JP2001308718A - Method and device for variable length encoding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable length encoding device which can decode both to the forward direction and to the reverse direction, and can compose a variable length code high in encoding efficiency with few useless bit patterns. SOLUTION: The variable length encoding device assigns a cord word having a code length responding to the occurrence probability to an orthogonal transformation coefficient generated by performing orthogonal transformation of a block unit, and outputs the cord word corresponding to the orthogonal transformation coefficient generated by a dynamic image encoder 709 as coded data. Furthermore the variable length encoding device composes the first cord word table storing a plurality of cord words which can be decoded to the forward direction and to the reverse direction for every encoding mode making respond to the orthogonal transformation coefficient other than the last of a block and the second cord word table provided in common to each encoding mode, and storing the plurality of cord words which can be decoded to the forward direction and to the reverse direction making respond to the orthogonal transformation coefficient of the last of the block, and selects the cord word corresponding to the orthogonal transformation coefficient from the first and second cord word tables to output it as the coded data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable length coding method and apparatus.

[0002]

2. Description of the Related Art A variable-length code is based on the frequency of occurrence of a symbol.
A symbol system which rarely appears is a code system in which a code having a long code length is assigned so that the code length becomes short on average. Therefore, when the variable length code is used, the data amount can be significantly reduced as compared with the data before encoding. As a method of constructing such a variable length code, Huffman's algorithm which is optimal for a memoryless information source is known.

[0003] As a general problem of the variable length code, when an error is mixed in the coded data due to a transmission line error or other reasons, the data after the error is mixed is decoded by the influence of the error. The point is that decoding cannot be performed correctly by the device. Therefore, when there is a possibility that an error may occur in the transmission path, a method is generally adopted in which a synchronization code is periodically inserted at certain intervals to prevent the propagation of the error. A bit pattern that does not appear in a combination of variable length codes is assigned to the synchronization code. According to this method, even if an error occurs in encoded data and decoding becomes impossible, finding the next synchronization code prevents the propagation of the error and enables correct decoding. However, even when the synchronization code is used in this way, as shown in FIG. 39 (a), the encoded data from the point where an error occurs and cannot be decoded correctly to the point where the next synchronization code is found is not decoded. Can not do.

Therefore, the variable length code is changed from the normal configuration shown in FIG. 40 to that shown in FIG. 41, so that not only the characteristic that can be decoded from the normal forward direction as shown in FIG. There is known a method of forming a code that can be decoded also from a direction. In addition, since such a code can read encoded data in the reverse direction, it can be used for reverse reproduction in a storage medium such as a disk memory for storing encoded data. Such a variable length code that can be decoded not only in the forward direction but also in the reverse direction is referred to as a reversible code here. One example of a reversible code is
For example, it is described in JP-A-5-300027 "Reversible variable length coding system". In the reversible code of this known example, as shown in FIG. 41, each codeword has a longer code length at the end of the codeword of the Huffman code which is a variable length code decodable from the forward direction as shown in FIG. This is a variable-length code that can be decoded in the opposite direction by adding bits under conditions that do not match the end of another codeword.

However, in this reversible code, since bits are added to the end of a code word of a variable length code that can be decoded only in the forward direction, useless bits increase and the average code length increases. As a result, the coding efficiency is greatly reduced as compared with a variable length code that can be decoded only in the forward direction.

[0006] Another problem of the conventional reversible code is that when the number of information symbols is large, the amount of storage required by the variable-length encoding / decoding device increases, so that it is not suitable for practical use. There was no point. An example of a case where the number of information symbols is large is DCT coefficient encoding which is often used in image encoding of a moving image or a still image. Normally, in image coding, 8 × 8 DCT (discrete cosine transform) is performed, and 8-bit linear quantization is performed on orthogonal transform coefficients obtained as DCT coefficients. Further, a zigzag scan is performed on the quantized DCT transform coefficients from a low frequency band, and variable length coding is performed using a set of zero-run and non-zero coefficients.

For example, ITU-T DRAFT Rec
ommendation H .; In H.263 (1995), the quantization index value is -127 to +127 (because the index value 0 is a run, the index number is 25
3) Since the number of zero runs is a maximum of 63, and the coding that discriminates whether the last DCT coefficient of the block is a non-zero coefficient is adopted, the number of information symbols is 253.
It is a very large number of × 64 × 2 = 32384. Then, H. In H.263, the DCT coefficient with a high appearance probability is coded with a variable length code, but the DCT coefficient with a low appearance probability is a 1-bit code and a zero run as a code indicating whether it is the last non-zero coefficient of a block. 6-bit code, 8-bit code for quantization index, total 1
The fixed-length coding is performed using a 5-bit code, and a code called an escape code is added to the head of the fixed-length code.

[0008] Encoding / decoding is possible even if all codewords are stored as a codeword table. However, with the above-described code configuration, a fixed-length 15-bit code is variable-length. Since encoding / decoding can be performed separately from codes, it is only necessary to prepare a code word table of DCT coefficients and escape codes having a high appearance probability. Therefore, it is possible to reduce the storage capacity by reducing the codeword table of the variable length code.

However, as described above, the conventional reversible code cannot add an escape code because it is necessary to add a bit to the end of a variable-length code word that can be decoded only in the forward direction. Therefore, even when the number of information symbols is large, it is necessary to prepare code words corresponding to all information symbols, and the storage amount becomes enormous.

[0010]

As described above, a reversible code according to the prior art, that is, a variable length code that can be decoded in both the forward and reverse directions, is a code word of a variable length code that can be decoded only in the forward direction. Since the reversible code is configured by adding a bit to the end of the code, the useless bit pattern increases, the average code length increases, and the coding efficiency decreases compared to a variable length code that can be decoded only in the forward direction. And a variable-length encoding / decoding device using such a reversible code needs to prepare a codeword table having codewords corresponding to all information symbols in some form. When the number of information symbols is large as in image coding, there is a problem that a large storage amount is required. There is a problem in that.

SUMMARY OF THE INVENTION An object of the present invention is to provide a variable-length coding method and apparatus which can be decoded in both forward and reverse directions and which is practical.

More specifically, it is an object of the present invention to provide a variable length coding method and apparatus capable of decoding in both the forward and reverse directions and having a small amount of useless bit patterns and high coding efficiency. .

It is another object of the present invention to provide a variable length coding method and apparatus which can decode in both forward and backward directions and do not require a large storage amount even when the number of information symbols is large. I do.

[0014]

In order to solve the above-mentioned problems, the present invention provides an orthogonal transform coefficient which can be generated by performing an orthogonal transform in block units, and a code length corresponding to the occurrence probability of the orthogonal transform coefficient. In the variable-length coding method of allocating codewords having the following formulas and outputting codewords corresponding to the orthogonal transform coefficients generated by the video encoder as coded data, for each of a plurality of coding modes, A first codeword table storing a plurality of codewords that can be decoded in the opposite direction and corresponding to orthogonal transformation coefficients other than the last of the block, and a common codeword table is provided for the plurality of encoding modes. A second codeword table in which a plurality of codewords that can be decoded in both the forward and reverse directions are stored in correspondence with the last orthogonal transform coefficients of the block, and the first and second codeword tables are stored. And outputs as coded data from the issue word table by selecting a code word corresponding to the orthogonal transform coefficients.

