JPH04139968A - Noise reducer - Google Patents

Abstract

PURPOSE:To prevent production of after-image and to improve the S/N momentarily setting a different delay time to a variable delay circuit in the case of transit from a moving picture to a still picture and from a till picture to a moving picture. CONSTITUTION:When an output of a frame memory 3 changes from a moving picture to a still picture as a transition from a time t. to a time t4, a variable delay circuit 6 reduces its delay to advance the time for a still picture. Thus, no transient state appears in an output signal S in the case of a change from a moving picture to a still picture. Moreover, a still picture is outputted with extension from a time t1 till a time t2 in the case of a change from a still picture to a moving picture. Thus, the still picture whose S/N is improved is outputted and the after-image in the case of transition from a moving picture to a still picture is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise reducer for television equipment.

[Prior Art] FIG. 3 is a block diagram showing a conventional noise reducer. In this conventional noise reducer, the television signal An input to the input signal terminal 1 is input to the arithmetic circuit 2.
The output of the arithmetic circuit 2 is input to the frame memory 3. The output signal Bn of this frame memory 3 is output to the output signal terminal 7. The still image area detection circuit 4 compares the input television signal An and the output signal Bn to detect a portion of the screen that appears stationary. The still image area control circuit 5 controls constants of the arithmetic circuit 2.

In the conventional noise resolution user configured as described above, after the television signal is converted into a digital signal by A/1 conversion, this differential television signal is input to the input signal terminal 1. Then, in the arithmetic circuit 2, the arithmetic operation of (1-K)An+KBn is performed. However, An is an input television signal, Bn is an output signal of the frame memory 3 at the subsequent stage of the arithmetic circuit 2, and K is a variable constant. Then, the output signal from the arithmetic circuit 2 is input to the frame memory 3, and one frame is stored in the frame memory 3. As a result, a television signal with improved S/N in the still image area is output from the frame memory 3 via the output signal terminal 7.

The still image area detection circuit 4 detects a portion that appears stationary on the screen by comparing the input signal An and the output signal Bn of the frame memory 3, and the still image area control circuit 5 is set in the arithmetic circuit 2. Controls the constant K of the arithmetic expression. Conventional noise reducers are
(2) acts as a semi-fixed constant in the still image area, and varies on a frame-by-frame basis corresponding to each pixel in the still image area.

[Problems to be Solved by the Invention] However, since this conventional noise reducer improves the S/N by feeding back the output signal Bn to the arithmetic circuit 2, when moving from a moving image area to a still image area, ,S/
There is a problem that an afterimage occurs due to the improvement of N. Another problem is that even in a still image state, it takes time for the S/N ratio to improve.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a noise reducer that does not cause afterimages and instantly improves the S/N ratio when transitioning from a moving image to a still image.

[Means for Solving the Problems] A noise reducer according to the present invention includes an arithmetic circuit that performs predetermined arithmetic operations from a television signal, a frame memory into which the output of the arithmetic circuit is input, and a variable output of the frame memory. a variable delay circuit that outputs the output to an output terminal with a delay of a predetermined time; a still image area detection circuit that detects a still image area from the television signal and the output of the frame memory; and a detection result of the still image area detection circuit. and a still image area control circuit that controls the arithmetic coefficients of the arithmetic circuit and the delay time of the variable delay circuit based on the above.

[Operation] In the present invention, a variable delay circuit is provided at the subsequent stage of the frame memory, and after the output signal is once delayed, it is output to the output terminal. And the still image area control circuit is
Different delay times are set in the variable delay circuit when transitioning from a moving image to a still image and when transitioning from a still image to a moving image.

As a result, it is possible to output an output signal that does not have an excessive state when transitioning from a moving image to a still image.

[Example] Next, an example of the present invention will be described with reference to the accompanying drawings.

After the television signal is A/D converted, it is input to the input signal terminal 1 as a digital signal. This input signal An
In the arithmetic circuit 2, the calculation of (1-K)An+KBn is performed. However, An is the input television signal, B
n is the output signal of the frame memory 3 after the arithmetic circuit 2;
An+Bn(7)n is the number of frame units, and K is a variable constant. The calculation result of the calculation circuit 2 is stored in the frame memory 3 for only one frame, and the calculation result of the calculation circuit 2 is stored in the frame memory 3.
/N is improved.

