JP2001309391A - Decoder for moving image and method for decoding moving image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a moving image decoder which is high in error resistance. SOLUTION: A code string includes DCT coefficient information obtained by quantizing a predictive residual signal being the error signal of an inputted moving image signal and a predictive signal generated by predicting each of plural block obtained by dividing an input image forming the input moving image signal, by using a prediction mode selected from plural prediction modes including a motion compensation prediction mode and an in-frame prediction mode, the code string is obtained by gathering DC component information and AC component information on a DCT coefficient concerning each block respectively by plural blocks and multiplexing the DC component information on the DCT coefficient in the neighborhood of information showing the prediction mode concerning each block compared with the AC component information and the code string is inputted and decoded to reproduce the original moving image signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving picture decoding apparatus and a moving picture decoding method for decoding a compressed coded signal to reproduce an original moving picture signal, and more particularly to an error in a transmission path / storage medium. TECHNICAL FIELD The present invention relates to a video decoding apparatus and a video decoding method which are strong in a video.

[0002]

2. Description of the Related Art A video signal is transmitted / received in a TV telephone, a TV conference system, a portable information terminal, a digital video disk system, a digital TV broadcast system, and the like.
In a storage system, a moving image signal is compression-encoded to the smallest possible amount of information, a code string as an obtained compression-encoded signal is transmitted / stored on a transmission path / storage medium, and the transmitted / stored code string is transmitted. The original video signal is reproduced by decoding.

Techniques such as motion compensation, discrete cosine transform (DCT), sub-band coding, and pyramid coding, and a combination thereof, are used as compression coding techniques for video signals applied to such a system. Various schemes have been developed. In addition, ISO / MPEG1, MPEG2, ITU-
T.H. 261, H .; 262 are defined. All of these coding systems are based on a combination of motion-compensated adaptive prediction and discrete cosine transform, and are described in Hiroshi Yasuda, "International Standard for Multimedia Coding," Maruzen, eds. (June) and the like.

By the way, when a code string obtained by coding a moving picture signal in this way is transmitted / stored through a medium in which an error is likely to occur, such as a radio transmission path, an image reproduced on a decoding side is required. A signal may be deteriorated due to an error in transmission / storage. As a countermeasure against such errors,
For example, under the condition that a code string can be transmitted through a plurality of transmission paths having different error probabilities, the code string is divided into several layers in order to reduce the image quality degradation due to errors, and the code string in the upper layer is more likely to have a higher error probability. Hierarchical coding schemes for performing transmission on a transmission path with a low transmission rate are known. To separate the hierarchy,
A method has been proposed in which mode information, motion compensation information, a low frequency component of an image signal is set as an upper layer, and a high frequency component of an image signal is set as an upper layer.

[0005] As an example of a conventional hierarchical video coding device, a video coding device using motion compensated adaptive prediction and DCT will be described with reference to FIG. In FIG. 5, an input video signal 11 is first subjected to prediction by a prediction circuit 12. The prediction circuit 12 detects a motion vector between the input video signal 11 and a reference video signal already stored in the frame memory 13 and obtained by encoding / local decoding, and based on this motion vector, Motion compensation prediction is performed for each predetermined unit area (referred to as a prediction area), and a motion compensation prediction signal is created.

The prediction circuit 12 has a motion compensation prediction mode (inter-frame prediction mode) and an intra-frame prediction mode for encoding the input moving image signal 11 as it is. From these prediction modes, a mode optimal for encoding is determined. Then, a prediction signal 14 corresponding to each mode is output. That is, the prediction circuit 12 outputs the motion compensation prediction signal as the prediction signal 14 in the motion compensation prediction mode and “0” in the intra-frame prediction mode.

The subtractor 15 subtracts the prediction signal 14 from the input video signal 11 to obtain a prediction residual signal 16.
Is generated. The prediction residual signal 16 is subjected to discrete cosine transform by a discrete cosine transform (DCT) circuit 17 in units of blocks of a fixed size, and becomes DCT coefficient information 18. The DCT coefficient information 18 is quantized by a quantization circuit 19. The prediction signal 14 is "0" in the intra-frame prediction mode.
Therefore, the input video signal 11 is output from the subtracter 15 as the prediction residual signal 16 as it is.

[0008] The quantized DCT from the quantization circuit 19
The coefficient information 20 is bifurcated, and is variable-length coded by a first variable-length coding circuit 21 on the one hand and inverse-quantized by an inverse quantization circuit 22 on the other hand. The output of the inverse quantization circuit 22 is subjected to inverse discrete cosine transform by an inverse discrete cosine transform (inverse DCT) circuit 23. That is, the inverse quantization circuit 2
2 and the inverse DCT circuit 23, the quantization circuit 19 and D
The inverse processing of the CT circuit 17 is performed, and a signal similar to the prediction residual signal 16 is obtained at the output of the inverse DCT circuit 23.
The output of the inverse DCT circuit 23 is added to the prediction signal 14 from the prediction circuit 12 in the addition circuit 24, and a local decoded signal 25 is generated. This local decoded signal 25 is stored in the frame memory 13 as a reference image signal.

