JP2586715B2 - Video signal coding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a video signal encoding system using a band compression technique.

(Prior Art) As a coding method of a moving image signal using a conventional band compression technique, for example, an "ISDN-compatible color moving image television" described in Document No. D-233, 1989, National Institute of Information and Communication Technology Spring Meeting. Telephone devices "are known. In this moving image signal encoding method, a map is created by extracting a face area on a screen. Then, the image encoding unit performs inter-frame intra-frame adaptive prediction. At this time, if the region is a face region, the encoding is performed up to the last stage, and if the region is other than the region, the encoding is stopped at the previous stage. This reduces the amount of coding.

(Problems to be Solved by the Invention) However, in the above-described conventional moving image signal encoding method, unnecessary portions are generated due to noise in the background portion because the background portion other than the face is roughly encoded. Also, if the background changes from a background portion to a face portion between successive screens, the coding changes from coarse coding to fine coding, so that a considerable amount of predicted pixel signals are generated here, resulting in coding of useless information. turn into. As a result, the coding efficiency decreases.

(Means for Solving the Problems) The moving picture signal encoding method of the present invention is a moving picture signal encoding method using correlation between screens, and one screen of an input moving image signal is composed of a plurality of pixels. , And a difference from the previous screen is detected for each block. When the difference value is equal to or greater than a predetermined first threshold value, the block is regarded as an effective block, and the difference value is set to a predetermined first threshold value. Means for creating a first effective block map for each frame as an invalid block when it is less than, means for performing a first weighting on the first effective block map, and a sixth effective block map on the previous screen. A second weighting means, a first effective block map having the first weighting, and a sixth effective block map having the second weighting are added and synthesized. Weight Means for obtaining a second effective block map in which is performed, and referring to blocks near each block with respect to the second effective block map, the total value of the values of the neighboring blocks and the target block is determined in advance. Means for obtaining a third valid block map by performing segmentation by setting the target block as an effective block when the target block is equal to or more than the second threshold and setting the target block as an invalid block when the target block is less than the second threshold; In the invalid block in the effective block map, the neighboring block is referred to, and when the total value of the neighboring blocks is equal to or more than a predetermined third threshold value, the invalid block is replaced with the valid block, Means for obtaining a fourth valid block map by keeping the invalid block as an invalid block when the value is less than the threshold value; If the number of valid blocks in the map is equal to or greater than a predetermined fourth threshold value, all valid blocks in the fourth valid block map are replaced with invalid blocks to form a fifth valid block map, and the fourth valid block map is used. If the number of effective blocks is less than a predetermined fourth threshold value, the fourth effective block map is used as it is in the fifth case.
Means for delaying the fifth effective block map by one frame time to obtain a sixth effective block map, and means for obtaining the sixth effective block map from the input of the moving image signal. Means for giving a delay of time until generation to the moving image signal, and, for the moving image signal with the delay, a region defined as an effective block in the fourth effective block map, Means for performing coding by using the correlation within or both.

(Operation) In a videophone or the like, since the background portion is fixed and the speaker mainly moves, if the speaker portion is cut out and encoded, the amount of useless encoded information generated due to noise from the background or the like is reduced. The coding efficiency can be improved.

