JPH0797871B2 - Chroma signal processing circuit for video tape recorder - Google Patents

Description

The present invention relates to a chroma signal processing circuit of a video tape recorder for reducing noise components and the like.

B. SUMMARY OF THE INVENTION The present invention is, in a chroma signal processing circuit of a video tape recorder for reducing a noise component, limits the amplitude of a non-correlation part of a reproduced chroma signal to significantly reduce the feedback amount of the non-correlation part. By reducing the amount, it is possible to improve the droop of the waveform and obtain a high S / N improvement effect.

C. Conventional Technology Conventionally, as disclosed in Japanese Patent Laid-Open No. 57-160288, for example, a helical scan type video tape recorder for reproducing a video signal from a magnetic tape by a rotary magnetic head has adjacent tracks. A chroma signal processing circuit is provided for the purpose of removing crosstalk components and improving AM, PM and S / N. 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 the reproducing system of a video tape recorder compatible with the NTSC system will be described with reference to FIG. A reproduction chroma signal including a crosstalk component is supplied to the input terminal 101. Adder 10
The outputs from 2 are sent to the adders 103 and 104, respectively, and are also sent to the adders 103 and 104 via a 1H delay line 105 having a delay amount of 1H (horizontal period). Above adder 1
The output from 03, that is, the crosstalk component is fed back to the adder 102 via the attenuator 106. The correlation and non-correlation of the chroma signal are detected by the correlation and the non-correlation of the luminance signal, and the constant (feedback constant) k of the feedback loop determined by the attenuator 106.
Is set to k = 0 to 1. The reproduced chroma signal supplied to the terminal 101 has a noise component reduced by this feedback loop, and the crosstalk component is removed by the configuration of the adder 104 and the 1H delay line 105, and the chroma signal output from the output terminal 107 is performed. Is output.

D. Problems to be Solved by the Invention In the chroma signal processing circuit described above, even if the feedback constant k is set to k = 0, for example, the adder 104
Due to the comb-shaped configuration of the 1H delay line 105 and the 1H delay line 105, the chroma signal is vertically deviated by 1H (2H in the PAL method) in the uncorrelated portion. The vertical shift 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 or color blur occurs in the reproduced image.

The present invention has been proposed in view of the above-mentioned conventional problems, it is possible to improve the dripping of the waveform in the vicinity of the non-correlation part of the chroma signal, and the video tape recorder with a high S / N improvement effect. An object of the present invention is to provide a chroma signal processing circuit.

E. Means for Solving the Problems In order to achieve the above-mentioned object, the chroma signal processing circuit of the video tape recorder according to the present invention includes a first comb filter for removing a crosstalk component from an input reproduced chroma signal. Switching means for selecting the input reproduction chroma signal and the reproduction chroma signal from which the crosstalk component has been removed by the first comb filter; and an adder to which the reproduction chroma signal selected by the switching means is supplied. , An extracting means for extracting a non-correlation part and a noise component of a signal from the output of the adder, and an amplitude limiting means for subjecting the output from the extracting means to the non-correlation part for amplitude limiting processing and feeding back to the adder. And a second comb filter, which is a reproduction chroma signal obtained by removing a noise component from the reproduction chroma signal selected by the switching means by the second comb filter. It is characterized in that it has to retrieve the signal.

F. Action 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 is removed is removed. The noise component is removed by the comb filter. The second comb filter is supplied with the reproduced chroma signal from which the crosstalk component has been removed by the first comb filter, and is supplied from the output of the second adding means by the extracting means to uncorrelate the signal and the noise component. Is extracted, and the output from this extraction means is subjected to amplitude limiting processing on the non-correlation part by the amplitude limiting means and fed back to the second adding means, whereby the reproduced chroma signal from which the noise component has been removed is output to the second chroma signal. Output from the adding means. Further, in the chroma signal processing circuit of the video tape recorder according to the present invention, the input reproduction chroma signal and the reproduction chroma signal from which the crosstalk component is removed by the first comb-type filter are switched and selected by the switching means to select the second comb. It is supplied to the adder of the type filter and the reproduced chroma signal from which the noise component is removed by this second comb type filter is taken out.

G. Examples Hereinafter, examples of the present invention will be described in detail with reference to the drawings. In the embodiments described below, the present invention is applied to a chroma signal processing circuit of a helical scan type video tape recorder which reproduces an image signal from an NTSC type magnetic tape by a rotary magnetic head.

Here, in this video tape recorder, crosstalk components due to adjacent tracks can be removed by azimuth loss and H · H shift for luminance signals, and PI system and PS system for chroma signals, respectively. High-density recording is performed, and in order to meet the demand for high resolution as the performance of magnetic tape improves, the processing by the comb filter is minimized and the crosstalk component is set by setting the head width for the recording track. In order to remove, the SP mode (standard mode), LP mode (long time mode) is equipped with dedicated heads for each. In particular, a head that is narrower than the standard track amount by a few microns is used for the SP mode, and the crosstalk component is extremely small to the extent that a comb filter is not required.