Further, according to the present invention, a code word having a code length corresponding to the probability of occurrence of the orthogonal transform coefficient is assigned to an orthogonal transform coefficient which can be generated by performing an orthogonal transform on a block basis. Variable-length coding apparatus that outputs codewords corresponding to orthogonal transform coefficients generated by the encoder as coded data, for each of a plurality of coding modes, a plurality of codes that can be decoded in both the forward and reverse directions. A first codeword table in which codewords are stored corresponding to orthogonal transform coefficients other than the end of the block, and are provided in common for the plurality of coding modes, and can be decoded in both forward and reverse directions. And a second codeword table that stores a plurality of codewords corresponding to the last orthogonal transform coefficient of the block, and a codeword corresponding to the orthogonal transform coefficient from the first and second codeword tables. And having a coding means for selecting a code word as the coded data.

In a moving picture encoder / decoder, since there is a syntax in an encoding method, it is necessary not only to be able to decode a variable length code from both directions but also to be able to decode the syntax from both directions. The variable length coding according to the present invention can meet this demand. That is, the syntax in the moving picture encoder is such that, for example, mode information indicating a coding mode, motion vector information, and the like are set as an upper layer, and orthogonal transform coefficients such as DCT coefficients are set as a lower layer. It is assumed that the coding mode of each block (macroblock) in the lower layer is already known from the decoding of the upper layer, and that the decoding is possible in both directions if the block break is known. It has become.

In the present invention, the first codeword table corresponding to the orthogonal transform coefficients other than the last of the block is individually formed for a plurality of encoding modes, but the first codeword table is corresponding to the last orthogonal transform coefficient of the block. The second codeword table to be used is common to each coding mode, so that it is possible to cope with a change in the codeword table depending on the coding mode, and to decode a codeword representing the last orthogonal transform coefficient of a block during decoding. Since a block delimiter can be identified by the appearance of a codeword representing the last orthogonal transform coefficient of the previous block, decoding can be performed from both directions in terms of syntax.

In addition, since the orthogonal transform coefficients to be generated and their appearance frequencies are different between different encoding modes, for example, between the intra mode and the inter mode, the second codeword tables corresponding to these are separately formed. By
Encoding efficiency is improved.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a variable length encoding / decoding device according to one embodiment of the present invention. The variable-length encoding / decoding device according to the present embodiment is roughly divided into a codeword table creation unit 101, an encoding unit 114, a transmission or accumulation system 104, and a decoding unit 115. First, the function of each of these units will be briefly described. The codeword table creation unit 101 creates a codeword table based on the occurrence probabilities of information symbols, and the codeword table 102 in the encoding unit 114 and the decoding unit 115 To the forward codeword table 110 and the backward codeword table 112. Encoding section 114 encodes the information symbol into a variable-length code, and outputs the variable-length code to transmission system or storage system 104 as encoded data. Decoding section 115 decodes the coded data input via transmission system or storage system 104 to reproduce the original information symbols.

Next, the detailed configuration and operation of each part of the present embodiment will be described. In the encoding unit 114, the input information symbols are input to the encoder 103. On the other hand, the codeword table 102 stores information symbols created in advance by the codeword table creation unit 101 and codewords of variable-length codes in association with each other. The encoder 103 selects a codeword corresponding to the input information symbol from the codewords stored in the codeword table 102 and outputs the selected codeword as encoded data. This encoded data is sent to the decoding unit 115 via the transmission system or the storage system 104.
At this time, a synchronization code is inserted into the encoded data at regular intervals.

In the decoding unit 115, a synchronization code is detected by the synchronization code detection unit 105 from the encoded data input from the transmission system or the storage system 104, and the encoded data between the synchronization codes is stored in the buffer 106. accumulate. The forward decoder 110 starts decoding from the beginning of the encoded data stored in the buffer 106 based on the forward decoding tree from the forward decoding tree creating unit 111, and the backward decoder 108 The decoding is started from the end of the encoded data stored in the buffer 106 based on the backward decoding tree from the backward decoding tree creating unit 113.

The decoding value judgment unit 109 decodes the decoding result obtained by the forward decoding unit 107 (referred to as a forward decoding result) and the decoding result obtained by the backward decoding unit 108 (referred to as a backward decoding value). , And a final decoding result is output. That is, the decryption value determination unit 109
In the case where there is an error in the encoded data, a bit pattern that does not appear in the decoding tree is generated, so that the presence of the error can be known. Therefore, the decoded value is determined from the forward decoding result and the backward decoding result as shown in FIG. FIG. 2 shows a method of determining a decoded value between synchronization codes.

First, as shown in FIG. 2 (a), if the position of a code word at which an error is detected in the forward decoding result and the backward decoding result does not intersect (error detection position), no error is detected. Only the decoding result is used as the decoding value, and the decoding results at the two error detection positions are not used as the decoding values and are discarded.

When the error detection positions of the forward decoding result and the backward decoding result intersect as shown in FIG. 2B, the decoding result in which no error is detected in both cases is used as the decoding result value. . In this case, the decoding result between the codewords at the two error detection positions is not used as a decoding value,
Abandon.

Also, as shown in FIG. 2C, when an error is detected only in the one-way decoding result of the forward decoding result and the backward decoding result (in this example, the error is detected only in the forward decoding result). Has been detected), the decoded value for the codeword at the error detection position is discarded, and the decoded values for the subsequent codewords use the decoded results in the reverse direction.

Further, when an error is detected in both the forward decoding result and the backward decoding result for the same code word as shown in FIG. Are discarded, and the decoded values for the subsequent code words use the decoded results in the reverse direction.

The codeword table creation unit 101 creates a codeword table of codes that can be decoded in both forward and backward directions based on the occurrence probability of information symbols. The codeword table created by the codeword table creation unit 101 is
It is sent to the codeword table 102 in the encoding unit 114 and to the forward codeword table 110 and the backward codeword table 112 in the decoding unit 115. Forward decoding tree creation unit 1
At 11, a forward decoding tree is created from the forward codeword table 110. Also, in the backward decoding tree creating unit 113,
A backward decoding tree is created from the backward codeword table 112.

FIG. 3 is a block diagram showing the configuration of the codeword table creation unit 101. The code selection unit 21 receives information on the occurrence probabilities of the information symbols as input, selects a code system having the smallest average code length from the selectable code systems based on this information, and sends the selection result to the codeword configuration unit 22. send. The codeword configuration unit 22 configures the codeword of the code selected by the codeword selection unit 21 and creates a codeword table. The codeword table created by the codeword configuration unit 22 is stored in the codeword table 102 and the decoding unit 11 in the encoding unit 114.
5 to the forward codeword table 110. To the backward codeword table 112 in the decoding unit 115, a codeword table described in a direction opposite to the forward direction is sent.

