JP2004007766A - Moving image coding device and moving image coding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a moving image coding device whose error resistance is high. <P>SOLUTION: This moving image coding device is provided with: a means for dividing an input image into a plurality of blocks; a means for performing in a prediction mode selected from a plurality of prediction modes including a motion compensation mode and an in-frame mode for each block to generate a prediction signal; a means for subjecting a prediction residual signal being an error signal between an input moving image signal to DCT(discrete cosine transformation) and a prediction signal to obtain DCT coefficients; a means for quantizing the DCT coefficients; and a multiplexing means for arranging information indicating the prediction mode of the frame in the picture header of each frame of the input image, putting together, for a plurality of blocks, information indicating the predication mode related to each block, motion vector information detected when the motion compensated prediction mode is selected and the information of the DCT coefficients related to each block behind the picture header, and arranging those pieces of information in the descending order of significance for multiplexing them. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a moving picture coding apparatus and a moving picture coding method for compressively coding a moving picture signal with high efficiency, and more particularly to a moving picture coding apparatus and a moving picture coding which are resistant to errors in a transmission path / storage medium. About the method.
[0002]
[Prior art]
2. Description of the Related Art In a system for transmitting / storing a moving image signal such as a TV phone, a TV conference system, a portable information terminal, a digital video disk system, and a digital TV broadcasting system, the moving image signal is compression-encoded to a minimum amount of information and obtained. The code sequence, which is the compression-encoded signal, is transmitted / stored in a transmission path / storage medium, and the transmitted / stored code sequence is decoded to reproduce the original moving image signal.
[0003]
Various techniques such as motion compensation, discrete cosine transform (DCT), sub-band coding, pyramid coding, and a combination of these techniques are available as compression coding techniques for video signals applied to such a system. Is being developed. In addition, ISO / MPEG1, MPEG2, ITU-T / H. 261, H .; 262 are defined. Each of these coding systems is a system based on a combination of motion compensated adaptive prediction and discrete cosine transform. Reference 1: edited by Hiroshi Yasuda, “International Standard for Multimedia Coding”, Maruzen, (1991 (June) and the like.
[0004]
By the way, when transmitting / accumulating a code sequence obtained by encoding a moving image signal in such a way as to cause an error-prone medium such as a wireless transmission path, the image signal reproduced on the decoding side is transmitted. / Degradation may occur due to an error during storage. As a countermeasure against such errors, for example, under a 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 to reduce image quality deterioration due to errors, and Hierarchical coding schemes for transmitting a hierarchical code string through a transmission path with a lower error probability are known. As a method of classifying layers, 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 encoding device, a video encoding 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.
[0006]
The prediction circuit 12 has a motion compensation prediction mode (inter-frame prediction mode) and an intra-frame prediction mode for encoding the input video signal 11 as they are, and selects an optimal mode for encoding from these prediction modes. , And outputs a prediction signal 14 corresponding to each mode. That is, the prediction circuit 12 outputs a motion compensation prediction signal as the motion compensation prediction signal in the motion compensation prediction mode and “0” as the prediction signal 14 in the intra-frame prediction mode.
[0007]
The subtractor 15 subtracts the prediction signal 14 from the input video signal 11 to generate a prediction residual signal 16. 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. Since the prediction signal 14 is “0” in the intra-frame prediction mode, the input video signal 11 is output from the subtracter 15 as the prediction residual signal 16 as it is.
[0008]
The quantized DCT coefficient information 20 from the quantization circuit 19 is bifurcated, one is variable-length encoded by a first variable-length encoding circuit 21, and the other is inversely quantized by an inverse quantization circuit 22. . 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, in the inverse quantization circuit 22 and the inverse DCT circuit 23, the inverse processing of the quantization circuit 19 and the DCT 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.
[0009]
The 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 path / storage medium (not shown). You. That is, the upper layer code string 31 is output to a transmission line / storage medium with a relatively low probability of occurrence of an error due to transmission / storage, and the lower layer code string 32 is output to a transmission line / path having a relatively high probability of an error due to transmission / storage. Output to the storage medium.