In the present invention, the coding efficiency is increased by cutting out the speaker portion and coding only the speaker portion. The method of extracting a speaker will be described in detail with reference to the drawings. Assume that the speaker has moved as shown at times t0, t1, and t2 in FIG. Then, when the difference between the screens at the time t0 and the time t1 is obtained, an area shown by oblique lines in FIG. 2 is obtained,
It is assumed that an isolated hatched portion in the background is a difference signal generated by background noise. Next, the screen is divided into blocks each including a plurality of pixels of n pixels in the horizontal direction × n pixels in the vertical direction, and when the sum of absolute values of the difference signals in each block is equal to or larger than a predetermined first threshold value, Is an effective block, and when the sum of absolute values of the difference signal is less than the first threshold value, the block is regarded as an invalid block. FIG. 3B shows an effective block map at time t1 obtained by the above processing. The portion painted black in FIG. 3 (B) is an effective block. FIG. 3A shows time t0 and time t0.
It is assumed that it is the sixth effective block map obtained between the screens at time t0-1 one screen before. Then, first weighting is performed on the effective block map of the current screen (FIG. 3 (B)), that is, the first effective block map, and the sixth block which is the effective block map of the previous screen (FIG. 3 (A)) is obtained. The second weighting is performed for the effective block map. An example of weighting is shown below. For example, the valid block of the previous frame is set to 1 and the invalid block is set to 0. The number of valid blocks in the current frame is 2, and the number of invalid blocks in the current frame is 0, like the invalid blocks in the previous frame. The weighted effective block map of the previous frame and the weighted effective block map of the current frame are added and synthesized to obtain a second effective block map. The second effective block map is as shown in FIG. Next, segmentation is performed on the second effective block map obtained by addition and synthesis in FIG. 3 (C). An example of the segmentation will be described with reference to FIGS. 3 and 4. For example, if k in FIG. 4 is a target block for segmentation, blocks a, b, c, d,
Refer to the values of e, f, g, h. That is, the second of FIG.
Refer to the value of the effective block map. Nearby blocks
When the sum of the values of a, b, c, d, e, f, g, h and the block k is equal to or greater than a predetermined second threshold, the target block k
Is an effective block, and neighboring blocks a, b, c, d, e, f, g, h
When the sum of the values of the block k and the block k is smaller than a second predetermined threshold value, the target block k is regarded as an invalid block.

FIG. 3D shows a third effective block map newly obtained by segmentation. In some cases, an isolated invalid block area may occur in a moving portion in the third valid block map. This is because when a first effective block map is obtained, a block in which a difference between screens in a moving portion is slightly lower than a first threshold value becomes an invalid block, and an isolated invalid block region occurs in the moving portion. I do. FIG. 5 shows an example of the isolated invalid block area. As shown in FIG. 5, the third area including the isolated invalid block area
When only the effective block area in the effective block map is encoded, the isolated invalid block area in the effective block area is not encoded. Loss of continuity,
Coding distortion occurs. As a result, the encoded image may be very unsightly. Therefore, the isolated invalid block area is removed. As a method for removing an isolated invalid block area, a process similar to the segmentation is performed on an invalid block. That is, a block near the invalid block is referred to, and when the total value of the blocks in the vicinity is equal to or larger than a predetermined third threshold, the target invalid block is replaced with a value indicating the valid block. By the above processing, the area which was the isolated invalid block in FIG. 5 is removed, and the fourth valid block map is obtained. FIG. 3D shows a fourth effective block map.

Next, the processing at time t2 will be described. When the difference between the screens at the time t1 and the time t2 is obtained, and the validity / invalidity determination is performed according to the first threshold, the first time shown in FIG.
Is obtained. The first weighting is performed on the first effective block map. Then, since the effective block map at the time t1, which is the previous screen, is that shown in FIG. 3D, the effective block map shown in FIG. 3D is subjected to the second weighting and the first weighting. The second effective block map shown in FIG. 6 (B) is obtained by addition and synthesis with the first effective block map. When the above-described segmentation is performed on the second effective block map of FIG. 6 (B) using the second threshold value, a third effective block map shown in FIG. 6 (C) is obtained. Next, an isolated invalid block area is removed from the third valid block map. Since the isolated invalid block area did not exist in the third valid block map of FIG. 6C, the third valid block map was used as it is in the fourth valid block map.
And a speaker area obtained by the segmentation. The actual speaker area at the time t2 is almost in the left half of the screen, whereas the speaker area obtained by the segmentation protrudes considerably into the background part of the right half of the screen. )
If the fourth effective block map is used as it is, the background noise may be coded, which is not preferable. When the motion is large and the number of effective blocks obtained by the segmentation is large as in the case of the times t1 and t2, the speaker area on the previous screen expands due to the effect of the effective block map on the previous screen. Because.
Therefore, when the movement between the screens is large, that is, when the number of effective blocks of the fourth effective block map is equal to or more than a predetermined fourth threshold value, the fourth effective block map is reset and the fourth effective block map is reset. All the valid blocks in the fourth effective block map are replaced with invalid blocks to form a fifth effective block map. The fifth effective block map is delayed by one frame time to become the sixth effective block map, and is used for segmentation at the next time. For example, FIG. 3A is a fourth effective block map of the previous frame, and FIG. 3B is an effective block map of the current frame, that is, a first effective block map. If the number of valid blocks in the fourth valid block map obtained at time t1 is equal to or greater than the fourth threshold, all valid blocks in the fourth valid block map are replaced with invalid blocks, and Since the fifth effective block map is the fifth effective block map, all the sixth effective block maps at time t2 obtained by delaying the fifth effective block map by one frame time are also invalid blocks. As a result, the first valid block map at time t2 is
6 (A), the weighted second effective block map is as shown in FIG. 6 (D), and a second threshold value is set for this second effective block map. When the above-described segmentation is performed, a third effective block map as shown in FIG. 6A is obtained. This third
Does not include an isolated invalid block area, the third valid block map becomes the fourth valid block map as it is, and the background portion can be deleted.