The code selecting section 21 rearranges the input information symbols in descending order of the probability of occurrence to obtain S = {S1, S
2,..., Sn}, and based on the probability of occurrence P of these information symbols S = {p1, p2,.

[0031]

(Equation 1)

The code c satisfying the above is selected. Where L
i is a code length that can be calculated by the weight of the code word provided from the code word forming unit 22. The code word weight in this case refers to the number of “1” or “0” in the code word.

Hereinafter, a method of forming a code word in the code word forming unit 22 will be described.

FIG. 4 shows an example of how to form a binary code sequence having a constant weight serving as a basis of a variable length code according to the present embodiment. As shown in FIG. 4A, from the start point e
Form a grid-like directed graph to the nd point. When following the route from the start point to the end point in this directed graph, “0” is selected when the left route is selected, and “1” is selected when the right route is selected. Is generated.
In this example, the code length is 5 bits and the weight (the number of “1”)
Generates a binary code sequence of 2. In general, there are as many binary code sequences having a code length of n bits and a weight of w as the number of combinations that select w from n. Here, there will be 10 binary code sequences, the number of combinations of selecting two out of five.

FIG. 5 shows a first method of constructing a codeword of a variable length code (hereinafter, referred to as a reversible code) that can be decoded in the forward and backward directions in the codeword constructing section 22. First, as shown on the left side of FIG. 5, the weight (the number of “1”) is constant (the number of “1”) by the method of FIG. 4 only for (information symbols−1) (in this case, 9) in ascending code length. In this case, one binary code sequence is created. Next, as shown on the right side of FIG. 5, "1" is added to the beginning and end of each of the binary code sequences, and "0" is assigned to the shortest code, thereby forming a codeword of the reversible code. This reversible code always starts with a code “0” for information symbol A and a code “1” for other information symbols B to J. If three “1” appear in all, This is a code configuration in which the code ends, that is, a configuration where the code delimiter (code length) is known.

A necessary and sufficient condition for a variable length code to be a reversible code, that is, a code that can be decoded in both the forward and reverse directions, is that all codewords are assigned to the leaves of the forward and backward decoding trees. Is to be done. The leaf of the decoding tree is the end of the decoding tree, that is, a place where there is nothing earlier. For example, in the variable-length code of FIG. 5, the codewords corresponding to all the information symbols A to J are the leaves of the forward decoding tree shown in FIG. 6A and the leaves of the backward decoding tree shown in FIG. , It can be seen that decoding can be performed in both the forward and reverse directions.

The parameters of the method of constructing the code word of the variable length code shown in FIG.
By setting the above natural number w, it is possible to cope with the occurrence probabilities of various information symbols. Of course, the same applies to the case where the bit is inverted and the number "0" is considered as a weight and discussed.

FIG. 7 shows a second method of forming a codeword of a reversible code in the codeword forming unit 22. First, as shown on the left side of FIG. 7, the weight (the number of “1”) is constant (in this case, one) by the method of FIG. Create a hexadecimal code sequence. Next, as shown in the center of FIG. 7, "1" is added to the beginning and end of each of the binary code sequences, and further, as shown on the right side of FIG. Add words.

In this variable length code, the code length can be determined by counting the number of symbols at the beginning of each code. In the example of FIG. 7, the first symbol of each code is 4
The code configuration is such that the code ends when it appears once, that is, the code configuration allows the code delimiter (code length) to be known.

In the variable length code of FIG. 7, the codewords corresponding to all the information symbols A to J are also applied to the leaves of the decoding tree in the forward direction shown in FIG. Since it is also assigned to the leaves of the tree, it can be seen that decoding can be performed in both the forward and reverse directions.

FIG. 9 shows a third method of forming a codeword of a reversible code in the codeword forming unit 22. The reversible code has a code configuration in which the number of “0” and “1” are the same, so that the code length of the codeword can be known. That is, considering the lattice-like directed graph shown in FIG. 9A, “0” is selected when the left route is selected and the right route is selected, and “1” is selected for the directed graph, starting from the start point. Correspond, sta
A path that reaches a diagonal black dot passing through the rt point is generated as a codeword.

In this case, the code words corresponding to all the information symbols A to J are assigned to the leaves of the forward decoding tree shown in FIG. 10A and the leaves of the backward decoding tree shown in FIG. 10B. Thus, it can be seen that decoding can be performed in both the forward direction and the reverse direction.

Next, a method for shortening a reversible code according to the present invention will be described. Since the number of information symbols, that is, the number of codes of the variable length code is finite, it is possible to shorten some codes of the variable length code. Here, shortening refers to reducing the code length of some codes without increasing the code length of other codes. FIG. 11 shows an example of a method for shortening a reversible code.

For example, in the reversible code shown in FIG. 7, even if the last bit of the codeword corresponding to the information symbols G, H, I, and J is deleted, decoding can be performed in either the forward direction or the reverse direction. It is possible. By utilizing this, in FIG. 11, the code lengths of the four codewords corresponding to the information symbols G, H, I, and J are reduced.

The variable length code shown in FIG.
Code words corresponding to all information symbols A to J are shown in FIG.
Since it is assigned to both the leaves of the forward decoding tree shown in FIG. 12A and the leaves of the backward decoding tree in FIG. 12B, it can be seen that decoding is possible in both the forward and backward directions.

Next, a method for extending a reversible code according to the present invention will be described with reference to FIG. Extension of a reversible code can be realized by adding an equal-length code to at least one of the beginning and end of each code to increase the number of codewords having the same code length. In the example of FIG. 13, a 2-bit equal length code is added to the end of each of the reversible codes shown on the left side. In this case, the code length of each code of the reversible code is increased by 2 bits as a whole, but the number of codewords having the same code length is quadrupled. In general, when an n-bit equal-length code is added, the code length increases by n bits as a whole, but the number of code words having the same code length can be increased by 2 ⁿ times. Since the isometric code is obviously a reversible code, even if the isometric code is added to the beginning or end of the reversible code, it is still a reversible code.

FIG. 14 shows a known example (Japanese Unexamined Patent Publication No. 5-300) of a reversible code obtained by subjecting an information symbol, which is an English alphabet, to variable length coding according to the present invention.
027) in comparison with the reversible code disclosed in Japanese Patent Application Laid-Open No. 027). The reversible code according to the present invention shown in FIG. 14 is a code obtained by expanding a code when the weight of a code word is set to 0 in the method shown in FIG. It is.

The reversible code according to the present invention is:
Although it is inferior to the Huffman code, which is the optimal code of the variable length code that can be decoded only in the forward direction, the average code length is shorter than that of the reversible code disclosed in the known example, indicating that the Huffman code has excellent performance. This is because the known reversible code is a variable-length code that can be decoded only in the forward direction with a bit added to the end of a Huffman code, whereas the present invention does not add an extra bit, This is because the reversible code is formed from the beginning, so that there is little useless bit pattern.

