JPS6139792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise removal circuit that removes noise in a video signal.

For example, the video signal played back from a VTR is normally FM modulated during recording, and then FM demodulated during playback, but in the case of FM modulation recording, so-called triangular noise occurs. It is known that there is a lot of high-frequency noise in the video signal.

Therefore, as a noise removal circuit for removing noise from a video signal containing such noise, a circuit having a configuration as shown in FIG. 1 has been used. That is,
Reference numeral 1 denotes an input terminal to which a video signal containing noise is supplied, and the video signal is supplied to a low-pass wave generator 2 and a high-pass wave generator 3, respectively. The output of the high-pass wave filter 3 is then supplied to the nonlinear circuit 4. A coring circuit is used as this nonlinear circuit 4, and as shown in FIG. This is a circuit in which the relationship between the input level and the output level is linear when the absolute value of ΔW ₁ in Fig. 2 is greater than a predetermined value.
indicates the dead band width. Then, the output from the low-pass wave filter 2 and the output from the nonlinear circuit 4 are supplied to the synthesizer 5 and added, and a noise-free video signal is obtained at the output terminal 6 as the added output. be.

The video signal in the current television system is
Since the signal is a series of pixel signals obtained by scanning the screen in the horizontal direction and in the vertical direction, the noise removal circuit shown in Fig. It can only remove noise from the video signal.

However, when considering a screen, such noise does not necessarily exist only in the line scanning direction, that is, the horizontal scanning direction, but also in the plane scanning direction,
That is, it goes without saying that it also exists in the vertical scanning direction.
Therefore, in a video signal noise removal circuit, noise removal in the plane scanning direction of the video signal should also be considered.

For example, when considering a screen consisting of horizontal stripes as shown in Figure 3, the video signal has few high frequency components in the horizontal scanning direction, but has many high frequency components when considering the vertical scanning direction. . Therefore, this third
Considering the case of removing noise from a video signal based on a screen as shown in the figure, especially high-frequency noise, the noise removal circuit shown in Figure 1 can remove high-frequency noise in the horizontal scanning direction. However, it is not possible to remove noise in the vertical scanning direction.
Also, if the screen has vertical stripes as shown in Figure 4 and
In the case where the screen has checkered stripes as shown in the figure, high-frequency component noise in the horizontal scanning direction cannot be removed either.

Therefore, when removing noise from a video signal, it is necessary to consider how to remove noise in the line scanning direction and the image scanning direction.

In view of this, the present invention proposes a noise removal circuit that can remove noise even in the plane scanning direction of a video signal.

The noise elimination circuit according to the present invention supplies an input video signal to a delay line having a delay time of approximately one horizontal period, and subtracts the output of this delay line from the input video signal to obtain a vertical correlation output of the input video signal. The vertical correlation output is detected, and this vertical correlation output is supplied to a nonlinear circuit, and the output of this nonlinear circuit and the input video signal are synthesized by a synthesis circuit, and in the nonlinear circuit and the synthesis circuit, the vertical correlation output is smaller than a predetermined level. When the vertical correlation output is a noise component, it is removed from the input video signal, and when the vertical correlation output is larger than a predetermined level, it is used as an effective video signal component and is synthesized with the input video signal. This is what I did.

The present invention will be described in detail below with reference to some embodiments thereof with reference to the drawings. FIG. 6 shows a first embodiment, which is a noise eliminator circuit designed to remove high-frequency noise in the vertical and horizontal scanning directions of a video signal. Reference numeral 11 denotes an input terminal to which a video signal containing noise is supplied, and this video signal is supplied to a low-pass wave filter 12 having a cutoff frequency of about 3 MHZ to extract low-frequency components in the horizontal scanning direction. At the same time, the output signal from the low-pass wave filter 12 is subtracted from the video signal supplied to the input terminal 11 in the synthesizer 13, and the output signal from the synthesizer 13 is a high-frequency signal in the horizontal scanning direction of the video signal. ingredients are obtained.
The output of this synthesizer 13 is the comb waveform generator 1.
5A.

