JPH09233489A - Noise reduction circuit - Google Patents

Abstract

(57) Abstract: A noise reduction circuit for color signals in a television receiver or the like that performs a digital signal processing of an image that can obtain a large noise removal effect without causing image blurring. A color signal input from an input terminal 1 is input to a subtraction circuit 2, a contour detection circuit 4, and an addition circuit 6.
The subtraction circuit 2 takes the difference between the signal delayed by the 1-pixel delay circuit 3 and the input signal, and inputs the difference to the nonlinear processing circuit 5. The signal from the one-pixel delay circuit is a signal after noise removal, and this difference signal is a signal of a noise component and a contour component of the image. The contour signal of the contour detection circuit 4 is also input to the non-linear processing circuit 5, predetermined input / output signal characteristics of the non-linear processing circuit 5 are controlled by the contour signal, and only the noise component signal is output from the difference signal. Noise is removed by adding the output and the input signal in the adder circuit 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal noise reduction circuit, and more particularly to a MUSE (Multiple Multiple
The present invention relates to a high-definition television signal decoder of a sub Nyquist Sampling Encoding system, and a noise reduction circuit of a color signal in a television receiver or the like that performs digital signal processing of an image in an EDTV receiver or the like.

[0002]

2. Description of the Related Art When a moving image and a still image are distinguished from each other and subjected to different signal processing, such as a MUSE decoder or an EDTV receiver, the moving image signal and the still image signal are mixed based on the motion information of the image. In the motion adaptive image processing system, the cyclic noise removal method using a frame memory is used in the still image portion. However, in the moving image part, the cyclic noise removal method using the frame memory cannot be used because it causes an adverse effect such as a double image. Here, FIG. 5 shows a configuration of a conventional color noise reduction circuit for moving image signals. In the figure, 18 is an input terminal for inputting an image signal, 19 is a low-pass filter (hereinafter referred to as "LPF"), 20 is a subtraction circuit, 21 is a non-linear processing circuit, and 22 is an addition circuit. , 23 denote output terminals, respectively. The signal input from the input terminal 18 is the LPF1
9, the subtraction circuit 20 and the addition circuit 22. LP
F19 removes the high frequency component from the input signal and outputs only the reduced component. The subtraction circuit 20 subtracts the signal input to the input terminal 18 from the output signal of the LPF 19. As a result, a high frequency signal component is extracted from the output of the subtraction circuit 20. After this is processed by the non-linear processing circuit 21, it is added to the original input signal by the adding circuit 22 and output from the output terminal 23 as a noise-reduced signal.

FIG. 6 shows an example of input / output characteristics of the non-linear processing circuit 21 used in the conventional color noise reduction circuit.
As is clear from FIG. 6, the output is set to “0” as an error in the range where the input level is extremely small (portion A). Next, in a range where the input level is large to some extent (portion B), a level proportional to the input level is output as noise. Further, in the range where the input level is large (portion C), it is assumed that the input signal is a mixture of noise and contour components of the image, and the proportion of contour components increases as the input level increases. , Outputs a level that is inversely proportional to the input level. In this case, the settings of the respective ranges A, B, and C having different input / output characteristics are empirically determined, and the noise component and the contour component are distinguished only by the level of the input signal. It was difficult to remove noise without deterioration.

As a conventional color signal noise reduction technique, for example, a "noise reduction circuit" described in JP-A-6-113315 is known. This noise reduction circuit detects the contour of the image, extracts the noise component by a high-pass filter in the flat portion of the image, removes this extracted noise component from the input signal, and in the contour portion of the image, The input signal is output as it is.

