JPH07111605A - Noise elimination circuit - Google Patents

Abstract

PURPOSE:To obtain a noise elimination circuit effectively eliminating noise, keeping balance for the way of seeing noise due to the signal level of a video signal.. CONSTITUTION:This circuit is provided with a selector 7 where the output signals of plural low-pass filters 1, 2 and 3 which are different in input signals and bands are supplied. In a signal level detection circuit 4 and a decision circuit 6, the signal level of an input video signal is detected and the selector 7 is controlled in accordance with the detection result. Thus, because the smaller the signal level of the input video signal is, the narrower band low pass filter output is selected, the lower luminance level is, the larger a noise elimination effect is, and noise can be effectively eliminated, keeping balance for the way of seeing noise from a high luminance level to a low luminance level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise removing circuit which is applied to a television receiver, a video camera and the like and removes noise of an input video signal.

[0002]

2. Description of the Related Art As a conventional noise removing circuit for removing noise from a video signal, there is a noise coring circuit (for example, JP-A-62-172889 and JP-A-4-63).
09 publication). FIG. 10 is a block diagram of a conventional noise coring circuit.

In FIG. 10, 200 is a low-pass filter, 201 is a non-linear circuit, 202 is a subtractor, and 203 is an adder. The video signal input to the noise coring circuit in FIG. 10 is band-limited by the low pass filter 200. The band-limited output is subtracted from the original signal in the subtractor 202, and a high frequency component is obtained at the output of the subtractor 202. The high frequency component is non-linearly converted in the non-linear circuit 201 and added to the original signal in the adder 203.

The input / output characteristic of the non-linear conversion circuit 201 is, for example, the characteristic shown in FIG. When the non-linear characteristic of FIG. 11 is used, when the high frequency level obtained by the subtractor 202 is small, it operates as a low pass filter as a whole and removes noise. When the high-frequency level becomes large, it gradually approaches the all-pass characteristic and prevents the resolution from decreasing.

[0005]

However, the conventional noise coring circuit as described above operates according to the high frequency component level of the video signal, and controls the noise removal level according to the signal level of the video signal. is not. In general, visual characteristics follow Weber-Fechner's law. That is, the noise mixed in the video signal is noticeable at a low luminance level and is hard to notice at a high luminance level. That is, if the noise removal is applied more strongly to the low brightness level, the appearance of the noise at the high brightness level and the appearance of the noise at the low brightness level are balanced and the image quality is improved.

In the noise coring circuit as described above, the degree of noise improvement is the same regardless of the signal level of the video signal. Therefore, noise at the low luminance level is noticeable with respect to the high luminance level, and the noise appearance is unclear. There is a problem in that balance occurs and image quality is deteriorated. Further, when the noise removal is strongly used in order to balance the appearance of noise (enlarge the region of gain = 1 of the characteristic shown in FIG. 11), there is a problem that resolution deterioration occurs.

In view of the above problems, the present invention provides a noise elimination circuit for eliminating noise while balancing the appearance of noise according to the signal level of a video signal. Further, the present invention provides a noise elimination circuit that maintains the balance of appearance of noise and eliminates noise without causing resolution degradation.

[0008]

[Means for Solving the Problems] To achieve the above object,
The noise removing circuit of the first invention (claim 1) comprises a noise removing means capable of controlling the noise removing effect and a signal level detecting means for detecting the signal level of the input video signal. The configuration is such that control is performed so that the noise removal effect of the noise removal means is increased.

A noise eliminating circuit according to a second aspect of the present invention (claim 2) is a noise eliminating means capable of controlling a noise eliminating effect, and a signal level detecting means for detecting a signal level of an input video signal.
High-frequency component detecting means for detecting high-frequency components of the input video signal, and the noise removing means as the detection level from the signal level detecting means is low and the detection level from the high-frequency component detecting means is low. The configuration is such that control is performed so that the noise removal effect of is increased.

A noise removing circuit according to a third aspect of the present invention (claim 3) is a noise removing means capable of controlling a noise removing effect, and a signal level detecting means for detecting a signal level of an input video signal.
A frequency distribution detecting means for detecting a frequency distribution of the input video signal, a detection level from the signal level detecting means is small, and a frequency distribution result from the frequency distribution detecting means is distributed in a low frequency range. The configuration is such that control is performed so that the noise removal effect of the noise removal means becomes greater.