This comb waveform generator 15A includes a delay circuit 16 that delays an input signal by one horizontal period, and a synthesizer 1 that combines the input signal and the output of this delay circuit 16.
It consists of 7. In this case, combiner 17
is configured to subtract the output of the delay circuit 16 from the input signal. Therefore, as is well known, the comb waveform has a subcarrier frequency of 3.58M.
Since it exhibits a band-pass comb characteristic centered on Hz, this comb waveform generator 15A has the following characteristics:
Signal change in the vertical scanning direction in the input signal
This is a high-pass transducer that allows high-frequency components within approximately 1MHz around 3.58MHZ to pass through. In this case, the input signal supplied to the comb waveform generator 15A is a high frequency component in the horizontal scanning direction of the video signal supplied to the input terminal 11. Further, in this comb waveform generator 15A, for example, the attenuation ratio is -
0.5 (- indicates that the signal is phase inverted) is provided, the output of the comb waveform generator 15A is supplied to this attenuator 19, and the output of the comb waveform generator 15A is supplied to the comb waveform generator 15A in the combiner 18. After adding the input signal to be supplied and the output of this attenuator 19, the signal is supplied to the delay circuit 16. In this way, by changing the cutoff frequency of the low-pass wave filter 12 and the attenuation ratio of the attenuator 19, the frequency band range for noise removal can be varied. The output of the circuit 15A', which is constructed by adding the above-mentioned attenuator 19 to the comb waveform generator 15A thus obtained, is passed through the nonlinear circuit 20 through an attenuator 20 with an attenuation ratio of 0.5.
1 to remove noise in the vertical scanning direction and horizontal scanning direction of the video signal. In this example, the nonlinear circuit 21 is a coring circuit similar to that described in connection with FIG. 2 above.

Then, in the synthesizer 22, the output from the attenuator 20 is subtracted from the video signal supplied to the input terminal 11, the output is supplied to the synthesizer 23, and added to the output from the nonlinear circuit 21. In this way, the high-pass waveform composed of the low-pass waveform generator 12 and the subtractor 13 extracts high-frequency components in the horizontal scanning direction, for example, high-frequency components of 3 MHz or more, and these high-frequency components are further combed. The signal is supplied to the transducer 15A, and high-frequency components in the vertical scanning direction, for example, components within about 1 MHz centered around 3.58 MHz, are extracted. The output of this comb waveform generator 15A is supplied to a coring circuit 21, and this coring circuit 2
1, low-level high-frequency components in the horizontal scanning direction and vertical scanning direction, that is, noise components are removed. Of course, the output of the coring circuit 21 does not lose any low-frequency components in either the horizontal or vertical scanning directions. In this way, a video signal from which high-frequency noise has been removed in the vertical scanning direction, that is, the plane scanning direction, and in the horizontal scanning direction, that is, the line scanning direction, is obtained at the output terminal 25.

FIG. 7 shows the frequency characteristics of the circuit 15A' described above. The horizontal axis is frequency and the vertical axis is level. In the figure, fh indicates the horizontal frequency. K is the attenuation ratio of the attenuator 19 mentioned above. In this example, K=-0.5 is used.

Next, with reference to FIG. 8, the case of removing high-frequency noise in the plane scanning direction and the line scanning direction of a video signal, and the case of a noise canceler circuit, will be explained. The same reference numerals are given to corresponding parts and redundant explanation will be omitted. In this embodiment, a video signal containing noise supplied to the input terminal 11 is supplied to a high-pass wave generator 26 having a cutoff frequency of about 3 MHz, and high-frequency components in the horizontal scanning direction are extracted. The output of the high-pass waveform generator 26 is then supplied to a circuit 15A' including a comb waveform generator 15A. On the other hand, the video signal containing noise supplied to the input terminal 11 is supplied to the synthesizer 24 through the delay amount adjustment circuit 14. Further, the high frequency component in the horizontal scanning direction of the input signal is supplied to the circuit 15A', and the high frequency component in the vertical scanning direction is obtained. The output of this circuit 15A' is supplied to a nonlinear circuit 21' via an attenuator 20 with an attenuation ratio of 1/2.

In this case, the nonlinear circuit 21' is a stripping circuit whose input level-output level characteristics are shown in FIG. 9, and when the absolute value of the input level is below a predetermined level, the relationship between the input power level and the output level is This circuit is linear, and the output level is 0 when the absolute value of the input level is above a predetermined level. The range in which the input level and the output level have a linear relationship is ΔW ₂ . In this case, the output obtained at the output side of the nonlinear circuit 21' becomes a noise component in the plane scanning direction and the line scanning direction in the video signal.

The output of this nonlinear circuit 21' is then
4', the signal is subtracted from the output from the delay amount adjustment circuit 14, and a noise-free video signal is obtained at the output terminal 25.