Next, another embodiment of the present invention will be described.
FIG. 15 is a diagram illustrating a variable-length coding / coding scheme according to another embodiment of the present invention.
It is a block diagram which shows the structure of a decoding device. The variable-length encoding / decoding device according to the present embodiment is roughly divided into a codeword table creation unit 201, an encoding unit 213, a transmission or storage system 205, and a decoding unit 214.

The function of each of these units will be briefly described. The codeword table creation unit 201 creates a codeword table based on the occurrence probability of information symbols,
3 and sends the created codeword parameters of the codeword table to the decoded graph / decoded value table creation unit 208 in the decoding unit 214. The encoding unit 213 encodes the information symbol into a variable length code, and outputs the variable length code to the transmission system or the storage system 205 as encoded data. Decoding section 214 decodes the encoded data input via transmission system or storage system 205 to reproduce the original information symbols.

Next, the detailed configuration and operation of each part of the present embodiment will be described.

[0052] In the coding section 213, the input information symbols are input to the encoder 203. The codeword table 202 stores information symbols created in advance by the codeword table creation unit 201 and codewords of variable-length codes in association with each other. However, the codewords stored in the codeword table 202 do not necessarily correspond to all of the information symbols that can be input. Is stored. The encoder 203 selects a codeword corresponding to the input information symbol from the codewords stored in the codeword table 202 and outputs the selected codeword as encoded data.

On the other hand, the encoding unit 213 stores the codeword table 2
When an information symbol having no code word corresponding to 02, that is, an information symbol having a relatively low appearance frequency is input, a fixed-length code corresponding to the information symbol is created by the fixed-length code encoding unit 204, and Codeword table 20
2 is added to the beginning and end of the fixed-length code to form a codeword, which is output as encoded data.

Thus, the encoder 20 in the encoder 213
3 is transmitted to the decoding unit 214 through the transmission system or the storage system 205. At this time, a synchronization code is inserted into the encoded data at regular intervals.

The decoding section 214 is provided with the synchronization code detecting section 20.
6, buffer 207, decoded graph / decoded value table creating section 208, forward decoder 209, fixed length decoding section 21
0, a backward decoder 211 and a decoded value judging unit 212. First, a synchronous code detecting unit 206 detects a synchronous code from encoded data input from a transmission system or a storage system 205, and outputs a synchronous code and a synchronous code. The encoded data between them is stored in the buffer 207. The forward decoder 209 starts decoding from the beginning of the coded data stored in the buffer 207, and the backward decoder 211 starts decoding from the end of the coded data stored in the buffer 207. In the decoded value determination unit 212, the forward decoder 209
The decoding result (referred to as forward decoding value) obtained by
A decoding value is determined from a decoding result (referred to as a backward decoding value) obtained by the backward decoder 211, and a final decoding result is output.

FIG. 16 is a diagram showing a method of constructing a code word by adding an escape code to the beginning and end of a fixed-length code in the code word table creating unit 201 in FIG. As shown in FIG. 16A, when the information symbol is other than “A”, the code word created by the code word table creation unit 201 has a code delimiter because three “1” s appear. It is based on reversible codes that can be understood. This reversible code is referred to as code (1).

On the other hand, reference numeral (2) shown in FIG.
Codeword “1” corresponding to information symbol “C” of code (1)
"011" as an escape code for indicating the beginning and end of the fixed-length code, a code word formed by adding to the beginning and end of the 3-bit fixed-length code, a code word newly added to code (1). However, the part of the reversible code corresponding to the code (1) in the code (2) is the code word “101” used as the escape code in the code (2).
1 "is not used, and only code words corresponding to information symbols A to I which are one less than code (1) are used.
As is clear from the comparison between (a) and (b), the code (2) has the number of information symbols that can be coded is “10” of the code (1).
To "17".

In order to decode such a code (2), as can be seen from FIGS. 16 (a) and 16 (b), the code (1) must be always decoded regardless of whether it is decoded in the forward direction or in the reverse direction. Since the fixed-length code can be decoded in both the forward and reverse directions, if the code (1) can be decoded in both the forward and reverse directions, the code (2) is also decoded. Decoding is possible from both directions.

In the case of the conventional reversible code, it is necessary to prepare all the codewords corresponding to the information symbols that can be inputted in the coding section 213 and the decoding section 214 as a codeword table. On the other hand, code (2)
According to the above, for the fixed-length code part, 3 bits 2
Since the fixed-length code encoding unit 204 and the fixed-length code decoding unit 210 can be separately prepared as binary codes, the codeword table 202 needs to store only the codeword of the code (1). Therefore, compared with the conventional reversible code, the storage amount of the variable-length encoding / decoding device can be significantly reduced.

Decoded graph / decoded value table creation unit 208
Creates a decoding graph and a decoding value table based on the Sharkwijk algorithm, and generates a forward decoder 2
09 and the backward decoder 211 perform decoding based on the decoded graph and the decoded value table.

FIG. 17 shows a method of counting a binary code sequence having a constant weight. JPMShalkwijk is an algorithm for counting binary code sequences with a constant weight:
“Analgorithm for source coding”, IEEE Trans.Infr
om Theory, vol. IT-18, no. 3, pp. 395-399, May 1972.
It is well-known as a halkwijk algorithm. In the Sharkwijk algorithm, FIG.
As shown in (a), a grid-like directed graph from the START point to the END point is formed based on the “Pascal's triangle”. The value indicated by a number at each node is ST
Assuming that the value of the node at the ART point is 1, it is the sum of the values of the nodes at the starting points of the two arrows entering each node.
That is, the value of each node is determined by the Pascal's triangle.

In the directed graph of FIG. 17A, when following the route from the START point to the END point according to the input information symbol, when the left-side route (arrow) is selected, the codeword “0” is selected. When the path (arrow) on the right side is selected, a binary code sequence having a weight of 2 can be generated by associating the codeword “1” with each other. Here, the value obtained by subtracting the value of the node at the start of the arrow from the value of the node at the end of the arrow when “0” is selected is the code word of the same code length of the binary code sequence. Is the ordinal value of For example, if the input information symbol is "01001", the sum of the differences of the node values with respect to three "0" s is (1-1) + (3-
2) + (4-3) = 2 is the order value. Here, the sequential value is a value for ordering different code words having the same code length. FIG. 17B shows the relationship between information symbols and order values in this case.

An example in which the Sharkwijk algorithm is applied to encoding is known. In this case, encoding is performed by converting a value corresponding to the above order value into a binary code. In contrast, in the present embodiment, this algorithm is used for decoding as described below.