[0010]
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, the mode information indicating the prediction mode in the prediction circuit 12 from the variable-length coding circuit 22 as shown in FIG. The low band DCT coefficient information of the vector information (MV) and the variable length coded DCT coefficient information from the variable length coding circuit 21 is applied to the upper layer code sequence 31, and the variable length coding from the variable length coding circuit 21 is performed. The remaining high frequency DCT coefficient information of the obtained DCT coefficient information is applied to the lower layer code sequence 32.
[0011]
Such a conventional hierarchical video encoding device 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, all the motion vector information (MV) may be applied to the upper layer code sequence 31 as shown in FIG. However, in general, there is a limit on the ratio of the code amount of the code sequence of each layer to the total code amount of the code sequence of all layers. Thus, 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.
[0012]
Also, since each code word of the transmitted / stored code strings 31 and 32 is composed of a variable length code created by the variable length encoding circuits 21 and 27, the variable length code is generated at the time of decoding due to an error. Out of sync may occur. However, in the conventional moving picture coding apparatus, as shown in FIG. 6, important predictions such as mode information and motion vector information in which a decoded picture is greatly degraded when an error occurs are shown in the code strings 31 and 32 of each layer. Related information and DCT coefficient information of a prediction residual signal that does not cause significant degradation even when an error occurs are mixed and multiplexed. For this reason, if out-of-synchronization occurs during the decoding of a codeword carrying insignificant information, errors may propagate to the codeword carrying important information, resulting in a large degradation in the decoded image. Cause. In such a case, the synchronization cannot be recovered until the synchronization code appears, so that all the information of the decoded image up to that point becomes erroneous and a large deterioration occurs in a wide area in the screen. is there.
[0013]
[Problems to be solved by the invention]
As described above, in the conventional video coding apparatus, only one prediction-related information, such as motion vector information, which greatly reduces the quality of a decoded image when an error occurs, is encoded for each prediction region. Error tolerance is low.
[0014]
In order to increase the error resilience, all information related to prediction must be transmitted / stored by a transmission line / storage medium with a low error probability. Since there is a limit to the ratio that can be taken in the code amount, a hierarchical structure is obtained in which the transmission / storage of the code sequence using a plurality of transmission paths / storage media having different error probabilities results in mitigating image quality degradation due to errors. A problem arises in that the characteristics of encoding cannot be used.
[0015]
Further, in the conventional video coding apparatus, since relatively important information such as information related to prediction and other relatively insignificant information are mixed and included in a code string, unimportant information However, there is a problem in that the error generated in the above has an influence on important information and causes a large deterioration in image quality.
[0016]
Accordingly, an object of the present invention is to provide a moving picture coding apparatus and a moving picture coding method having high error resilience.
[0017]
[Means for Solving the Problems]
In order to solve the above problem, the present invention divides an input image forming an input video signal into a plurality of blocks, and selects an input image from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each block. A prediction residual signal which is an error signal between a prediction signal generated when the prediction is performed in the motion compensation prediction mode and the input moving image signal, or a prediction in the intra-frame prediction mode. When the input moving image signal is subjected to DCT conversion to obtain DCT coefficients and the moving image coding for quantizing the DCT coefficients is performed, a prediction mode of the frame is included in a picture header of each frame of the input image. After the picture header, information indicating a prediction mode and information indicating the prediction mode among information related to prediction of each block. Relatively low importance information is collected for each of a plurality of blocks, and the information indicating the prediction mode for the plurality of blocks and the relatively low importance information for the plurality of blocks are arranged and multiplexed in ascending order of importance. It is characterized by the following.
[0018]
Further, when performing the same moving image encoding, the present invention arranges information indicating a prediction mode of the frame in a picture header of each frame of the input image, and behind the picture header, relates to prediction of each block. The information indicating the prediction mode and the information of the DCT coefficient among the information are grouped into a plurality of blocks, respectively, and the information indicating the prediction mode obtained by grouping a plurality of blocks and the information of the DCT coefficient obtained by grouping the plurality of blocks are arranged and multiplexed in descending order of importance. Is characterized in that
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described 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.
[0020]
In FIG. 1, an input video 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 moving image 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.