By coding the effective block area of the fourth effective block map obtained as described above, that is, the speaker area using the correlation between the screens, the correlation within the screen, or both, the noise caused by the background or the like is reduced. The generated unnecessary information can be easily deleted, and the encoding efficiency can be improved.

As the above thresholds and weights, optimal values statistically checked in advance are used. The arrangement of the reference blocks in the segmentation and the removal of the isolated invalid block may be an arrangement other than the above and the number of blocks.

(Example) Next, an example of the present invention will be described in detail with reference to the drawings. FIG. 7 shows an embodiment of the present invention. The input moving image signal is sent to a valid / invalid determination unit 1 via a line 100.
And to the delay unit 11. The valid / invalid determination unit 1 stores a moving image signal of the previous screen, obtains a frame difference signal between the moving image signal on the previous screen and the moving image signal newly input via the line 100, and calculates the frame difference. The signal is divided into blocks each including a plurality of pixels of n pixels in the horizontal direction × n pixels in the vertical direction, and for each block, the sum of absolute values of frame difference values in the block is obtained. If the sum of absolute values of the obtained frame difference values is equal to or greater than a predetermined first threshold, the block is regarded as a valid block, and if the sum of absolute values of the frame difference values is less than the first threshold, the block is invalidated. As a block, a first valid block map is obtained. The first valid block map obtained by the valid / invalid determination unit 1 is provided to the weighting unit 2. The weighting unit 2
The first valid block map given by the valid / invalid determination unit 1 is subjected to a predetermined first weighting.
The first effective block map weighted by the weighting unit 2 is provided to the adder 4. The adder 4 adds the first effective block map provided from the weighting unit 2 and the sixth effective block map, which is an effective block map in the previous screen, provided from the weighting unit 3 and the weighting is performed. Obtain the generated second effective block map. The second effective block map obtained by the adder 4 is provided to the segmentation unit 5. The segmentation unit 5 performs a segmentation process on all blocks in the second effective block map provided from the adder 4. For example, if a block to be segmented is k as shown in FIG. 4, the values of blocks a, b, c, d, e, f, g, and h near k and k are referred to, and Is equal to or greater than a second predetermined threshold, the block k is regarded as an effective block. If the value of the neighboring blocks and the value of k are smaller than the second threshold, the block k is regarded as an effective block.
Is used as an invalid block to obtain a third valid block map. The third valid block map obtained by the segmentation unit 5 is provided to the isolated invalid block removal unit 6. The isolated and invalid block removing unit 6 connects the effective blocks to the invalid blocks included in the third valid block map provided from the segmentation unit 5 by using the isolated and invalid block removing process. The processing of an isolated invalid block refers to a block near the target invalid block in the same manner as the segmentation, and if the total value of the blocks in the vicinity is equal to or larger than a third threshold value, the isolated invalid block is determined. Let the block be a valid block. If the total value of the neighboring blocks is less than the third threshold value, the invalid block remains an invalid block, and the fourth valid block map from which the isolated invalid block has been removed by the above processing. Get. The fourth valid block map obtained by the isolated invalid block removing unit 6 is provided to the valid block number determining unit 8, the valid block reset unit 9, and the encoding unit 7. Effective block number determination unit 8
When the number of valid blocks in the fourth valid block map provided from the isolated invalid block removing unit 6 is equal to or larger than a predetermined fourth threshold value, the reset instruction is issued to the valid block reset unit 9. When the number of valid blocks in the fourth valid block map provided from the isolated / invalid block removing unit 6 is less than a predetermined fourth threshold, the valid block number determining unit 8 determines whether the valid block is a valid block reset unit 9. To stop resetting. When receiving an instruction to execute reset from the number of valid blocks determination unit 8, the valid block reset unit 9 replaces all valid blocks in the fourth valid block map supplied from the isolated invalid block removal unit 6 with invalid blocks. To obtain a fifth effective block map. Also, an effective block reset unit 9
When the reset stop instruction is given from the valid block number determining unit 8, the fifth valid block map supplied from the isolated invalid block removing unit 6 is directly processed in the fifth valid block map without performing any processing. This is an effective block map. The fifth effective block map obtained by the effective block reset unit 9 is provided to the frame delay unit 10. Frame delay section
The reference numeral 10 delays the fifth effective block map provided from the effective block reset unit 9 by one frame time to obtain a sixth effective block map. The sixth effective block map obtained by the frame delay unit 10 is provided to the weighting unit 3. The weighting unit 3 performs the second weighting on the sixth effective block map provided from the frame delay unit 10 and provides the weighted fourth effective block map to the adder 4. . The delay unit 11 performs delay time compensation for the input moving image signal from when the input moving image signal is supplied to when the fourth effective block map is supplied to the encoding unit 7, and outputs the fourth effective block map. And the input moving image signal. The time-compensated video signal output from the delay unit 11 is provided to the encoding unit 7. The encoding unit 7
The moving image signal given from the delay 11 is coded only for the effective block area in the fourth effective block map provided from the isolated invalid block removing unit 6, that is, for the portion indicated as the speaker area. , The background portion indicated by the invalid block is not coded.

