JPH05168035A - Noise removing circuit for composite video signal - Google Patents

Abstract

PURPOSE:To provide a noise removing circuit which can satisfactorily and directly remove a noise component from a composite video signal. CONSTITUTION:In the noise removing circuit for the composite video signal superimposing a chroma signal modulated by a prescribed color sub carrier to a luminance signal, the input composite video signal is supplied to a luminance/chroma separating circuit 32 and separated into the luminance signal and the chroma signal, the noise components contained in these separated luminance signal and chroma signal are extracted, these respective noise components are subtracted from the input composite video signal by a subtracter 40, and the composite video signal removing noise is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise eliminating circuit for a composite video signal, which is suitable for application to a video disc reproducing apparatus.

[0002]

2. Description of the Related Art Generally, in a video disc, a video signal is directly recorded as a composite video signal. That is, for example, an NTSC video signal has a 3.58 MHz
The chroma signal phase-modulated by the color sub-carrier is superposed on the luminance signal to form a composite video signal. When this composite video signal is recorded on a video tape, a home-use V
In TR, a process of converting a chroma signal into a low frequency band is generally performed. However, in the case of a video disc, since the recording band thereof has a relatively large margin, the composite video signal is directly frequency-modulated (FM). And then recorded.

[0003]

When reproducing the video signal recorded as it is, it is necessary to remove the noise component contained in the composite video signal by the reproducing system circuit. There are various inconveniences in the circuit for directly removing the noise component from the.

FIG. 4 shows an example of a conventional noise removing circuit of this type. The composite video signal obtained at the input terminal 1 is supplied to the subtracter 2 and the color subcarrier signal 3.
Trap circuit 3 for trapping the 58 MHz frequency band
To remove the chroma component from the composite video signal to leave only the luminance signal component. Then, the luminance signal component output from the trap circuit 3 is converted into a plurality of band pass filters 4
are supplied to the limiter amplifiers 5a, 5b, ... Via a, 4b, ... And the noise components in the corresponding band (signals of high amplitude and small amplitude) are extracted. Then, the noise component of the extracted band is supplied to the subtractor 2, and this noise component is subtracted from the video signal directly supplied from the input terminal 1 to the subtractor 2,
The subtraction signal is supplied to the output terminal 6 as a noise-removed composite video signal.

In the noise eliminating circuit thus constructed, there is a disadvantage that the noise component included in the vicinity of 3.58 MHz of the luminance signal cannot be eliminated. In addition, since the phase of the component subtracted as noise cannot be strictly controlled, distortion such as ringing occurs in the composite video signal obtained at the output terminal 6, and the waveform characteristics deteriorate.

As another noise elimination circuit having another structure, as shown in FIG. 5, the composite video signal obtained at the input terminal 11 is supplied to the luminance / chroma separation circuit 12 so that the luminance signal Y and the chroma signal C can be obtained. And the separated luminance signal Y
Is supplied to the subtractor 14 via the low-pass filter 13. Further, the output of the low-pass filter 13 is supplied to the limiter amplifiers 16a, 16b, ... Through a plurality of band-pass filters 15a, 15b, ... And the noise components in the corresponding band are extracted. Then, the noise component in the extracted band is supplied to the subtractor 14, the noise component is subtracted from the luminance signal directly supplied from the low-pass filter 13 to the subtractor 14, and the subtraction signal is used as a luminance signal from which noise is removed. It is supplied to the luminance signal output terminal 17. Further, the luminance signal from which this noise has been removed is supplied to the mixer 18.

The chroma signal C separated by the luminance / chroma separation circuit 12 is supplied to the subtractor 22 via the bandpass filter 21. Then, the bandpass filter 2
1 output via the trap circuit 23 limiter amplifier 2
4 to extract the noise component of the chroma signal and supply this noise component to the subtractor 22. Then, the subtractor 22 subtracts the noise component from the chroma signal directly supplied from the bandpass filter 21 side, and the subtracted signal is used as a chroma signal from which noise has been removed, and the chroma signal output terminal 25
Supply to. Further, the chroma signal from which this noise has been removed is supplied to the mixer 18.

