JPH0223786A - Method and device for pre-processing moving image signal and encoding device using them - Google Patents

Abstract

PURPOSE:To suppress the generation of excessive information quantity accompanied with sudden motion, and to remove the discontinuity of the motion due to the stopping of encoding by switching the characteristic of a processing filter in conformity to the situation of the moving image signal of an input. CONSTITUTION:A pre-processing circuit is provided with a frame memory 1, a control circuit 2 and a pre-processing filter 100. Then, the moving image signal of the input supplied to the frame memory 1 and the control circuit 2. The frame memory 1 delays the supplied moving image signal by one frame time, and supplies it to the control circuit 2. The control circuit 2 generates a switching signal to select the passing characteristic of the pre-processing filter 100 based on the supplied moving image signal of a present frame and the moving image signal of the previous frame supplied by the frame memory 1.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a moving image signal preprocessing method and apparatus, and an encoding apparatus using the same.

(Prior art) In conventional video encoding, in order to prevent the encoding efficiency from decreasing due to noise contained in the input video signal, a noise resolution user removes noise from the input video signal. After that, encoding was performed.

(Problem to be solved by the invention) In conventional encoding of moving image signals, when excessive information is generated due to sudden or large movements, encoding stops in low bit rate encoding. This often occurs, causing discontinuity in the encoded image and making it very unsightly. In such cases, noise reducers were powerless. SUMMARY OF THE INVENTION An object of the present invention is to provide a preprocessing technique for moving image signals that can suppress the generation of an excessive amount of information due to sudden movements and the like, and can solve the above-mentioned problems.

(Means for Solving the Problem) According to the first invention of the present application, the amount of change in a moving image signal between screens is detected, and the passage characteristics of the moving image signal are narrowed as the amount of change becomes larger. A method for preprocessing a moving image signal is obtained.

Further, according to the second invention of the present application, a frame memory to which an input moving image signal is supplied, a control section to which the input moving image signal and the frame memory output are supplied and outputting a passing characteristic instruction signal, and a plurality of A preprocessing device for a moving image signal, comprising a preprocessing signal output means having a pass characteristic and giving the frame memory output a pass characteristic according to the pass characteristic instruction signal, the control unit means for accumulating the absolute value of the difference signal between the moving image signal and the frame memory output for each predetermined interval; and as the output of the accumulating means increases, the passing characteristic of the preprocessed signal output means narrows. There is obtained a preprocessing device for a moving image signal, which comprises means for outputting a pass characteristic instruction signal specifying the pass characteristic.

According to a third invention of the present application, the control unit in the second invention includes means for determining the area of a moving portion of the input video signal from the input video signal and the frame memory output, and and means for outputting a pass characteristic instruction signal that specifies a pass characteristic in which the pass characteristic of the pre-processed signal output means becomes narrower as the pre-process signal output means becomes narrower.

According to a fourth invention of the present application, the control unit according to the second invention accumulates the absolute value of the difference signal between the input moving image signal and the frame memory output for each predetermined section;
means for determining the area of a moving portion of the input video signal from the input video signal and the frame memory output;
A preprocessing device for a moving image signal is obtained, which is comprised of means for generating the passage characteristic indicating signal according to the cumulative value and the area of the moving portion.

Further, according to the fifth invention of the present application, there is provided a preprocessing filter that has a plurality of pass characteristics and applies a pass characteristic designated by a pass characteristic instruction signal to an input image signal, and a means for obtaining a prediction error signal; prediction means for generating the prediction signal from the prediction error signal and the prediction signal using at least interframe prediction; and means for outputting the pass characteristic instruction signal that specifies a characteristic in which the pass characteristic becomes narrower among the plurality of filter characteristics of the preprocessing filter as the change amount increases. Accordingly, an encoding device for a moving image signal is obtained.

