wave 1 and zero regardless of the coefficient k of the feedback system. It will never happen. Therefore, the second comb filter 2
With 0, the transfer function is always smaller than 1 and does not diverge, so that stable noise reduction operation can be performed.

[0016]

As described above, in the chroma signal processing circuit of the video tape recorder according to the present invention, in the second comb filter, the uncorrelated portion and the noise component of the signal are extracted from the output of the second adding means. Since the output of the extracting means is subjected to amplitude limiting processing by the amplitude limiting means to the non-correlation part and fed back to the second adding means, it is possible to improve the dripping of the waveform near the non-correlation part. Misalignment and color fringing can be prevented. Further, regarding the noise component, since the amplitude is not limited and appropriate feedback is performed, a high S / N improvement effect can be obtained. Furthermore, since the reproduced chroma signal from which the noise component has been removed by the second comb filter has been extracted from the reproduced chroma signal from which the crosstalk component has been removed by the first comb filter, the above-mentioned second comb filter is used. It is possible to prevent the provided amplitude limiting means from being saturated due to the crosstalk component and adversely affecting the noise reduction operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a chroma signal processing circuit of a video tape recorder according to the present invention.

FIG. 2 is a block diagram showing a conventional example of a chroma signal processing circuit.

[Explanation of symbols]

 10 First Comb Filter 11, 21, 22 Adder 12, 23 1H Delay Line 20 Second Comb Filter 24 Limiter 30 Changeover Switch

Claims (1)

[Claims] 1. A chroma signal processing circuit of a video tape recorder for reproducing a video signal from a magnetic tape by a rotary magnetic head, wherein the chroma signal of the reproduced video signal is input, and the chroma signal of the video signal The first delay means delays a predetermined horizontal period according to the horizontal period, and the first signal adding means adds the output signal from the first delay means and the polarity inversion signal of the chroma signal. A first comb filter whose main purpose is to remove the crosstalk component in the chroma signal by reproduction, and a second adding means to which the chroma signal from which the crosstalk component has been removed by the first comb filter is supplied. And a non-correlated portion of the signal and a noise component are extracted from the output of the second adding means, and the crosstalk component is removed by the first comb filter. Extraction means for taking out the extracted chroma signal from the input side, and amplitude limiting means having a predetermined gain for subjecting the output from this extraction means to the non-correlation part for amplitude limiting processing and returning it to the second adding means. And a second comb-shaped filter composed of the following: a chroma signal processing circuit for a video tape recorder.