The digital television signal with improved S/N is input to the variable delay circuit 6. In the variable delay circuit 6, this television signal is delayed for a certain period of time (in units of frames) and then outputted to the output signal terminal 7. In this case, the delay time of the variable delay circuit 6 is controlled by the still image area control circuit 5 as follows. That is, during a certain period of a transient state when moving from a moving image area to a still image area, the delay amount of the variable delay circuit 6 is reduced by that still image area, and the time of the still image is advanced. As a result, a still image with an improved S/N ratio is outputted to the output signal terminal 7 without a transient state when changing from a moving image area to a still image area as in the conventional case. Furthermore, when moving from a still image area to a moving image area, the output time of the still image area signal is extended by the time that was advanced when moving from the moving image area to the still image area.

The still image area detection circuit 4 detects a still image area by comparing the input signal An and the output signal Bn of the frame memory 3. The still image area control circuit 5 controls the calculation formula set in the calculation circuit 2. K is O in the moving image domain, and acts as a semi-fixed constant in the still image domain. Alternatively, the still image area control circuit 5 can also vary K on a frame-by-frame basis corresponding to each pixel in the still image area, thereby efficiently improving the S/N ratio. Further, as described above, the still image area control circuit 5 also sends a control signal for reducing the amount of delay during a certain period of the transition state from the moving image area to the still image area, and a control signal for changing the transition from the still image area to the moving image area. A control signal for extending the still image area signal by the amount of time that was being advanced at the time of the change is output to the variable delay circuit 6.

Next, the operation of the noise reducer according to this embodiment configured as described above will be explained.

FIG. 2 is a diagram showing the relationship between the still image state and the moving image state in this embodiment.

The diagram shown in FIG. 2(a) shows an example of a television screen in which a state change occurs between a still image area and a moving image area, and a car is running from left to right. Sample point A is selected as a sample point where the state of the image changes from a still image to a moving image when the car runs from left to right.

FIG. 2(b) shows the states of the input signal An of the television signal input to the input signal terminal 1, the noise-reduced signal Bn which is the output of the frame memory 3, and the output signal S output to the output signal terminal 7. shows. The input signal An indicates the change in the still image state and the moving image state at the sample point A.

The output signal Bn of the frame memory 3 enters a transient state when transitioning from a moving image to a still image. The output signal S is originally delayed by the variable delay circuit 6, but the time when the input signal An is in the moving image state, that is, from time t2 to t3, and the period during which the output signal S is in the moving image state are It is shown that they match.

When the output of the frame memory 3 changes from a moving image to a still image, as from time t3 to time t4, the variable delay circuit 6 reduces the amount of delay and advances the time of the still image.

Therefore, no transient state appears in the output signal S when changing from a moving image to a still image. Furthermore, when a still image changes to a moving image, the output signal S changes from time t to time t.
2 and output a still image. As a result, s/
It is possible to output a still image with improved N, and it is also possible to eliminate afterimages when transitioning from a moving image to a still image.

[Effects of the Invention] As explained above, the present invention provides a variable delay circuit at the subsequent stage of the frame memory to delay the output signal by a certain period of time (in units of frames), and when transitioning from the moving image area to the still image area. By reducing the delay amount of the variable delay circuit in the still image region and advancing the time of the still image during a certain period of the transient state of the still image, a still image with an improved S/N ratio can be output. Furthermore, when transitioning from a still image area to a moving image area, the still image area signal is extended by the advancing time and output. This makes it possible to eliminate afterimages when transitioning from a moving image signal to a still image signal, and to instantly improve S/H when transitioning from a moving image signal to a still image signal.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a noise reducer according to an embodiment of the present invention, Fig. 2 is a diagram showing changes in the state of a still image and a moving image in this embodiment, and Fig. 3 is a block diagram showing a noise reducer according to an embodiment of the present invention. FIG. 1; Input signal terminal; 2; Arithmetic circuit; 3; Frame memory; 4; Still image area detection circuit; 5; Still image area control circuit; ; Variable delay circuit; 7; Output signal terminal

Claims (2)

[Claims] (1) An arithmetic circuit that performs predetermined arithmetic operations from a television signal, a frame memory into which the output of this arithmetic circuit is input, and a variable delay circuit that delays the output of this frame memory by a variable predetermined time and outputs it to an output terminal. a still image area detection circuit that detects a still image area from the output of the television signal and the frame memory; and a still image area detection circuit that controls the calculation coefficient of the calculation circuit based on the detection result of the still image area detection circuit; A noise reducer comprising: a still image area control circuit that controls a delay time of a delay circuit. (2) The still image area control circuit advances the time of the still image of the output signal when transitioning from a moving image to a still image, and extends the still image of the output signal when transitioning from a still image to a moving image. The noise reducer according to claim 1, characterized in that: