JP3590117B2 - Method and apparatus for detecting S / N value of television video signal - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method and an apparatus for detecting an S / N value of a television video signal, and more particularly to a measurement of the S / N value.
[0002]
[Prior art]
Conventionally, to detect the S / N value of this type of television video signal, a signal of a known level is defined as a part of the video, and a difference between the signal and the known level is determined to obtain a noise amount. The S / N value was calculated. In other words, instead of evaluating the amount of noise included in the video in the true sense, the amount of noise suffered by the system through which the video has passed was detected. Alternatively, when limiting to a still image, the S / N value is calculated using noise that changes with time as noise. However, when limiting to this still image, it is necessary to detect the noise amount only in the still image portion obtained by a method such as motion detection and motion correction. However, in general, it is difficult to accurately detect a motion portion and a vector from an image, and cannot be applied to all types of motion.Therefore, the effect is limited despite the complexity of an algorithm and an increase in hardware scale. Have been.
[0003]
[Problems to be solved by the invention]
That is, conventionally, to detect the S / N value of a television video signal of this type, it is necessary to determine a signal of a known level as a part of the video, that is, to detect the amount of noise in the system through which the video has passed However, there is a problem that it is not an evaluation of the amount of noise included in the video in a true sense, or that only an S / N value limited to a still image can be detected.
Therefore, an object of the present invention is to solve the above-described problems and use complex motion detection and motion correction by separating and testing noise from video by focusing on the difference between the video amplitude and the stochastic distribution of noise. It is an object of the present invention to provide a method and an apparatus for detecting an S / N value of a television video signal, which can estimate an S / N value of a real video without any need.
[0004]
[Means for Solving the Problems]
To achieve the above object, an S / N value detecting method for a television image signal according to the present invention is a method for detecting an S / N value of a television image signal, wherein a plurality of input television image signals are displayed on a screen. , And for each pixel of each of the divided small blocks, the difference between the video signal and the signal averaged in the time axis direction within each small block and / or the two-dimensional difference within each of the small blocks The difference between the signal and the averaged signal is calculated, and the distribution of the difference is compared with the noise distribution of the statistical distribution rule prepared for S / N value detection in advance to determine the significance, and it is determined that there is significance. The S / N value based on the difference between the small blocks is adopted, and the comparison and examination are successively continued in the entire screen, and the occurrence frequency of the S / N value adopted in the entire screen is obtained. Effective S / N value from the distribution of It is characterized in that the detecting.
[0005]
Also, the method of detecting the S / N value of a television image signal according to the present invention is characterized in that the small block is moved from left to right and from top to bottom on the screen for each pixel and each scanning line. is there.
[0006]
Further, according to the method of detecting an S / N value of a television image signal of the present invention, when detecting an effective S / N value from the distribution of the occurrence frequency of the determined S / N value in the entire screen, the distribution of the occurrence frequency is determined. The determination threshold value is set in consideration of the variance.
[0007]
Further, the method of detecting an S / N value of a television video signal according to the present invention is characterized in that a temporal change is considered in the determination threshold value.
[0008]
Further, the method of detecting the S / N value of a television image signal according to the present invention is characterized in that a temporal change is considered in the detection of the effective S / N value.
[0009]
The S / N value detecting device for a television image signal of the present invention is a device for detecting the S / N value of a television image signal, and divides an input television image signal into a plurality of small blocks on a screen. Means, for each pixel of each small block divided by the means, a difference between a video signal and a signal averaged in the time axis direction in each small block and / or two-dimensional averaging in each small block Means for calculating the difference from the signal obtained, and comparing the distribution of the difference obtained by the means with the noise distribution of a statistical distribution rule prepared in advance for S / N value detection to determine the significance and determine that there is significance. Means for adopting the S / N value based on the difference between the small blocks and outputting the S / N value to the next stage, means for accumulating the S / N value adopted and output over the entire screen, Adopted within the screen Means for determining the frequency of S / N value, and is characterized in by comprising comprises means for detecting a valid S / N value from the distribution of the occurrence frequency obtained by said means.
