JPH0358231B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a noise reduction circuit, and in particular to a circuit that reduces noise contained in a video signal that is superimposed on a video signal portion that transitions from black to white. Regarding.

Prior Art FIG. 8 shows a block diagram of an example of a conventional noise reduction circuit. In the figure, a reproduced video signal a as shown in FIG. 9A, which is reproduced from a magnetic tape, for example, is input to an input terminal 1. This reproduced video signal contains noise, which can be regarded as a small-amplitude high-frequency component. The reproduced video signal a is noise-removed by the first low-pass filter 2 to become a signal b as shown in FIG. 9B, and then supplied to the first subtraction circuit 3, where it is subtracted from the input reproduced video signal a. Then, the high frequency component c of the reproduced video signal containing noise as shown in FIG. 9C is extracted. This high frequency component c is supplied to the first limiter 4, where it is shown in FIG.
The amplitude is limited by the limiting levels indicated by L ₁ and L ₂ and taken out as a small amplitude signal d shown in FIG. By subtracting the small amplitude signal d from the input reproduced video signal a, the subtracting circuit 5 obtains a result in which the noise in the reproduced video signal a is substantially canceled out since the small amplitude signal d is mostly noise. A reproduced video signal e as shown in is taken out and outputted to the output terminal 6.

Problems to be Solved by the Invention Here, since large-amplitude high-frequency signal components are present at each large-amplitude rising and falling edge of the reproduced video signal a, So-called whiskers with large amplitudes as shown by c ₁ and c ₂ appear in FIG.
Therefore, among the noises included in the reproduced video signal a, the noise immediately after the large amplitude edge that is removed by the limiter 4 is not canceled out by the subtraction circuit 5, and N ₁ , It remains as shown by N ₂ . Of these noises N ₁ and N ₂ , the noise N ₂ immediately after the edge portion where the video signal falls from white to black is not visually noticeable because the brightness level of the noise superimposed portion is black. Regarding the noise N ₁ immediately after the edge part rising from black to white,
There was a problem in that noise _N1 was visible on the screen and degraded the image quality.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a noise reduction circuit that solves the above-mentioned problems by reducing the low frequency range of noise close to the edges.

Means and Effects for Solving the Problems The present invention provides a high-pass filter that extracts the high-frequency component of an input information signal, an amplitude selection circuit that extracts the high-amplitude portion of the high-frequency component, and an output signal of the amplitude selection circuit. A second low-pass filter that blunts the waveform, a first low-pass filter to which the input information signal is supplied, and the output signals of the second low-pass filter are added together, and the output signal is sent to a first subtraction circuit. By providing an adder circuit that subtracts the input information signal,
This is designed to suppress the occurrence of a large amplitude portion of the output signal of the first subtraction circuit, and each embodiment thereof will be described below with reference to FIGS. 1 to 7.

Embodiment FIG. 1 shows a block diagram of a first embodiment of a noise reduction circuit according to the present invention. In the figure, the same components as in FIG. 8 are denoted by the same reference numerals, and their explanations will be omitted. In the present invention, since the output signal waveform of the low-pass filter 2 is rounded, a large amplitude portion is generated at the output end of the subtracter circuit 3, which exceeds the limiting level of the limiter 4, and as a result, immediately after the edge of the video signal. Focusing on the cause of image quality deterioration in conventional circuits, which is the lack of S/N improvement, the present invention corrects the rounding of the rise of the waveform at the output end of the low-pass filter 2.

In FIG. 1, a reproduced video signal a shown in FIG. 2A, which has entered an input terminal 1, passes through a low-pass filter 2 and is converted into a signal b shown in FIG. 2B, while being supplied to a high-pass filter 10. Note that the signals a and b shown in FIGS. 2A and B are the signals a and b shown in FIGS. 9A and B.
b, and Fig. 2 F, G, H, which will be described later.
The signals c', d', and e' shown in FIG. 9 are similar to the signals c, d, and e shown in FIG. 9C, D, and E. The signal components and noise (hereinafter referred to as high-frequency components) in the high frequency region of the reproduced video signal a that has been waved and extracted by the high-pass filter 10 have a waveform as shown in FIG. The portion corresponding to the edge portion of the video signal a has a large amplitude. This high frequency component f is supplied to the limiter 11, where the second
The amplitude part larger than the limiting level L ₃ shown in Figure C and the limiting level L ₄ (however,
The amplitude portions smaller than L ₄ <L ₃ ) are removed together, and the amplitude portions between the limiting levels L ₃ and L ₄ are allowed to pass.