Then, the luminance signal and the chroma signal supplied from the mixer 18 are mixed into a composite video signal, and the composite video signal is supplied to the composite video signal output terminal 19.

According to the circuit thus constructed,
A noise-removed composite video signal is obtained at the output terminal 19, and noise-removed luminance signals and chroma signals are obtained at the output terminals 17 and 25.

In this example, since the noise removal processing is performed separately for the luminance signal and the chroma signal, the noise removal itself can be performed well, but the mixer 17 mixes the noise-removed luminance signal and the chroma signal. Since they are mixed to form a composite video signal, it is necessary to exactly match the phases of the luminance signal and the chroma signal supplied to the mixer 17, and in practice, such exact phase matching is difficult. Therefore, the composite video signal obtained at the composite video signal output terminal 19 is deteriorated due to the phase shift between the luminance signal and the chroma signal.

In view of the above points, an object of the present invention is to provide a noise removing circuit which can remove noise components directly from a composite video signal.

[0012]

According to the present invention, as shown in FIG. 1, for example, in a noise removing circuit for a composite video signal in which a chroma signal modulated by a predetermined color subcarrier is superimposed on a luminance signal, an input composite The video signal is supplied to the luminance / chroma separation circuit 32 to be separated into a luminance signal and a chroma signal, noise components contained in the separated luminance signal and chroma signal are extracted, and the respective noise components are input and combined. A subtractor 40 subtracts the video signal from the video signal to obtain a composite video signal from which noise has been removed.

[0013]

According to the present invention, the separated luminance signal and chroma signal are used to detect the noise component contained in each signal, so that good noise can be detected and
Since the detected noise component is directly subtracted from the composite video signal, the luminance component and the chroma component of the composite video signal are not out of phase, and a good composite video signal from which the noise component is removed can be obtained.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

First, the basic structure of this embodiment will be described with reference to FIG. 1. In FIG. 1, reference numeral 31 denotes an input terminal for a composite video signal, and the input terminal 31 is reproduced from, for example, a video disc. Then, the composite video signal demodulated is supplied. Then, the composite video signal obtained at the input terminal 31 is supplied to the luminance / chroma separation circuit 32. In the luminance / chroma separation circuit 32, the luminance signal Y and the chroma signal C are separated by using line correlation or the like, and the separated luminance signal is directly supplied to the subtractor 33 and the noise extraction circuit 34. Then, the noise component of the luminance signal extracted by the noise extraction circuit 34 is supplied to the subtractor 33 and the subtractor 40. In this case, the noise extraction circuit 34 is configured similarly to the conventional noise extraction circuit. For example, as shown in FIG. 5, a bandpass filter and a limiter amplifier extract a high-frequency small-amplitude signal included in a luminance signal, and use this high-frequency small-amplitude signal as a noise component.

Then, the noise component extracted by the noise extraction circuit 34 is subtracted from the luminance signal supplied from the separation circuit 32 side to the subtractor 33, and the subtraction signal is used as a luminance signal from which the noise component has been removed, and a luminance signal output terminal. 35.

The chroma signal separated by the separation circuit 32 is directly supplied to the subtractor 36 and is also supplied to the noise extraction circuit 37, and the noise component of the chroma signal extracted by the noise extraction circuit 37 is subtracted by the subtractor 36. And the subtractor 40. The noise extraction circuit 37 in this case is also configured similarly to the conventional noise extraction circuit.

Then, the noise component extracted by the noise extraction circuit 37 is subtracted from the chroma signal supplied from the separation circuit 32 side to the subtractor 36, and the subtraction signal is used as a chroma signal from which the noise component has been removed, and the chroma signal output terminal. 38.

Further, the composite video signal obtained at the composite video signal input terminal 31 is supplied to the delay circuit 39, and the delay circuit 39 delays the composite video signal by the time required for the separation processing in the luminance / chroma separation circuit 32. Let Then, the composite video signal delayed by the delay circuit 39 is supplied to the subtractor 40. In the subtractor 40, the noise extraction circuits 34 and 37 are extracted from the composite video signal supplied from the delay circuit 39.
The noise component supplied from is subtracted, and the composite video signal from which this noise component is subtracted is output as the composite video signal output terminal 41.
Supply to.