[0010]
In the S / N value detecting apparatus for a television image signal according to the present invention, the means for calculating the difference moves the small block from left to right and from top to bottom on the screen for each pixel and each scanning line. It is characterized by performing.
[0011]
In the S / N value detecting apparatus for a television image signal according to the present invention, the means for detecting the effective S / N value sets a determination threshold value in consideration of the variance of the occurrence frequency distribution. It is characterized by the following.
[0012]
Further, the S / N value detecting device for a television video signal according to the present invention is characterized in that the determination threshold value is configured to take into account a temporal change.
[0013]
Further, the S / N value detecting apparatus for a television video signal according to the present invention is characterized in that the detection of the effective S / N value takes into account a temporal change.
[0014]
【Example】
According to the principle of the present invention, in detecting the S / N value of a television video signal, the entire screen is divided into a plurality of small blocks, and the distribution of noise for each small block is compared with a statistical distribution rule prepared in advance. The significance is obtained, the measured value of the small block having no significance is discarded, this is applied to the entire screen, and then the occurrence frequency of the S / N value adopted in the entire screen is obtained. , An effective S / N value is detected from the data, and thus erroneous detection by video is reduced.
[0015]
In general, when a video is a still image, noise is easily detected from a difference between a video signal and a signal averaged in the time axis direction for each pixel. However, in the case of a moving image, an error due to motion occurs in this difference. On the other hand, noise can be detected by using a difference from a signal averaged two-dimensionally in the small block so as not to be affected by the motion of the image. However, errors due to video signal components are mixed in this difference.
As described above, errors occur in the respective noise detection methods depending on the image content, and therefore, it has been difficult to detect noise in a conventional general image.
[0016]
Hereinafter, the present invention will be described in detail with reference to the block diagram shown in FIG.
In the present invention, first, an input video signal is divided into a plurality of small blocks (for example, a size of 8 pixels × 8 pixels) on a screen by using a small block processing 1, and each of the divided small blocks is For each pixel, the difference 4 from the signal averaged in the time axis direction by the time axis direction averaging process 2 and / or the difference from the signal averaged in the x, y two-dimensional space by the two-dimensional averaging process 3 Find 5
[0017]
Next, the distribution of these differences is compared with the noise distribution of the statistical distribution rule prepared in advance for S / N value detection to determine the significance, and the S / N value due to the difference between the small blocks determined to have significance is calculated as Adopt this. This processing is executed in the difference significance determination processing 6 in FIG. When the noise distribution is, for example, a normally distributed noise, a test of a normal distribution, that is, a normal chi-square test is used. In each of the small blocks of the subdivided screen, erroneous detection can be eliminated in a video part in which a difference occurs due to motion and in a video part in which a difference occurs due to a two-dimensionally strongly correlated video component. .
[0018]
The test of these small blocks is sequentially continued in the entire screen, and the S / N values of only the small blocks whose distribution has passed the test as noise are accumulated by the S / N value accumulation processing 7. With the accumulated S / N values, a frequency distribution (histogram) is created by the frequency distribution creating process 8 over the entire screen. When the best S / N value is determined immediately from the created histogram, it may be output through the S / N value determination processing 9. In general, the peak value, the average value, and the variance are obtained from the histogram. A threshold value is given to the histogram, and the best S / N value equal to or higher than the threshold value and the best S / N value from the peak value and the average value are subjected to S / N value determination processing 9. Output via As a result, the S / N value can be detected as much as possible without the influence of the image. In addition, even if the detected S / N value is erroneously detected, a better S / N value than the actual S / N value is output. Is fail-safe (of course, it can be reversed in the opposite way).
[0019]
In addition, the influence of the video can be further reduced by dispersing the threshold value of the occurrence frequency and referring to the past value. This is performed in the system of the processing blocks 10, 11, and 9 shown in FIG. Further, by detecting the time change of the detection value, it is possible to further reduce erroneous detection by the video, and to estimate the noise amount in the actual video. This processing path is shown in FIG. 1 by feedback processing from the output of the processing block 9 via the delay circuit 12.