That is, the decoding graph / decoding value table creation unit 208 creates a directed graph as a decoding graph based on the above-mentioned Sharkwijk algorithm. That is, this decoded graph is a directed graph in which values determined by Pascal's triangle are used as node values and codewords "1" and "0" are used as arrows.
(A). FIG. 18B shows an example of a method of calculating a decoded value in the forward decoder 208 and the backward decoder 211 using the decoded graph.

Code (1) shown in FIG. 16 (a) is a reversible code in which, when the head is other than "0", a break can be recognized at the point where three "1" appear. When calculating the decoded value of the reversible code of the code (1), if the head of the reversible code is "0" in the forward direction, the decoded value is set to 0; Is deleted, and the order value is calculated by the Sharkwijk algorithm. The number of codewords having a code length shorter than the codeword to be decoded is EN EN in FIG.
Since the sum of the values of the diagonal right nodes at the point D is +1, the sum of the value and the order value is the decoded value.

On the other hand, in the reverse direction, as in the case of the above-mentioned forward direction, first, if the head of the reversible code is "0", the decoded value is set to 0; otherwise, the head and tail "1" are deleted. Then, after inverting the remaining part, S
The order value is calculated by the algorithm of halkwijk.
Then, a value obtained by adding +1 to the sum of the nodes at the upper right of the END point to the order value is set as a decoded value.

More specifically, with reference to FIGS. 18A and 18B, for example, if the code word to be decoded for the reversible code is “10101”, first, the leading and trailing “1” are deleted and “ 010 ". Sh for this “010”
When the order value is obtained by the algorithm of alkwijk, 2
For one “0”, (1-1) + (3-2) = 1. In this case, the sum of the values of the nodes at the diagonally upper right of the END point is 1 + 2 = 3, so this value + 1 (= 4) is added to the order value (= 1), and the decoded value is obtained as 5.

When decoding is performed using such a decoding graph, the amount of storage can be greatly reduced. FIG.
(A) and (b) show a decoding method using a conventional decoding tree;
FIG. 11 is a diagram illustrating a difference in storage amount required in a decoding method using a decoding graph according to the present embodiment. Comparing both with the number of nodes, the number of arrows coming out of each node is the same for both, but the number of arrows coming into each node is always one in the case of the decoding tree in FIG. . On the other hand, in the case of the decoded graph of FIG. 19B, since two arrows enter each node, the total number of nodes required by the same codeword is reduced by that amount. In this example, the decoding tree in FIG. 19A requires 15 nodes, whereas the decoding graph in FIG. 19B requires only 8 nodes. Therefore, the decoding method of the present embodiment using the decoding graph has an advantage that the required storage amount is smaller than that of the conventional method using the decoding tree.

In this embodiment, in order to decode the code (2) to which the escape code shown in FIG. 16B is added, the decoded value table of the code (1) shown in FIG. Two fixed value code decoded value tables shown in FIG. 20 (b) are prepared, and when the escape code is decoded in the code (1) decoded value table, the fixed length code decoded value table is read. For example, if the codeword is "10110011"
In the case of “011”, if the leading “1011”, that is, the escape code is decoded, the next three bits “001” are regarded as a fixed-length code and are decoded by the fixed-length code decoding unit 210. In this case, Since 1 is obtained as the decoded value of “001”, the decoded result is an information symbol “K” from the fixed-length code decoded value table of FIG.

Next, an embodiment in which the present invention is applied to a moving image encoder / decoder will be described. FIG. 21 is a block diagram showing a schematic configuration of a moving image encoder / decoder in which the above-described variable length encoding / decoding device is incorporated.

The moving picture encoder 709 shown in FIG.
, The data coded by the information source coder 702 is subjected to variable-length coding, channel coding, multiplexing, and the like by a video multiplexing unit 703, and further to a transmission buffer 704.
After the transmission speed is smoothed in step (1), the data is sent to the transmission system or storage system 705 as encoded data. The encoding control section 701 considers the buffer amount of the transmission buffer 704 and takes into account the information source encoder 702 and the video multiplexing section 70.
3 is performed.

On the other hand, in the moving picture decoder 710 shown in FIG. 21B, the coded data from the transmission system or the storage system 705 is temporarily stored in the reception buffer 706, After the demultiplexing of the encoded data, channel code decoding and variable length code decoding,
The information is sent to the information source decoder 708, and the moving image is finally decoded.

FIG. 22 shows the syntax of the moving picture coding method in the moving picture coder 709 and the moving picture multiplexing / demultiplexing section 707 in FIG. Among the picture layers shown in FIG. 22A, information other than DCT coefficients such as macroblock mode information and motion vector information and INTRA DC is arranged in an upper layer, and DCT coefficient information is arranged in a lower layer. Thus, the reversible code according to the present invention is applied to the lower layer part.

FIGS. 23A and 23B are block diagrams showing a more detailed configuration of the moving picture multiplexing section 703 and the moving picture multiplexing / demultiplexing section 707 in FIG. FIG. 23 (a)
In the moving image multiplexing unit 703 shown in FIG. 21, among the encoded data from the information source encoder 702 in FIG.
Information other than DCT coefficients, such as C, is set as an upper layer, and after normal variable-length coding is performed by an upper-layer variable-length encoder 901, the redundancy is higher in an upper-layer communication channel encoder 902. The data is channel-coded by an error correction detection code having a high correction capability and sent to the multiplexing unit 905.

On the other hand, among the encoded data from the information source encoder 702, the DCT coefficient is
In step 03, the signal is encoded into a reversible code. In the lower layer channel encoder 904, the channel is encoded with an error correction detection code having a low degree of redundancy, and then sent to a multiplexing unit 905. The multiplexing unit 905 multiplexes the encoded data of the upper layer and the encoded data of the lower layer, and
Send to 4.

The moving image demultiplexing / separating unit 7 shown in FIG.
At 07, first, the coded data from the reception buffer 706 is separated by the demultiplexer 906 into an upper layer and a lower layer. The encoded data of the upper layer is decoded by the upper layer channel decoder 907, and the decoding result is sent to the upper layer variable length decoder 909. The lower layer encoded data is decoded by the lower layer channel decoder 908, and the decoding result is sent to the lower layer variable length decoder 910.

The lower layer variable length decoder 910 decodes the reversible code, and outputs the decoding result to the information source decoder 70.
8 and the upper layer variable length decoder 909. The upper layer variable length decoder 909 decodes a variable length code which is encoded data of an upper layer, and rewrites the encoding result based on the decoding result of the lower layer variable length decoder 910.

Here, the lower-layer variable-length encoder 903 in FIG. 23A has the encoding unit 213 in FIG.
The lower layer variable length decoder 910 in (b) corresponds to the decoding unit 214 in FIG.

As can be seen from the moving picture encoder / decoder of this embodiment, when the encoding scheme has the syntax shown in FIG. 22, the variable length code itself can be decoded from both directions. In addition, it is necessary to be able to decode from both directions in terms of syntax. In the present embodiment, this request is realized by using a codeword table described below.

