JPS62171282A - Correlation adaptive type noise reducing device - Google Patents

Abstract

PURPOSE:To apply the optimum noise reduction suited to the characteristic of a video signal by connecting at lest 2 circuits or over in parallel in conventional 3 kinds of noise circuits, inputting a video signal and combining the outputs of each circuit after synthesizing them via a coefficient device. CONSTITUTION:The outputs of a line correlation detector 4 and a frame correlation detector 5 are inputted to a control section 6, which outputs signals 7a, 8a, 9a deciding coefficients K1, K2, K3 of coefficient devices 7, 8, 9 of conventional 3 kinds of noise reduction circuits. The outputs of the coefficient devices 7, 8, 9 are synthesized by as synthesizing circuit 10 and the result is sent. The input terminal is shown in caption 1, the present time is obtained at the midpoint 2 between 1H delay elements 201, 202 of a line correlation noise reduction circuit 200 and a noise coring circuit 300 and a frame correlation noise reduction circuit 100 are connected in parallel with the midpoint 2. The control circuit 6 inputs the output of the detectors 4, 5 and generates a control signal to the coefficient devices 7-9 by a prescribed reference. Thus, the noise reduction suited to the characteristic of the video signal is applied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise reduction circuit in equipment such as televisions and VTRs that handle video signals.

[Conventional technology]

The following three methods are known as methods for reducing noise in video signals.

(2) A method that uses frame correlation characteristics using an 11-frame memory (2) A method that uses line correlation characteristics using a line memory (3) A method that separates high-frequency noise components and removes them from the original signal (noise coring [Problems to be Solved by the Invention] (11) A method using the frame correlation characteristic is: ■ Store frames in a frame memory, take the difference in memory data from the data of the current frame, and multiply it by a coefficient. The most widely used method is to subtract the difference from the current frame.Noise components have no correlation and appear as the difference, so noise can be removed.This method is useful for still images with large frame correlations. In the case of , the noise reduction effect is great, but in the case of moving images, the image becomes blurred.For this reason, a motion compensation type is considered, and there is a circuit to change the coefficient, but it becomes more complicated.

(2) A method using line correlation characteristics uses, for example, the correlation between the current line and the previous line, or between the current line and the next line, and the circuit is simple because IH delay elements are used. Furthermore, since there is almost no temporal movement with respect to frame correlation, there is little blurring due to movement. However, since calculations are performed in the vertical direction of the screen, the vertical resolution deteriorates.

(3) Noise coring does not blur motion at all, but it tends to make the screen look flat because the high frequency components of the image that represent minute parts are distorted to some extent.

In summary, it is difficult to completely reduce noise using a single method without degrading image quality.

An object of the present invention is to overcome the above circumstances and provide a noise reduction device that combines the three methods described above and adaptively adjusts the degree of noise reduction by each method depending on the image. .

Means for Solving Problem C] The device of the present invention includes three types of noise reduction circuits: a frame correlation noise reduction circuit equipped with a frame correlation detector; a line correlation noise reduction circuit equipped with a line correlation detector; At least two of the noise coring circuits are connected in parallel, a video signal is input, and the outputs of each circuit are combined via a coefficient unit and output. A control section inputting the output of the correlation detector of the circuit determines the coefficients of the coefficient multiplier based on a predetermined standard, thereby performing optimal noise reduction adapted to the characteristics of the video signal.

[Effect]

A numerical example will be shown in the embodiment, but depending on the nature of the image, an optimal image can be obtained by combining circuits from three types of noise reduction circuits and selecting coefficient values of the coefficient multiplier. Since the nature of an image (such as whether it is close to a still image or a moving image) is approximately expressed by frame correlation and line correlation, the control unit may determine each coefficient value empirically based on this correlation.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. This embodiment is a combination of all three types of noise reduction circuits, and a circuit block diagram thereof is shown in FIG. Each noise reduction circuit has various circuit configurations, and the one shown in FIG. 1 is an example. Due to their nature, the frame correlated noise reduction circuit and the line correlated noise reduction circuit can easily attach each correlation detector using a signal generated within the circuit. In the figure, 100, 200, and 300 are a frame correlation noise reduction circuit, a line correlation noise reduction circuit, and a noise coring circuit, respectively. Attached line correlation detector4. The output of the frame correlation detector 5 is input to a control section 6, which controls the coefficient multipliers of the various circuits 100, 200, and 300. , 8.9 for each coefficient, , 2. signal 7a which determines 3.

8a and 9a are output. The outputs of the coefficient multipliers 7, 8, and 9 are combined by a combining circuit 10 and sent to the subsequent stage. The input terminal is 1, but at present the IT of the line correlated noise reduction circuit 200 (the midpoint 2 of the delay elements 201 and 202, and the noise coring circuit 300 and the frame correlated noise reduction circuit 100 are connected to the midpoint 2 of the delay elements 201 and 202). connected in parallel.

Each of the noise reduction circuits shown in the embodiments is well known, but will be briefly explained. The frame correlation noise reduction circuit 100 extracts the difference between the previous frame signal stored in the frame memory 102 and the current signal as a noise component using a subtracter 103, and removes it from the current signal via a coefficient unit 104 using a subtracter 101. . In the case of the motion compensation type, the coefficient of the coefficient unit 104 is variable, but in this embodiment, it is set to a constant value for simplicity. The output of the subtractor 103 also represents the degree of frame correlation and is led to the frame correlation detector 5.

This value becomes large for moving images.

The line correlated noise reduction circuit 200 includes an adder 203.20
4 cancels noise components without line correlation.

Therefore, the outputs of adders 203 and 204 are combined to give 1/
Output 2 of adder 205 which is multiplied by 4. OOa becomes a signal from which noise components have been removed due to line correlation.

The line correlation detector 4 uses a subtracter 40 to take the difference between the input signal and the output of the delay element 202, and the correlation detector 41 calculates the amount of line correlation.

The noise coring circuit 300 is a high-pass filter 301
The high frequency component is extracted from the original signal by a subtracter 303 via a limiter 302. The signal 303a becomes a signal from which high frequency noise components have been removed. The limiter 302 is provided to prevent image edge components from being removed from the original signal.

The control section 6 controls the line correlation detector 4. The output of the frame correlation detector 5 is input, and control signals to each of the coefficient units 7 to 9 are generated according to predetermined standards.

The coefficients of coefficient multipliers 7 and 8.9 in this device are, , , K
An example of selection 3 is shown below.

K, K2 K3 +a+frame correlation 0.8~1.0 1.0 0 0
(b) Frame correlation O~0.8 0 1.0 0 Line correlation 0.5~1.0 (C) Frame correlation 0~0.8 0 0 1.0 Line correlation 0~0.5 The above example is , a combination of all noise reduction circuits, but a combination of two may also be used. In this case, for example, in the combination of the frame correlation noise reduction circuit 100 and the noise coring circuit 300, the frame correlation is 0.8 to 0.8.
When 1.0, KI=1.0. 3=0, and when the frame correlation is 0 to 0.8, K+=0°K3=1.0.

〔Effect of the invention〕

As seen in the selection of the coefficients above, in areas where the ta+frame correlation is strong, deterioration of vertical resolution in the case of using line correlation is prevented, and there is no lack of fine areas due to coring. (
In areas where the bl frame correlation is weak and the line correlation is strong, image blurring due to frame correlation is prevented, and there is no lack of fine parts due to coring. (C) When both frame correlation and line correlation are weak, image blurring caused by frame correlation and vertical resolution deterioration caused by line correlation are prevented. In this part, the movement of the image is large, so the lack of fine parts due to coring does not pose a visual problem.

In the above selection, one coefficient was set to 1 and the other coefficients were set to zero, but the present invention is not limited to this, and it goes without saying that appropriate values may be selected for a plurality of coefficient values. In the embodiment, if the input video signal is an NTSC composite signal, a chroma inverter is inserted as appropriate to invert the color signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit block diagram of an embodiment of the present invention. 4-line correlation detector, 5-frame correlation detector, 6-control unit, 7-9... coefficient unit, 10...- synthesis circuit, 100-- frame correlation noise reduction circuit, 200-- line correlation Noise reduction circuit, 300-noise coring circuit.

Claims (1)

[Claims] At least two of three types of noise reduction circuits, namely, a frame correlation noise reduction circuit equipped with a frame correlation detector, a line correlation noise reduction circuit equipped with a line correlation detector, and a noise coring circuit, are connected in parallel. A noise reduction device that inputs a video signal, synthesizes the outputs of each circuit via a coefficient multiplier, and outputs the synthesized output, wherein a control unit that inputs the output of a correlation detector of the circuit selects the coefficient multiplier according to a predetermined standard. 1. A correlation adaptive noise reduction device characterized in that it performs optimal noise reduction that adapts to the characteristics of a video signal by determining respective coefficients.