As a coding method, a method using correlation between screens such as motion compensation, a method using correlation within a screen such as orthogonal exchange, or an encoding method using correlation between both screens and within a screen Is used.

For each of the threshold values and the reference block arrangement, an optimal value statistically checked in advance is used. As an example,
When the effective weight of the current frame is set to 2 and the invalid block is set to 0 by the first weight, and the valid block of the previous frame is set to 1 and the invalid block is set to 0 by the second weight, the second block is set.
Is set to 8 and the third threshold is set to 5.

(Effects of the Invention) As described in detail above, the moving picture signal encoding method according to the present invention encodes only the speaker region obtained by the segmentation, so that wasteful noise caused by background noise is generated. Information can be deleted, and coding efficiency can be improved.

[Brief description of the drawings]

FIG. 1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, and FIG. 6 are diagrams for explaining the operation of the present invention, and FIG. 1 valid / invalid determination unit 2,3 weighting unit 4, adder 5, segmentation unit 6, isolated invalid block removal unit 7, coding unit 8, effective block Number judging section, 9 effective block reset section, 10 frame delay section, 11 delay section.

Claims (1)

(57) [Claims] In a moving picture signal encoding method utilizing correlation between screens, one screen of an input moving picture signal is divided into blocks composed of a plurality of pixels, and a difference from a previous screen is detected for each block. When the difference value is equal to or greater than a predetermined first threshold, a first effective block map is created for each frame as an invalid block when the difference value is less than a first threshold. Means, means for performing a first weighting on the first effective block map, means for performing a second weighting on a sixth effective block map in the previous screen, and the first weighting Means for obtaining a weighted second effective block map by adding and combining the first effective block map having been subjected to the above and the sixth effective block map having been subjected to the second weighting; 2 for the effective block map, refer to the blocks near each block, and when the total value of the values of the neighboring blocks and the target block is equal to or greater than a predetermined second threshold, set the target block as an effective block; When the value is smaller than the second threshold value, the target block is segmented as an invalid block,
Means for obtaining an effective block map, and referring to a nearby block for an invalid block in the third effective block map, and when the total value of the neighboring blocks is equal to or more than a predetermined third threshold value, Means for obtaining a fourth valid block map by replacing the block with a valid block and leaving the invalid block as an invalid block when the value is less than a third threshold value, and the number of valid blocks in the fourth valid block map is predetermined. If it is equal to or greater than the fourth threshold, all effective blocks of the fourth effective block map are replaced with invalid blocks to form a fifth effective block map,
When the number of effective blocks in the fourth effective block map is less than a predetermined fourth threshold value, the fourth effective block map is used as it is as a fifth effective block map; Means for delaying the block map by one frame time to obtain a sixth effective block map;
Means for giving a delay of the time from the input of the video signal to the generation of the fourth effective block map to the video signal, and for the video signal given a delay,
Means for coding a region determined as an effective block in the fourth effective block map using a correlation between screens, a correlation within a screen or both of them. method.