FIGS. 24 to 28 show examples of codeword tables of variable length codes of DCT coefficients used in the lower layer variable length encoder 903. FIG. FIG. 29 shows a codeword table of escape codes.

In the information source encoder 702, the 8
For a block with a DCT coefficient of × 8, scanning inside the block is performed, and LAST (0: non-zero coefficient not at the end of the block, 1: non-zero coefficient at the end of the block), RUN
(Number of zero runs up to non-zero coefficient) and LEVEL (absolute value of coefficient) are obtained and sent to the moving picture encoder 709.

The lower layer variable length encoder 903 in the moving picture encoder 709 includes INTRA and INTER non-LAST coefficients, RUN, and LEVEL shown in FIGS.
And a non-LAST coefficient codeword table (first codeword table) corresponding to reversible code (VLC_CODE), and INTRA and INT shown in FIGS.
It has a code word table (second code word table) of LAST coefficients in which a reversible code (VLC_CODE) is associated with the LAST coefficient, RUN, and LEVEL of ER. Then, based on the mode information, the coding is performed by selecting the code word table of the non-LAST coefficient and the LAST coefficient of the INTRA at the time of INTRA and the code word table of the non-LAST coefficient and the LAST coefficient of the INTER at the time of INTER. Note that VLC_ in FIGS.
“S” of the last bit of CODE indicates the sign of LEVEL, and when “S” is “0”, the sign of LEVEL is positive,
It is negative when “1”.

For the coefficients not present in this code word table, as shown in FIG. 29, the absolute values of RUN and LEVEL are encoded into fixed-length codes, and escape codes are added to the beginning and end of the fixed-length codes. The last bit of the escape code is encoded so that the positive and negative of the LAST coefficient and LEVEL can be distinguished. FIG. 28 is a codeword table of this escape code. The last bit “t” of VLC_CODE used as an escape code indicates whether or not it is a LAST coefficient when added to the beginning of a fixed-length code.
When this is "0", it is a non-LAST coefficient, and when it is "1", it is a LAST coefficient. “T” represents the LEVEL code when added to the end of the fixed-length code. When this is “0”, the LEVEL code is positive, and when it is “1”, it is negative.

FIG. 30 shows an example of encoded data in the present embodiment. As shown in the figure, when decoding is performed in the lower layer from the forward direction, the 8 × 8 pixel D
Since the sign of the LAST coefficient always exists at the end of the block of the CT coefficient, the end of the block can be determined. On the other hand, when decoding is performed in the reverse direction, the beginning of the block can be determined by the appearance of the code of the LAST coefficient of the block one address earlier. This code is LA
Since the ST coefficient is shared between the INTRA mode and the INTER mode, the head of a block can be determined even if a mode exists for each macro block.

For the first block of the lower layer, a dummy LAST coefficient is coded at the beginning of the lower layer by the lower layer variable length encoder 903 or the lower layer variable length decoder 910 generates The number of bits in the lower layer is calculated in advance from the number of bits up to the synchronization code of the next frame, and the calculated number is compared with the number of bits decoded. Alternatively, a buffer in the lower layer variable length decoder 910 is used. By inserting a dummy LAST coefficient at the head of the lower layer, it is possible to determine the head of the lower layer when decoding in the reverse direction.

The reversible codes stored in the code word tables shown in FIGS. 24 to 27 are read in the forward direction if the first bit is “0” until two “0” appear, and If it is "1", it is read until two "1" appear, and it can be seen that the next one bit is the last bit indicating the positive / negative of LEVEL. In the case of the reverse direction, the first one bit indicates the sign of LEVEL, and the next one bit is “0”.
Then, it is sufficient to read until two "0" appear, and if it is "1", it is sufficient to read until two "1" appear.

FIG. 31 shows a decoding graph for decoding a reversible code applied to the variable length code of the DCT coefficient used in the lower layer variable length encoder 903 in the present embodiment. A decoded value can be calculated from the decoded graph of the encoded data except for the first two bits and the last two bits of the codeword when viewed from the forward direction.

In this decoded graph, the first bit is “0”.
Then, when "0" appears, the right arrow advances, and when "1" appears, the left arrow advances. If the first bit is "1", the right arrow is advanced if "1" appears, and the left arrow is advanced if "0" appears.

In order to determine the order value for a binary code sequence having the same code length, according to the Sharkwijk algorithm described above, when the left arrow is selected, the value of the node at the end point of the arrow and the value of the node at the start point are determined. The sum of the subtracted values may be used as the order value at the code length.

On the other hand, in order to obtain the decoded value, if the leading bit is “0”, a value obtained by adding twice the sum of the values of the nodes at the upper right corner of the terminal node to the order value as the decoded value do it.
If the first bit is “1”, the decoded value may be twice the sum of the values of the nodes at the upper right of the terminal node plus the order value to the value of the terminal node.

For example, if the code string to be decoded is “01101”
If “01”, the first bit and the last two bits are removed from the forward direction and set to “1101.” Since the first bit is “0”, if “0” appears in the decoded graph, the right arrow is drawn. Go to the left mark if "1" appears.
In this case, the difference between the nodes when the left arrow is advanced is (1-
1) + (1-1) + (4-3) = 1, the order value is 1
It is. Since the most significant bit is “0”, it is twice (1 + 2 + 3) × 2 = 1 the total of the nodes diagonally right above the terminal node.
When the order 1 is added to 2, the result becomes 13, and the decoded value of this code word is obtained as 13.

FIGS. 32 to 34 show an example of a decoded value table used in the lower layer variable length decoder 910.
33 shows a non-LAST coefficient obtained by associating a decoded value with a non-LAST coefficient, RUN, and LEVEL of INTRA and INTER.
FIG. 34 (a) and FIG. 34 (b) are decoded value tables of T coefficients, and LAST coefficients, RUN,
It is a decoded value table of the LAST coefficient which made the decoded value correspond to LEVEL. FIG. 34C shows a decoded value table of the escape code.

In this example, for example, the decoded value 13 is
As can be seen from (a), the LAST coefficient is RUN number 3, the absolute value of LEVEL is 1, and the least significant bit is "1", indicating that LEVEL is negative. . Further, as can be seen from FIG. 34C, when the decoded value 41 is decoded, it is determined that the escape code has been decoded. The last bit of this escape code is used to determine whether it is a LAST coefficient or a non-LAST coefficient.
After decoding the absolute values of RUN and LEVEL at 10, the escape code is decoded again, and the sign of LEVEL is determined by the last bit.

As an example, if the code string to be coded is "11
000000010000111000101111000
010. In this case, since the last bit of the leading escape code “11000010” is “0”, it is a non-LAST coefficient, and the subsequent 13-bit fixed-length code is calculated. Since 6 bits represent the RUN, the RUN is 7, with "000111".
Since the lower 7 bits represent the absolute value of LEVEL, "00"
01011 ”, the absolute value of LEVEL is 12, and the last bit of the last escape code“ 11000010 ”is“ 0 ”.
Therefore, LEVEL can be decoded as positive.