Next, still another embodiment of the present invention will be described with reference to FIG. 10, but parts corresponding to those in FIGS. 6 and 8 described above are given the same reference numerals, and redundant explanation will be omitted. In this embodiment, noise is removed from a video signal containing noise by removing low-frequency components in both the surface scanning direction and the line scanning direction, and then removing noise from the remaining portion. In this case, in the comb waveform generator 15B, the input signal and the signal obtained by supplying the input signal to the delay circuit 16 and delayed by one horizontal period are added in the synthesizer 17' as shown in FIG. 6 above. and the comb wave device 1 of the embodiment shown in FIG.
This comb wave generator 15 is different from 5A.
B is a low-pass transducer that extracts low-frequency components of the input signal in the plane scanning direction, that is, in the vertical scanning. And this comb wave device 1
An attenuator 19 is added to the circuit 5B to constitute a circuit 15B'. Its damping ratio K is about 0.5.

Now, the video signal containing noise supplied to the input terminal 11 is supplied to the low-pass wave generator 12, and its output is supplied to the circuit 15B'. Thus circuit 15
The output of B' is a low frequency signal in both the surface scanning direction and the line scanning direction of the video signal supplied to the input terminal 11. Then, in the synthesizer 28, the signal obtained from this circuit 15B' is subtracted from the video signal supplied to the input terminal 11. This synthesizer 28 outputs a high frequency signal in the vertical scanning direction, a low frequency signal in the horizontal scanning direction, a high frequency signal in both the vertical and horizontal scanning directions, and a low frequency signal in the vertical scanning direction. , a signal consisting of a high-frequency signal in the horizontal scanning direction is obtained, and this signal is supplied to the nonlinear circuit 21. This nonlinear circuit 21 is a coring circuit as shown in FIG. 2 mentioned above. Then, the output of the nonlinear circuit 21 and the output of the circuit 15B' are added in a synthesizer 24, and a video signal from which noise has been removed is obtained from an output terminal 25. This first
The circuit shown in Figure 0 has a noise eliminator configuration.

Next, referring to FIG. 11, a method of removing noise similar to that in FIG. 10, but in the case of a noise canceller, will be described. In this case as well, a circuit 15B' having a comb waveform generator 15B similar to that in FIG. 10 is used. First, a video signal containing noise from the input terminal 11 is supplied to the low-pass wave generator 12, and its output is supplied to the circuit 15B'. and,
In the combiner 28, the output of the circuit 15B' is subtracted from the signal supplied to the input terminal 11, and the output is supplied to the nonlinear circuit 21'. The nonlinear circuit 21' in this case is a stripping circuit as shown in FIG. 9 mentioned above. Then, in the synthesizer 24', the output from the nonlinear circuit 21' is subtracted from the video signal supplied to the input terminal 11, and the output from the nonlinear circuit 21' is subtracted from the video signal supplied to the input terminal 11.
5, a video signal with noise removed is obtained.

As the above-mentioned nonlinear circuit, a coring circuit, a stripping circuit, or a limiter circuit can be used, and in short, it is a circuit that has a linear part and a nonlinear part respectively when the absolute value of the input level is below a predetermined value or above a predetermined value. Any one of them is sufficient, and they are selected depending on the noise eliminator circuit and noise canceler circuit, respectively.

According to the above-described noise removal circuit of the present invention, noise can also be removed in the plane scanning direction of the video signal. Therefore, by appropriately selecting the plane scanning direction and line scanning direction of the video signal, it is possible to effectively remove noise in a desired band, and by selecting the method for removing the noise, the video signal itself can be Noise can be effectively removed without causing distortion.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional noise removal circuit, Fig. 2 is a characteristic curve diagram for explaining the circuit, and Fig. 3 is a block diagram showing a conventional noise removal circuit.
4 and 5 are screen diagrams for explaining the present invention, FIG. 6 is a block diagram showing an embodiment of the present invention, FIG. 7 is a characteristic curve diagram for explaining the same, and FIG. is a block diagram showing another embodiment of the present invention,
FIG. 9 is a characteristic curve diagram for explaining the same, and FIGS. 10 and 11 are block diagrams showing still other embodiments of the present invention. 15A and 15B are comb wavers, 21 and 2
1' is a nonlinear circuit.

Claims (1)

[Claims] 1. The input video signal is supplied to a delay line having a delay time of approximately one horizontal period, and the output of this delay line and the input video signal are subtracted to detect the vertical correlation output of the input video signal, and the vertical correlation output of the input video signal is detected. The correlation output is supplied to a nonlinear circuit, and the output of the nonlinear circuit and the input video signal are synthesized by a synthesis circuit, and in the nonlinear circuit and the synthesis circuit,
When the vertical correlation output is smaller than a predetermined level, the vertical correlation output is treated as a noise component and removed from the input video signal, and when the vertical correlation output is larger than the predetermined level, it is effective. A noise removal circuit characterized in that this is synthesized with the input video signal as a video signal component.