JPH01198879A - Noise reduction device - Google Patents

Abstract

PURPOSE:To reproduce the picture of good quality without making a noise at the outline part of the picture prominent by using a vertical correlation when the noise component has the vertical correlation and correcting the noise component with a BPF and a limiter circuit having non-linear characteristics and subtracting the corrected noise component from its original signal when the noise component has no correlation. CONSTITUTION:A video signal (b) is subtracted from an original video signal (a), which is delayed for 1H at a 1H delaying circuit 12, and from which its clock frequency of 3.58MHzX4 and its high frequency component are eliminated, at a subtracting circuit 14. Since the noise component has no correlation, it is outputted as a random noise signal (c) and inputted to an equalizer circuit 15, near about 3.58MHz in the random noise signal (c) is emphasized, and after that, the emphasized random noise signal (c) is inputted through a BPF16 and a limiter circuit 17 having the non-linear characteristics to a phase correcting circuit 18 and phase-corrected. Next, the phase-corrected emphasized random noise signal (c) is passed through a buffer amplifier 19 and an inversion amplifier 20, and the corrected noise signal is subtracted from the original video signal at a mixing circuit 21. Thus, an S/N can be improved, and the picture of the good quality can be obtained without damaging the resolution of the high frequency component.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to reducing noise components contained in a video signal demodulated by a video tape recorder (hereinafter referred to as VTR), a disk player, etc. The present invention relates to a noise reduction device used.

[Prior art l] When performing FM demodulation of a video signal recorded by FM modulation on a recording medium such as a tape or a disk in a VTR or disc player, as the frequency of the video signal increases, it contains more noise components, so-called triangular Noise occurs and reduces image quality.

Conventionally, as means for reducing such noise components in a video signal, a signal processing form using an emphasis circuit consisting of a pre-emphasis circuit and a de-emphasis circuit has been adopted.

Signal processing by this emphasis circuit is performed by emphasizing and recording high frequency components of the video signal using a pre-emphasis circuit during recording, and suppressing the emphasized high frequency components using a de-emphasis circuit with opposite characteristics during playback. This is to reduce high-frequency noise components generated in the recording/reproducing system.

This emphasis processing has a great effect of reducing noise components, and is widely used to improve image quality. However, from the perspective of image quality processing, it can be This can be said to be a process of adding information to manipulate frequency characteristics.

However, recently, as a method for noise reduction processing of television signals, vertical emphasis processing, in which emphasis is applied to the television signal in the vertical direction, has been partially introduced. According to this vertical emphasis processing, the image quality improvement effect can be further enhanced without impairing the conventional emphasis processing described above.

In other words, vertical emphasis processing, which has been introduced in some areas as a noise reduction processing method for television signals, takes advantage of the difference in the fundamental properties of television signals and noise. Screen (T)
is composed of many horizontal scanning lines (IIL), but the contents of the signals (Sn) and (Sn-1) included in the adjacent horizontal scanning lines ()ILn) and ()ILn-1) are almost the same. This takes advantage of the property of vertical correlation that they are the same.

Since television signals have a large vertical correlation, signals can be added or subtracted by considering their polarity, phase, etc. On the other hand, noise cannot be easily added or subtracted because its polarity and phase are not constant and are random, so when these noises are added together, the sum becomes the square root of the square of each noise amount.

In other words, as shown in Figure 8, when the signal (Sn) of one scanning line is delayed and added to the signal (Sn-1) one line before it, the amplitude of that signal (Ss) is vertically correlated. Due to its nature, the noise (N) is doubled or the noise (N) is multiplied by σ, thus improving the S/N ratio of the image.

Figure 5 is a principle diagram showing the configuration of a reproduction system for vertical emphasis processing in a conventional noise reduction device applying the above principle. In the figure, (1) is the input terminal of the video signal, and (2) is the original and a delayed video signal delayed by one horizontal scanning line (hereinafter referred to as IH); (3) is an IH delay line made of CCD or glass; (4) is the This is an adjuster for adjusting the amplitude level of the delayed video signal applied to the adder (2) to the amplitude level of the original video signal, and generally consists of an attenuator.

(6) is a subtracter that subtracts the signal output from the adder (2) from the original video signal. (5) is an attenuator for adjusting the amplitude level of the signal applied to this subtracter (6). (8) is a limiter composed of a diode, etc., and the subtracter (6) is connected to this limiter (8).
The signal transmission system to is also provided with an attenuator (7) for adjusting the amplitude level. (9) is the limiter (8) above.
a subtractor that subtracts the output signal of from the original video signal, (1
0) is a signal output terminal.

