JPH1084552A - Noise reduction circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise reduced circuit having a small circuit scale and to provide a noise reduction circuit having a high reduction effect on both a reflected noise component or a chroma component and a random noise component without simultaneous use of two kinds of noise reduction circuits. SOLUTION: A video signal is separated into signals inside and a outside a frequency band where many reflected noise components or chroma components are included and cyclic noise reduction is applied to the signal outside the band and acyclic noise reduction is applied to the signal inside the band. Concretely, the circuit is provided with means 6, 10 to separate a frame difference signal into signals inside and outside the frequency band, means 12, 14 which reduce the noise component outside the frequency band, and means 15, 2 which delay a frame of the signal whose out-band noise is reduced, and computer 8, 16 which reduce the in-band noise from the signal whose out-band noise is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a noise reducer circuit, and more particularly to a noise reducer circuit for a video device.

[0002]

2. Description of the Related Art Conventionally, this kind of noise reducer circuit is included in a video signal as shown in, for example, "Digital Signal Processing for Images, Enhancement Edition, by Takahiko Fukinuki", pp. 115-118, January 1985. It is used for the purpose of reducing noise components.

[0003] In the process of recording / reproducing, transmitting and processing video signals, if noise components unrelated to the original video signals are mixed in, they will be extremely disturbing to human eyes when viewed as a video. Perceived as degraded. Therefore, reducing this noise component is a very important technique for improving the image quality of video equipment.

Here, the noise components included in the video signal include a aliasing noise component and a random noise component.
The characteristics of each noise component are shown below.

First, the characteristics of the aliasing noise component will be described. This noise is continuous in the frame direction, the phase of the noise component is inverted between frames, and the noise is concentrated and generated in a specific frequency band. It has the characteristic. M
A high-frequency aliasing component generated by the USE-NTSC converter corresponds to this. Although not a noise component, the chroma signal component of the NTSC signal has similar properties.

Next, if the characteristics of the landing noise component are shown,
This noise is independent in the frame direction and in the horizontal and vertical directions within the frame, and has a feature that it has no correlation between frames and a feature that it is generated by being distributed over a wide frequency band. Noise generated in a VTR reproduction signal and a tuner signal when a weak electric field signal is received correspond to this.

To reduce the noise, there is a noise reducer circuit suitable for each characteristic. A non-cyclic noise reducer is suitable for reducing aliasing noise components, and a cyclic noise reducer is suitable for reducing random noise components. Reducers are suitable. Conventionally, a noise reducer circuit is properly used according to the type of a noise component to be reduced.

FIG. 4 is a block diagram showing an example of a conventional acyclic noise reducer circuit, and FIG. 5 is a chart diagram of an example of signal processing of the circuit. The input signal 1 is delayed by one frame by the frame memory 2, and the frame delay signal 3
Get. This signal and the input signal 1 are input to the arithmetic circuit 4,
A frame difference signal 5 is obtained. This signal is input to the motion adaptive coefficient unit 6, and the noise component signal 7 in which the motion component is reduced
Get. This signal and the delay signal of the input signal 1 are input to the arithmetic circuit 8, and an output signal 9 is obtained.