[0021]
In the subtractor 105, a prediction residual signal 106 is generated by subtracting the prediction signal 104 from the input moving image signal 101. 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 input video signal 101 is output from the subtracter 105 as the prediction residual signal 106 as it is.
[0022]
The quantized DCT coefficient information 110 from the quantization circuit 109 is bifurcated, one 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 subjected to inverse discrete cosine transform by an inverse discrete cosine transform (inverse DCT) circuit 113. That is, in the inverse quantization circuit 112 and the inverse DCT circuit 113, the inverse processing of the quantization circuit 109 and the DCT circuit 107 is performed, and a signal similar to the prediction residual signal 106 is obtained in the output of the inverse DCT circuit 113. The output of the inverse DCT circuit 113 is added to the prediction signal 104 from the prediction circuit 102 in an addition circuit 114, 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.
[0023]
As will be described later, the large area prediction mode / motion vector information 116 and the small area prediction mode / motion vector information 117 are output from the prediction circuit 102 as information relating to the prediction, and the variable length encoding circuits 118 and 119 output the variable length coding modes 118 and 119, respectively. Encoded. The code strings output from the variable length coding circuits 111, 118, and 119 are multiplexed by the multiplexer 120, divided into an upper layer code string 121 and a lower layer code string 122, and transmitted to a transmission path / storage medium (not shown). Is output.
[0024]
Here, under the condition that the code string can be transmitted / stored through a plurality of transmission paths / storage media with different error probabilities, the transmission path / storage medium with a lower error probability is used for the upper layer code string 121. , And the lower-layer code sequence 122 is transmitted / stored through a transmission path / storage medium with a higher error probability, so that an error is less likely to occur in the upper-layer code sequence 121 as much as possible. To do. 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.
[0025]
Next, the configuration and operation of the prediction circuit 102 will be described in detail with reference to FIG. In the prediction circuit 102, the input video signal 101 is sequentially divided into more and more regions from an upper stage to a lower stage, and motion compensation prediction is performed 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 divided into smaller areas as necessary, as indicated by broken lines in the figure (called small areas), and motion compensation prediction is performed on these small areas with fine pixel accuracy.
[0026]
Then, the variable length encoding circuits 118 and 119 encode not only the information about the prediction for the large area output from the prediction circuit 102 but also the information about the prediction for the large area for the small area. 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 a rough accuracy if the information about the prediction for the large area is decoded without error. This can prevent the degradation of the image quality of the decoded image.
[0027]
The information related 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 motion vector information for the other regions may be variable-length coded.
[0028]
On the other hand, the information indicating the prediction mode of the small area and the information indicating the motion vector (indicated by the dashed arrow in FIG. 2), that is, the small area prediction mode / motion vector information 117 are subjected to the variable length coding Is done. 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.
[0029]
FIG. 3 shows a configuration example of the upper layer code sequence 121 and the lower layer code sequence 122. In the upper layer code sequence 121 shown in FIG. 3A, a synchronous code that can be uniquely decoded is inserted at the head for each encoded frame or for each area. PSC indicates a frame-based synchronization code. A picture header indicating the coding 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
[0030]
Furthermore, 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 accuracy of the motion compensation is increased. Can be varied in frame units to control the code amount of the motion vector information. 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 restriction 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.
[0031]
The characteristic feature is that, behind the picture header of the upper layer code sequence 121 shown in FIG. 3A, the coded information of each area is arranged in order from the information having the highest importance. 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 sequence of prediction mode information among the code sequences obtained by encoding the region prediction mode information 117 by the variable length coding circuit 118 is entered.
[0032]
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 subjected to variable-length coding. The code string of the DC component of the code string obtained by encoding in the circuit 111 is inserted. 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, large area prediction mode / motion vector information 116 output from the prediction circuit 102 is variable length. The code sequence of the motion vector information in the code sequence obtained by encoding by the encoding circuit 118 is entered.
[0033]
On the other hand, in the lower layer code sequence 122 shown in FIG. 3B, the motion vector information (small region MV) of the small region, that is, the small region prediction mode / motion vector information 117 output from the prediction circuit 102 is a variable length code. A code string of motion vector information in the code string obtained by encoding by the quantization circuit 119 is inserted, and a high frequency component of the DCT coefficient information, that is, the prediction residual signal 106 is further added to the code string by the DCT circuit 107 and the quantization circuit 109. The code string of the high-frequency component of the code string obtained by encoding the DCT coefficient information obtained through the above by the variable length encoding circuit 111 is entered.