With this configuration, the output terminal 41
The resulting composite video signal is a signal obtained by directly subtracting the luminance noise component and the chroma noise component by the subtractor 40 from the composite video signal. Here, the noise component itself is
Since the noise signals are detected by the respective noise extraction circuits 34 and 37 based on the luminance signal and the chroma signal separated by the chroma separation circuit 32, the noise component contained in each signal is well extracted. Then, by directly subtracting each of these noise components from the composite video signal, the composite video signal itself is not separated by the luminance / chroma separation circuit 32, and the phase is not disturbed by the separation processing, and good noise removal is achieved. Done. Further, since the composite video signal and the noise component supplied to the subtractor 40 are synchronized in timing by the delay circuit 39, the phase of the composite video signal is not disturbed by the noise removal processing, and from this point as well, there is no phase difference. A good composite video signal without noise can be obtained.

In this example, since the noise signal-removed luminance signal and chroma signal are obtained at the output terminals 35 and 38, a separate output terminal (referred to as S terminal) for the luminance signal and the chroma signal is also provided. can get.

Next, an example in which the noise removal circuit of this example is combined with an actual luminance / chroma separation circuit will be described.
First, an example in which the 3-line type digital luminance / chroma separation circuit 50 is used will be described with reference to FIG. 2. A composite video signal (digital composite video signal in this example) obtained at the composite video signal input terminal 31 is converted into a luminance / chroma signal. It is supplied to the series circuit of the delay circuits 51 and 52 of the separation circuit 50. Each of the delay circuits 51 and 52 is a circuit that delays the input signal by one horizontal scanning period (1H). Then, the input signal of the delay circuit 51, the output signal of the delay circuit 51, and the output signal of the delay circuit 52 are supplied to the bandpass filters 53, 54, 55, respectively. Then, the video signals output from the band pass filters 53, 54, 55 are supplied to the correlation detection / adder 56, and the correlation detection / adder 56 outputs 3
While detecting the correlation of the line-shifted video signals, addition processing is performed according to the detected correlation.

The video signal output from the bandpass filter 54 is supplied to the subtractor 57, and the correlation detector / adder 56 is supplied.
The signal added by is supplied to the subtractor 57 via the band pass filter 58. Then, the subtractor 57 subtracts the video signal output by the correlation detector / adder 56 from the video signal output by the bandpass filter 54, and the subtracted output is the separated luminance signal Y. In addition, the bandpass filter 58
Is output as a chroma signal C. Further, the output of the delay circuit 51 is output from the luminance / chroma separation circuit 50 as a composite video signal delayed by 1H with respect to the input composite video signal.

Then, the luminance signal Y output from the luminance / chroma separation circuit 50 is supplied to the subtractor 33 and the noise extraction circuit 34 in the same manner as the circuit of the configuration of FIG.
Then, the noise component is subtracted from the luminance signal Y to obtain the noise-removed luminance signal Y at the output terminal 35. The chroma signal is also supplied to the subtractor 36 and the noise extraction circuit 37, and the subtractor 36 subtracts the noise component from the chroma signal,
A noise-removed chroma signal is obtained at the output terminal 38. Then, the composite video signal extracted from the delay circuit 51 of the luminance / chroma separation circuit 50 is supplied to the subtractor 40, and the subtractor 40 subtracts the luminance noise component and the chroma noise component. Then, the composite video signal from which the noise component has been subtracted is supplied to the output terminal 41.

This 3-line type luminance / chroma separation circuit 5
In the configuration using 0, the luminance / chroma separation circuit 5
Since the composite video signal delayed by the delay circuit 51 in 0 can be supplied to the subtractor 40, a delay circuit (corresponding to the delay circuit 39 in FIG. 1) is provided separately from the luminance / chroma separation circuit 50.
It is not necessary to provide any, and it can be simply configured.