[0011]

According to the first aspect of the invention, the noise removal effect is controlled to increase as the signal level of the video signal decreases (closer to the black level), so that noise can be seen from a high brightness level to a low brightness level. It is possible to effectively remove noise while keeping a good balance between the two.

According to the second aspect of the present invention, the noise removal effect is controlled to increase as the signal level of the video signal decreases and the high frequency component level decreases. Therefore, noise is reduced from the high luminance level to the low luminance level. It is possible to effectively remove noise while maintaining a balanced appearance and without causing deterioration in resolution.

According to the third aspect of the invention, the noise removal effect is increased so that the signal level of the video signal is low and the video signal is distributed in the low frequency range.
It is possible to more effectively remove noise while balancing the appearance of noise from a high luminance level to a low luminance level and without causing deterioration of resolution.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A noise elimination circuit according to a first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a noise elimination circuit according to an embodiment of the present invention.

In FIG. 1, 1 is a first low-pass filter, 2 is a second low-pass filter, 3 is a third low-pass filter, 4 is a signal level detecting circuit, 6 is a judging circuit, and 7 is a selector.

In FIG. 1, the input video signal includes a selector 7, a first low pass filter 1, a second low pass filter 2,
The video signal and the input video signal that are supplied to the third low-pass filter 3 and band-limited by the first to third low-pass filters are respectively supplied to the selector 7. The input video signal is supplied to the signal level detection circuit 4, the output signal of the signal level detection circuit 4 is supplied to the determination circuit 6, and the output signal of the determination circuit 6 controls the selector 7.

In the noise elimination circuit shown in FIG. 1, the first,
The bands of the second and third low-pass filters have the characteristics as shown in FIG. 2, for example, and are set so as to be gradually narrower from the first low-pass filter to the third low-pass filter. The signal level detection circuit 4 is composed of, for example, the circuit shown in FIG.

In FIG. 3, reference numerals 41, 42 and 43 denote comparators, each of which has an appropriate threshold value th set in advance.
1, th2, th3 are given. Where th1>
th2> th3. In each comparator, the input signal is compared with the threshold value, and when it is larger than the threshold value, for example, a logical value "1" is output, and when it is smaller, "0" is output. Judgment circuit 6
Then, the signal level of the input video signal is determined based on the comparison logic value, and the signal to be selected by the selector 7 is determined. The relationship between the comparison logic value and the signal level of the input video signal and the selected signal have the relationship shown in (Table 1).

[0019]

[Table 1]

According to the relationship shown in (Table 1), the narrower band signal is selected as the signal level of the input video signal becomes smaller. In general, it is clear that the narrower the band of a video signal, the better the S / N. Therefore, according to the noise removal circuit having the above configuration, the lower the luminance level is, the greater the S / N improvement degree is. Therefore, the S / N is improved as a whole, and the noise is visible at the high luminance level and the low luminance level. One can be balanced.

The second embodiment of the present invention will be described below with reference to the drawings. FIG. 4 shows the configuration of a noise elimination circuit according to the second embodiment of the present invention.

In FIG. 4, 1 is a first low-pass filter, 2 is a second low-pass filter, 3 is a third low-pass filter, 4 is a signal level detection circuit, 5 is a high frequency component detection circuit, 66 is a decision circuit, and 7 is It is a selector.

The difference from the first embodiment shown in FIG. 1 is that
The high frequency component detection circuit 5 is provided, the output signal of the high frequency component detection circuit 5 and the output signal of the signal level detection circuit 4 are supplied to a new determination circuit 66, and the selector 7 is controlled by the output signal of the determination circuit 66. That is the point. The configuration of the signal level detection circuit 4 is the same as that described in the first embodiment.

In the noise eliminating circuit of the second embodiment shown in FIG. 4, the high frequency component detecting circuit 5 is composed of, for example, the circuit shown in FIG. In FIG. 5, 51 is a high-pass filter, 52 is an absolute value circuit, and 53 is a comparator. Comparator 5
A preset threshold value k3 is given to 3. The high frequency component of the input video signal is extracted by the high-pass filter 51, the absolute value circuit 52 converts the input video signal into an absolute value, and the comparator 53 compares it with a threshold value. In the comparator 53, the absolute value conversion signal is the threshold value k3.
If it is larger, "1" is output, and if it is smaller, "0" is output.