As a result, a signal g as shown in FIG. 2D is taken out from the limiter 11. Here, the above limiting levels L ₃ and L ₄ are both high frequency components f
Since the level is selected to be greater than the center level of the signal g, the pulse width of the signal g is extremely narrow, and the noise superimposed on the amplitude portion below the limiting level _L4 is removed together with that amplitude portion. Noise is superimposed only on the slope of signal g.
This signal g has sharply curved corners, and when it is added to the output signal b of the low-pass filter 2, the steep corners degrade the waveform. The waveform is shaped to be round. The output signal of this low-pass filter 12 becomes a signal h as shown in FIG. 2E, and the level adjuster 1
3 and an amplifier 14, the signal is level-adjusted and then supplied to an adder circuit 15. In addition, the low-pass filter 12
also has the effect of suppressing noise superimposed on the waveform slope portion of the signal g.

The adder circuit 15 adds the signals h and b, respectively, to obtain a signal i in which the rounding of the waveform of the rising edge of the signal b shown by the solid line in FIG. 2B is corrected as shown by the broken line.
is supplied to the subtraction circuit 16, where it is subtracted from the input reproduced video signal a. As a result, as shown in FIG. 2F, the subtraction circuit 16 outputs small-amplitude noise within the range of the limiting levels L ₁ and L ₂ of the limiter 4 even immediately after the large-amplitude rising edge of the reproduced video signal a. A signal c′ containing . this signal
After c' is amplitude-limited by limiter 4 to form signal d' shown in FIG. 2G, it is supplied to subtraction circuit 5 and subtracted from input reproduced video signal a. As a result, as shown in FIG. 2H, the subtracting circuit 5 sends a reproduced video signal to the output terminal 6 with reduced noise even immediately after a rising edge of large amplitude in the reproduced video signal a.
e′ is output.

In this embodiment, the noise immediately after the falling edge of large amplitude of the reproduced video signal a is not reduced as in the conventional circuit, as shown by _N2 in FIG. 2H, but this noise _N2 is reduced as described above. Since the brightness level immediately after the video signal falls from white to black is superimposed on the signal portion that is close to black, the noise is less visually noticeable.
There is no practical problem. Although the limiter 11 cuts the top and bottom of the waveform, it is also possible to use a limiter that cuts only the bottom of the waveform to select the characteristics of the low-pass filter 12, the amount of adjustment of the level adjuster 13, and the gain of the amplifier 14. By doing so, the waveform of signal b can be corrected. The waveform of the main part at that time is shown in the third
Shown in Figures A-D. FIG. 3C shows the waveform of the output signal g' of the limiter which cuts only the lower side of the waveform, and the output signal of the low-pass filter 12 at this time is as shown by h' in FIG. 3D. If a limiter that cuts only the lower side of the waveform is used, the configuration of the limiter 11 will be simpler than in the first embodiment. On the other hand, in the case of the first embodiment, it is possible to prevent the addition circuit 15 from adding noise existing in the portion immediately after the rising edge.

Next, a second embodiment of the circuit of the present invention will be described. FIG. 4 is a block system diagram of a second embodiment of the circuit of the present invention, in which the same components as those in FIG. FIG. 5 is a waveform diagram for explaining the operation of the second embodiment shown in FIG. 4. Waveforms that are the same as those in FIG. , and a dashi is attached. In FIG. 4, the high frequency component f (shown in FIG. 5 C) extracted from the high frequency filter 10 is:
It is supplied to limiters 11 and 18, respectively. The limiter 18 has limiting levels indicated by broken lines L ₅ and L ₆ (L ₅ >L ₆ ) in FIG. .
Thereby, the limiter 18 passes only the amplitude portion between the limiting levels _L5 and _L6 of the negative amplitude partial region of the high frequency component f.

The adder circuit 19 adds and synthesizes the output signals of both the limiters 11 and 18 to generate a signal g'' as shown in FIG. After forming the signal h'' as shown in FIG. 5E, it is supplied to the adder circuit 15.
The adder circuit 15 receives a signal having a waveform in which only the corner portions of the waveform of signal b shown in FIG. 5B are shown by broken lines.
i' is generated and supplied to the subtraction circuit 16. As a result, as shown in FIG. _L1 , _L2
Small amplitude signals and noises c″ and d″ within the range of are extracted. As a result, as shown in FIG. 5G, the output terminal 6 outputs a reproduced video signal e'' in which noise is reduced even immediately after each of the large-amplitude rising and falling edges of the reproduced video signal a. .