(Function) In conventional low bit rate video encoding, when the movement of the input video signal becomes intense, encoding is temporarily stopped, suppressing the generation of excessive information, and increasing the encoding speed. and the speed of the transmission line was matched. However, in such a method, discontinuity occurs in the encoded image when encoding is stopped, resulting in unnatural motion and being very unsightly. According to the present invention, when performing low bit rate video encoding, preprocessing is performed on the video signal to be encoded, thereby suppressing the generation of excessive information due to rapid movement of the video. , which attempts to eliminate discontinuities in encoded images due to stopping of encoding. The preprocessing method of the present invention uses a filter in the time direction, and the passing characteristics of the filter are switched depending on the magnitude of movement in the moving image or the amount of generated information, so that the generation of information is smooth in terms of time. control so that it is The preprocessing of the present invention is constituted by a frame memory 1, a control circuit 2, and a preprocessing filter 100, as shown in FIG. There are various specific methods for switching the characteristics of this pre-processing filter. The filter characteristics are switched by calculating the sum of absolute values of the inter-frame differences and comparing that value with a predetermined threshold.

0 When changing the filter characteristics based on the ratio of the area of motion within the screen, first the motion area within the screen is determined. Several methods of determining a motion area are already known. For example, the specification of Japanese Patent Application No. 59-194110 [
As described in ``Dynamic and static separation device for moving image signals'', the screen is divided into blocks of a certain size, the frame difference values of each pixel within the block are added within the block, and the result of this addition is compared with a predetermined threshold value. There is a method of determining the block by comparing the size. Alternatively, a method called a gradient method can be used to obtain a pixel-by-pixel motion vector from the luminance gradient within a frame and a frame difference value, and a set of pixels for which this motion vector is not zero can be defined as a motion region. In the present invention, any method may be used for separating motion and static. Which filter characteristics should be selected for the number of motion blocks in the screen is determined in advance through statistical investigation. Then, the filter characteristics are switched by comparing the number of moving blocks obtained by the dynamic and static separation with a predetermined value. Additionally, both frame difference values and motion areas can be used. For example, even if the moving area is large, if the image is flat, inter-frame differences will not occur much. In addition, if the motion area is not very large and the input image signal contains a large amount of fine noise, a considerable amount of interframe difference signal will be generated. Since the encoded information is removed by In such a case, if the determination is made using both the frame difference value and the motion area, more accurate filter characteristics can be selected. In this case as well, the characteristics of the filter are switched by comparing the ratio of the sum of absolute values of frame differences and the motion area with a predetermined value, as described above.

Next, the preprocessing filter will be explained. As the preprocessing filter, for example, a time axis filter as shown in FIG. 2 can be used. The input moving image signal is subtracted from the moving image signal of one frame before by a subtracter 3, and a frame difference signal is provided to a ROM (read only memory) 4.

A plurality of characteristics as shown in FIG. 3 are written in advance in the ROM, and are switched by a switching signal. The horizontal axis of the characteristics in FIG. 3 is input, and the vertical axis is output. For example, select characteristic (a) for a frame with small movement or a frame with a small frame difference signal, and select characteristic (b) for a frame with medium movement or a medium frame difference signal. , characteristic (C) is selected when the frame has thick motion or a large number of frame difference signals.

In characteristic (a), the degree of amplification is 1, so the differential signal passes through as is, but in characteristic (b), the degree of amplification is less than 1, so the large differential signal generated due to movement is suppressed, and as a result, The passband of the moving image signal is narrowed. Characteristic(
Since characteristic (c) has an even lower amplification degree than characteristic (b), it is possible to strongly suppress an excessive differential signal, and the pass band is further narrowed than in characteristic (b). In addition, it is also possible to provide a plurality of characteristics in which the degree of amplification is smaller than 1 as the difference value increases, and to use a characteristic that has stronger nonlinear characteristics as the movement increases.

The suppressed differential signal of the output of the ROM is added to the signal of one frame before by an adder 5, and a moving image signal in which generation of excessive information is suppressed is obtained. This signal is also supplied to the frame memory 6 and used for filtering the next frame. In this way, by switching the characteristics of the preprocessing filter in response to the situation of the input video signal, the amount of generated information is smoothed, and the generation of instantaneous sudden information is suppressed.
A visually pleasing encoded image can be obtained by removing discontinuities in motion caused by stopping encoding.