A prediction mode / motion vector information 26 is output from the prediction circuit 12 as information relating to prediction, and is subjected to variable length coding by a variable length coding circuit 27. The code strings output from the variable length coding circuits 21 and 27 are multiplexed by the multiplexer 30 and divided into an upper layer code string 31 and a lower layer code string 32, which are output to a transmission line / storage medium (not shown). You. That is, the upper layer code sequence 31 is output to a transmission line / storage medium where the probability of error due to transmission / storage is relatively low, and the lower layer code sequence 32 is output to a transmission line / channel where the probability of error due to transmission / storage is relatively high. Output to the storage medium.

Here, the separation of the upper-layer code sequence 31 and the lower-layer code sequence 32 by the multiplexer 30 is performed by, for example, a mode representing the prediction mode in the prediction circuit 12 from the variable length coding circuit 22 as shown in FIG. Information, motion vector information (MV) and low-frequency DCT coefficient information of the variable-length coded DCT coefficient information from the variable-length coding circuit 21 The remaining high-frequency DCT coefficient information of the long-coded DCT coefficient information is applied to the lower layer code sequence 32.

[0011] Such a conventional hierarchical video coding apparatus has the following problems. First, if an error occurs, the image quality is greatly degraded.Since there is only one motion vector information for each prediction region, if an error occurs in the motion vector information, no motion information can be decoded for that prediction region. That is, the image quality is greatly deteriorated. In order to reduce such image quality deterioration, FIG.
As shown in (a), all motion vector information (MV) may be applied to the upper layer code sequence 31. However, in general, there is a limit to the ratio that the code amount of the code sequence of each layer can take in the total code amount of the code sequence of all layers, and when all the motion vector information is included in the upper layer code sequence 31, May exceed this limit. If the motion vector information is applied to the lower hierarchical code sequence 32 in order to prevent this, a problem occurs that error resilience is greatly reduced.

Further, the transmitted / stored code strings 31, 32
Are composed of variable-length codes created by the variable-length encoding circuits 21 and 27, the variable-length codes may be out of synchronization during decoding due to errors.
However, in the conventional video encoding apparatus, as shown in FIG. 6, important predictions such as mode information and motion vector information in which the decoded image is greatly degraded when an error occurs are shown in the code strings 31 and 32 of each layer. Related information and the DCT of the prediction residual signal that does not cause much degradation even if an error occurs.
Coefficient information and the like are mixed and multiplexed. For this reason, if synchronization is lost during decoding of a codeword carrying insignificant information, an error may propagate to the codeword carrying important information, resulting in a large degradation in the decoded image. Cause. In such a case, since the synchronization cannot be recovered until the synchronization code appears, all the information of the decoded image up to that point becomes erroneous and a large deterioration occurs over a wide area in the screen. is there.

[0013]

As described above, in the conventional moving picture coding apparatus, information relating to prediction, such as motion vector information, which greatly degrades the quality of a decoded picture when an error occurs, is used for each prediction. Since only one code is encoded for each area, error resilience is low.

In order to improve the error resilience, all information relating to prediction must be transmitted / stored by a transmission line / storage medium having a low error probability. Since there is a limit to the ratio that can be taken in the total code amount of the column, a plurality of transmission paths /
By transmitting / accumulating a code string using a storage medium, a problem arises in that the characteristic of hierarchical encoding that mitigates image quality degradation due to errors cannot be utilized.

Further, in the conventional video coding apparatus, since relatively important information such as information relating to prediction and other relatively unimportant information are mixed and included in a code string, There has been a problem that an error caused by non-important information has an influence on important information and causes a large deterioration in image quality.

Accordingly, an object of the present invention is to provide a moving picture decoding apparatus and a moving picture decoding method having high error resilience.

[0017]

In order to solve the above-mentioned problems, the present invention provides an input video signal and a motion compensation prediction mode for each of a plurality of blocks obtained by dividing an input image constituting the input video signal. A prediction is performed in a prediction mode selected from a plurality of prediction modes including a prediction mode, and a quantized DCT of a prediction residual signal which is an error signal from the prediction signal
Means for inputting a code string including coefficient information, wherein (1)
When the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficient relating to each block are collected for a plurality of blocks, respectively, and the DCT coefficient of the DCT coefficient is collected.
Means for inputting a code string in which component information is multiplexed closer to information indicating a prediction mode relating to each block than the AC component information; (2) DCT relating to each block when the intra-frame prediction mode is selected Means for combining the DC component information of the coefficients and the AC component information for each of a plurality of blocks, and inputting a code string obtained by multiplexing the DC component information of the DCT coefficients adjacent to information indicating a prediction mode relating to each block; (3) When the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficients related to each block are collected for a plurality of blocks, respectively, and the D
Means for inputting a code string in which DC component information of CT coefficients is arranged closer to information indicating a prediction mode relating to each block than the AC component information; (4) when an intra-frame prediction mode is selected, Of DCT coefficient related to
Means for combining C component information and AC component information for a plurality of blocks, respectively, and inputting a code string in which the DC component information of the DCT coefficient is arranged adjacent to information indicating a prediction mode relating to each block; (5) intra-frame prediction When a mode is selected, DC component information of DCT coefficients relating to a plurality of blocks is multiplexed as a code string having relatively high importance near information indicating a prediction mode relating to each block, and DCT coefficients relating to a plurality of blocks are multiplexed. Means for inputting a code string multiplexed after the AC component information as a code string of relatively low importance, (6) DC component information of DCT coefficients relating to a plurality of blocks when an intra-frame prediction mode is selected Is multiplexed adjacent to information indicating a prediction mode related to each block as a code string having relatively high importance, and a DC related to a plurality of blocks is multiplexed. Means for inputting a multiplexed code string by separating the AC component information of the coefficient as a code string having relatively low importance, (7) indicating a prediction mode relating to a plurality of blocks when the intra-frame prediction mode is selected Information and DC
Means for arranging the DC component information of the T coefficient as a code string of relatively high importance, and inputting a code string in which the AC component information of the DCT coefficient relating to a plurality of blocks is arranged as a code string of relatively low importance; 8) When the intra-frame prediction mode is selected, information indicating the prediction mode relating to a plurality of blocks and DC component information of the DCT coefficient are generated as a code string having relatively high importance, and the DCT coefficient relating to the plurality of blocks is generated. A means for inputting a code string in which the AC component information is generated as a code string having relatively low importance; and a means for decoding the input code string and reproducing the original moving image signal. And