Next, the operation of the above configuration will be explained.

As shown in the 6th UA (a), a video signal (St) containing a noise component (N), such as a VTR playback signal, for example.
is applied to the input terminal (1), this video signal (S
l) is adder (2) → IH delay line (3) → attenuator (4)
Figure 6 (
As shown in b), the signal from which the noise component has been removed (
Sl). This signal (Sl) is passed through an attenuator (
5), the signal (S3) as shown in FIG. 6(C) whose amplitude level has been adjusted is added to the subtracter (6), and in this subtracter (6) As shown in Figure 6(d), the noise (N
) is the bypass signal (S4).

Next, this bypass signal (S4) is turned into a signal (S5) whose amplitude level is adjusted by an attenuator (7) as shown in FIG. 6(e), and is input to a limiter (8). The signal (S6) shown in FIG. 6(f) output from this limiter (8) is input to the subtracter (9).
), the noise component (
N) removed video signal (S7) is obtained.

[Problems to be Solved by the Invention] The conventional noise reduction device that utilizes the property of vertical correlation is configured as described above, so it is possible to effectively reduce noise components in flat parts of images that are visually noticeable. Although it is possible to improve the S/N ratio by removing the
There were some drawbacks, such as noticeable noise in the contours of images, and low-level high-frequency signals, such as the detail of hair in close-up images of people being removed, resulting in a sticky image.

In addition, in 5-VH5 VTRs that aim for high resolution by separating luminance signals and chroma signals, the transient part of the luminance signal affected by the chroma signal remaining in the luminance signal is not sufficiently improved, and the outline of the image is There was a problem with the noise in some parts being noticeable.

This invention was made in order to solve the above-mentioned problems, and it is possible to improve the S/N ratio by effectively removing the noise components in the flat part of one image, while also impairing the resolution of high-frequency components. An object of the present invention is to provide a noise reduction device capable of obtaining high-quality images without any noise.

[Means for Solving the Problems] A noise reduction device according to the present invention includes a delay circuit for IH delaying a video signal, and an IH delay circuit for delaying a video signal by IH.
A subtraction circuit for subtracting the H-delayed delayed video signal from the original video signal, a bandpass filter circuit, a limiter circuit with nonlinear characteristics, and a mixing circuit for subtracting the output signal of the limiter circuit from the original video signal. [Operation] According to the present invention, when a video signal containing a noise component, such as a reproduced signal of a VTR, is input, the input signal is delayed by IH, and the delayed signal is delayed by IH. By subtracting the obtained signal from the original video signal, which has a strong vertical correlation, using a subtraction circuit, the signal becomes almost zero. Three-way, since the noise component composed of random noise has no vertical correlation,
After being corrected through a bandpass filter and a limiter circuit, it is input to a mixing circuit, where the above-mentioned corrected noise component is subtracted from the noise-containing video signal to reduce the noise component.

[Embodiments of the invention: 1. An embodiment of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing the configuration of a noise reduction device according to an embodiment of the present invention.
1) is an input terminal for the reproduced video signal, (11) is a buffer amplifier, and (12) is an IH delay circuit. This IH delay circuit (12) is composed of a CCD and uses a clock to faithfully delay the video signal. The frequency is 4 fsc (3,
It is desirable to operate at 58MHz x 4) and have 1000 or more stages. (13) is a low-pass filter circuit (hereinafter referred to as LPF) whose cut-off frequency is 7M) to remove interference from the clock frequency and high frequency components.
z and faithfully passes delayed video signals. (14) is a subtraction circuit;
subtracts the IH delayed video signal from the original video signal containing the noise component.

(15) is an equalizer circuit that corrects the frequency and phase of the noise component output from the subtraction circuit (14). (16) is a band pass filter circuit (hereinafter referred to as BPF) whose frequency characteristics are as shown in FIG.
58 Ml (z is the center frequency. (17) is a limiter circuit composed of nonlinear elements, (18) is a phase correction circuit that corrects the phase, (19) is a buffer amplifier, (
20) is an inverting amplifier for matching polarity.

(21) is a mixing circuit, and this mixing circuit (21) converts the original video signal into the IH delay circuit (12), LPF (1
3), subtraction circuit (14), equalizer circuit (15), B
The noise component signals corrected through the P F (16), the limiter circuit (17), and the phase correction circuit (18) are mixed and subtracted and removed. (22) is a delay element of approximately 400 nsec, which matches the time lag between the original video signal and the noise component signal. (10) is an output terminal.

FIG. 2 is a specific characteristic diagram of the above B P F (16).

