JPS62263794A - Chroma signal processing circuit for video tape recorder - Google Patents

Abstract

PURPOSE:To improve the sag of a waveform and to obtain a high S/N improving effect by limiting the amplitude of the non-correlation part of a reproducing chroma signal and reducing the feedback quantity of the non-correlation part. CONSTITUTION:When the reproducing chroma signal is supplied to an input terminal 1, a crosstalk component is generally removed by a comb-line filter 10 and fed to the adder 21 of a comb-line filter 20. The non-correlation part and the noise component of the signal are outputted from an adder 22 and the noise component of small amplitude is amplified with a prescribed gain and outputted and the non-correlation part of large amplitude is amplified and limited in amplitude and outputted and attenuated by an attenuator 25. The output of the attenuator 25 is fed back to the adder 21 and the chroma signal output of the difference component to the reproducing chroma signal is outputted from an output terminal 2. As for the non-correlation part, a feed back constant k 0 is obtained by the operation of a limiter 24, the feedback quantity is extremely reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a chroma signal processing circuit for a video tape recorder for reducing noise components.

B0 Summary of the Invention The present invention is a chroma signal processing circuit of a video tape recorder that is used to reduce noise components, etc., by limiting the amplitude of the uncorrelated part of the reproduced chroma signal to extremely reduce the amount of feedback of the uncorrelated part. By doing so, it is possible to improve the droop of the waveform and obtain a high effect of improving the signal N.

C1 Conventional technology Conventionally, for example, a helical scan type video tape recorder has a chroma signal processing circuit (Japanese Patent Application Laid-open No. Showa 57-1602
(See Publication No. 88, etc.).

For example, a comb filter using a delay line is used in the chroma signal processing circuit, and a cyclic type or an acyclic type is known. - As an example, a chroma signal processing circuit used in a reproduction system of a video tape recorder compatible with the NTSC system will be explained with reference to FIG. The input terminal 101 is supplied with a reproduced chroma signal containing a crosstalk component. The output from adder 102 is sent to adders 103 and 104, respectively, and IH (
The signals are sent to the adders 103 and 104 via an IH delay line 105 having a delay amount of 1 horizontal period). The output from the adder 103, that is, the crosstalk component,
The uncorrelated part of the signal and the noise component are removed by attenuator 1.
06 to the adder 102.

The correlation and non-correlation of the chroma signal are detected by the correlation and non-correlation of the luminance signal, and the constant (feedback constant) k of the feedback loop determined by the attenuator 106 is:
1 (= Q ~ 1. In the reproduced chroma signal supplied to the terminal 101, the noise component is reduced by this feedback looseness, and the crosstalk component is reduced by the configuration of the adder 104 and the IH delay line 105. removed,
It is output from the output terminal 107 as a chroma signal output.

D0 Problems to be Solved by the Invention By the way, in the above-mentioned chroma signal processing circuit, even if the feedback constant k is set to =o, the adder 10
4 and the comb configuration of the IH delay line 105, the chroma signal is shifted by IH (2H in the PAL system) in the vertical direction in the uncorrelated part. Such vertical deviation of the chroma signal with respect to the luminance signal (so-called misregistration) is not much of a problem when the feedback constant k is set to a small value, but the amount of noise reduction, that is, the It becomes less effective. Therefore, if the feedback constant k is increased, that is, if the amount of feedback is increased, the effect of improving the N will increase, but the uncorrelated part of the chroma signal circulating in the feedback loop will not attenuate easily.
The waveform has a step difference, and a so-called sag in the waveform occurs over several hours, for example. As a result, color shift or color blurring occurs in the reproduced image.

The present invention has been proposed in view of the above-mentioned conventional problems, and is a video tape recorder that can improve the droop of the waveform near the uncorrelated part of the chroma signal and has a high effect of improving the signal noise. The purpose of this invention is to provide a chroma signal processing circuit.

Means for Solving the E0 Problem In order to achieve the above-mentioned object, the chroma signal processing circuit for a video tape recorder according to the present invention uses an adder to which a reproduced chroma signal containing a small crosstalk component is supplied. and extraction means for extracting the uncorrelated part and noise component of the signal from the output of the adder, and amplitude limiting means for limiting the amplitude of the uncorrelated part of the output from the extracting means, The present invention is characterized in that the output from the limiting means is fed back to the adder, and the difference component from the reproduced chroma signal is taken out as an output.

F2 Effect According to the present invention, the amplitude limiting means limits the width of the uncorrelated part of the reproduced chroma signal, and the amount of feedbank (feedback amount) of the uncorrelated part becomes extremely small.

G. Examples Examples of the present invention will now be described in detail with reference to the drawings. In the two embodiments described below, the present invention is applied to a chroma signal processing circuit of a video tape recorder compatible with the NTSC system.

G-1, First Embodiment FIG. 1 shows the chroma signal processing circuit of the first embodiment. An input terminal 1 to which a reproduced chroma signal containing crosstalk components due to adjacent tracks is supplied is connected to an adder 11 and is also connected to the adder 11 via an IH delay line 12. The adder 11 and the IH delay line 12 constitute a comb filter 10 whose main purpose is to remove the crosstalk component.

The adder 11 is connected to an adder 21.

Moreover, this adder 21. is connected to the adder 22, and is also connected to the adder 22 via an IH delay line 23. The adder 22 and the IH delay line 23 constitute extraction means, and the uncorrelated part and noise component of the signal are extracted from the output of the adder 21. The adder 22 is connected to a limiter 24 which is amplitude limiting means. This limiter 24 has a predetermined gain, and noise components with small amplitudes are amplified to the extent that they do not reach the threshold level for amplitude limiting and are output as they are, while uncorrelated parts of signals with large amplitudes are amplified. As a result, the signal reaches the threshold level and becomes saturated, so that the amplitude is limited and output. The limiter 24 is connected to the adder 21 via an attenuator 25. Further, the adder 21 is connected to the output terminal 2.

The adders 21, 22. LH delay line 23. limiter 24
．． The attenuator 25 constitutes a comb-shaped filter 20 whose main purpose is to reduce noise components, that is, to improve the signal N. Further, the feedback constant of the feedback loop is determined by multiplying the constant by the limiter 24 by 1 and the constant by the attenuator 25 by 2, so that k=.k2. Note that the limiter 24 does not limit the amplitude of noise components with small amplitudes, but limits the amplitude of uncorrelated parts of signals with large amplitudes, so the constant is automatically set to 1 according to the input amplitude. Conceivable.

In the chroma signal processing circuit having the above-described configuration, when a reproduced chroma signal containing a crosstalk component is supplied to the input terminal 1, the comb filter 10 approximately removes the crosstalk component. The reason why the crosstalk component is removed is to prevent the limiter 24 of the comb filter 20 in the subsequent stage from becoming saturated with the crosstalk component, which would adversely affect the noise reduction operation. The output from the comb filter 10, that is, the reproduced chroma signal containing small amplitude crosstalk components, is sent to the adder 21 of the comb filter 20. Then, the uncorrelated part and noise component of the signal are output from the adder 22 and sent to the limiter 24. Limiter 2 above
In No. 4, small amplitude noise components are amplified with a predetermined gain and output as they are, while large amplitude uncorrelated parts are amplified and, as a result of being amplified, reach a threshold level and are amplitude limited and output.

The output from the limiter 24 is attenuated by the attenuator 25. Here, the noise component is attenuated to about the original amplitude, and the uncorrelated part is removed by the limiter 24.
As the amplitude is limited by , the amplitude becomes as small as the amplitude of the noise component. This means that for the uncorrelated part, the feedback constant k is #0. The output from the attenuator 25 is fed back to the adder 21, and a chroma signal output, which is a difference component from the reproduced chroma signal supplied to the adder 21, is output from the output terminal 2.

That is, the amplitude of small-amplitude noise components is not limited, and an appropriate amount of feedback is obtained, resulting in a good noise reduction operation. The theoretical value of pupil improvement by the comb filter 20 is 101□,9(1+2k) [:dB), and the theoretical value of pupil improvement of the whole circuit is 3+101o11(1+2k) (dB), so a high pupil improvement effect can be obtained. It will be done. Further, although the vertical deviation of the luminance signal in the uncorrelated part is caused by the comb filter 10 at the lowest IH, as mentioned above, the feedback constant becomes 0 due to the action of the limiter 240 in the uncorrelated part. Since the amount of feedback is extremely small, there is almost no waveform droop, and no color shift or color blurring occurs.

G-2, Second Embodiment By the way, in general, in helical scan video tape recorders, luminance signals suffer from azimuth loss and H
-H shift, and P″11 for chroma signal
The S method makes it possible to remove crosstalk components caused by adjacent tracks, and performs guard panless high-density recording. However, as the performance of magnetic tape has improved, the demand for high resolution has increased. A videotape recorder is known which is equipped with dedicated ports for the LP mode (standard mode) and the LP mode (long time mode). In particular, for the SP mode, a head whose width is several microns narrower than the standard one-rank width is used, and the crosstalk component is so small that it is not necessary to use a comb filter. In this second embodiment, the present invention is applied to a chroma signal processing circuit of a video tape recorder as described above.

FIG. 2 shows a chroma signal processing circuit of a second embodiment. Note that each part corresponding to the first embodiment is given the same reference numeral and a description thereof will be omitted. This chroma signal processing circuit has a changeover switch 30 between a comb filter 10 and a comb filter 20. That is, the selected terminal 31 of the 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.
are connected to each.

In the SP mode, the selected terminal 31 is selected, and the reproduced chroma signal supplied to the input terminal 1 is passed through the comb filter 2.
0 directly. This is because, as described above, the crosstalk component is minimal in the SP mode, and there is no need to use the comb filter 10. Therefore, since the signal does not pass through the comb filter 10, the vertical deviation of the uncorrelated part of the chroma signal with respect to the luminance signal becomes extremely small. In particular, in the PAL system, 2H
The influence of the delay line is eliminated, resulting in a significant improvement in image quality.

Further, in the LP-mode, the selected terminal 32 is selected, the same operation as the circuit of the first embodiment is performed, and the same effect is obtained.

H0 Effects of the Invention In the chroma signal processing circuit of the video tape recorder of the present invention, the amplitude of the uncorrelated part of the uncorrelated part and the noise component of the chroma signal extracted by the extracting means is limited by the amplitude limiting means. This minimizes the feedback of grasshoppers. Therefore, it is possible to improve the drooping of the waveform near the uncorrelated part, and it is possible to prevent color shift and color blurring. In addition, with regard to noise components, appropriate feedback is performed without limiting the amplitude, and a high effect of improving the noise component can be obtained.

[Brief explanation of drawings]

1 is a block circuit diagram showing a first embodiment of a chroma signal processing circuit for a video tape recorder according to the present invention; FIG.
The figure is also a block circuit diagram showing the second embodiment. FIG. 3 is a block circuit diagram showing a conventional example of a chroma signal processing circuit. 21.22... Adder 23... IH delay line 24... Limiter

Claims (1)

[Scope of Claims] An adder to which a reproduced chroma signal containing a crosstalk component with a small amplitude is supplied; an extracting means for extracting the uncorrelated part and noise component of the signal from the output of the adder; and the extracting means. amplitude limiting means for limiting the amplitude of the uncorrelated part of the output from the amplitude limiting means, and feeding back the output from the amplitude limiting means to the adder;
A chroma signal processing circuit for a video tape recorder, characterized in that a difference component from the reproduced chroma signal is extracted as an output.