According to the present invention, an input video signal and a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode are selected for each of a plurality of blocks obtained by dividing the input image constituting the input video signal. (1) a code string including quantized DCT coefficient information of a prediction residual signal, which is an error signal from a prediction signal obtained by performing prediction in a prediction mode,
When the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficient relating to each block are collected for a plurality of blocks, respectively, and the DCT coefficient of the DCT coefficient is collected.
A code string in which the component information is multiplexed closer to the information indicating the prediction mode related to each block than the AC component information,
(2) When the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficients related to each block are grouped into a plurality of blocks, respectively, and the DC component information of the DCT coefficients is set to the prediction mode related to each block. (3) When the intra-frame prediction mode is selected, the DC related to each block is selected.
A code sequence in which the DC component information of the T coefficient and the AC component information are grouped into a plurality of blocks, respectively, and the DC component information of the DCT coefficient is arranged closer to the information indicating the prediction mode related to each block than the AC component information; ) When the intra-frame prediction mode is selected, DC related to each block
A code string in which the DC component information of the T coefficient and the AC component information are grouped into a plurality of blocks, and the DC component information of the DCT coefficient is arranged adjacent to information indicating a prediction mode relating to each block; Is selected, DC component information of DCT coefficients relating to a plurality of blocks is multiplexed as a code string having relatively high importance near information indicating a prediction mode relating to each block, and AC of DCT coefficients relating to a plurality of blocks is multiplexed. (6) a code string obtained by multiplexing the component information as a code string having relatively low importance,
When the intra-frame prediction mode is selected, DC component information of DCT coefficients relating to a plurality of blocks is multiplexed as information having a relatively high importance adjacent to the information indicating the prediction mode relating to each block, and is multiplexed into a plurality of blocks. DCT involved
A code string obtained by separating AC component information of a coefficient as a code string having relatively low importance and multiplexing it. (7) Information indicating a prediction mode relating to a plurality of blocks and a DCT coefficient when an intra-frame prediction mode is selected And (8) an intra-frame prediction mode in which the DC component information is arranged as a code string having relatively high importance, and the AC component information of the DCT coefficients relating to a plurality of blocks is arranged as a code string having relatively low importance. Is selected, the information indicating the prediction mode relating to the plurality of blocks and the DC component information of the DCT coefficient are generated as a code string having relatively high importance, and the DC related to the plurality of blocks is generated.
The method is characterized in that any one of the code sequences generated as the code sequence having relatively low importance as the AC component information of the T coefficient is input, and the code sequence is decoded to reproduce the original moving image signal.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of a moving picture coding apparatus according to the present invention, and shows an example in which the present invention is applied to a moving picture coding apparatus combining motion compensation adaptive prediction and DCT.

In FIG. 1, an input moving image signal 101 is first subjected to prediction by a prediction circuit 102. That is, the prediction circuit 102 detects a motion vector between the input video signal 101 and the reference video signal already stored in the frame memory 103 and obtained by encoding / local decoding, and based on this motion vector, Thus, a motion compensation prediction signal is created. The prediction circuit 102 has a motion compensation prediction mode (inter-frame prediction mode) and an intra-frame prediction mode for encoding the input video signal 101 as it is. Is output. That is, the prediction circuit 102 outputs a motion compensation prediction signal as the motion compensation prediction signal in the motion compensation prediction mode and “0” as the prediction signal 104 in the intra-frame prediction mode.

In the subtracter 105, the input moving image signal 101
Is subtracted from the prediction signal 104 to generate a prediction residual signal 106. The prediction residual signal 106 is subjected to discrete cosine transform by a discrete cosine transform (DCT) circuit 107 in units of blocks of a fixed size, and becomes DCT coefficient information 108. The DCT coefficient information 108 is quantized by a quantization circuit 109. In the intra-frame prediction mode, since the prediction signal 104 is “0”, the subtracter 105
From the input video signal 101 as the prediction residual signal 106.
Is output as is.

The quantized DC from the quantization circuit 109
The T-coefficient information 110 is split into two branches, one of which is variable-length encoded by a first variable-length encoding circuit 111 and the other is inversely quantized by an inverse quantization circuit 112. The output of the inverse quantization circuit 112 is an inverse discrete cosine transform (inverse DCT) circuit 1
13 performs an inverse discrete cosine transform. That is, in the inverse quantization circuit 112 and the inverse DCT circuit 113, processing opposite to that of the quantization circuit 109 and the DCT circuit 107 is performed.
A signal approximating the prediction residual signal 106 is obtained at the output of the inverse DCT circuit 113. The output of the inverse DCT circuit 113 is added to the prediction signal 10 from the prediction circuit 102 by the addition circuit 114.
4 and a local decoded signal 115 is generated. The local decoded signal 115 is stored in the frame memory 103 as a reference image signal.