The decoding value determination section 212 compares the decoding result obtained by the forward decoder 209 (referred to as forward decoding result) with the decoding result obtained by the backward decoder 211 (reverse decoding result). A decoded value is determined from the decoded value, and a final decoded result is output. That is, if there is an error in the encoded data, the decoded value determination unit 212 recognizes the presence of the error because the decoding result of the lower layer channel decoder 908 or a bit pattern that did not exist as a codeword occurs. Therefore, a decoded value is determined from the forward decoding result and the backward decoding result as shown in FIG. FIG. 36 shows a method of determining a decoded value of a lower layer.

First, as shown in FIG. 36 (a), when the macroblock position (error detection position) where an error is detected in the forward decoding result and the reverse decoding result does not intersect, no error is detected. Only the decoding result of the macroblock is used as a decoding value, and the decoding results of two error detection positions are not used as decoding values. Then, based on the decoding result of the mode information of the upper layer, the INTER
The decoding result of the upper layer is rewritten so that the R macroblock is displayed only by the motion compensation from the previous frame.

When an error detection position intersects between a forward decoding result and a backward decoding result as shown in FIG. 36 (b), a decoding result in which no error is detected in both is used as a decoding result value. I do. Also, in this case, the decoding result between the codewords at the two error detection positions is not used as a decoding value, and IN
The decoding result of the upper layer is rewritten so that the previous frame is displayed as it is for the TRA macroblock, and only the motion compensation is displayed for the INTER macroblock from the previous frame.

As shown in FIG. 36 (c), when an error is detected only in the one-way decoding result among the forward decoding result and the backward decoding result (in this example, only the forward decoding result has an error). Is detected), the macroblock at the error detection position is not used as a decoded value, and based on the decoding result of the mode information of the upper layer, the previous frame is displayed as it is for the INTRA macroblock,
The decoding result of the upper layer is rewritten so that the INTER macroblock is displayed only by the motion compensation from the previous frame. The decoded value for the subsequent macroblock uses the decoding result in the reverse direction.

Further, when an error is detected in both the forward decoding result and the backward decoding result in the same macroblock as shown in FIG. 36 (d), the decoded value of the macroblock at the error detection position is abandoned. Without using it as a decryption value.
Based on the decoding result of the mode information of the upper layer, INTR
The decoding result of the upper layer is rewritten so that the previous frame of A macroblock is displayed as it is, and the macroblock of INTER is displayed only by motion compensation from the previous frame. Use the decryption result of

The order of encoding / decoding macroblocks may be a method other than the above embodiment. For example, when an error occurs, a more important central portion of the decoded image is rescued. A method shown in FIG. 37 may be used. That is, assuming that decoding is performed from both directions, the probability that the first part and the last part of the encoded data between the synchronization codes are correctly decoded is high. The order is determined so that is in the center.

In the above embodiment, the present invention is applied to variable-length coding of DCT coefficients. However, it goes without saying that the same variable-length coding can be applied to other information symbols.

In the above embodiment, only the binary code has been discussed. However, the present invention can be easily extended to a multiple code, and similar effects can be obtained.

Finally, as an application example of the present invention, an embodiment of an image transmitting / receiving apparatus to which the variable length encoding / decoding apparatus according to the present invention is applied will be described with reference to FIG. An image signal input from a camera 1002 provided in a personal computer (PC) 1001 is encoded by a variable-length encoding device incorporated in the PC 1001. The information symbol in this case is not limited to this,
For example, DCT coefficient data obtained by performing discrete cosine transform by a DCT circuit on an input image signal or a prediction error signal which is a difference between the input image signal and the predicted image signal, and further quantizing by a quantization circuit. The coded data output from the variable length coding device is multiplexed with other voice and data information, transmitted by radio by the wireless device 1003, and received by the other wireless device 1004. Radio 1
The signal received at 004 is decomposed into coded data of the image signal and information of voice and data. Of these,
The encoded data of the image signal is transmitted to the workstation (EW
S) It is decoded by the variable length code decoding device incorporated in 1005 and displayed on the display of EWS 1005.

On the other hand, an image signal input from a camera 1006 provided in the EWS 1005 is
6 is encoded in the same manner as described above using the variable length encoding device incorporated in 6. The encoded data is multiplexed with other voice or data information, transmitted wirelessly by the wireless device 1004, and received by the wireless device 1003. Wireless device 100
The signal received by 3 is decomposed into encoded data of an image signal and information of voice and data. Among them, the coded data of the image signal is decoded by the variable-length code decoding device incorporated in the PC 1001,
01 is displayed on the display.

The variable length coding / decoding device of the present invention has a code length corresponding to the frequency of appearance of information symbols, has less wasteful bit patterns and is more efficient than the conventional one, Since it is possible to form a reversible variable length code that can be decoded in the reverse direction as well, it is particularly effective in a transmission / reception apparatus using a transmission line having many errors such as the wireless transmission line shown in FIG.

As described in the above embodiment, the variable-length encoding / decoding device of the present invention can decode with a smaller storage amount as compared with the conventional one, and cannot be applied conventionally. It can also be applied to coding with a large number of information symbols.

More specifically, the present invention can be applied to a moving picture encoding / decoding apparatus, and can provide a moving picture encoding / decoding apparatus that is resistant to errors.

[0108]

As described above, according to the present invention, a variable length code which can be decoded in both the forward and reverse directions, and which is practical in terms of coding efficiency and storage capacity required for the apparatus. An encoding / decoding device can be provided.

That is, in the present invention, the first codeword tables corresponding to the orthogonal transform coefficients other than the end of the block for a plurality of encoding modes are individually formed, but correspond to the last orthogonal transform coefficients of the block. The second codeword table to be used is common to each coding mode, so that it is possible to cope with a change in the codeword table depending on the coding mode, and to decode a codeword representing the last orthogonal transform coefficient of a block during decoding. Since the block delimiter can be identified by the appearance of a codeword representing the last orthogonal transform coefficient of the previous block, decoding can be performed from both directions in terms of syntax, as well as in intra mode and inter mode. By separately providing a second codeword table for a plurality of encoding modes having different occurrence frequencies from the orthogonal transform coefficients generated in It can be improved Goka efficiency.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a variable-length encoding / decoding device according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of a decoded value determination unit in FIG.

FIG. 3 is a block diagram of a codeword table creation unit in FIG. 1;

FIG. 4 is a diagram showing a method for generating a binary code sequence having a constant weight as a basis of a variable length code according to the present invention;

FIG. 5 is a diagram showing a first codeword configuration method in a codeword configuration unit in FIG. 3;

FIG. 6 is a diagram showing forward and backward decoding trees created from codewords configured by the first code configuration method;

FIG. 7 is a diagram showing a second codeword configuration method in the codeword configuration unit in FIG. 3;

FIG. 8 is a diagram showing forward and backward decoding trees created from codewords configured by a second code configuration method;

9 is a diagram showing a third code configuration method in the codeword configuration unit in FIG. 3;

FIG. 10 is a diagram showing forward and backward decoding trees created from codewords configured by a third code configuration method;

FIG. 11 is a diagram showing a code shortening method in the code word forming unit in FIG. 3;

FIG. 12 is a diagram showing forward and backward decoding trees created from codewords shortened by a code shortening method.