[0034]
In this way, the motion compensation prediction is performed in a hierarchical manner, and mode information indicating the prediction mode and large area motion vector information indicating the rough prediction information are stored in the upper layer code string 121, and fine motion vector information is stored in the lower layer code string 122. 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. Can be used to perform motion compensation prediction with rough accuracy, so that the probability that significant image quality degradation will occur in the decoded image can be reduced.
[0035]
Further, in the present embodiment, since the code strings are arranged in the order of important information also in each of the upper and lower hierarchical code strings 121 and 122, errors caused by unimportant information do not spread to important information. Significant image quality degradation can be prevented.
[0036]
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.
[0037]
4, an upper layer code string 121 and a lower layer code string 122 output from the moving picture coding apparatus of FIG. 1 are an upper layer code string 201 and a lower layer code string input via a transmission path / storage medium. 202 is demultiplexed 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. , 208, and 209, respectively.
[0038]
The variable length decoding circuit 207 outputs the quantized DCT coefficient information 210 by subjecting the variable length code 204 to variable length decoding. The quantized DCT coefficient information 210 is inversely quantized by the inverse quantization circuit 213, and further subjected to inverse discrete cosine transform by the inverse DCT circuit 214 to generate the 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.
[0039]
On the other hand, in the variable length decoding circuits 208 and 209, the large area prediction mode / motion vector information 211 and the 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 predicts a moving image signal from the reference image signal stored in the frame memory 218 and the large area prediction mode / motion vector information 211 and the small area prediction mode / motion vector information 212, and generates a prediction signal 219. I do.
[0040]
The error determination circuit 220 determines the presence or absence of an error in the upper-layer code sequence 201 and the lower-layer code sequence 202 based on the states of the demultiplexer 203 and the variable-length decoding circuits 207, 208, and 209. 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 prediction in FIG. 1 based on the reference image signal stored in the frame memory 218. The prediction signal 219 identical to the signal 104 is output.
[0041]
The above process is a process of reproducing an image signal corresponding to the moving picture encoding device of FIG. 1, and the processes performed by the inverse quantization circuit 213, the inverse DCT circuit 214, the addition circuit 216, and the frame memory 218 are respectively The processing is basically the same as the processing of the inverse quantization circuit 112, the inverse DCT circuit 113, the addition circuit 114, and the frame memory 103 in FIG. Further, the variable length decoding circuits 207, 208, 209 and the multiplexer 203 respectively perform processes reverse to the processes of the variable length coding circuits 111, 118, 119 and the multiplexer 120 in FIG.
[0042]
On the other hand, when an error is detected in at least one of the upper and lower hierarchical code strings 201 and 202 in the error determination circuit 220, the information is reproduced using information having higher importance than the information in which the error is detected, for example, as follows. An image is created.
[0043]
That is, (1) when an error is detected in the DCT coefficient information of a block for which motion compensation prediction has been performed, which is included in the lower layer code sequence 122, the prediction residual signal of the block is set to 0, and the block is correctly decoded. A reproduced image signal 221 is obtained using a motion compensated prediction signal obtained using the mode information, the large area motion vector information and the small area motion vector information as a prediction signal 219.
[0044]
(2) When an error occurs in the small area motion vector information, a reproduced image signal 221 is obtained for the small area using the motion compensated prediction signal obtained using the large area motion vector information as the prediction signal 219. .
[0045]
Further, (3) when an error occurs in the large area motion vector information, the motion compensation of the large area can be performed from the surrounding area or the motion vector information of the already decoded frame when the motion compensation prediction of the large area can be performed. If the estimated value is used and the surrounding motion vector information also has an error, the image signal of the already decoded frame is used as it is as the reproduced image signal 221.
[0046]
(4) When an error occurs in the AC component of the DCT coefficient information of the block for which the intra-frame prediction mode is selected, the image of the block is obtained from the DC component of the DCT coefficient information and the image signal of the surrounding block that has been correctly decoded. A signal is predicted to be a reproduced image signal 221, or an image signal of an already decoded frame is predicted by using a predicted signal of a correctly decoded image signal of a surrounding block from a previously decoded image signal of a frame. Signal 221 is assumed.