(Embodiment) An embodiment of the present invention will be described in detail with reference to FIGS. 4, 5, 6, 7, and 8. First, explanation will be given with reference to FIG. The input video signal is
It is supplied via line 10 to frame memory 1 and control circuit 2. Frame memory 1 delays the moving picture signal supplied via line 10 by one frame time and supplies it via line 12 to control circuit 2 and subtracter 3 . The control circuit 2 selects the pass characteristic of the preprocessing filter based on the current frame moving image signal supplied via the line 10 and the previous frame moving image signal supplied from the frame memory 1 via the line 12. generates a switching signal to

The control circuit 2 has a configuration as shown in FIG. 5 when switching the filter characteristics based on the frame difference value. The moving image signal of the current frame supplied via the line 10 and the moving image signal of the previous frame supplied via the line 12 are supplied to a subtracter 21 included in the control circuit 2. The subtracter 21 subtracts the signal of the previous frame and the signal of the current frame to obtain a frame difference signal. The frame difference signal obtained by the subtracter 21 is supplied to an absolute value accumulator 22. The absolute value accumulator 22 converts the frame difference signal supplied from the subtracter 21 into an absolute value and accumulates it over one frame. Then, the accumulated value is supplied to the ROM 23. Further, the absolute value accumulator 22 is reset at the beginning of the frame by a reset signal supplied from the sync separator 24. In the ROM 23, a threshold value for filter switching that has been statistically investigated in advance is written, and the absolute value sum of the frame difference values for each frame supplied from the absolute value accumulator 22 is set as an address, and the value written in each address is stored in the ROM 23. A switching signal is generated to select the pass characteristics of several types of preprocessing filters according to the following. The switching signal generated in the ROM 23 is transmitted to the control circuit 2.
It is supplied to the ROM 4 as an output switching signal. The sync separator 24 separates the sync from the image signal of the current frame supplied via the line 10, and generates a reset signal for resetting the absolute value accumulator at the beginning of the frame based on the separated sync signal. and supplies it to the absolute value accumulator 22.

The control circuit 2 for switching filters depending on the ratio of moving area has a configuration as shown in FIG. The signal of the current frame is sent to a subtracter 21 and a sync separator 2 via a line 10.
40. The signal of the previous frame is supplied via line 12 to subtractor 21 . The subtracter 21 subtracts the current frame signal and the previous frame signal to obtain a frame difference signal. The frame difference signal obtained by the subtracter 21 is supplied to a scan converter 220. The scan converter 220 performs scan conversion on the frame difference signal supplied from the subtracter 21 to convert it into blocks of a predetermined size. The frame difference signal blocked by scan converter 220 is supplied to absolute value accumulator 230 . The absolute value accumulator 230 performs absolute value conversion on the blocked frame difference signal supplied from the scan converter 220, and accumulates the values within the block. Further, the absolute value accumulator 230 resets the value of the accumulator at the timing of the beginning of the block by a block reset signal supplied from the sync separator 240 via the line 2423. The accumulated values for each block are supplied to ROM 250. The sync separator 240 separates the sync from the current frame signal supplied via the line 10, and generates a block-by-block reset signal and a frame-by-frame reset signal based on the separated sync signal. The reset signal for each block generated by the sync separator 240 is sent to the absolute value accumulator 2 via a line 2423.
30. The frame-by-frame reset signal generated by sync separator 240 is also provided to accumulator 260 via line 2426. The ROM 250 determines motion blocks based on the cumulative result of the absolute values of frame differences within the block supplied from the absolute value accumulator 230.
The threshold value that forms the boundary between a moving block and a stationary block is statistically investigated in advance. Then, when the cumulative result exceeds the threshold, it outputs a signal 1 indicating that it is a motion block,
When the cumulative result is less than or equal to the threshold, a signal 0 indicating that the block is a stationary block is output. The output signal of ROM 250 is supplied to accumulator 260 . The accumulator 260 is a ROM 250
The signals supplied from the CPU are accumulated for one frame. Accumulator 2
The signal accumulated at 60 is supplied to the ROM 270 as a signal indicating the area of the moving part in that frame.

Accumulator 260 also connects line 2426 from sync separator 240 to
A frame reset signal supplied via the frame resets the accumulator at the beginning of the frame. ROM270
In this method, which filter characteristic should be selected for the value of the motion area is statistically investigated in advance, and a switching signal for selecting the filter is written. Then, a filter switching signal corresponding to the value of the motion area supplied from the accumulator 260 is output. The switching signal output from the ROM 270 is supplied to the ROM 4 as an output signal from the control circuit 2.