[0020]
The above description is about the embodiments according to claims 1, 3 to 6 and 8 to 10. In claims 2 and 7, the pixel of interest moves as the pixels on the screen are scanned. A more detailed processing method can be said to be a method provided one by one for each pixel of interest. Further, it is obvious that the present invention is not limited to the embodiments described herein, and that various modifications and changes are possible within the gist of the invention.
[0021]
【The invention's effect】
According to the present invention, an S / N value in a normal television moving image can be detected with high accuracy. As a result, the amount of noise reduction can be optimized according to the change in the S / N value of the image, the noise reducer can be effectively operated, and fine image quality management can be performed.
[Brief description of the drawings]
FIG. 1 is a processing block diagram showing a flow system of signal processing of the method and apparatus of the present invention.
[Explanation of symbols]
1 Small block processing 2 Time axis direction averaging processing 3 Two-dimensional averaging processing 4,5 Subtractor 6 Difference significance determination processing 7 S / N value integration processing 8 Histogram creation processing 9 S / N value determination processing 10 Peak Detection of values, averages, variances, etc. 11, 12 Delay processing

Claims (10)

A method for detecting an S / N value of a television video signal, comprising dividing an input television video signal into a plurality of small blocks on a screen, and for each pixel of each of the divided small blocks, a video signal and The difference between the signal averaged in the time axis direction in each small block and / or the difference between the signal averaged two-dimensionally in each small block is obtained, and the distribution of the difference is detected in advance by the S / N value. The significance is obtained by comparing with the noise distribution of the statistical distribution rule prepared for use, and the S / N value based on the difference of the small block determined to be significant is adopted, and such comparison and examination is performed on the entire screen. , The frequency of occurrence of the S / N value adopted in the entire screen is obtained, and the effective S / N value is detected from the distribution of the occurrence frequency. / N value detection method. 2. The method according to claim 1, wherein the small block is moved from left to right and from top to bottom on the screen by one pixel and one scanning line, respectively. . 3. The method according to claim 1, wherein the variance of the occurrence frequency distribution is taken into account in detecting an effective S / N value from the distribution of occurrence frequencies of the obtained S / N values in the entire screen. A method for detecting an S / N value of a television video signal, comprising setting a determination threshold value. 4. The method according to claim 3, wherein a temporal change is considered in the determination threshold value. The method according to any one of claims 1 to 4, wherein a time-varying change is considered in the detection of the effective S / N value. An apparatus for detecting an S / N value of a television video signal,
Means for dividing the input television video signal into a plurality of small blocks on the screen,
For each pixel of each small block divided by the means, the difference between the video signal and the signal averaged in the time axis direction in each small block and / or the signal averaged two-dimensionally in each small block Means for calculating the difference from
The distribution of the difference obtained by the means is compared with the noise distribution of the statistical distribution rule prepared in advance for detecting the S / N value to determine the significance, and the S by the difference of the small block determined to be significant is determined. Means for adopting this value and outputting it to the next stage,
Means for integrating the output S / N value adopted by the means over the entire screen;
A means for calculating the frequency of occurrence of the S / N value adopted in the entire screen by the means; and a means for detecting an effective S / N value from the distribution of the frequency of occurrence determined by the means. S / N value detecting device for a television video signal. 7. The television according to claim 6, wherein the means for calculating the difference is performed by moving the small block from left to right and from top to bottom on the screen for each pixel and each scanning line. S / N value detection device for video signal. 8. The television according to claim 6, wherein the means for detecting the effective S / N value sets a determination threshold value in consideration of a variance of the distribution of the occurrence frequency. S / N value detection device for video signal. 9. The apparatus according to claim 8, wherein the determination threshold value is configured to consider a temporal change. 10. The S / N value detection of a television video signal according to claim 6, wherein the detection of the effective S / N value considers a temporal change. apparatus.

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