FIG. 6 shows a block diagram of a third embodiment of the circuit of the present invention. In the figure, the same components as those in FIG. This embodiment uses a slice circuit 21 as an amplitude selection circuit, and in FIG. 6, the input reproduced video signal a shown in FIG.
The middle high-frequency component f (shown in FIG. 7B) is supplied to the slicing circuit 21, where the dashed line S ₁ ,
A small amplitude portion centered on the center level within the slice level range indicated by S ₂ is prevented from passing, and a large amplitude portion above the slice level S ₁ and below S ₂ is allowed to pass. Therefore, the slice circuit 21
A signal g as shown in FIG. Supplied.
The signal h has a waveform in which the noise superimposed on the slope portion of the waveform of the signal g is lowered by the low-pass filter 12. By correcting the roundness of the waveform of the output signal of the low-pass filter 2 using this signal h, the noise is reduced to a low frequency close to (immediately after) the edges of the large amplitude rising and falling edges, as in the second embodiment. be able to.

Note that the present invention can be applied not only to reproduced video signals, but also to video signals that have arrived via a transmission path, and further to other analog information signals in which waveform distortion is a problem.

Effects of the Invention As described above, according to the present invention, it is possible to reduce noise even immediately after an edge of a large amplitude of an input information signal, and therefore, it is possible to reduce the adverse effects of noise that remains immediately after an edge that occurs in conventional circuits. In particular, when applied to video signals, it has features such as being able to eliminate the deterioration in image quality caused by noise immediately after an edge that rapidly changes from black to white with large amplitude, which occurs in conventional circuits. It is something that you have.

[Brief explanation of drawings]

1, 4, and 6 are block system diagrams showing respective embodiments of the circuit of the present invention, FIG. 2 is a signal waveform diagram for explaining the operation of the block system shown in FIG. 1, and FIG.
The figure is a signal waveform diagram for explaining the operation when the main part of the block system shown in FIG. 1 is changed, and FIGS. 5 and 7 are signal waveform diagrams for explaining the operation of the block system shown in FIGS. FIG. 8 is a block system diagram showing an example of a conventional circuit, and FIG. 9 is a signal waveform diagram for explaining the operation of the block system shown in FIG. 1... Reproduction video signal input terminal, 2, 12... Low-pass filter, 3, 5, 16... Subtraction circuit, 4, 1
1, 18... limiter, 10... high frequency filter,
15, 19...Addition circuit, 21...Slice circuit.

Claims (1)

[Claims] 1. An input information signal containing noise to be reduced is passed through a first low-pass filter, and the input information signal and the input information signal are respectively supplied to a first subtraction circuit; A first limiter extracts a small amplitude portion of the output signal of the subtraction circuit and subtracts it from the input information signal in a second subtraction circuit, and the second subtraction circuit outputs the input information signal with its noise reduced. A noise reduction circuit that extracts a high frequency component of the input information signal, and an amplitude selection circuit that extracts a high amplitude portion of the high frequency component output from the high frequency filter.
A second low-pass filter that blunts the waveform of the output signal of the amplitude selection circuit and both output signals of the first and second low-pass filters are added, and the output signal is supplied to the first subtraction circuit. A noise reduction circuit comprising: an adder circuit for subtracting the input information signal from the input information signal. 2. The amplitude selection circuit is a second limiter that selectively outputs a high amplitude component in a positive amplitude region or a negative amplitude region of the output high frequency component of the high frequency filter. The noise reduction circuit described in item 1. 3. The amplitude selection circuit includes a second limiter that extracts a portion of the high amplitude waveform in the positive amplitude region of the output high frequency component of the high frequency filter, and a portion of the high amplitude waveform in the negative amplitude region of the high frequency component. 2. The noise reduction circuit according to claim 1, further comprising: a third limiter for extracting the output signals; and a mixing circuit for adding and synthesizing both the output signals of the second and third limiters, respectively. 4. The noise reduction circuit according to claim 1, wherein the amplitude selection circuit is a slice circuit that blocks passage of a small amplitude portion of the output high-frequency component of the high-pass filter.