The control circuit 2 for switching filters based on the frame difference value and the motion area has a configuration as shown in FIG. The current frame signal is supplied via line 10 to subtractor 21 and sync separator 2400. The signal of the previous frame is
It is fed via line 12 to subtractor 21 . The subtracter 21 subtracts the current frame signal and the previous frame signal to obtain a frame difference signal. The frame difference signal obtained by the subtracter 21 is sent to a scan converter 2200 and an absolute value accumulator 28.
00.

The scan converter 2200 performs scan conversion on the frame difference signal supplied from the subtracter 21 to convert it into blocks of a predetermined size. The frame difference signal blocked by the scan converter 2200 is sent to the absolute value accumulator 23.
00. The absolute value accumulator 2300 performs absolute value conversion on the blocked frame difference signal supplied from the scan converter 2200, and accumulates the value within the block. Further, the absolute value accumulator 2300 resets the value of the accumulator at the timing of the beginning of the block by a block reset signal supplied from the sync separator 2400 via the line 2324. The accumulated value for each block is
Supplied to ROM2500. The sync separator 2400 is
Synchronization is separated from the signal of the current frame supplied via line 10, and a reset signal for each block and a reset signal for each frame are generated based on the separated synchronization signal. The block-by-block reset signal generated by sync separator 2400 is provided to absolute value accumulator 2300 via line 2324. The frame-by-frame reset signal generated by the sync separator 2400 is also sent to the accumulator 2600 via line 2624.
and is supplied to the absolute value accumulator 2800. ROM2500
The motion block is determined based on the cumulative result of the absolute values of the frame differences within the block supplied from the absolute value accumulator 2300, but the threshold value at the boundary between a motion block and a still block is statistically investigated in advance. When the cumulative result exceeds the threshold, a signal 1 indicating that the block is a moving block is output, and when the cumulative result is below the threshold, a signal O indicating that the block is a stationary block is output. ROM250
The zero output signal is provided to accumulator 2600. Accumulator 2600 accumulates one frame of signals supplied from ROM 2500. The signal accumulated by accumulator 2600 is supplied to ROM 2700 via line 2627 as a signal indicating the area of the moving portion in that frame. Accumulator 2600 also connects line 262 from sync separator 2400 to
The frame reset signal supplied via 4 resets the accumulator at the beginning of the frame. The absolute value accumulator 2800 converts the frame difference signal supplied from the subtracter 21 into an absolute value and accumulates it over one frame. Then, the accumulated absolute value sum is passed through line 2827 to RO
Supply to M2700. Further, the absolute value accumulator 2800 is
It is reset every frame by a reset signal provided on line 2624 from sync separator 2400. R
The OM 2700 statistically examines and writes in advance which filter characteristics are to be selected based on the value of the sum of absolute values of the motion area and the frame difference. And ROM2700 is
A filter characteristic switching signal is output in response to the motion area value supplied from the accumulator 2600 and the absolute value sum of the frame difference supplied from the absolute value accumulator 2800. R
A switching signal output from the OM 2700 is supplied to the ROM 4 as an output from the control circuit 2.

In addition, in the above explanation of FIGS. 6 and 7, if the input moving image signal is input in a scan-converted state, the scan converters 220 and 2200 of FIGS. 6 and 7 are unnecessary. .

Return to Figure 4. The subtracter 3 subtracts the signal supplied from the frame memory 1 and the predicted signal supplied from the frame memory 6 to obtain an interframe difference signal. The interframe difference signal obtained by the subtracter 3 is supplied to the ROM 4. The ROM 4 has a plurality of input/output related signal passing characteristic values written in advance as shown in FIG. When it is indicated that it is not necessary to carry out the above, select the characteristic as shown in (a) of FIG.

When the frame difference signal is a medium frame and the switching signal indicates that the input signal is to be suppressed to a medium degree, a characteristic as shown in FIG. 3(b) is selected. When the switching signal indicates strong suppression of the input signal in a frame with many frame difference signals, (C
).

The filtered difference signal of the output of ROM4 is
It is supplied to an adder 5. The adder 5 adds the filtered difference signal supplied from the ROM 4 and the filtered previous frame signal supplied from the frame memory 6 to produce a moving image signal that has been subjected to time-axis filter processing. get.

