JP2629928B2 - Chroma signal noise reducer - Google Patents

Description

The present invention relates to a television signal noise reducer.
More specifically, the present invention relates to a noise reducer for a chroma signal.

2. Description of the Related Art Conventionally, it has been known to use a correlation between fields or between frames in a television video signal to remove random noise that does not have a strong correlation between fields or between frames. ing.

FIG. 4 is a block diagram showing a conventional chroma signal noise reducer. In FIG. 4, (1) is an input terminal of an analog chroma signal, and the analog chroma signal input here is supplied to an A / D converter (2). Is converted into a digital chroma signal. (3) is a field memory, which serves as delay means for the digital chroma signal. (4) is a subtractor,
A difference signal (εo) is obtained by subtracting the digital chroma signal before one field stored in the field memory (3) from the delayed digital chroma signal.
(5) is an attenuator for attenuating the difference signal (εo) with a predetermined attenuation characteristic. (6) is an adder for adding the attenuated difference signal (εo) to the input digital chroma signal.
(7) is a D / A converter, which converts the output from the adder (6) into an analog signal and outputs it to an output terminal (8).

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

Difference signal (εo) output by the subtractor (4)
Is a signal component having no correlation between adjacent fields, and takes a positive value when the input digital chroma signal is smaller than the delayed digital chroma signal, and takes a negative value when the input digital chroma signal is larger than the delayed digital chroma signal. Next, the difference signal (εo) is attenuated by an attenuator (5) with a predetermined attenuation characteristic, and then is added to an adder (6).
Is added to the input digital chroma signal. The output of the adder (6) is converted into an analog chroma signal by a D / A converter (7), output from an output terminal (8), and stored in a field memory (3).
That is, since the input chroma signal is processed and output so that the difference between the input chroma signal and the output chroma signal one field before is reduced, the image signal component having a correlation of 1 between adjacent fields is Components such as random noise that is output as it is without being attenuated and has no correlation between adjacent fields are averaged and attenuated. Thus, the noise of the chroma signal is reduced,
The signal-to-noise ratio is improved.

The difference signal (εo) described above includes only a random noise component in the case of a still image, but includes a motion-based component in the case of a moving image. Therefore, if this motion component is averaged and attenuated, an afterimage is generated and the image quality is degraded.

On the other hand, in the difference signal between the fields, the random noise component generally has a small amplitude, and the motion component has a large amplitude. Therefore, the attenuation characteristics of the attenuator (5) are set as shown in the graph of FIG. That is, the difference signal (ε
o) can be regarded as a random noise component. In the range of -a <εo <a, the attenuation rate (K) is set to a large value of about 0.8,
The output of the attenuator (5) is fixed in the range of -b <εo ≦ −a and a ≦ εo <b. That is, the difference signal (ε
As the absolute value of o) increases, the attenuation rate (K) is gradually decreased, and the output of the attenuator (5) is set to 0, that is, the attenuation is reduced in the range of εo <−b and b <εo, which can be regarded as a motion component. The rate (K) is set to 0.

By setting the attenuation characteristic as described above, the averaging of the motion component is restricted, and the deterioration of the image quality due to the occurrence of an afterimage is improved.

[Problems to be Solved by the Invention] Generally, the mixed noise level is constant irrespective of the level of the color saturation, so that a chroma signal having a low color saturation, that is, a low level, has a relatively low noise component. Is larger than the signal component. Therefore, according to the conventional chroma signal noise reducer configured as described above, when the level of the input chroma signal is low, the noise (εo) between the fields is slightly attenuated by the attenuator (5). The level of the correction signal may be equal to the level of the input chroma signal, or the former may be larger. In such a case, if the noise is reduced, a minute signal component of the input chroma signal is damaged by the noise correction signal, and the color tone of the output image changes. On the other hand, when the attenuation rate of the attenuator is set to be small, there is a problem that the noise reduction effect for a signal having a high color saturation is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and a chroma signal which exhibits a sufficient noise reduction effect without causing a color tone change of an output image regardless of the degree of saturation of an input chroma signal. It is an object to provide a signal noise reducer.