As will be described later, the prediction circuit 102 outputs large area prediction mode / motion vector information 116 and small area prediction mode / motion vector information 117 as information relating to prediction, and the variable length coding circuits 118 and 11
9 are respectively subjected to variable length coding. The code strings output from the variable length coding circuits 111, 118, and 119 are multiplexed by the multiplexer 120, and the upper layer code string 121 and the lower layer code string 122 are multiplexed.
And output to a transmission path / storage medium (not shown).

Here, under the condition that a code string can be transmitted / stored through a plurality of transmission paths / storage media having different error probabilities, the transmission path with a lower error probability is used for the upper layer code string 121. By transmitting / accumulating via a transmission / accumulation medium and transmitting / accumulating the lower layer code string 122 via a transmission path / storage medium having a higher error probability, the upper layer code string Is difficult to occur. When error correction coding is performed on the coded sequences 121 and 122, stronger error correction is performed so that the upper layer coded sequence 121 has a lower error rate than the lower layer coded sequence 122. Perform encoding.

Next, the configuration and operation of the prediction circuit 102 will be described in detail with reference to FIG. The prediction circuit 102 sequentially divides the input video signal 101 into more and more regions from the upper stage to the lower stage, and performs motion compensation prediction on the input video signal for each of the regions divided at each stage. Generate a prediction signal. In the example of FIG. 2, the region division and prediction in the prediction circuit 102 are performed in two stages. That is, in the first stage, the prediction circuit 102 divides the input video signal 101 into large areas as shown by solid-line areas (referred to as large areas) in FIG. 2 and performs motion compensation prediction with coarse pixel accuracy on these large areas. Next, in the second stage, the large area is further divided as necessary, as indicated by the broken line area (small area) in the figure, and motion compensation prediction is performed on these small areas with fine pixel accuracy.

Then, the variable length coding circuits 118 and 119
Thus, not only the information about the prediction for the large region output from the prediction circuit 102 but also the information about the prediction for the large region for the small region is encoded. By doing in this way, even if the information about the prediction for the small area is lost due to an error, the decoding apparatus can perform the prediction with rough accuracy if the information about the prediction for the large area is decoded without error. This can prevent significant deterioration in the image quality of the decoded image.

The information relating to prediction output from the prediction circuit 102 includes information indicating a prediction mode and information indicating a motion vector. The information indicating the prediction mode of the large area and the information indicating the motion vector (indicated by a solid arrow in FIG. 2), that is, the large area prediction mode / motion vector information 116 are variable-length coded by the variable-length coding circuit 118. . At this time, with respect to the motion vector information, the difference from the motion vector information of the adjacent already coded large area may be variable-length coded, or may be fixed-length coded without taking the difference. Alternatively, the motion vector information may be fixed-length coded for each region at a certain interval, and the variable vector may be coded for the motion vector information in other regions.

On the other hand, the information indicating the prediction mode of the small area and the information indicating the motion vector (indicated by a broken arrow in FIG. 2), that is, the small area prediction mode / motion vector information 117 are:
The variable length coding circuit 119 performs variable length coding. In this case, the difference between the motion vector information and the large area motion vector information may be obtained for each small area and variable-length coding may be performed, or block coding, vector quantization, etc. may be collectively performed for each large area. Encoding may be performed. In the case where the difference value is variable-length coded, if a large area motion vector can be represented by a reversible function (for example, an average value) based on the small area motion vector, one of the small area motion vectors is large. Since it can be obtained by calculation based on the area motion vector and other small area motion vectors, there is no particular need for encoding.

FIG. 3 shows an example of the structure of the upper layer code string 121 and the lower layer code string 122. FIG.
In the upper layer code sequence 121 shown in (a), a synchronous code that can be uniquely decoded is inserted at the beginning of each encoded frame or a certain region. PSC indicates a frame-based synchronization code. A picture header indicating the encoding information of the frame is attached after the synchronization code PSC.
The picture header includes a frame number indicating a temporal position of the frame, information indicating a prediction mode of the frame (mode information), and information indicating a length of a code string of each of an upper layer and a lower layer of the frame (code amount). Consists of

Further, as shown in FIG. 3A, if information (large area MC precision, small area MC precision) indicating the size of the large area and the small area and the pixel precision of the motion compensation is added to the picture header, the motion It is possible to control the code amount of the motion vector information by varying the compensation accuracy on a frame basis. Accordingly, even when the ratio of the code amount of the upper layer code sequence 121 to the code amount of the lower layer code sequence 122 is defined by the restrictions of the transmission path / storage medium, etc., the code amount distribution corresponding to the ratio is possible. In addition, since the total code amount of the motion vector information of each frame can be controlled, it is possible to select the optimal motion compensation accuracy in view of the relationship between the motion compensation accuracy and the code amount of the motion vector information. Efficiency can be improved.