As described above, in any of the conventional color noise reduction circuits described above, since the means for removing the high frequency components is adopted, the high frequency noise can be reduced. There is also a problem that the high frequency component of the video signal is also removed, and as a result, the image quality of the moving image deteriorates (blurring). That is, there is a trade-off relationship that the image quality of a moving image deteriorates instead of obtaining the noise reduction effect.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems in the prior art, and the television receiver is designed to obtain a large noise removal effect without blurring of moving images. It is an object of the present invention to provide a color noise reduction circuit for a computer, etc.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 of the present invention provides a color signal input terminal and the color signal connected to the input terminal, respectively. A subtraction circuit, a contour detection circuit, and an addition circuit that are input, an output terminal of the addition circuit, and a color signal in which noise generated in the output terminal is reduced are input, and a one-pixel delay that connects the output side to the subtraction circuit Circuit, the difference signal from the subtraction circuit and the output signal of the contour detection circuit are input, and a non-linear processing circuit whose output side is connected to the addition circuit is used to output the noise component signal. And a non-linear processing circuit in which the non-linear characteristics of its input and output are controlled by the output signal of the circuit. Then, in the present invention, a difference signal between the current pixel and the color signal one pixel before is obtained, and the difference signal is input to the non-linear processing controlled by the separately detected contour detection signal. This is because the output from this non-linear processing circuit is made smaller when the contour signal is large and is made larger when the contour signal is small, thereby reducing the noise reduction amount in the contour portion of the image and suppressing the blurring of the image. Except for the contour portion of the image, increasing the noise reduction amount brings about a large noise reduction effect for the entire image. Furthermore, the present invention is used in a motion adaptive image processing system where a moving image and a still image are mixed to obtain a noise reduction effect equal to or higher than the frame cyclic noise reduction method used for a still image, An image with no S / N difference between a still image and a moving image will be output.

According to a second aspect of the present invention, a color signal input terminal, a plurality of one-pixel delay circuits cascade-connected to the input terminal, and a plurality of one-pixel delay circuits at both ends of the one-pixel delay circuit are provided. For each of the circuits, an averaging circuit for averaging the signals at the input and output terminals, a subtraction circuit connected to the output of the addition averaging circuit, an absolute value circuit connected to the output of the subtraction circuit, and the absolute value circuit. A contour detecting circuit is provided, which is provided with an output terminal of a value circuit, and separates noise from a contour even when the S / N is low to accurately detect only the contour.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a noise reducing circuit according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic block diagram showing an embodiment of a color noise reduction circuit according to the present invention according to claim 1. In the figure, 1 is an input terminal for inputting an image signal, 2 is a subtraction circuit, 3 is a 1-pixel delay circuit, 4 is a contour detection circuit, 5
Is a non-linear processing circuit, 6 is an adder circuit, and 7 is an output terminal. The color signal input from the input terminal 1 is input to the subtraction circuit 2, the contour detection circuit 4, and the addition circuit 6. In the subtraction circuit 2, the difference between the signal delayed by the 1-pixel delay circuit 3 and the input signal is taken and input to the nonlinear processing circuit 5. Here, since the delayed output signal from the one-pixel delay circuit is the signal after noise removal which is the output of this reduction circuit, this difference signal is, in other words, the signal of the noise component and the signal of the contour component of the image. Is. Further, the contour signal detected by the contour detection circuit 4 is also input to the non-linear processing circuit 5, and predetermined contour input / output signal characteristics of the non-linear processing circuit 5 are controlled by the contour signal, and a signal of a noise component from the difference signal. Will only be output. Noise is removed by adding the output of the non-linear processing circuit 5 and the input signal in the adding circuit 6.

FIG. 2 is a diagram showing an example of input / output characteristics of the non-linear processing circuit 5. Then, FIG. 3 is a diagram showing an impulse response of the color noise reduction circuit in this embodiment. 2 and 3, when the contour signal is small, the output of the non-linear circuit 5 is increased, and the impulse response is also lengthened accordingly, that is, noise is removed by using many pixels. Grows larger. On the other hand, when the contour signal is large, the nonlinear circuit 5
Output is reduced and the impulse response is shortened accordingly, that is, noise is removed with a small number of pixels, so the noise removal effect is reduced, but image blur is suppressed. Further, as shown in FIG. 1, by adopting the cyclic structure, the impulse response of the filter can be realized only by changing the input / output characteristic of the nonlinear processing circuit 5, and the circuit scale can be reduced in terms of hardware.