Next, the operation of the non-cyclic noise reducer circuit will be described. The frame difference signal 5 (FIG. 5-c) is
The input signal 1 (FIG. 5A) and the frame delay signal 3 (FIG.
−b), which is a signal representing a change between frames. While 0 is output in a still portion of the video, a non-zero signal is output in a moving portion or a portion having a noise component. That is, the frame difference signal 5 includes a video noise component and a motion component. In the stationary part of the video,
Since the frame difference signal 5 contains only a noise component, this component may be subtracted from the input signal 1 as it is. However, if the subtraction is performed as it is in the moving part of the video, the motion component is also subtracted, and an afterimage occurs. Therefore, the frame difference 5 is input to the motion adaptive coefficient unit 6, where the motion component is limited, and is output as the noise component signal 7 from which only the noise component is extracted. As a method of the motion adaptive coefficient unit, various methods such as a motion detection circuit, a coefficient unit, and a nonlinear filter can be considered. For example, if the magnitude of the movement is k
When (k: 0 to 1) is set, an operation of multiplying an input signal by 1-k and outputting the signal is considered. However, since the method of the motion adaptive coefficient unit is not directly related to the essence of the noise reducer circuit, no particular method is specified here. In this example, it is assumed that there is no motion component in the video, the motion adaptive coefficient unit is through, and the noise component signal 7 is the same as the frame difference signal 5. This is subtracted from the delayed signal of the input signal 1 to obtain an output signal 9 with reduced noise components (FIG. 5).
d). Usually, since the noise component signal 7 is delayed by the motion adaptive coefficient unit 6, the input signal 1 is also delayed by the same amount.
The phases must be matched. The output signal 9 obtained by this procedure becomes the average of the input signal 1 and the frame delay signal 3 after all. An aliasing noise component that is continuous between frames and whose component is inverted is completely removed by the averaging process. On the other hand, the amplitude of the random noise component independent between frames is reduced to half by the averaging process.

FIG. 6 is a block diagram showing an example of a conventional cyclic noise reducer circuit, and FIG. 7 is a chart diagram of an example of signal processing of the circuit. The difference from the non-recursive noise reducer circuit is that the output of the arithmetic circuit 4 is one time, and the input of the frame memory 2 is not the input signal 1,
That is, the output signal 9 is obtained. That is, the signal after noise reduction circulates through the frame memory 2.

Next, the operation of the cyclic noise reducer circuit will be described. The output signal 9 (FIG. 7-h), that is, the signal after noise reduction, is input to the frame memory 2 and becomes a frame delay signal (FIG. 7-a). This and input signal 1
From FIG. 7B, a frame difference signal 5 (FIG. 7C) is obtained. Since the processing from here is the same as the non-cyclic type,
Description is omitted. In a portion determined to be still, that is, through, by the motion adaptive coefficient unit, all changes between frames are processed as noise. A return noise component whose component is inverted between frames remains as a pattern at the start or a vibration pattern as shown in FIGS. On the other hand, the random noise component that is independent between frames is the change between frames =
It is completely removed as a noise component.

When it is desired to reduce both the aliasing noise component and the random noise component, as shown in FIG.
It is necessary to connect different kinds of noise reducers in series. In the circuits 1 to 9 in FIG. 8, the aliasing noise component is reduced, and in the circuits 11 to 19, the random noise component is reduced. The operations 1 to 9 and 11 to 19 in FIG. 8 are as described above, and will not be described here.

[0013]

In the non-cyclic noise reducer circuit, the effect of reducing the aliasing noise component is high, but the effect of reducing the random noise component is low. On the other hand, in the cyclic noise reducer circuit, the reduction of the random noise component is reduced. The effect is high, but the effect of reducing the aliasing noise component is low.

Therefore, when it is desired to reduce both the aliasing noise component and the random noise component, both the acyclic noise reducing circuit and the cyclic noise reducing circuit described above are prepared and connected in series as shown in FIG. The problem is that it must be done. As a result, the circuit scale becomes large, and an expensive frame memory must be used twice.

Further, in general, in a noise reducer circuit, the occurrence of an afterimage often becomes a problem due to a malfunction of the motion adaptive coefficient unit. However, the probability of occurrence of the afterimage increases when connected in series. is there.

An object of the present invention is to provide a noise reducer circuit having a small circuit scale.

Another object of the present invention is to provide a noise reducer circuit having a high effect of reducing both a return noise component or a chroma component and a random noise component without simultaneously using two types of noise reducer circuits. Is to do.

Still another object of the present invention is to provide a noise reducer circuit that suppresses the afterimage generation rate lower than when two types of noise reducer circuits are used simultaneously.