[Means for Solving the Problems] A chroma signal noise reducer according to the present invention comprises a delay means for delaying an input chroma signal by at least one field, and a difference between the input chroma signal and the delayed chroma signal delayed by the delay means. A difference signal detecting means for obtaining a signal; a signal attenuating means for attenuating the difference signal with a predetermined attenuation characteristic; and an attenuated difference signal attenuated by the signal attenuating means combined with the input chroma signal to generate noise. Composite signal output means for obtaining a chroma output signal from which
Means for determining the magnitude of the degree of saturation of the input chroma signal, wherein the output of the degree of saturation determination is supplied to the signal attenuating means so that the attenuation characteristic of the signal attenuating means is reduced by the input chroma signal. Is controlled in accordance with the magnitude of the saturation degree.

According to the present invention, when the saturation of the input chroma signal is low, the attenuation rate of the attenuator is set small to prevent a change in the color tone of the output chroma signal, and the saturation of the input chroma signal is high. In such a case, the noise reduction effect can be sufficiently increased by setting the attenuation rate of the attenuator large.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic block diagram of a chroma signal noise reducer according to an embodiment of the present invention. In FIG. 1, components denoted by the same reference numerals as those in the conventional example of FIG. Detailed description is omitted.

In FIG. 1, reference numeral (10) denotes a chroma signal saturation determination circuit. The saturation determination circuit (10) determines the magnitude of the saturation of the input chroma signal in three stages. For example, as shown in FIG. 2, a level 1 when the color saturation is less than 10%, a level 2 when 10% or more and less than 30%, and a level 3 when the color saturation is 30% or more.

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

Since the operation is basically the same as that of the conventional example shown in FIG. 4, only the differences will be described.

When the input chroma signal converted into a digital signal by the A / D converter (2) is supplied to the saturation judgment circuit (10), the level 1, level 2, and level 2 are changed according to the degree of saturation of the input chroma signal. It is determined to be level 3. Then, it outputs a control signal corresponding to each level and supplies it to the attenuator (5). The attenuator (5) receives the control signal and generates a third signal.
As shown in the figure, the attenuation characteristic is changed. That is, at the level 1, the characteristic 1 with the smallest attenuation rate is selected, at the level 2, the characteristic 2 with the medium attenuation rate is selected, and at the level 3, the characteristic 3 with the largest attenuation rate is selected.

[Effects of the Invention] As described above, according to the present invention, a sufficient noise reduction effect is exhibited when the color saturation is high without causing a change in the color tone when the color saturation of the input chroma signal is low. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a chroma signal noise reducer according to one embodiment of the present invention, FIG. 2 is a diagram showing the classification of a saturation degree determiner in the chroma signal noise reducer of FIG. 1, and FIG. FIG. 4 is an attenuation characteristic diagram of an attenuator in the chroma signal noise reducer of FIG. 4, FIG. 4 is a block diagram showing a conventional chroma signal noise reducer, and FIG. 5 is an attenuation characteristic diagram of an attenuator in the noise reducer of FIG. (1) ... analog chroma signal input terminal, (2) ... A /
D converter, (3) field memory, (4) subtractor, (5) attenuator, (6) adder, (7)
... D / A converter, (8) ... analog chroma signal output terminal, (10) ... saturation judgment circuit. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (1)

(57) [Claims] A delay means for delaying the input chroma signal by at least one field; a difference signal detecting means for detecting a difference signal between the delayed chroma signal delayed by the delay means and the input chroma signal; Signal attenuating means for attenuating the obtained difference signal with predetermined attenuation characteristics, and combining the attenuated difference signal attenuated by the signal attenuating means with the input chroma signal to output a chroma signal from which noise has been removed. A chroma signal noise reducer comprising: a signal output means; and a saturation degree determining means for determining the degree of saturation of the input chroma signal and outputting the output to the signal attenuating means. Is controlled in accordance with the degree of saturation of the input chroma signal.