The moving image signal output from the adder 5 and subjected to time-domain filter processing is supplied to a frame memory 6 and an encoder 7. The frame memory 6 delays the moving image signal supplied from the adder 5 and subjected to the time axis filter processing by one frame time, and uses the subtracter 3 and the adder as a signal for filtering the next frame. Supply to 5. The encoder 7 is a normal video encoder that uses correlation between screens. The encoder 7 encodes the moving image signal supplied from the adder 5 and subjected to time-domain filter processing, and outputs it to the transmission path.

In addition, when an encoder that utilizes the correlation between screens is used as shown in FIG. 8, it is also possible to generate a filter characteristic switching signal using a frame difference signal obtained by the encoder. In this case, the subtracter 21 of the control circuit 2 in FIG. 5, FIG. 6, or FIG.
An interframe difference signal supplied from the encoder is supplied instead of the output signal of the encoder. Further, the sync separators 24, 240, and 2400 included in the control circuit 2 are supplied with the input signal of the preprocessing filter as the signal of the current frame. Furthermore, it goes without saying that the synchronization separator may not be provided in the control port 2 and the synchronization signal may be supplied separately.

(Effects of the Invention) As explained in detail above, by using the preprocessing of the moving image signal of the present invention, it is possible to suppress the generation of excessive information due to sudden movement, and as a result, the encoded image due to the stop of encoding can be suppressed. Discontinuities are removed and a visually pleasing encoded image is obtained. As described above, when the present invention is put into practical use, the image quality improvement effect in encoding moving images is extremely significant.

[Brief explanation of the drawing]

Figures 1, 2, and 3 are diagrams explaining the invention in detail, and Figures 4, 5, 6, 7, and 8 are diagrams explaining the invention in detail. It is. In the figure, 6...Frame memory 219. control circuit
3.21...Subtractor 4.23.250.270
．． 2500.2700...ROM 5...Adder 7...Encoder 22.230.2300.2
800... Absolute value accumulator 24.240, 2400
... Synchronous separator 220. 2200...Scan converter 260. 2600...accumulator.

Claims (5)

[Claims] (1) A method for preprocessing a moving image signal, which comprises detecting the amount of change in the moving image signal between screens, and narrowing the passage characteristic of the moving image signal as the amount of change increases. (2) a frame memory to which an input moving image signal is supplied, a control section to which the input moving image signal and the frame memory output are supplied and outputting a passing characteristic instruction signal, and a control unit having a plurality of passing characteristics; A preprocessing device for a moving picture signal, comprising a preprocessing signal output means for giving a memory output a pass characteristic according to the pass characteristic instruction signal, the control unit controlling the output of the input moving picture signal and the frame memory output. means for accumulating the absolute value of the difference signal between the two for each predetermined interval, and a pass characteristic instruction for specifying a pass characteristic in which the pass characteristic of the preprocessed signal output means narrows as the output of the accumulating means increases. A preprocessing device for a moving image signal, comprising means for outputting a signal. (3) In the moving image signal preprocessing device according to claim (2), the control section includes means for determining the area of a moving portion of the input moving image signal from the input moving image signal and the frame memory output, and A preprocessing device for a moving image signal, comprising: means for outputting a pass characteristic instruction signal specifying a pass characteristic in which the pass characteristic of the preprocess signal output means becomes narrower as the preprocess signal output means becomes larger. (4) In the moving image signal preprocessing device according to claim (2), the control section includes means for accumulating the absolute value of a difference signal between the input moving image signal and the frame memory output for each predetermined section; Composed of means for determining the area of the moving portion of the input moving image signal from the input moving image signal and the frame memory output, and means for generating the passing characteristic instruction signal according to the cumulative value and the area of the moving portion. A preprocessing device for moving image signals. (5) a preprocessing filter that has a plurality of pass characteristics and applies a pass characteristic designated by a pass characteristic instruction signal to an input image signal; and means for obtaining a prediction error signal from the preprocessing filter output and the prediction signal; a prediction means for generating the prediction signal from the prediction error signal and the prediction signal using at least inter-frame prediction; and means for outputting the pass characteristic instruction signal that specifies a characteristic in which the pass characteristic narrows among the plurality of filter characteristics of the preprocessing filter as the amount of change increases. Device.