In this embodiment, the input terminal 1 to which the reproduced chroma signal including the crosstalk component due to the adjacent track is supplied is
It is connected to the adder 11 and is also connected to the adder 11 via the 1H delay line 12. 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. Above adder
The 22 and the 1H delay line 23 constitute 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 of the amplitude limit 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 24 is connected to the adder 21 via an attenuator 25. The adder 21 is connected to the output terminal 2.

The adders 21 and 22, the 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
By the product of the constant k _{1 according to the above} and the constant k ₂ according to the attenuator 25, k = k ₁ · k ₂ is determined. The above limiter 24
A small noise component amplitudes without amplitude limitation, since the uncorrelated portion of the large amplitude signal to the amplitude limitation, and functions as automatically sets the constant k ₁ in accordance with the amplitude of the input.

The chroma signal processing circuit of this embodiment includes a changeover switch 30 between the first comb filter 10 and the second comb filter 20. Selected terminal 31 of this changeover switch 30
Is connected to the input terminal 1, the selected terminal 32 is connected to the adder 11, and the selection terminal 33 is connected to the adder 21.

In the chroma signal processing circuit having the above configuration, the LP
In the mode, the selected terminal 32 of the changeover switch 30 is selected.

When the reproduction chroma signal including the crosstalk component is supplied to the input terminal 1, the first comb filter 10 removes the crosstalk component. Here, the crosstalk component is removed in order to prevent the limiter 24 of the second comb filter 20 in the subsequent stage from being saturated by the crosstalk component and adversely affecting the noise reduction operation. . The output from the first comb-shaped filter 10, that is, the reproduced chroma signal in which the amplitude of the included crosstalk component is small, is added by the adder 21 of the second comb-shaped filter 20.
Sent to. Then, the uncorrelated portion of the signal and the noise component are output from the adder 22 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 and, as a result, the threshold level is applied and the amplitude is limited and output. The output from the limiter 24 is the attenuator 25.
Attenuated by Here, the noise component is attenuated to about the initial amplitude, and the non-correlation part has a small amplitude equivalent to the amplitude of the noise component because the amplitude is limited by the limiter 24. This is for the uncorrelated part,
This means that the feedback constant k becomes k≈0. The output from the attenuator 25 is fed back to the adder 21, and the chroma signal output which is the difference component with the reproduced chroma signal supplied to the adder 21 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. The S / N improvement logic value by the second comb filter 20 is 10log (1 + 2k) [dB], and the S / N improvement logic value of the entire circuit is 3 + 10log (1 + 2k) [dB], which is a high S / N improvement effect. Is obtained. Further, the vertical deviation with respect to the luminance signal in the uncorrelated portion is at least 1H due to the first comb filter 10. However, as described above, the feedback coefficient k≈0 in the uncorrelated portion due to the action of the limiter 24. 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 never becomes 0 regardless of the coefficient k of the feedback system. Therefore, since the transfer function of the second comb filter 20 is always smaller than 1 and does not diverge, stable noise reduction operation can be performed.

Further, in this chroma signal processing circuit, the selected terminal 31 of the changeover switch 30 is selected in the SP mode.

That is, as described above, since it is not necessary to remove the crosstalk component by the first comb filter 10 in the SP mode, the reproduced chroma signal supplied to the input terminal 1 is the second comb filter 20. Sent directly to.

Therefore, since it does not pass through the first comb filter 10, the vertical shift of the uncorrelated portion of the chroma signal with respect to the luminance signal becomes extremely small. Especially in the PAL system, the influence of the 2H delay line is eliminated, and the image quality is greatly improved.

H. Effects of the Invention 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.

Moreover, in the chroma signal processing circuit of the video tape recorder according to the present invention, the first comb filter for removing the crosstalk component from the input reproduction chroma signal, and the crosstalk component by the input reproduction chroma signal and the first comb filter The reproduction chroma signal from which the noise has been removed is switched and selected by the switching means and supplied to the adder of the second comb filter. , The second comb filter directly performs noise removal processing,
A high S / N improvement effect can be obtained with a small amount of delay in the uncorrelated portion.

[Brief description of drawings]

FIG. 1 is a block circuit 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 circuit diagram showing a conventional example of a chroma signal processing circuit. 10 …… First comb filter 11,21,22 …… Adder 12,23 …… 1H delay line 20 …… Second comb filter 24 …… Limiter

Claims (1)

[Claims] 1. A first comb filter for removing a crosstalk component from an input reproduced chroma signal; a reproduction chroma signal from which the crosstalk component has been removed by the input reproduced chroma signal and the first comb filter. Switching means, an adder to which the reproduced chroma signal selected by the switching means is supplied, an extracting means for extracting a non-correlation part and a noise component of the signal from the output of the adder, and an output from the extracting means. And a second comb filter including amplitude limiting means for subjecting the non-correlation part to amplitude limiting processing and feeding back to the adder. The second comb filter is selected from the reproduced chroma signals selected by the switching means.
A chroma signal processing circuit for a video tape recorder, wherein a reproduced chroma signal from which a noise component is removed by a comb filter is taken out.