FIG. 4 is a schematic block diagram showing an embodiment of a contour detecting circuit according to the present invention as defined in claim 2.
In the figure, 8 is an input terminal for inputting an image signal,
Reference numerals 9, 10, 11, 12 denote 1-pixel delay circuits, 13, 14
Is an addition and averaging circuit, 15 is a subtraction circuit, 16 is an absolute value circuit, and 17 is an output terminal. The signal input from the input terminal 8 is input to the 1-pixel delay circuit 9, and the 1-pixel delay circuits 10, 11, 1 which are cascade-connected to the 1-pixel delay circuit 9.
It is sequentially delayed by 2. The average value of the input signal and the output signal of each of the 1-pixel delay circuits 9 and 12 is the averaging circuit 1.
3 and 14, the absolute value of the difference between the average values is output from the output terminal 17 as a contour signal. Thus, by taking the difference between the average values, the influence of the noise component can be suppressed and only the contour component can be accurately extracted. Therefore, as in the embodiment of the present invention according to claim 1, the contour signal can be obtained. When used in a noise reduction circuit whose characteristics are changed by, a highly accurate contour adaptive noise reduction circuit can be realized.

[0012]

As is apparent from the above description, the present invention has the following effects. (1) Effect corresponding to claim 1: By controlling the input / output characteristics of the non-linear processing circuit between the contour portion and the flat portion of the image by the contour signal of the image, noise can be removed without causing image quality deterioration. . (2) Effect corresponding to claim 2: Even at low S / N, the contour can be detected without being affected by noise.

[Brief description of drawings]

FIG. 1 is a schematic block diagram showing an embodiment of a noise reduction circuit according to the present invention according to claim 1.

FIG. 2 is a graph showing input / output characteristics of a nonlinear circuit used in the embodiment of FIG.

FIG. 3 is a diagram showing an impulse response in the embodiment of FIG.

FIG. 4 is a schematic block diagram showing an embodiment of a contour detection circuit according to the present invention as defined in claim 2;

FIG. 5 is a block diagram showing a configuration of a conventional noise reduction circuit.

FIG. 6 is a graph showing an input / output characteristic example of a non-linear circuit used in a conventional noise reduction circuit.

[Description of Reference Signs] 1,8,18 ... Image signal input terminal, 2,15,20 ... Subtraction circuit, 3,9,10,11,12 ... 1 pixel delay circuit,
4 ... Contour detection circuit, 5, 21 ... Non-linear processing circuit, 6, 2
2 ... Adder circuit, 7, 17, 23 ... Output terminals, 13, 14
... averaging circuit, 16 ... absolute value circuit, 19 ... low-pass filter (LPF).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yuichi Ninomiya 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the broadcasting technology research institute of Japan Broadcasting Corporation (72) Koichi Yamaguchi 1-10-11 Kinuta, Setagaya-ku, Tokyo No. 2 within the Broadcasting Technology Research Institute of the Japan Broadcasting Corporation (72) Seiichi Koshi 2-2-1 Jinnan, Shibuya-ku, Tokyo Inside the Broadcasting Center of the Japan Broadcasting Corporation (72) Masahide Naemura 1-10 Kinuta, Setagaya-ku, Tokyo No. 11 Japan Broadcasting Corporation Broadcasting Technology Laboratory (72) Inventor Atsushi Fukuda 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside Japan Broadcasting Corporation Broadcasting Technology Laboratory

Claims (2)

[Claims] 1. A color signal input terminal, a subtraction circuit, a contour detection circuit, and an adder circuit connected to the input terminal to input the color signal, an output terminal of the adder circuit, and the output terminal. Is input to the subtraction circuit, the difference signal from the subtraction circuit and the output signal of the contour detection circuit are input, and the output side is connected to the output side. A non-linear processing circuit connected to the adder circuit, wherein the non-linear processing circuit whose input / output non-linear characteristics are controlled by an output signal of the contour detection circuit so as to output a noise component signal. Color signal noise reduction circuit that does. 2. Input / output of a color signal input terminal, a plurality of one-pixel delay circuits cascade-connected to the input terminals, and each of the circuits at both ends of the plurality of one-pixel delay circuits. An arithmetic mean circuit for arithmetically averaging end signals, a subtraction circuit connected to an output of the arithmetic mean circuit, an absolute value circuit connected to an output of the subtraction circuit, and an output terminal of the absolute value circuit. The contour detecting circuit is characterized in that even when the S / N is low, the contour is separated from the noise so that only the contour is accurately detected.