JPS6058777A - noise removal filter - Google Patents

Abstract

PURPOSE:To reduce the influence of blur of a picture and to eliminate sticking noise by turning on and off of a nonlinear circuit or changing its characteristic in accordance with the occupation quantity of a buffer memory where the output of an encoder which encodes the output of a noise eliminating filter is stored. CONSTITUTION:The output signal of a differential value of an adder 4 is encoded by an encoder 6 and is stored in a buffer memory 7 and is read out in accordance with the timing of a transmission line and is outputted. The output of the occupied quantity of the buffer memory 7 is supplied as a control signal to a nonlinear circuit 2 to control the operation of this curcuit 2. The filter operation is turned off when the occupied quantity of the buffer memory is <=1/2 of a maximum value, and the filter operation is turned on until the occupied quantity of the buffer memory exceeds 1/2 of the maximum value to reach the maximum value. When the occupation quantity of the buffer memory exceeds 1/2 of the maximum value, the nonlinear circuit 2 operates the noise eliminating filter to dull the operation. When the occupied quantity is <=1/2 of the maximum value, the nonlinear circuit 2 is not operated, and an original picture is stored in a frame memory 5 as it is.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a noise removal filter for an image transmission device, and more particularly to a noise removal filter that removes "sticky noise" to reduce visual disturbances.

Prior Art and Problems In image transmission devices, noise removal filters are used to remove noise on both sides. Conventional noise removal filters have used a method in which when the inter-frame difference value of an image signal is relatively small, it is treated as noise and is forcibly set to 0 to remove the noise. However, if this is done, the moving image portion will be blurred because the image signal has movement. Also, since a frame memory is used to store the difference value between frames, when the difference between the current pixel and the pixel of the previous frame is less than a certain darkness value, it remains in the frame memory and causes so-called "sticky noise".
However, there was a problem in that it caused visual interference.

FIG. 1 shows the configuration of a conventional noise removal filter. In the figure, an input digital signal consisting of, for example, 8 bits is applied to a subtracter 1. The subtracter 1 calculates the difference value between the current pixel in the input digital signal and the pixel one frame before in the one-frame delay circuit 3, and outputs it as a signal A. The signal A is applied to the nonlinear circuit 2, subjected to nonlinear processing in the human output using a certain dark value, and then applied to the adder 4, where it is added to the signal of one frame before the one frame delay circuit 3, and is converted into 8 bits. A difference value output signal consisting of digital signals is generated. In the nonlinear circuit 2, its nonlinear processing is controlled by an external on/off control signal.

As shown in FIG. 2, when the difference between a pixel in the current frame and a pixel in the previous frame is as small as (-2 to 2), it is regarded as noise and the difference in the output is set to 0. In this case, the same signal as the one frame previous signal is output from the noise removal filter.

Moreover, when the difference is (3 or more, -3 or less), the difference is compressed and output. In FIG. 1, the solid line shows the characteristics when the noise removal filter is on, and the broken line shows the characteristics when the noise removal filter is off. Therefore, when such a noise removal filter is used, in an image encoding device that transmits only the difference between frames of a television signal,
This is effective because the amount of data generated is reduced.

However, the input TV/TV signal is generally a moving image, so if a noise removal filter such as the one described above is used, slight movement will be treated as noise and removed.
A ``blur'' occurs in the image resulting from the signal after passing through the noise removal filter, which becomes a visual disturbance.

Furthermore, if a frame memory is used in the one-frame delay circuit shown in Figure 1, the image of the previous frame will be
It remains as a "sticking noise" and causes visual disturbance.

OBJECTS OF THE INVENTION The present invention attempts to solve the problems of the prior art, and its purpose is to reduce noise removal filter 111.
L controls the operation of the noise removal filter according to the amount of occupancy of the buffer memory that stores the output of the encoder that encodes the power. An object of the present invention is to provide a novel 1ilt sound removal filter capable of removing "sound noise".

Embodiment of the Invention FIG. 3 shows the configuration of an embodiment of the noise removal filter of the invention. In this figure, the same parts as in FIG. 1 are designated by the same numbers, and their operation is also the same as in FIG. 1. 5 is a frame memory which operates as a one frame delay circuit. Further, 6 is an encoder, and 7 is a buffer memory.

