JPH01314477A - Noise reducing circuit for video signal - Google Patents

Abstract

PURPOSE:To reduce a noise without leaving an after-image even for a picture having a movement by detecting an auto-correlation degree for each of sampling values near a picture one frame before and reducing the noise using one sampling value having the maximum correlation degree. CONSTITUTION:A signal delayed for one frame by a frame delay circuit 1 generates one sampling value delayed for one frame by a delay circuit 2, three sampling values before the above-mentioned sampling value, and three sampling values after the above-mentioned sampling value, namely, seven sampling values in total, sends these seven sampling values to an auto-correlation degree detector 3, detects respective auto-correlation degrees, sends the respective auto- correlation degrees to a control circuit 4, and switches a 7-1 selector 5, a (k) coefficient multiplier 7, and a (2-k) coefficient multiplier 8. The signals, which are multiplied by coefficients in these coefficient multipliers 7 and 8, are added in an adder 9, the 1/2 of this added output is made into a luminance signal output, this output is inputted to a frame memory, a cyclic type filter is composed, and the noise is reduced. Therefore, the title device can follow even the vertical movement on a television picture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise reduction circuit using digital signal processing of video signals, and particularly to a noise reduction circuit using frame (or field) correlation.

[Conventional technology]

Conventionally, this type of noise reduction circuit converts digitally encoded luminance signals into DR as shown in the block diagram of FIG.
Input to one frame delay circuit composed of AM etc.
A motion detection circuit 20 detects motion by comparing the input signal A with the signal delayed by one frame time (IH) by the delay circuit 19, and a motion detection circuit 20 detects motion by comparing the input signal A with the signal delayed by one frame time (IH) by the delay circuit 19. The coefficient of the signal is increased, the coefficient of the signal delayed by one frame is decreased, and when the motion is small, the coefficient of the input signal is decreased, the coefficient of the signal delayed by one frame is increased, and the coefficient of the input signal is 1 A coefficient unit 7.8 so that the sum of the coefficients of the frame-delayed signal becomes 2,
By providing an adder 9 for adding the outputs from these coefficient units 7.8, noise in the video signal is reduced.

[Problem to be solved by the invention]

The conventional noise reduction circuit described above reduces noise only using signals delayed by one frame, so if movement occurs, the noise reduction effect will be reduced or an afterimage will occur. There were drawbacks.

SUMMARY OF THE INVENTION An object of the present invention is to provide a video signal noise reduction circuit that solves these problems and can reduce noise even on a moving screen without causing side effects such as afterimages.

[Means to solve the problem]

The configuration of the video signal noise reduction circuit of the present invention includes a frame delay circuit that delays a digitally encoded video output signal by one frame (or one field), and a frame delay circuit that delays a digitally encoded video output signal by one frame (or one field), and a frame delay circuit that delays a digitally encoded video output signal by one frame (or one field). ) An autocorrelation degree detector that detects the degree of autocorrelation between signals in the vicinity of the previous screen and the input video signal, and a screen one frame (or one field) before from the degree of correlation from this autocorrelation degree detector. a selector that selects the signal with the highest degree of autocorrelation from the neighboring signals; first and second coefficient multipliers that respectively form signal coefficients so that the sum thereof becomes a constant value; a control circuit that controls these coefficient multipliers and a selector; and an adder that outputs an output signal.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention. The signal used in this embodiment is an 8-bit video luminance signal obtained by sampling an NTSC signal at a frequency four times the color subcarrier frequency.

The frame delay circuit 1 is a circuit that delays an input signal by one frame. The signal delayed by one frame by the frame delay circuit 1 is a sampling value delayed by one frame by the delay circuit 2.

A total of seven sampling values are created, including three sampling values before and after that, and these are sent to the autocorrelation degree detector 3, which detects the degree of autocorrelation with the input sampling value. The degree of correlation detected in this way is sent to the control circuit 4, which controls the 7-1 selector 5, the coefficient unit 7, and the 2-1 selector 5.
and the coefficient unit 8. To this, a coefficient unit 7 and (2-k
>The coefficient unit 8 is set so that the sum of both coefficients is always 2. These coefficients 7. The signal input to the coefficient unit 8 is adjusted by the delay circuit 6 and the delay circuit 2 in order to absorb the delay caused by the autocorrelation degree detector 3 and the control circuit 4.