[0047]
By the way, when a variable length code is used for encoding various kinds of 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 or the like. In such a case, the subsequent code is not used for decoding. For example, when an error occurs in the small area motion vector information in the lower layer code sequence 122, the error may propagate to the motion vector information after the small area and the DCT coefficient information following the error. Does not use the information with the error spread for decoding. Even when such out-of-synchronization occurs, codewords are arranged in the code sequence in the order of importance, so errors that occur in information of low importance can spread to information of high importance. In addition, it is possible to prevent the reproduced image from being significantly deteriorated.
[0048]
As a specific method of detecting that an error has occurred in the code strings 201 and 202 by the error determination unit 220, the following method can be given.
[0049]
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.
[0050]
Second, when the variable-length decoding circuits 207, 208, and 209 detect a codeword that does not exist in the codeword table representing the correspondence between the input codeword and the output value, it detects this as an error. This is a method of determining. In particular, when a variable length code is used, the error may spread not only in the part where the error is detected but also in the code string before and after the part, so that error detection is performed for all the codewords. Perform processing.
[0051]
Third, are the motion vector information, the prediction signal, the DCT coefficient information, the prediction residual signal, the reproduced image signal, and the like reproduced based on the decoded codeword, a signal that cannot be generated in the encoding of the moving image? This is a method of making an error judgment by judging whether or not there is no error. The use of this method is characteristic of the present invention, and will be described in more detail.
[0052]
For example, when the motion vector indicated by the motion vector information exceeds the search range defined in advance or extends off the screen, it is determined that an error has occurred.
[0053]
In addition, it is possible to detect an error by determining the DCT coefficient information that has been inversely quantized by the inverse quantization circuit 213. Assuming that 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 × N, the DCT coefficient takes a value within the following range.
[0054]
<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) to (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, for the block in which the error is detected, all or some of the DCT coefficients may be set to 0, or the decoded value may be estimated from the decoded values of the surrounding blocks.
[0055]
Further, it is also 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 reproduction image signal 221 may be obtained by performing inverse DCT, or may be estimated from the pixel values of blocks around the reproduction image signal 221.
[0056]
As described above, according to the present invention, the error determination by the error determination unit 220 in the moving picture decoding apparatus determines whether the reproduced information or signal is information or a signal that cannot occur in the transmission path / storage medium. In addition, 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.
[0057]
The present invention can be implemented with various modifications. For example, in the above-described embodiment, an example in which the code sequence output from the video encoding device is divided into two layers has been described, 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 to the first layer at the highest level, and the DC component (intra DC) of the DCT coefficient information and the large area motion vector information in the intra prediction mode are set to the second layer. DCT coefficient information other than the DCT coefficient information in which the small area motion vector information is allocated to the third layer and the first layer may be allocated to the fourth layer. Further, the DCT coefficients may be further divided into several layers such as a low-frequency component and a high-frequency component for encoding.
[0058]
In addition, in the coding of the large area motion vector information, the difference between the motion vector information for which the fixed-length coding is performed as described above and the motion vector information for which the fixed-length coding is performed is obtained by the variable-length coding. When coding is performed in two ways, fixed-length coded motion vector information in which an error does not spread to a subsequent code string due to loss of synchronization is put together in a frame or a certain area unit, and is first put. It is effective to insert the variable length coded motion vector information at the end. 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 image quality degradation of a reproduced image due to an error.
[0059]
Note that the method of determining whether or not the information reproduced by the moving picture decoding apparatus of FIG. 4 is information that cannot be generated in moving picture coding is not limited to a hierarchically coded code string, and may be a general moving picture. The present invention can also be applied to a moving picture decoding apparatus that decodes an original image signal from a code sequence obtained by an image coding apparatus.
[0060]
【The invention's effect】
As described above, according to the present invention, there is provided a moving picture coding apparatus and a moving picture coding method with high error resilience, that is, with little degradation of the picture quality of a decoded picture due to an error occurring during transmission / storage of a coded sequence. can do.