It is characteristic that the coded information of each area is arranged in order from the information having the highest importance behind the picture header of the upper layer code sequence 121 shown in FIG. Here, the information having a high degree of importance is information that causes a large deterioration in a decoded image when an error occurs. That is, after the picture header of the upper layer code sequence 121, first, information (mode information) indicating the prediction mode with the highest importance, that is, the large area prediction mode / motion vector information 116 output from the prediction circuit 102 and the small The code string of the prediction mode information among the code strings obtained by coding the area prediction mode information 117 by the variable length coding circuit 118 is entered.

Next, the DC component (intra DC) of the DCT coefficient information in the region where the intra-frame prediction mode is selected, that is, the DCT coefficient information obtained by passing the prediction residual signal 106 through the DCT circuit 107 and the quantization circuit 109 is varied. DC of the code sequence obtained by encoding in the length encoding circuit 111
Enter the code sequence of the component. Further, in an area where the motion compensation prediction mode is selected, large area motion vector information (large area MV) indicating rough motion information, that is, the prediction circuit 102
Region prediction mode / motion vector information 1 output from
The code sequence of the motion vector information in the code sequence obtained by encoding 16 in the variable length encoding circuit 118 is entered.

On the other hand, the lower hierarchical code string 1 shown in FIG.
22, the motion vector information (small area MV) of the small area,
That is, the code sequence of the motion vector information of the code sequence obtained by encoding the small area prediction mode / motion vector information 117 output from the prediction circuit 102 by the variable length coding circuit 119 is inserted, and the DCT is further added thereto. The high frequency component of the coefficient information, that is, the prediction residual signal
The variable-length encoding circuit 111 encodes the DCT coefficient information obtained through the quantization circuit 109, and inserts a high-frequency component code sequence among the code sequences obtained.

As described above, the motion compensation prediction is performed in a hierarchical manner, and the mode information indicating the prediction mode and the large area motion vector information indicating the rough prediction information are stored in the upper layer code string 121.
And the detailed motion vector information is
2 respectively. Therefore, even if the small area motion vector information included in the lower layer code sequence 122 is lost due to an error in the transmission path / storage medium, the moving picture decoding apparatus uses the large area motion vector information included in the upper layer code sequence 121. , Motion compensation prediction can be performed with rough accuracy, so that the probability of significant image quality degradation occurring in a decoded image can be reduced.

Further, in this embodiment, since the code strings are arranged in the order of important information even in the upper and lower hierarchical code strings 121 and 122, errors caused by non-important information may spread to important information. , And significant image quality degradation can be prevented.

Next, an embodiment of the moving picture decoding apparatus according to the present invention will be described. FIG. 4 is a block diagram showing a configuration of a video decoding device corresponding to the video encoding device of FIG.

In FIG. 4, an upper layer code string 121 and a lower layer code string 122 output from the moving picture coding apparatus shown in FIG. 1 have an upper layer code string 201 and a lower layer code string input via a transmission line / storage medium. The hierarchical code sequence 202 is separated by a demultiplexer 203 into a variable length code 204 for quantized DCT coefficient information, a variable length code 205 for large area prediction mode / motion vector information, and a variable length code 206 for small area prediction mode / motion vector information. After that, they are input to the variable length decoding circuits 207, 208 and 209, respectively.

The variable length decoding circuit 207 has a variable length code 2
04 is subjected to variable length decoding to output quantized DCT coefficient information 210. This quantized DCT coefficient information 210
Is inversely quantized by an inverse quantization circuit 213, and further subjected to inverse discrete cosine transform by an inverse DCT circuit 214 to generate a prediction residual signal 215. The prediction residual signal 215 is added by the addition circuit 216 to the prediction signal 219 from the prediction circuit 217 to generate a reproduced image signal 221. The reproduced image signal 221 is output to the outside of the video decoding device, and is stored in the frame memory 218 as a reference image signal.

On the other hand, in the variable length decoding circuits 208 and 209, large area prediction mode / motion vector information 211 and small area prediction mode / motion vector information 212 are variable length decoded from the variable length codes 205 and 206. These pieces of information 211 and 212 are input to the prediction circuit 217. The prediction circuit 217 calculates the reference image signal stored in the frame memory 218 and the large area prediction mode / motion vector information 2
11 and small area prediction mode / motion vector information 212
, And a prediction signal 219 is generated.

The error judgment circuit 220 includes a demultiplexer 203 and variable length decoding circuits 207, 208, and 209.
, The presence / absence of an error in the upper layer code sequence 201 and the lower layer code sequence 202 is determined, and the determination result is provided to the prediction circuit 217. When the error determination circuit 220 does not detect any error in any of the upper and lower hierarchical code strings 201 and 202, the prediction circuit 217 performs the processing shown in FIG. 1 based on the reference image signal stored in the frame memory 218.
And outputs the same predicted signal 219 as the predicted signal 104 in.

The above processing is processing for reproducing an image signal corresponding to the moving picture coding apparatus shown in FIG. 1, and processing performed by the inverse quantization circuit 213, the inverse DCT circuit 214, the addition circuit 216, and the frame memory 218. Are respectively the inverse quantization circuit 112, the inverse DCT circuit 113, and the addition circuit 11 in FIG.
4. The processing is basically the same as that of the frame memory 103. Also, the variable length decoding circuits 207, 208, 209,
The multiplexer 203 includes the variable length coding circuits 111, 118, and 119 in FIG.
The reverse process of the process 20 is performed.

On the other hand, when an error is detected in at least one of the upper and lower hierarchy code strings 201 and 202 by the error determination circuit 220, for example, information having a higher importance than the information in which the error is detected is as follows. A reproduction image is created using the reproduction image.