In other words, the comparator 53 compares the high frequency component due to noise (generally the detected signal level is small) and the significant high frequency component of the video signal (the contour portion included in the video signal) by comparing with the threshold value k3. And the detected signal level is higher than the above) at the k3 boundary.
The determination circuit 66 determines the signal selectively output by the selector 7 based on the comparison result from the signal level detection circuit 4 and the comparison result from the high frequency component detection circuit 5 so as to have the control characteristic shown in FIG. 6, for example. .

According to the control characteristic shown in FIG. 6, if the signal level of the video signal becomes smaller, the narrow band low-pass filter output is selected as described in the first embodiment. When the high-frequency component level is large (when it is a significant high-frequency component due to contours, etc.), it operates so as to select a slightly wide band low-pass filter output, which can improve the S / N ratio of the video signal. Therefore, it is possible to prevent the deterioration of resolution due to the low-pass filter in the contour portion and the like.

Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 7 is a diagram showing the configuration of a noise elimination circuit according to the third embodiment of the present invention.

In FIG. 7, 1 is a first low-pass filter, 2 is a second low-pass filter, 3 is a third low-pass filter, 4 is a signal level detecting circuit, 666 is a judging circuit, and 7 is.
Is a selector, 100, 101 and 102 are subtractors, 10
3, 104 and 105 are absolute value circuits, and 106, 107 and 108 are comparators.

The difference from the first embodiment shown in FIG. 1 is that the outputs of the first, second and third low-pass filters are subtracted by a subtractor 10.
0, 101, and 102 subtract from the input signal, respectively, and the subtraction results are absolute value circuits 103, 104, and 105.
After making absolute value in
The threshold values a1, a2 and a3 set in advance are compared with each other to obtain the comparison result and the signal level detection circuit 4 described above.
The comparison result from 1 is supplied to a new determination circuit 666, and the selector 7 is controlled by the output signal of the determination circuit 666. The configuration of the signal level detection circuit 4 is the same as that described in the first embodiment.

In the noise elimination circuit of the third embodiment shown in FIG. 7, a high pass filter is formed as the subtraction result of the subtractors 100, 101 and 102. That is, it is obvious that the operation of subtracting the band-limited signal from the input video signal is totally the same as the high-pass filter processing. The frequency characteristic of the high-pass filter configured as the output of each subtractor is as shown in FIG. 8, which is the inverse characteristic of the first, second, and third low-pass filters.

In FIG. 8, the cutoff frequencies of the respective high-pass filters are ω1, ω2, ω3 (ω1>ω2> ω).
3). The high frequency components having different characteristics extracted by these high-pass filters are converted into absolute values by the absolute value circuits 103, 104 and 105, and then compared with the threshold values a1, a2 and a3 by the comparators 106, 107 and 108, and obtained. From the comparison result obtained, the maximum frequency of the significant high frequency component included in the video signal can be detected. The comparison result and the maximum frequency of the significant high-frequency component have the relationship of (Table 2).

[0032]

[Table 2]

It is obvious that resolution deterioration will not occur unless the maximum frequency of a significant high frequency component is detected based on (Table 2) and the frequency is not limited to that frequency or less. Therefore, the determination circuit 666 determines the signal selectively output by the selector 7 based on the comparison result and the comparison result from the signal level detection circuit 4 so as to have the control characteristics shown in FIG. 9, for example. According to the control characteristics shown in FIG. 9, a narrow band low-pass filter output is selected based on the maximum frequency of a significant high-frequency component of the video signal within a range in which the resolution is not deteriorated. / N can be improved, and resolution deterioration does not occur. Further, when the signal level of the video signal becomes smaller, the control is performed so as to select the narrow band low-pass filter output, and the appearance of noise depending on the signal level of the video signal is kept balanced.

Although a plurality of low-pass filters are used as the noise removing means in the first, second and third embodiments, the present invention is not limited to this, and any noise removing means capable of controlling the noise removing effect can be used. Any type may be used, for example, a noise coring circuit as described in the conventional example may be used to control the area of gain = 1 according to the signal level, the high frequency level or the frequency distribution.

Further, in the first, second and third embodiments, the low-pass filter is a horizontal one-dimensional low-pass filter, but the present invention is not limited to this, and horizontal and vertical two-dimensional low-pass filters are used. I don't mind. Two
By using the dimensional low-pass filter, it is possible to remove noise in the vertical high frequency component or the diagonal component.

Further, the switching of four inputs as the selector input has been described, but the present invention is not limited to this, and a low pass filter having a different band may be added to perform switching in multiple stages. In this case, more natural switching is possible.

Although a plurality of low-pass filters having different bands are separately configured, the present invention is not limited to this, and a plurality of low-pass filters having different bands are connected in a cascade to obtain desired characteristics. A configuration for extracting a signal may be used. In this case, the circuit scale can be significantly reduced.

[0038]

As described above, the present invention comprises the noise removing means capable of controlling the noise removing effect and the signal level detecting means for detecting the signal level of the input video signal, and the noise level decreases as the detection level decreases. With the configuration in which the noise removing effect of the removing unit is controlled to be large, it is possible to effectively remove the noise while balancing the appearance of the noise from the high luminance level to the low luminance level of the video signal.

Further, there are provided noise removal means capable of controlling the noise removal effect, signal level detection means for detecting the signal level of the input video signal, and high frequency component detection means for detecting the high frequency component of the input video signal. The noise removal effect of the noise removal means increases as the detection level from the signal level detection means decreases and the detection level from the high frequency component detection means decreases.
It is possible to effectively remove the noise while balancing the appearance of the noise from the high luminance level to the low luminance level of the video signal and without causing the deterioration of the resolution.

Further, there are provided noise removing means capable of controlling the noise removing effect, signal level detecting means for detecting the signal level of the input video signal, and frequency distribution detecting means for detecting the frequency distribution of the input video signal. The control is performed such that the noise removal effect of the noise removal means increases as the detection level from the signal level detection means decreases and the frequency distribution result from the frequency distribution detection means is distributed to lower frequencies. Thus, it is possible to more effectively remove noise while balancing the appearance of noise from the high luminance level to the low luminance level of the video signal and without causing deterioration of resolution.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a noise removing circuit according to a first embodiment of the present invention.

FIG. 2 is a frequency characteristic diagram of a low-pass filter according to each embodiment of the present invention.

FIG. 3 is a configuration diagram of a signal level detection circuit in first, second and third embodiments of the present invention.

FIG. 4 is a configuration diagram of a noise elimination circuit according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a high frequency component detection circuit according to a second embodiment of the present invention.

FIG. 6 is a selection characteristic diagram in the second embodiment of the present invention.

FIG. 7 is a configuration diagram of a noise removing circuit according to a third embodiment of the present invention.

FIG. 8 is a frequency characteristic diagram of a high pass filter according to a third embodiment of the present invention.

FIG. 9 is a selection characteristic diagram in the third embodiment of the present invention.

FIG. 10 is a configuration diagram of a noise removal circuit in a conventional example.

FIG. 11 is a non-linear conversion characteristic diagram of the noise elimination circuit in the conventional example.

[Explanation of symbols]

 1 1st low pass filter 2 2nd low pass filter 3 3rd low pass filter 4 Signal level detection circuit 5 High frequency component detection circuit 6 Judgment circuit 7 Selector

Claims (5)

[Claims] 1. A noise removing circuit for removing noise from a video signal, comprising: noise removing means capable of controlling the noise removing effect; and signal level detecting means for detecting a signal level of an input video signal. A noise removal circuit, which controls so that the noise removal effect of the noise removal means increases as the detection level decreases. 2. A noise removing circuit for removing noise of a video signal, the noise removing means capable of controlling the effect of removing the noise, a signal level detecting means for detecting a signal level of an input video signal, and the input. High-frequency component detecting means for detecting high-frequency components of the video signal, and the noise level of the noise removing means decreases as the detection level from the signal level detecting means decreases and the detection level from the high-frequency component detecting means decreases. A noise elimination circuit characterized by controlling so as to increase the elimination effect. 3. A noise removing circuit for removing noise of a video signal, the noise removing means capable of controlling a noise removing effect, a signal level detecting means for detecting a signal level of an input video signal, and the input video signal. And a frequency distribution detecting means for detecting the frequency distribution of the signal level detecting means, wherein the detection level from the signal level detecting means is small, and the frequency distribution result from the frequency distribution detecting means is distributed to a low frequency, the noise removal is performed. A noise elimination circuit characterized by controlling so that the noise elimination effect of the means becomes large. 4. The noise removing circuit according to claim 1, wherein the noise removing means is composed of a plurality of band limiting means. 5. The frequency distribution detecting means comprises a plurality of high pass filters, and detects the frequency distribution based on output levels from the plurality of high pass filters. Noise elimination circuit.