FIG. 13 is a diagram showing a code enlarging method in the code word forming unit in FIG. 3;

FIG. 14 is a diagram showing a comparison between characteristics of the variable length code configured in the present embodiment and a variable length code of a known example.

FIG. 15 is a diagram illustrating variable-length coding / coding according to another embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration of a decoding device.

16 is a diagram showing a code configuration method in the codeword configuration unit in FIG.

FIG. 17 is a diagram showing a method of counting a binary sequence having a constant weight.

FIG. 18 is a diagram showing operations of a forward decoder and a backward decoder in FIG.

FIG. 19 is a diagram showing a comparison between a conventional decoding tree and a decoding graph according to the present embodiment;

FIG. 20 is a view for explaining a decoded value table according to the embodiment;

FIG. 21 is a block diagram showing a schematic configuration of a moving image encoder / decoder incorporating the variable length encoding / decoding device according to the present invention;

FIG. 22 is a view showing the syntax of encoded data in the video encoder / decoder according to the embodiment;

FIG. 23 is a block diagram showing a configuration of a moving image multiplexing unit and a moving image multiplexing / demultiplexing unit in FIG. 21;

FIG. 24 shows INTRA and INT in the embodiment.
The figure which shows a part of codeword table of the non-LAST coefficient of ER

FIG. 25 shows INTRA and INT in the embodiment.
The figure which shows another part of codeword table of the non-LAST coefficient of ER

FIG. 26 shows INTRA and INT in the embodiment.
FIG. 4 is a diagram illustrating a part of a codeword table of LAST coefficients of ER;

FIG. 27 shows INTRA and INT in the embodiment.
The figure which shows another part of codeword table of the LAST coefficient of ER

FIG. 28 is a diagram showing a codeword table of an escape code in the embodiment.

FIG. 29 is a diagram showing an encoding method of a codeword not in a codeword table in the embodiment.

FIG. 30 is a view showing an example of encoded data in the embodiment.

FIG. 31 is a view showing a decoding graph in the embodiment;

FIG. 32 shows INTRA and INT in the embodiment.
The figure which shows a part of decoding value table of the non-LAST coefficient of ER

FIG. 33 shows INTRA and INT in the embodiment.
The figure which shows the other part of the decoding value table of the non-LAST coefficient of ER

FIG. 34 shows INTRA and INT in the embodiment.
The figure which shows the decoding value table of the LAST coefficient of ER

FIG. 35 is a view showing a decoded value table of an escape code in the embodiment.

FIG. 36 is a diagram for explaining the operation of the decoded value determination unit in FIG.

FIG. 37 is a diagram showing an encoding / decoding order of macro blocks in the embodiment.

FIG. 38 is a diagram showing an example of an apparatus in which the variable length encoding / decoding apparatus according to the present invention is incorporated.

FIG. 39 is a diagram showing a general decoding method of a reversible code.

FIG. 40 is an explanatory diagram of a normal variable length code.

FIG. 41 is an explanatory diagram of a conventional reversible code.

[Explanation of symbols]

 101 codeword table creation unit 102 codeword table 103 encoder 104 transmission or storage system 105 synchronization code detector 106 buffer 107 forward decoder 108 backward decoder 109 decoding Value judging unit 110: forward decoded word table 111: forward decoding tree creating unit 112: backward codeword table 113 ... backward decoding tree creating unit 114: encoding unit 115: decoding unit 21: code selecting unit 22 ... Codeword configuration unit 201 Codeword table creation unit 202 Codeword table 203 Encoder 204 Fixed length code encoding unit 205 Transmission or storage system 206 Synchronous code detection unit 207 Buffer 208 Decoding graph Decoded value table creation unit 209: forward decoder 220: fixed-length code decoding unit 211: backward decoder 212: decoding Signal value determination unit 213 Encoding unit 214 Decoding unit 701 Encoding control unit 702 Information source encoder 703 Moving image multiplexing unit 704 Transmission buffer 705 Transmission system or accumulation system 706 reception buffer 707 ··· Moving picture multiplexing and demultiplexing unit 708 ··· Information source decoder 709 ··· Moving picture encoder 710 ··· Moving picture decoder 901 · · · Lower layer variable length decoder 902 · · · Upper layer channel encoder 903 · Lower layer Variable length encoder 904: Lower layer channel encoder 905: Multiplexer 906 ... Demultiplexer 907 ... Upper layer channel decoder 908 ... Lower layer channel decoder 909: Upper layer variable length decoding 910: Lower layer variable length decoder 1001: Personal computer 1002: Workstation 1003: Wireless device 1004: Wireless device 1005: Camera 1006… Camera

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 5C059 KK09 MA23 ME03 ME10 ME13 ME15 RE01 SS06 SS11 UA02 UA05 UA34 5J064 AA04 BA09 BA16 BB08 BB09 BC01 BC02 BC14 BD02

Claims (2)

[Claims] A codeword having a code length corresponding to the probability of occurrence of orthogonal transform coefficients is assigned to orthogonal transform coefficients that can be generated by performing orthogonal transform in block units. In a variable-length encoding method for outputting a codeword corresponding to a generated orthogonal transform coefficient as encoded data, a plurality of codewords that can be decoded in both forward and reverse directions for each of a plurality of encoding modes. A first codeword table stored in correspondence with orthogonal transform coefficients other than the last of the block, and a plurality of codeword tables provided in common for the plurality of encoding modes and capable of decoding in both forward and reverse directions. Constitutes a second codeword table in which codewords corresponding to the last orthogonal transform coefficients of the block are stored, and codes corresponding to the orthogonal transform coefficients from the first and second codeword tables. Variable length coding method characterized by select the output as coded data. 2. A codeword having a code length corresponding to an occurrence probability of the orthogonal transform coefficient is assigned to an orthogonal transform coefficient which can be generated by performing an orthogonal transform on a block basis. In a variable-length encoding device that outputs codewords corresponding to generated orthogonal transform coefficients as encoded data, a plurality of codewords that can be decoded in both forward and reverse directions for each of a plurality of encoding modes. A first codeword table stored corresponding to orthogonal transform coefficients other than the last of the block, and a plurality of codeword tables provided in common for the plurality of encoding modes and capable of decoding in both forward and reverse directions. A codeword corresponding to the orthogonal transform coefficient is selected from a second codeword table storing the codewords corresponding to the last orthogonal transform coefficient of the block, and a codeword corresponding to the orthogonal transform coefficient from the first and second codeword tables. To the variable length coding apparatus characterized by comprising an encoding means for outputting as encoded data.