That is, (1) When an error is detected in the DCT coefficient information of a block in the lower layer code sequence 122 which has been subjected to motion compensation prediction, the prediction residual signal of the block is set to 0 and decoding is performed correctly. A reproduced image signal 221 is obtained as a motion compensated prediction signal obtained using the converted mode information, large area motion vector information and small area motion vector information as a prediction signal 219.

(2) If an error occurs in the small area motion vector information, the motion compensation prediction signal obtained using the large area motion vector information is used as the prediction signal 219 for the small area. 221 is obtained.

(3) When an error occurs in the large area motion vector information, the motion compensation prediction of the large area is performed based on the motion vector information of the surrounding area or the already decoded frame. When possible, the estimated value is used. When an error occurs in the surrounding motion vector information, the image signal of the already decoded frame is used as the reproduced image signal 221 as it is.

(4) If an error occurs in the AC component of the DCT coefficient information of the block for which the intra-frame prediction mode has been selected, the DC component of the DCT coefficient information and the correctly decoded image signal of the surrounding block are used to determine the error. The image signal of the block is predicted to be a reproduced image signal 221, or the image signal of the block is predicted from the image signal of the already decoded frame by using the prediction signal of the image signal of the surrounding block correctly decoded. To be a reproduced image signal 221.

When a variable-length code is used to encode various information, an out-of-synchronization occurs due to an error, and the error may propagate to a succeeding code until synchronization is recovered by detecting a synchronization code. In such a case, the subsequent code is not used for decoding. For example, the lower layer code sequence 12
2, when an error occurs in the small area motion vector information, the error may propagate to the motion vector information after the small area and the DCT coefficient information following the error. In such a case, the error is propagated. Is not used for decryption. Even when such out-of-synchronization occurs, codewords are arranged in the code string in the order of importance, so that errors caused by information of low importance can spread to information of high importance. In addition, it is possible to prevent significant deterioration of the reproduced image.

Code strings 201 and 202 are determined by error determination section 220.
The following method can be given as a specific method for detecting that an error has occurred.

The first is a method using an error detection code such as a parity code and a CRC code. In this case, error detection encoding is performed on the variable-length code in the multiplexer 120 of the video encoding device illustrated in FIG. 1, and error detection processing is performed in the demultiplexer 203 of the video decoding device illustrated in FIG. The detection result is provided to the error determination unit 220.

Second, the variable length decoding circuits 207 and 20
8, 209, when a codeword that does not exist in the codeword table indicating the correspondence between the input codeword and the output value is detected, it is determined to be an error. In particular, when a variable-length code is used, errors may spread not only in the part where the error is detected but also in the code string before and after the part where the error is detected. Perform processing.

Third, a motion vector information, a prediction signal, DCT coefficient information, a prediction residual signal, a reproduced picture signal, etc., which cannot be generated in the encoding of a moving picture, based on the decoded codeword. This is a method of making an error determination by determining whether or not. The use of this method is characteristic of the present invention, and will be described in more detail.

For example, if the motion vector indicated by the motion vector information exceeds a predetermined search range or extends off the screen, it is determined that an error has occurred.

An error can be detected by judging the DCT coefficient information dequantized by the dequantization circuit 213. The possible range of the pixel value of the input image signal 101 is 0 to D-1, and the DCT block size is N ×
Assuming N, the DCT coefficient takes a value within the following range.

<Intra-frame prediction mode> DC component: 0 to N × D AC component: − (N / 2 × D) to (N / 2 × D) <Inter-frame prediction mode> − (N / 2 × D) （(N / 2 × D) Therefore, if the value of the decoded DCT coefficient takes a value outside this range, it is determined that an error has occurred. In this case, all or some of the blocks in which an error is detected
The CT coefficient may be set to 0, or the decoded value may be estimated from the decoded values of the surrounding blocks.

Further, it is possible to determine an error based on the pixel value of the reproduced image signal 221. Assuming that the possible range of the pixel value of the input image signal 101 is 0 to D−1, the DCT block size is N × N, and the quantization width is Q (in the case of linear quantization), the pixel value of the reproduced image signal 221 is obtained. The obtainable range is −N × Q to D + N × Q. Therefore, if the pixel value of the decoded reproduced image signal 221 exceeds this range, it is determined that an error has occurred. In this case, for example, in the inter-frame prediction mode (motion compensation prediction mode), the prediction residual signal 215 is set to “0”, and in the intra-frame prediction mode, a part of the DCT coefficients input to the inverse DCT circuit 214 is set to “0”. The inverse DCT is performed to obtain the reproduced image signal 221 or the reproduced image signal 2
What is necessary is just to estimate from the pixel value of the block around 21.

As described above, according to the present invention, in the error judgment by the error judgment unit 220 in the moving picture decoding apparatus, it is determined whether or not the reproduced information or signal is an information or signal that cannot be generated in the transmission path / storage medium. By adding such a determination, more accurate error determination can be performed. For this reason, it is possible to suppress deterioration in the quality of a reproduced image caused by using the erroneous information or signal for reproducing the moving image signal without performing error processing.