In FIG. 3, the output signal of the difference value of the adder 4 is encoded by an encoder 6 and stored in a buffer memory 7, and then read out according to the timing of the transmission line to produce an output. The output of the amount of occupancy in the buffer memory 7 is the nonlinear circuit F! 1r2 as a control signal to control its operation.

FIG. 4 shows an example of the relationship between buffer memory occupancy and filter operation in the circuit of FIG. 3. Fourth
In the figure, the buffer memory occupancy is 1/2 of the maximum value.
It is shown that the filter operation is off in the following cases, and that the filter operation is on until the buffer memory occupancy exceeds 1/2 of the maximum value and reaches the maximum value.

When the buffer memory occupancy is large, for example, 1/1 of the maximum value
2, the nonlinear circuit 2 operates according to the characteristics shown by the solid line in FIG. Since the buffer memory occupancy is large when the image is in a state of rapid movement, a noise removal filter is operated to blur the movement and suppress the generation of information. Due to human visual characteristics, when there is rapid movement, the sense of details in an image becomes dull, so even if this is done, there is no perceived deterioration in image quality.

When the buffer memory occupancy is small, for example, the maximum value of 1
/2 or less, the nonlinear circuit 2 does not operate as shown by the broken line in FIG. 2, and the original image is stored in the frame memory 5 as it is. When the noise removal filter is activated as described above, the image stops moving and becomes almost a still image, and the previously moving parts remain as "burr noise", but the amount of Panzer memory occupied When the amount of noise decreases and the image becomes similar to a still image, the "sticky noise" can be removed by stopping the operation of the noise removal filter and storing the original image as it is in the frame memory.

FIG. 5 shows the structure of another embodiment of the noise removal filter of the present invention. In this figure, the same parts as in Figure 3 are indicated by the same numbers, and their operations are also similar to those in Figure 3.
It is not different from the case shown in the figure. In FIG. 5, 8 is a changeover switch, 9'-1+9-2, --. 9-n is a non-linear characteristic circuit, and 10 is a decoder.

In FIG. 5, a decoder 10 generates different signals depending on the amount of occupancy of the buffer memory 7, and a selector switch 8 switches according to the signal from the decoder 10 to generate a non-linear characteristic circuit 9.
-l+ 9-2. −． 9-n is connected to adder 4. The noise removal filter characteristics change as shown in FIG. 6 depending on the buffer memory occupancy. This results in Figure 3.

Compared to the embodiment shown in FIG. 4, the image quality changes smoothly depending on the buffer memory occupancy, and visual deterioration is reduced.

As described in detail, according to the noise removal filter of the present invention, the nonlinear circuit (-h is Since a means for turning on and off or changing its characteristics is provided, the ""
In addition to reducing the effect of blur, since a frame memory is used in the one-frame delay circuit, it is possible to remove the overprint Qft sound caused by the residual image of the previous frame, which is extremely effective.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a noise removal filter since GLL,
FIG. 2 is a diagram showing an example of the characteristics of a nonlinear circuit, FIG. 3 is a diagram showing the configuration of an embodiment of the noise removal filter of the present invention, and FIG.
This figure shows an example of the operation of the LL sound removal filter shown in FIG. 3, FIG. 5 shows the configuration of another embodiment of the noise removal filter of the present invention, and FIG. FIG. 3 is a diagram illustrating an example of the operation of the illustrated noise removal filter. 1: Subtractor, 2: Nonlinear circuit, 3: 1 frame delay circuit, 4: Adder, 5: Frame memory, 6: Encoder, 7:
Buffer memory, 8: Selector switch, 9 I+ 9 2
．． −． 9-nH nonlinear circuit, 10: Decoder Patent applicant Fujitsu Limited agent Patent attorney Gobe Tamamushi (1 other person) fl Fig. 1 Fig. 2

Claims (1)

[Claims] A difference value between an input image signal and a signal obtained by delaying the input image signal by one frame is determined, and the signal of the difference value is converted into a signal delayed by one frame through a nonlinear circuit in which the input-to-output relationship changes nonlinearly. In a noise removal filter that obtains an output by adding, means for turning on or off the nonlinear circuit or changing its characteristics according to the amount of occupancy in a buffer memory that stores the output of an encoder that encodes the output of the noise removal filter. A noise removal filter characterized by being provided with.