Next, a three-dimensional type luminance / chroma separation circuit 6
An example using 0 will be described with reference to FIG. This three-dimensional luminance / chroma separation circuit is applied in the case of a video signal having a strong frame correlation, and the separation processing is performed by utilizing the correlation between one frames. That is, the composite video signal obtained at the composite video signal input terminal 31 is converted into a subtracter 61 of the luminance / chroma separation circuit 60 and a 525H delay circuit 62.
And the subtracter 63. In this case, the 525H delay circuit 62 is a circuit that delays the input video signal by 525 horizontal scanning periods, and the 525 horizontal scanning period corresponds to one frame. Then, the subtractor 63 subtracts the video signal of one frame before from the composite video signal obtained at the input terminal 31 by the delay circuit 62. Then, the subtraction output of the subtractor 63 is supplied to the subtractor 61, and the output of the subtractor 63 is subtracted from the composite video signal obtained at the input terminal 31. And this subtractor 6
The output of 1 is the luminance signal Y. The output of the subtractor 63 is supplied to the bandpass filter 64, and the output of the bandpass filter 64 is used as the chroma signal C.

Then, the luminance signal Y output from the luminance / chroma separation circuit 60 is supplied to the subtractor 33 and the noise extraction circuit 34 as in the circuit of the configuration of FIG.
Then, the noise component is subtracted from the luminance signal Y to obtain the noise-removed luminance signal Y at the output terminal 35. The chroma signal is also supplied to the subtractor 36 and the noise extraction circuit 37, and the subtractor 36 subtracts the noise component from the chroma signal,
A noise-removed chroma signal is obtained at the output terminal 38. Then, the composite video signal obtained at the input terminal 31 is supplied to the subtractor 40, and the subtractor 40 subtracts the luminance noise component and the chroma noise component. Then, the composite video signal from which the noise component has been subtracted is supplied to the output terminal 41.

This three-dimensional type luminance / chroma separation circuit 60
In the configuration using, the circuit is applied when the input video signal has a strong frame correlation, so the time difference between the output composite video signal and the noise component does not pose a problem, and the delay circuit There is no need to delay the video signal.

When the luminance / chroma separation circuit is constructed in an actual video disk reproducing device, for example, the movement of the reproduced video signal is detected, and a 3-line type luminance / chroma separation circuit is used at a moving portion. It is conceivable that a three-dimensional luminance / chroma separation circuit is used at a location where there is little motion and strong frame correlation, and the separation circuit is switched appropriately according to the video signal. By adopting a configuration in which the luminance / chroma separation circuit is switched in this way, more accurate separation processing (that is, noise removal processing) can be performed.

Further, in the above-mentioned embodiment, the example applied to the three-line type luminance / chroma separation circuit and the example applied to the three-dimensional type luminance / chroma separation circuit are shown. The present invention can be applied to a circuit.

Further, in the above-mentioned embodiment, the present invention is applied to the reproduction signal processing circuit of the video disk reproducing apparatus, but it goes without saying that the present invention can be applied to the composite video signal processing circuit of other video equipment.

[0032]

According to the present invention, the separated luminance signal and chroma signal are used to detect the noise component contained in each signal, so that good noise can be detected and the detected noise can be detected. Since the components are directly subtracted from the composite video signal, the luminance component and the chroma component of the composite video signal are not out of phase with each other, and a good composite video signal free of noise components can be obtained.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram when an embodiment is applied to a 3-line luminance / chroma separation circuit.

FIG. 3 is a configuration diagram when one embodiment is applied to a three-dimensional luminance / chroma separation circuit.

FIG. 4 is a configuration diagram showing an example of a conventional noise removal circuit for a composite video signal.

FIG. 5 is a configuration diagram showing another example of a conventional noise removing circuit for a composite video signal.

[Explanation of symbols]

 31 composite video signal input terminal 32 luminance / chroma separation circuit 33, 36, 40 subtractor 34, 37 noise extraction circuit 35 luminance signal output terminal 38 chroma signal output terminal 39 delay circuit 41 composite video signal output terminal 50 3 line type luminance / Chroma separation circuit 60 3D luminance / chroma separation circuit

Claims (1)

[Claims] 1. A noise removal circuit for a composite video signal in which a chroma signal modulated by a predetermined color subcarrier is superimposed on a brightness signal, and the input composite video signal is supplied to a brightness / chroma separation circuit to provide the brightness signal and the chroma signal. A noise-removed composite video signal by extracting the noise components contained in the separated luminance signal and chroma signal, and subtracting the respective noise components from the input composite video signal. A noise removing circuit for a composite video signal so obtained.