The present invention can be implemented with various modifications. For example, in the above-described embodiment, an example has been described in which a code string output from a video encoding device is divided into two layers, but encoding may be performed in three or more layers. For example, the frame synchronization code (PSC), the picture header, and the mode information are set as the highest first layer, and the DC in the intra-frame prediction mode is set.
The DC component (intra DC) of the T coefficient information and the large area motion vector information are on the second layer, and the small area motion vector information is on the third layer.
DC other than DCT coefficient information allocated to the first layer and the first layer
T coefficient information may be assigned to each of the fourth layers. Further, the DCT coefficient may be further divided into several layers such as a low-frequency component and a high-frequency component for encoding.

In the coding of the large area motion vector information, the difference between the motion vector information to be subjected to the fixed length coding as described above and the motion vector information to be subjected to the fixed length coding is obtained by the variable length coding. When encoding is performed in two types of vector information, fixed-length coded motion vector information in which an error does not spread to a subsequent code sequence due to loss of synchronization is grouped into a frame or a certain area unit, and is firstly performed. It is effective to insert the motion vector information after the variable length coding. In this way, even if an error occurs in the variable length coded part and the synchronization is lost, the error does not propagate to the variable length coded motion vector information. Since it is possible to estimate a motion vector in which an error has occurred based on the obtained motion vector information and generate a prediction signal with rough accuracy, it is possible to reduce deterioration in the image quality of a reproduced image due to an error.

The method of determining whether or not the information reproduced by the moving picture decoding apparatus shown in FIG. 4 is information that cannot occur in moving picture coding is not limited to a hierarchically coded code string. The present invention can also be applied to a moving image decoding device that decodes an original image signal from a code sequence obtained by a general moving image encoding device.

[0060]

As described above, according to the present invention, there is provided a moving picture decoding apparatus and a moving picture decoding apparatus which have high error resilience, that is, a picture quality of a decoded picture which is less deteriorated due to an error generated when transmitting / accumulating a coded stream. A decoding method can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a moving picture coding apparatus according to the present invention.

FIG. 2 is a diagram showing a motion compensation area and a motion vector corresponding to the motion compensation area in the moving picture coding apparatus of FIG.

FIG. 3 is a diagram showing an example of upper-layer and lower-layer code strings output from the video encoding device of FIG. 1;

FIG. 4 is a block diagram showing an embodiment of a video decoding device corresponding to the video encoding device of FIG. 1;

FIG. 5 is a block diagram showing an example of a conventional moving picture encoding device.

FIG. 6 is a diagram showing an example of a code string output from the moving picture coding device of FIG. 5;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 101 ... Input image signal 102 ... Prediction circuit 103 ... Frame memory 104 ... Prediction signal 105 ... Subtractor 106 ... Prediction residual signal 107 ... Discrete cosine transform circuit 108 ... DC
T coefficient information 109 quantization circuit 110 quantized DCT coefficient information 111 variable length coding circuit 112 inverse quantization circuit 113 inverse discrete cosine transform circuit 114 adder 115 local decoded signal 116 large area prediction mode / Motion vector information 117 ... small area prediction mode / motion vector information 118, 119 ... variable length coding circuit 120 ... multiplexer 121 ... upper layer code string 122 ... lower layer code string 201 ... upper layer code string 202 ... lower layer code string 203 ... Demultiplexer 204-20
6 Variable length codes 207 to 209 Variable length coding circuit 210 Quantized DCT coefficients 211 Large area prediction mode / motion vector information 212 Small area prediction mode / motion vector information 213 Inverse quantization circuit 214 Inverse discrete Cosine transform circuit 215 ... Predicted residual signal 216 ... Adder 217 ... Predicted circuit 218 ... Frame memory 219 ... Predicted signal 220 ... Error determination circuit 221 ... Reproduced image signal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeshi Taketake 1 Koga Toshiba-cho, Kochi-ku, Kawasaki-shi, Kanagawa Inside the Toshiba R & D Center (72) Inventor Takashi Ida Komukai, Kochi-ku, Kawasaki-shi, Kanagawa No. 1, Toshiba-cho, Toshiba R & D Center (72) Inventor Noboru Noguchi Yamaguchi No. 1, Komukai Toshiba-cho, Kawasaki-shi, Kanagawa, Japan Toshiba R & D Center (72) Inventor Ken Nakajo, Kawasaki-shi, Kanagawa No. 1, Komukai Toshiba-cho, Sachi-ku Inside Toshiba R & D Center

Claims (16)