Next, the operation of the above configuration will be explained.

A reproduced video signal with a poor S/N ratio applied to the input terminal (1) travels through a main path consisting of a delay element (22), a mixing circuit (21), and an output terminal (10), and at the same time passes through a buffer amplifier (11). ), IH delay circuit (12), LPF (1
3), etc., and proceed by separating into sub-routes. and,
In the sub-path, the separated reproduced video signal with a poor S/N ratio is amplified by a buffer amplifier (11) with a certain gain, then IH-delayed by an IH delay circuit (2), and roughly L P F (13), 3.58
The clock frequency of MHzX4 and its high frequency components are removed to obtain an IH-delayed video signal (b) that is the same as the original reproduced video signal (a) with a poor S/N ratio applied to the input terminal (1). .

Next, the original video signal with a poor S/N ratio (a) and the IH-delayed video signal with a poor S/N ratio (b) are combined with a subtraction circuit (
14) is subtracted. Here, in the case of a television signal, both signals (a) and (b) have a strong correlation in the vertical direction, so either a-b is zero, or the noise component composed of random noise is correlated. Therefore, it is output as a random noise signal (C). The amount of noise is multiplied by the square root of the square, that is, s7n times.

Next, the noise signal (c) is processed by the equalizer circuit (1
5), the frequency around 3.58 Hz is emphasized, and then the B P has a bandpass characteristic as shown in Fig. 2.
The signal passes through F (16), passes through a limiter circuit (17) having nonlinear characteristics, and is input to a phase correction circuit (18) for phase correction. Next, the buffer amplifier (I9
) and a polarity inverting amplifier (20) to the mixing circuit (20), where the noise component is reduced by subtracting the corrected noise signal from the original video signal.

Since the above noise signal processing circuit system includes a limiter circuit (17) with nonlinear characteristics, the noise reduction effect differs depending on the level of the signal, as shown in FIG. 3(a). Also, 3.58 Mtlz± 500
Within the band of B P F (16) of K11z, it has nonlinear comb layer characteristics as shown in FIG. 3(b).

As described above, according to the noise reduction device having the above configuration, noise components around 3.58 MHz can be effectively removed.
In a VHS system VTR, when the luminance signal (Y) and chroma signal (C) are separated as shown in Figure 4, the chroma signal component (C1) remaining in the transient part of the luminance signal (Y) can be removed. , it is possible to obtain a high-quality image by reducing noise in the outline of the image. In FIG. 4, (B) is a burst signal.

Note that the equalizer circuit (15)g and phase correction circuit (18) in the above embodiment are not limited to the configuration shown in FIG. 1, and the buffer amplifier (19) and polarity inverting amplifier (20) may be omitted. .

In addition, the characteristics of B P F (16) shown in the above embodiment are an effective example for use in the reproducing circuit of a VH5 type VTR, but it is possible to
There may also be one designed to improve the /N ratio.

[Effects of the Invention] As described above, according to the present invention, the strong vertical correlation property of television signals is utilized, while uncorrelated noise components are processed using BPF and nonlinear characteristics. The noise component can be reduced by correcting it with a limiter circuit and subtracting this corrected noise component from the original signal, effectively removing the noise component in the flat part of the image that is visually noticeable, and reducing the S/N. It is possible to achieve an improvement in the ratio, and also to reproduce a high-quality image without making the noise in the contour part of the image noticeable.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a noise reduction device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of BPF, FIG. 3 is a frequency characteristic diagram of a noise signal processing circuit system, and FIG.
The figure is a waveform diagram to explain the disturbance of the chroma signal remaining in the transient part of the luminance signal separated from the chroma signal. Figure 5 is a principle diagram showing the configuration of the reproduction system for vertical emphasis processing in a conventional noise reduction device. , 6th
This figure is a signal waveform diagram of each part in FIG. 5, and FIGS. 7 and 8 are schematic explanatory diagrams of vertical emphasis processing. (12) -IH delay circuit, (13)...LPF,
(14):...Subtraction circuit, (16)...B P F
, (17)--Limiter circuit, (2I)--Mixing circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) a delay circuit that delays a video signal by one horizontal scanning line; a subtraction circuit that subtracts the delayed video signal delayed by one horizontal scanning line by the delay circuit from the original video signal;
A band-pass filter circuit is placed after this subtraction circuit, a limiter circuit with non-linear characteristics is placed after this band-pass filter circuit, and the output signal of this limiter circuit is subtracted from the original video signal to generate noise. A noise reduction device characterized by comprising a mixing circuit for reducing components.