JP2548136B2 - Noise eliminator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal noise eliminator for use in a VTR, a video disc device or the like to reduce a minute noise component contained in a video signal.

2. Description of the Related Art FIG. 3 shows a block diagram of a conventional noise eliminator. 1
Is a video signal input terminal, 2 is a delay circuit for delaying the input video signal input from the input terminal 1 for one horizontal scanning period (referred to as 1H), 3 is a subtraction circuit for subtracting the output of the delay circuit 2 from the input video signal, Reference numeral 4 is an amplitude limiting circuit that limits the amplitude of the output of the subtracting circuit 3 when it is large, and 5 is a subtracting circuit that subtracts the output of the amplitude limiting circuit 4 from the input video signal.
6 is a high-pass filter (referred to as HPF) that extracts only the high-frequency component of the output of the subtraction circuit 5, 7 is an amplitude limiting circuit that limits the amplitude of the HPF 6 output, and 8 is the amplitude from the output of the subtraction circuit 5. A subtracting circuit for reducing the output of the limiting circuit 7 and an output terminal 9 for outputting a signal in which a minute noise component included in the input video signal is reduced at the output terminal of the conventional example.

The conventional noise eliminator configured as described above will be described below with reference to the frequency characteristic diagram of each part shown in FIG. Here, the horizontal axis of each figure of FIG. 4 shows the frequency of the signal, the vertical axis shows the gain thereof, and _H is the frequency of one horizontal scanning signal, and _H 1 = 1 / 1H≈15.73 KHz. First, the characteristic of a so-called comb filter composed of the delay circuit 2 and the subtraction circuit 3 is a frequency characteristic having a trap between frequencies O and _H as shown in FIG. 4A. Since the luminance signal and the color signal of the video signal are frequency-interleaved at intervals of 1/2 _H , the color signal component of the video signal is extracted by the characteristic A. The signal extracted by this characteristic A is
After the amplitude is limited by the amplitude limiting circuit 4, the subtraction circuit 5 subtracts it from the original signal, so that the output of the subtraction circuit 5 removes the color signal component of a minute level, and its characteristic is as shown in FIG. 4B. Become. Next, the HPF6 output takes out only the high frequency component of the output of the subtraction circuit 5 having the characteristic B, so that the characteristic becomes C. A minute level signal of the HPF6 output is taken out as high frequency noise by the amplitude limiting circuit 7 in the next stage and subtracted from the HPF6 input by the subtracting circuit 8. Therefore, the characteristics of the output signal to the output terminal 9 are as shown in FIG. 4D. In the video signal obtained as described above, first, a signal of a minute level having no correlation (no line correlation) in the vertical direction as in the characteristic B is removed, and then, in the horizontal direction, a high level noise component of a minute level. Will be the removed signal.

Problems to be Solved by the Invention However, although the above-described configuration has the effect of removing the color signal component superimposed on the input video signal due to the characteristic B, line correlation such as vertical edges or diagonal lines Since even a slight amount of the luminance signal component having no noise is attenuated, a large proportion is extracted as a low level high level noise in the horizontal direction by the HPF6 and the amplitude limiting circuit 7 in the subsequent stage, and as a result, as shown in the characteristic D It has a comb-shaped characteristic in the high frequency range, and the vertical noise removal and HP due to characteristic B
Double processing of horizontal denoising by F6 is performed to generate signal loss at the edge portion which affects the resolution of the image. Furthermore, although the signal component near the maximum frequency of the reproduced video band (denoted as ′ (FIG. 4)) itself has a small signal level, it has the greatest effect on the resolution of the image. If the limit level of the limit is increased, the signal component 'is attenuated, and the resolution is remarkably deteriorated, which is a serious problem.

In view of such a point, the present invention enhances the noise removal effect with respect to a noise component having no correlation in the vertical direction such as a chrominance signal component superimposed on a luminance signal of a video signal and a high level noise component having a minute level in the horizontal direction. Even so, it is an object of the present invention to provide a noise eliminator that does not significantly deteriorate the horizontal resolution.

Means for Solving the Problems A delay circuit that delays an input video signal by one horizontal scanning period (1H), a subtraction circuit that subtracts the output of the delay circuit from the input video signal, and a first circuit that limits the amplitude of the output of the subtraction circuit. 1, an amplitude limiting circuit, an adding circuit for adding the output of the delay circuit to the input video signal, a low-pass component extracted by a low-pass filter characteristic and a frequency component near the maximum frequency of a reproduction video signal band extracted by a band-pass filter characteristic. A filter for eliminating the output of the adder circuit and a second amplitude limiting circuit for limiting the amplitude of the filter output are provided, and the first amplitude limiting circuit output and the second amplitude limiting circuit output are output from the input video signal. It is a noise reduction device for video signals that is designed to be reduced.

Effect The present invention has the above-described configuration, and in the horizontal noise removal processing, in the signal correlated in the vertical direction by the 1H delay circuit and the adder circuit, the high frequency component excluding the component near the maximum frequency of the reproduced video signal band However, since the amplitude is limited and subtracted from the original signal, the resolution does not deteriorate even if the limit level of the amplitude limitation is increased in order to improve the noise removal effect.

Practical Example FIG. 1 shows a block diagram of a noise eliminating apparatus in an example of the present invention. In FIG. 1, 10 is an input terminal of a reproduced video signal, 11 is a delay circuit for delaying a signal for a 1H period, 12 is a subtraction circuit for subtracting the output of the delay circuit 11 from the input video signal, and 13 is an amplitude of an output of the subtraction circuit 12. A first amplitude limiting circuit for limiting the input signal, 14 is an adder circuit for adding the output of the delay circuit 11 to the input video signal, and 15 is only a DC component of the output of the adder circuit 14 and a component near the maximum frequency of the reproduced video signal band. Filter, 16 is a second amplitude control circuit for limiting the amplitude of the output of the filter 15, and 17 is the amplitude limiting circuit 13
An adder circuit for adding the output and the output of the amplitude limiting circuit 16, a subtraction circuit 18 for subtracting the output of the adder circuit 17 from the input video signal input to the input terminal 10, and 19 for the output terminal of the present embodiment, which is the input video A video signal in which a minute level noise component is removed from the signal is output.