[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 video encoding apparatus of FIG.
FIG. 3 is a diagram showing an example of an upper layer and a lower layer code string output from the video encoding apparatus 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]
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 DCT 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 ... locally 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-order code sequence
201: upper layer code sequence
202: Lower layer code string
203 ... Demultiplexer
204 to 206: Variable length code
207-209 ... variable length coding circuit
210: Quantized DCT coefficient
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: prediction residual signal
216 ... Adder
217 ... Prediction circuit
218 ... Frame memory
219 ... Predicted signal
220 ... Error determination circuit
221... Reproduced image signal

Claims (4)

Means for dividing an input image forming an input video signal into a plurality of blocks,
Prediction means for performing prediction by a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each block;
A prediction residual signal that is an error signal between a prediction signal generated when the prediction unit performs prediction in the motion compensation prediction mode and the input moving image signal, or the prediction unit performs prediction in the intra-frame prediction mode. Means for DCT transforming the input moving image signal to obtain DCT coefficients when
A moving image encoding apparatus comprising: means for quantizing DCT coefficients;
Information indicating a prediction mode of the frame is arranged in a picture header of each frame of the input image, and information indicating the prediction mode and information indicating the prediction mode among information related to prediction of each block are arranged after the picture header. The relatively less important information is grouped into a plurality of blocks, respectively, and the information indicating the prediction mode combined into the plurality of blocks and the relatively less important information combined into the plurality of blocks are arranged and multiplexed in descending order of importance. A moving picture encoding apparatus comprising a multiplexing means for performing the above operation. Means for dividing an input image forming an input video signal into a plurality of blocks,
Prediction means for performing prediction by a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each block;
A prediction residual signal that is an error signal between a prediction signal generated when the prediction unit performs prediction in the motion compensation prediction mode and the input moving image signal, or the prediction unit performs prediction in the intra-frame prediction mode. Means for DCT transforming the input moving image signal to obtain DCT coefficients when
A moving image encoding apparatus comprising: means for quantizing DCT coefficients;
Information indicating the prediction mode of the frame is arranged in a picture header of each frame of the input image, and information indicating the prediction mode and information of the DCT coefficient among information relating to prediction of each block are arranged after the picture header. A moving picture, comprising: multiplexing means for multiplexing a plurality of blocks, information indicating the prediction mode combined for a plurality of blocks, and information of the DCT coefficients combined for a plurality of blocks in order of decreasing importance. Encoding device. The input image forming the input moving image signal is divided into a plurality of blocks, and prediction is performed according to a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each block. The prediction residual signal which is an error signal between the prediction signal generated when performing prediction in the prediction mode and the input video signal, or the input video signal when performing prediction in the intra-frame prediction mode. In a moving picture coding method for obtaining DCT coefficients by performing DCT transform and quantizing the DCT coefficients,
Information indicating a prediction mode of the frame is arranged in a picture header of each frame of the input image, and information indicating the prediction mode and information indicating the prediction mode among information related to prediction of each block are arranged after the picture header. The relatively less important information is collected for each of a plurality of blocks, and the information indicating the prediction mode of the plurality of blocks and the relatively less important information of the plurality of blocks are arranged and multiplexed in ascending order of importance. A moving picture coding method characterized by the above-mentioned. The input image forming the input moving image signal is divided into a plurality of blocks, and prediction is performed according to a prediction mode selected from a plurality of prediction modes including a motion compensation prediction mode and an intra-frame prediction mode for each block. The prediction residual signal which is an error signal between the prediction signal generated when performing prediction in the prediction mode and the input video signal, or the input video signal when performing prediction in the intra-frame prediction mode. In a moving picture coding method for obtaining DCT coefficients by performing DCT transform and quantizing the DCT coefficients,
Information indicating the prediction mode of the frame is arranged in a picture header of each frame of the input image, and information indicating the prediction mode and information of the DCT coefficient among information relating to prediction of each block are arranged after the picture header. A moving picture coding method, comprising: multiplexing a plurality of blocks, information indicating the prediction mode of the plurality of blocks, and information of the DCT coefficients of the plurality of blocks, arranged in descending order of importance.

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