These coefficients 7. The signal multiplied by the coefficient by the coefficient unit 8 is
An adder performs addition, 1/2 of this addition output is used as a luminance signal output, and this output is input to a frame memory to configure a cyclic filter to reduce noise.

FIG. 2 is a block diagram of a second embodiment of the invention. The signal in this embodiment is also an NTS video luminance signal sampled at a frequency four times the color subcarrier frequency. The frame delay circuit 11 of this embodiment is composed of a DRAM or the like,
1. Delayed by one frame with respect to the input signal, and before the signal delayed by one frame. Signal 524H, 5 of the next 3 horizontal periods
It outputs five signals: 25H, 526H, 527H, and 528H. These output signals are delayed by 3 sampling periods by a delay circuit 12, and four signals, ie, no delay, 1 sampling period delay, 2 sampling period delay, and 3 sampling period delay, are input to the autocorrelation degree detector 14, respectively. As a signal for comparing the degree of autocorrelation, two IH delay circuits 17 are used to create a signal delayed by 1 horizontal period and 2,000 periods with respect to the input signal, and the three signals together with the input signal are subjected to autocorrelation. It is input to the degree detector 14.

The autocorrelation degree detector 14 detects three signals 524H, 525H, 526H, 525H,
526H, 527H 3 signals, 526H, 527H, 5
A total of 12 autocorrelation degrees are detected for the three 2sH signals and the two sampling values before and after each of the three signals.

This autocorrelation degree is sent to the control circuit 15, and this control circuit 1
5 controls the signal input from the delay circuit 13 which is input to the 12-1 selector 16. This 12-1 selector 16 sends the sampled value with the highest degree of correlation to the coefficient unit 8, which works in conjunction with the coefficient unit 7 to set the sum of both coefficients to 2, and the coefficients are switched depending on the magnitude of the degree of correlation. It will be done. The value is input to the adder 9 and added to the 1
/2 becomes the luminance signal output, and noise is reduced. Further, this noise-reduced signal is transmitted to the frame delay circuit 11.
and used as a cyclic filter.

Since this embodiment also handles signals with a horizontal period delay, it has the advantage of being able to follow vertical movements on the television screen as well.

〔Effect of the invention〕

As explained above, the present invention detects the degree of autocorrelation for each sampled value in the vicinity of the screen one frame before, and reduces noise by using the sampled value with the highest degree of correlation. This also has the effect of reducing noise on the screen without leaving any afterimages.

[Brief explanation of the drawing]

1 and 2 are block diagrams of first and second embodiments of the present invention, and FIG. 3 is a block diagram of an example of a conventional noise reduction circuit. 1.11.19...Frame delay circuit, 2.6°12
．． 13... Delay circuit, 3.14... Autocorrelation degree detector, 4, 15... Control circuit, 5... 7-1 selector, 7.8... Coefficient unit, 9... Adder, 16°...
12-1... Selector, 17... IH delay circuit, 2
0...Motion detection circuit. ■〕

Claims (1)

[Claims] One frame of the digitally encoded video output signal (
or 1 field) a frame delay circuit that delays the
An autocorrelation degree detector detects the degree of autocorrelation between a signal in the vicinity of the screen one frame (or one field) before, which is the output signal of this delay circuit, and the input video signal; A selector that selects the signal with the highest autocorrelation degree from neighboring signals on the screen one frame (or one field) before based on the correlation degree of this selector, and the output signal of this selector and first and second coefficient multipliers that respectively form signal coefficients on the delay-adjusted signal of the input video signal such that the sum thereof becomes a constant value; a control circuit that controls the coefficient multiplier and the selector; 1. A video signal noise reduction circuit comprising: an adder that adds outputs from each coefficient multiplier and outputs the video output signal.