In the present embodiment configured as described above, description will be made below with reference to the frequency characteristic diagram of each part in FIG. However, the characteristic of the signal obtained by subtracting the original signal from the signal delayed by 1H in the delay circuit 11 is the same as that of FIG. 4A described in the section of the prior art described above, and therefore is omitted from the characteristic diagram of FIG. To use. Therefore, the output of the subtraction circuit 12 becomes a signal having no correlation in the vertical direction as in the case of the above-mentioned conventional example, and the color signal component contained in the video signal is extracted from the output of the first amplitude limiting circuit 13. Next, the output of the adder circuit 14 in which the output of the delay circuit 11 is added to the original signal is
This is a signal component having a correlation in the vertical direction, and its frequency characteristic is a characteristic having traps at the _H interval from the frequency 1/2 _{H as} shown in FIG. 2E. From this signal component, only the luminance signal component of the video signal is extracted by the frequency interleaving method. In the signal extracted by the characteristic E, only the low frequency component and the signal component 'near the maximum frequency of the reproduced video signal are erased by the filter 15, and the signal is shown in FIG.
It has the following frequency characteristics. The characteristic G shows the characteristic of the output of the adding circuit 17 and is a characteristic obtained by adding the characteristic A of FIG. 4 and the characteristic F of FIG. In reality, the limiting level and gain of the first amplitude limiting circuit 13 for the vertical signal and those of the second amplitude limiting circuit 16 for the horizontal signal are substantially different, and each direction is different. The limit level and gain are set for the noise component that is superimposed on the signal, and the noise removal effect of this device is improved. Conceivable. However, in the present embodiment, in order to simplify the description of the operation, it is assumed that the amplitude limiting levels of the first amplitude limiting circuit 13 and the second amplitude limiting circuit 16 are sufficiently large and their gains are the same. The characteristics of the output signal obtained by subtracting the noise obtained by combining the noise components extracted in the vertical direction and the horizontal direction as described above from the input video signal by the subtraction circuit 18 are as shown in FIG. 2H.

As described above, according to the present embodiment, the 1H delay circuit 11, the subtraction circuit 12, and the addition circuit 14 perform the noise extraction processing separately from the signal components having a correlation in the vertical direction.
A luminance signal component having no correlation in the vertical direction such as an edge or an oblique line of the luminance signal is not attenuated doubly as in the above-mentioned conventional example, and there is little loss of the signal.
Does not pass the signal component 'near the maximum frequency of the reproduced video signal, the second noise removal effect is to that'.
Only vertical noise removal processing as shown in FIG. H is performed, and as a result, noise removal in the vicinity of'is performed without degrading the resolution of the image.

In addition, in the embodiment shown in FIG.
The noise components extracted in the vertical and horizontal directions are added and then subtracted from the original signal, but even if each is subtracted from the original signal, it is exactly the same as the characteristics of the present invention.

In addition to the analog signal processing technology in which the delay circuit 11 of this device uses a glass delay line or the like that is difficult to pass high frequency components, it can be realized by RAM or the like and delays signal components in all bands. It is effective to construct a digital signal processing technology capable of effectively performing noise removal processing in the vertical direction for the signal component ′. Further, in the digital signal processing technology, by appropriately selecting the sampling frequency, It is still effective because the trap characteristic like the filter 15 can be easily configured.

EFFECTS OF THE INVENTION As described above, according to the present invention, when performing noise removal in the vertical and horizontal directions of a reproduced video signal, in order to improve the noise removal effect, only the signal components having no correlation in the vertical direction are used. However, even if the signal component that has a correlation in the vertical direction is used and the level of the amplitude limit when extracting only the noise component is increased, a signal component that has no correlation in the vertical direction such as a vertical edge or diagonal line, In particular, since the signal component near the maximum frequency of the reproduced video band, which particularly affects the image resolution, is not attenuated, the noise removal effect can be enhanced without degrading the resolution, and its practical effect is great.

[Brief description of drawings]

1 is a block diagram of a noise eliminator in one embodiment of the present invention, FIG. 2 is a frequency characteristic diagram for explaining the operation of the embodiment, and FIG. 3 is a block diagram of a conventional noise eliminator.
FIG. 4 is a frequency characteristic diagram for explaining the operation of the conventional example. 11 ... Delay circuit, 12 ... Subtraction circuit, 13, 16 ... Amplitude limiting circuit, 14 ... Addition circuit, 15 ... Filter.

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-56-132878 (JP, A) JP-A-61-81083 (JP, A) JP-A-60-130986 (JP, A) JP-A-60- 121885 (JP, A) JP-A-58-57881 (JP, A)

Claims (1)

(57) [Claims] 1. A delay circuit for delaying an input video signal by one horizontal scanning period, a subtraction circuit for subtracting the output of the delay circuit from the input video signal, and a first amplitude limiting circuit for limiting the amplitude of the output of the subtraction circuit. , An adder circuit for adding the output of the delay circuit to the input video signal, and a low-pass component extracted by a low-pass filter characteristic and a frequency component near the maximum frequency of a reproduced video signal band extracted by a band-pass filter characteristic are deleted from the adder circuit output And a second amplitude limiting circuit that limits the amplitude of the filter output, and subtracts the first amplitude limiting circuit output and the second amplitude limiting circuit output from the input video signal. Noise eliminator.