[Claims] An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DCT of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code sequence including coefficient information, and when the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficients related to each block are grouped into a plurality of blocks, and the DC component information of the DCT coefficients is Means for inputting a multiplexed code string in the vicinity of information indicating a prediction mode relating to each block rather than the AC component information; and means for decoding the input code string to reproduce an original video signal. A moving picture decoding apparatus characterized in that: 2. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DCT of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code sequence including coefficient information, and when the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficients related to each block are grouped into a plurality of blocks, and the DC component information of the DCT coefficients is Means for inputting a multiplexed code string adjacent to information indicating a prediction mode relating to each block; and means for decoding the input code string and reproducing the original moving image signal. Moving image decoding apparatus. 3. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DCT of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code sequence including coefficient information, and when the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficients related to each block are grouped into a plurality of blocks, and the DC component information of the DCT coefficients is A means for inputting a code string arranged closer to information indicating a prediction mode relating to each block than the AC component information; and a means for decoding the input code string to reproduce an original video signal. A moving picture decoding apparatus characterized in that: 4. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DCT of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code sequence including coefficient information, and when the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficients related to each block are grouped into a plurality of blocks, and the DC component information of the DCT coefficients is Means for inputting a code string arranged adjacent to information indicating a prediction mode relating to each block; and means for decoding the input code string and reproducing the original video signal. Moving image decoding apparatus. 5. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DCT of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code sequence including coefficient information, wherein when the intra-frame prediction mode is selected, DC component information of DCT coefficients relating to a plurality of blocks is set as a code sequence having relatively high importance, and indicates a prediction mode relating to each block. Means for inputting a code string multiplexed in the vicinity of a plurality of blocks and converting the AC component information of DCT coefficients relating to a plurality of blocks into a code string having relatively low importance, and decoding the input code string to obtain Means for reproducing the moving image signal. 6. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DCT of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code sequence including coefficient information, wherein when the intra-frame prediction mode is selected, DC component information of DCT coefficients relating to a plurality of blocks is set as a code sequence having relatively high importance, and indicates a prediction mode relating to each block. Means for inputting a multiplexed code string by separating AC component information of DCT coefficients relating to a plurality of blocks as a code string of relatively low importance, and decoding the input code string Means for reproducing an original moving image signal. 7. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DCT of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code string including coefficient information, and when an intra-frame prediction mode is selected, information indicating a prediction mode relating to a plurality of blocks and DC component information of DCT coefficients are arranged as a code string having relatively high importance. , D involving multiple blocks
Means for inputting a code string in which AC component information of CT coefficients are arranged as a code string of relatively low importance; and means for decoding the input code string to reproduce the original moving image signal. A moving picture decoding apparatus characterized by the following. 8. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DCT of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
When the intra-frame prediction mode is selected, information indicating a prediction mode relating to a plurality of blocks and DC component information of DCT coefficients are generated as a code string having relatively high importance. , D involving multiple blocks
Means for inputting a code string in which the AC component information of the CT coefficient is generated as a code string of relatively low importance; and means for decoding the input code string and reproducing the original video signal. A moving picture decoding apparatus characterized by the following. 9. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DCT of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code sequence including coefficient information, and when the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficients related to each block are grouped into a plurality of blocks, and the DC component information of the DCT coefficients is A moving picture decoding method comprising: inputting a multiplexed code string in the vicinity of information indicating a prediction mode relating to each block rather than the AC component information; decoding the code string to reproduce an original moving picture signal; Method. 10. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DC of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code sequence including T coefficient information, wherein when the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficient relating to each block are grouped into a plurality of blocks, respectively, and the DC component information of the DCT coefficient is obtained. A multiplexed code string is input adjacent to information indicating a prediction mode related to each block, and the code string is decoded to reproduce an original moving image signal. 11. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DC of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code sequence including T coefficient information, wherein when the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficient relating to each block are grouped into a plurality of blocks, respectively, and the DC component information of the DCT coefficient is obtained. Is the AC
A moving picture decoding method comprising: inputting a code string arranged closer to information indicating a prediction mode relating to each block than component information; decoding the code string to reproduce an original moving picture signal. 12. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DC of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code sequence including T coefficient information, wherein when the intra-frame prediction mode is selected, the DC component information and the AC component information of the DCT coefficient relating to each block are grouped into a plurality of blocks, respectively, and the DC component information of the DCT coefficient is obtained. A code sequence arranged adjacent to information indicating a prediction mode relating to each block, and decoding the code sequence to reproduce an original video signal. 13. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DC of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
This is a code string including T coefficient information, and when the intra-frame prediction mode is selected, the DC component information of the DCT coefficient relating to a plurality of blocks is represented as a code string having relatively high importance, and the prediction mode relating to each block is indicated. A code string multiplexed in the vicinity of the information and AC component information of DCT coefficients relating to a plurality of blocks is input as a code string of relatively low importance, and a code string multiplexed behind the input is decoded. A video decoding method characterized by reproducing a signal. 14. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DC of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
This is a code string including T coefficient information, and when the intra-frame prediction mode is selected, the DC component information of the DCT coefficient relating to a plurality of blocks is represented as a code string having relatively high importance, and the prediction mode relating to each block is indicated. Multiplexed adjacent to the information, input the multiplexed code sequence by separating the AC component information of the DCT coefficients relating to a plurality of blocks as a code sequence having relatively low importance, and decode the code sequence to obtain the original moving image. A video decoding method characterized by reproducing an image signal. 15. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DC of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code string including T coefficient information, wherein when the intra-frame prediction mode is selected, information indicating a prediction mode relating to a plurality of blocks and DC component information of DCT coefficients are arranged as a code string having relatively high importance. A code sequence in which AC component information of DCT coefficients relating to a plurality of blocks is arranged as a code sequence of relatively low importance is input, and the code sequence is decoded to reproduce an original moving image signal. Video decoding method. 16. An input video signal and a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each of a plurality of blocks obtained by dividing an input image forming the input video signal. A quantized DC of a prediction residual signal, which is an error signal from the prediction signal after performing prediction.
A code string including T coefficient information, wherein when an intra-frame prediction mode is selected, information indicating a prediction mode relating to a plurality of blocks and DC component information of DCT coefficients are generated as a code string having relatively high importance. Then, a code sequence generated by generating AC component information of DCT coefficients relating to a plurality of blocks as a code sequence of relatively low importance is input, and the code sequence is decoded to reproduce an original video signal. Video decoding method.