[0019]

According to the present invention, a frame difference signal is separated into an inside and outside of a specific frequency band, a frame cyclic process is performed outside the band, and a frame non-cyclic process is performed within the band. A characteristic noise reducer circuit is obtained.

Further, according to the present invention, a YC separation function for separating a frame difference signal into and out of a chroma frequency band, performing a frame cyclic noise reducer process outside the band, and performing a YC separation process within the band. A noise reducer circuit characterized by having both is obtained.

Further, according to the present invention, the signal to be frame-delayed is a signal after performing processing outside the specific frequency band, so that the memory for the frame cyclic processing and the frame non-cyclic processing is shared. Is obtained.

[0022]

Next, a first embodiment of the present invention will be described in detail with reference to the drawings.

The noise reducer circuit of the present invention separates a video signal into and out of a frequency band (hereinafter, simply referred to as a "band") containing a large amount of aliasing or chroma components. It has a configuration for performing acyclic noise reduction. More specifically, means for separating the frame difference signal into and out of the band (6 and 10 in FIG. 1)
And means for reducing out-of-band noise components (12,
14), means for delaying the signal with reduced out-of-band noise by frame (15, 2 in FIG. 1), and means for reducing in-band noise from the signal with reduced out-of-band noise (FIG. 1) 8, 16).

According to the noise reducer circuit of the present invention, the frame difference signal is divided in advance into the band where the aliasing noise component or the chroma component exists, and
Since the signal to be delayed by the frame is a signal after reducing the noise outside the band, a cyclic noise reducer configuration having a high random noise component reduction effect outside the band can be obtained. In other words, it is possible to configure a non-cyclic noise reducer that is highly effective in reducing aliasing noise components or chroma components.
The effect of reducing both the aliasing noise component or the chroma component and the random noise component can be obtained, and the occurrence probability of an afterimage can be suppressed lower than that of a circuit in which two types of noise reducers are connected in series.

Now, referring to FIG. 1, the first computing unit 4
Is subtracted from the input signal 1 by the frame delay signal 3 delayed by one frame by the frame memory 2 to obtain a frame difference signal 5. This is input to a band-pass filter 6 that passes a band in which only the aliasing noise component exists, and an in-band frame difference signal 7 is obtained. This is input to a first motion adaptive coefficient multiplier 8 to obtain an in-band noise component signal 9 with reduced motion components. On the other hand, the in-band frame difference signal 7 is subtracted from the frame difference signal 5 using the second arithmetic unit 10 to obtain an out-of-band frame difference signal 11. This is input to a second motion adaptive coefficient unit 12 to obtain an out-of-band noise component signal 13 in which a motion component is reduced. The out-of-band noise component signal is subtracted from the delayed signal of the input signal 1 using the third arithmetic unit 4 to obtain a cyclic signal 15. This signal is input to the frame memory 2 and is delayed by one frame to become the previous frame delay signal 3. Then, the fourth computing unit 1
6 from the cyclic signal 15 to the in-band noise component signal 9
Is subtracted to obtain a final output signal 17.

Next, detailed operations of the band pass filter 6 and the second arithmetic unit 10 will be described. The frame difference signal 5 includes both a return noise component and a random noise component in addition to the motion component. Here, the aliasing noise component or the chroma component often occurs in a specific frequency band. By utilizing this property, the frame difference signal 5 is separated into a frequency band in which many aliasing noise components or chroma components are included and a frequency band in which many aliasing noise components or chroma components are not included. First, the frame difference signal is input to the band-pass filter 6 that allows only the specific band to pass, and an in-band frame difference signal is obtained. It is desirable that this band-pass filter efficiently passes through the folded component band or the chroma component band. Examples of the configuration include a band-pass filter, a line comb (comb) filter, a logical comb filter, and a composite filter thereof. When the separated in-band frame difference signal 7 is subtracted from the original frame difference signal 5 using the second arithmetic unit 10, the out-of-band frame difference signal 11 can be obtained. As a result, the in-band frame difference signal 7 includes the aliasing noise component or the chroma component, the in-band random noise component, and the in-band motion component. The out-of-band frame difference signal 11
Contains a random noise component outside the band and a motion component outside the band.

Although the two motion adaptive coefficient units are the same as those shown in the prior art, the first motion adaptive coefficient unit 8 has a random noise component On the other hand, the second motion adaptive coefficient unit 12
It is desirable to optimize the change of the coefficient with respect to the aliasing noise component.

Next, the operation of the circuit shown in FIG. 1 will be described with reference to a chart shown in FIG. Input signal 1
Is a video signal containing both the aliasing noise component and the random noise component (FIG. 2A). The frame delay signal 3 is a video signal one frame before, but the random noise component is reduced and the aliasing noise component remains. The reason will be described later (FIG. 2B). In the difference signal 5 obtained from these signals, the video component is canceled, and the aliasing noise component and the random noise component present in the input signal 1 are included (FIG. 2C). The band filter 6 and the second computing unit 10 described above
And the in-band frame difference signal 7 (FIG. 2-d),
It is separated into an out-of-band frame difference signal 11 (FIG. 2-e).

The fact that these components include motion components is as described in the section of the prior art. In order to reduce this component, the in-band frame difference signal 7 is input to the first motion adaptive coefficient multiplier to obtain an in-band noise component 9, that is, a folded noise component. On the other hand, the out-of-band frame difference signal 11 is input to the second motion adaptive coefficient unit to obtain an out-of-band noise component 13, that is, a random noise component.

In this example, as in the description of the prior art, it is assumed that the video has no motion component and the first and second motion adaptive coefficient units are through. That is, the in-band noise component signal 9 is the same as the in-band frame difference signal 7, and the out-of-band noise component signal 13 is the same as the out-of-band frame difference signal 11.

The noise of the input signal is reduced by subtracting these noise components from the input signal. However, as described in the related art, in a simple cyclic or non-cyclic configuration, a random noise component and The effect of reducing the aliasing noise component is a trade-off, and a sufficient effect cannot be obtained. Therefore, it is necessary to devise data to be delayed in the frame memory so that the cyclic noise processing is performed for the out-of-band random noise component, and the non-cyclic processing is performed for the aliasing noise component in the band. is there.

First, first, using the third computing unit 14,
A signal is obtained by subtracting twice the out-of-band noise component signal from the delayed input signal 1. Then, the random noise component outside the band is reduced, but the aliasing noise component inside the band is not changed. That is, this is a video signal in which the aliasing noise component remains. This signal is input to the frame memory 2 as a cyclic signal 15 (FIG. 2-f). The output of the frame delay signal 3 is, of course, a video signal in which aliasing noise components remain.

Second, out-of-band random noise components have already been reduced by the above procedure. After that, only the aliasing noise component in the remaining band is reduced. Fourth computing unit 16
Is used to subtract the in-band noise component signal from the cyclic signal 15 to obtain an output signal 17 (FIG. 2-g). This means that the random noise component and the aliasing noise component present in the input signal 1 have been sufficiently reduced.

A point to be noted is that the differential signal is separated into the inside and outside of the return noise component band, the data to be subjected to frame delay is circulated as a signal after noise reduction outside the band, and the signal within the band is reduced thereafter. Thus, the configuration is such that it does not patrol.

That is, a signal outside the band becomes a cyclic noise reducer, and a signal within the band becomes a non-cyclic noise reducer.

Next, a second embodiment of the present invention will be described.
This will be described with reference to FIG.

The frame difference signal 5 is input to a first C (chroma) separation filter 6 to become a C frame difference signal 7. Further, the first arithmetic unit subtracts the C frame difference signal 7 from the frame difference signal 5 to obtain a Y (luminance) frame difference signal 8. On the other hand, the input signal 1 is changed to the second C
The signal is input to the separation filter 18 to obtain a C-frame signal 19. The C frame difference signal is input to a first motion adaptive coefficient unit 8, and the signal in the C frame is input to a third motion detection circuit 20. The result of adding these outputs is referred to as C signal 9. The third motion adaptive coefficient unit 20 functions differently from the first and second. The size of the movement is k (k: 0-1)
In this case, the first and second motion adaptive coefficient multipliers function to multiply the input signal by 1-k, while the third motion adaptive coefficient multiplier functions by multiplying the input signal by k. That is, when the sum C signal 9 of the output signals is represented by k, C = k (signal 19 in a C frame) + (1−k) (C frame difference signal 7). The weight of the intra-frame signal is changed.

The second embodiment of the present invention is a circuit having a so-called three-dimensional YC separation filter function and a noise reducer function, to which the first embodiment is applied.
The three-dimensional YC separation realizes highly accurate separation of a Y signal and a C signal by adaptively performing calculation between frames in a still image portion and within a frame in a moving image portion.

The C signal included in the composite video signal utilizes the property that it exists continuously between frames, has a reversed phase, and exists in a specific band, similarly to the aliasing noise component. . The major difference from the first embodiment is that the extracted C signal is not noise but important information, and is adaptively mixed with the extracted C signal in the frame according to the magnitude of the motion and output. It is in.

In the second embodiment, there is an effect that high-precision YC separation of an input composite signal and reduction of a random noise component included in the Y signal can be simultaneously performed.

[0041]

According to the present invention, both the aliasing noise component or the chroma component and the random noise component can be reduced.

Accordingly, when it is desired to reduce both the aliasing noise component, the chroma component, and the random noise component, it is not necessary to prepare both a non-cyclic type and a cyclic type noise reducer circuit. Therefore, the circuit scale does not increase, and the probability of occurrence of an afterimage does not increase.

In addition, since the data to be delayed by the frame memory is devised so as to serve both as a cyclic memory and a non-cyclic memory, it is not necessary to use an expensive frame memory twice.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a time chart showing the operation of FIG.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram illustrating an example of a conventional acyclic noise reducer.

FIG. 5 is a time chart showing the operation of FIG. 4;

FIG. 6 is a diagram showing an example of a conventional cyclic noise reducer.

FIG. 7 is a time chart showing the operation of FIG. 6;

FIG. 8 is a diagram in which acyclic noise reducers and cyclic noise reducers are connected in series.

[Explanation of symbols]

Reference Signs List 1 input signal 2 frame memory 3 frame delay signal 4 arithmetic circuit 5 frame difference signal 6 motion adaptive coefficient unit (bandpass filter)
(C separation filter) 7 Noise component signal (in-band frame difference signal) (C frame difference signal) 8 Operation circuit (motion adaptive coefficient unit) (Y frame difference signal) 9 Output signal (in-band noise component signal) (C
Signal) 10 arithmetic unit 11 out-of-band frame difference signal 12 motion adaptive coefficient unit 13 out-of-band noise component signal 14 arithmetic unit 15 cyclic signal 16 arithmetic unit 17 output signal 18 C (chroma) separation filter 19 C-frame signal 20 motion detection circuit

Claims (3)

[Claims] 1. A noise reducer circuit which separates a frame difference signal into and out of a specific frequency band, performs a frame recursive process outside the band, and performs a frame non-recursive process within the band. 2. A YC separation function for separating a frame difference signal into and out of a chroma frequency band, performing a frame recursive noise reducer process outside the band, and performing a YC separation process inside the band. Noise reducer circuit. 3. A noise reducer circuit characterized in that a signal to be delayed for a frame is a signal after processing outside a specific frequency band, so that a memory for a frame cyclic process and a frame non-cyclic process are shared.