Moving picture coding and/or decoding systems, and variable-length coding and/or decoding system

Abstract

A coding and/or decoding system includes: a code-word table for storing therein a plurality of code words, which are capable of being decoded both in forward and backward directions and which are formed so that delimiters of the code words are capable of being identified by a predetermined weight of the code words, so that the code words correspond to different source symbols; an encoder for selecting code words corresponding to inputted source symbols from the code-word table; and a synchronization interval setting part for preparing coded data every predetermined interval using the code words selected by the encoder and for inserting stuffing codes capable of being decoded in the backward direction. Thus, it is possible to decrease useless bit patterns to enhance the coding efficiency by smaller amounts of calculation and storage, and to decode variable length codes both in the forward and backward directions even if the synchronization interval is set every interval using the stuffing bits.

What is claimed is:  
     
         1 . A variable length coding system, which assigns, to a plurality of source symbols, code words having a code length corresponding to the occurrence probability of the source symbols and which outputs code words corresponding to inputted source symbols as coded data, said variable length coding system comprising: 
 a code-word table for storing therein a plurality of code words including codes words, which are capable of being decoded both in forward and backward directions and which are formed so that delimiters of the code words are capable of being identified by a predetermined weight of the code words, so that said plurality of code words correspond to source symbols;    code-word selecting means for selecting code words corresponding to inputted source symbols from the code-word table; and    synchronization interval setting means for preparing coded data for each of predetermined synchronization intervals using code words selected by said code-word selecting means and for inserting stuffing codes capable of being decoded in the backward direction.    
     
     
         2 . A variable length coding system as set forth in  claim 1 , wherein said code words, which are capable of being decoded both in the forward and backward directions and which are formed so that the delimiters of the code words are capable of being identified by a predetermined weight of the code words, have first and second code words, which are capable of being decoded both in the forward and backward directions, said second code word being added to at least one of the prefix and suffix of said first code word.  
     
     
         3 . A variable length coding system as set forth in  claim 1 , wherein said code words, which are capable of being decoded both in the forward and backward directions and which are formed so that the delimiters of the code words are capable of being identified by a predetermined weight of the code words, have first and second code words, which are capable of being decoded both in the forward and backward directions, said second code word being added at least one of immediately before and after the respective bits of said first code word.  
     
     
         4 . A variable length coding system as set forth in  claim 1 , wherein said code words, which are capable of being decoded both in the forward and backward directions and which are formed so that the delimiters of the code words are capable of being identified by a predetermined weight of the code words, have code words, which are capable of being decoded both in the forward and backward directions and between the respectively bits of which code words of a fixed length code are inserted by predetermined bits.  
     
     
         5 . A variable length coding system as set forth in  claim 1 , wherein said code words, which are capable of being decoded both in the forward and backward directions and which are formed so that the delimiters of the code words are capable of being identified by a predetermined weight of the code words, have first and second code words, which are capable of being decoded both in forward and backward directions, said second code word being inserted between the respective bits of said first code word.  
     
     
         6 . A variable length coding system, which assigns, to a plurality of source symbols, code words having a code length corresponding to the occurrence probability of the source symbols and which outputs code words corresponding to inputted source symbols as coded data, said variable length coding system comprising: 
 layering means for layering inputted source symbols in accordance with importance;    a code-word table for storing therein a plurality of code words including codes words, which are capable of being decoded both in the forward and backward directions and which are formed so that the delimiters of the code words are capable of being identified by a predetermined weight of the code words, so that said plurality of code words correspond to the source symbols;    code-word selecting means for selecting code words corresponding to the inputted source symbols layered by said layering means, from the code-word table; and    synchronization interval setting means for preparing coded data of each of layers for each of predetermined synchronization intervals using code words selected by said code-word selecting means and for multiplexing the coded data of each of layers.    
     
     
         7 . A variable length coding system as set forth in  claim 6 , wherein said code words, which are capable of being decoded both in the forward and backward directions and which are formed so that the delimiters of the code words are capable of being identified by a predetermined weight of the code words, have first and second code words, which are capable of being decoded both in the forward and backward directions, said second code word being added to at least one of the prefix and suffix of said first code word.  
     
     
         8 . A variable length coding system as set forth in  claim 6 , wherein said code words, which are capable of being decoded both in the forward and backward directions and which are formed so that the delimiters of the code words are capable of being identified by a predetermined weight of the code words, have first and second code words, which are capable of being decoded both in the forward and backward directions, said second code word being added at least one of immediately before and after the respective bits of said first code word.  
     
     
         9 . A variable length coding system as set forth in  claim 6 , wherein said code words, which are capable of being decoded both in the forward and backward directions and which are formed so that the delimiters of the code words are capable of being identified by a predetermined weight of the code words, have code words, which are capable of being decoded both in the forward and backward directions and between the respectively bits of which code words of a fixed length code are inserted by predetermined bits.  
     
     
         10 . A variable length coding system as set forth in  claim 6 , wherein said code words, which are capable of being decoded both in the forward and backward directions and which are formed so that the delimiters of the code words are capable of being identified by a predetermined weight of the code words, have first and second code words, which are capable of being decoded both in the forward and backward directions, said second code word being inserted between the respective bits of said first code word.  
     
     
         11 . A variable length decoding system for decoding coded data, which are of variable length codes of code words containing code words capable of being decoded both in forward and backward directions and into which stuffing codes capable of being decoded in the backward direction are inserted every predetermined synchronization interval, said variable length decoding system comprising: 
 synchronization interval detecting means for detecting a synchronization interval of said coded data;    forward decoding means for decoding, in the forward direction, the coded data in the synchronization interval detected by said synchronization interval detecting means; and    backward decoding means for decoding, in the backward direction, the data in the synchronization interval detected by said synchronization interval detecting means.    
     
     
         12 . A variable length decoding system as set forth in  claim 11 , wherein when a code word, which does not exist in a code-word table of a variable length code, appears in the coded data, at least one of said forward decoding means and said backward decoding means detects the coded data as an error.  
     
     
         13 . A variable length decoding system as set forth in  claim 11 , wherein when the bit number of the decoded coded data is not coincident with the bit number of transmitted coded data, at least one of said forward decoding means and said backward decoding means detects as an error.  
     
     
         14 . A variable length decoding system as set forth in  claim 11 , wherein when a decoded value obtained by decoding the coded data is inadequate, at least one of said forward decoding means and said backward decoding means detects as an error or decoding processing.  
     
     
         15 . A variable length decoding system as set forth in  claim 11 , wherein said synchronization interval detecting means detects the bit number of said coded data by decoding said stuffing code in the backward direction.  
     
     
         16 . A variable length decoding system for decoding coded data, which are of variable length codes of code words containing code words capable of being decoded both in forward and backward directions and into which stuffing codes capable of being decoded in the backward direction are inserted every predetermined synchronization interval, said variable length decoding system comprising: 
 synchronization interval detecting means for detecting a synchronization interval of said coded data;    forward decoding means for decoding, in the forward direction, the coded data in the synchronization interval detected by said synchronization interval detecting means;    backward decoding means for decoding, in the backward direction, the data in the synchronization interval detected by said synchronization interval detecting means; and    decoded-value determining means for determining a decoded value on the basis of decoded results of said forward decoding means and said backward decoding means to output a final decoded result.    
     
     
         17 . A variable length decoding system as set forth in  claim 16 , wherein when a code word, which does not exist in a code-word table of a variable length code, appears in the coded data, at least one of said forward decoding means and said backward decoding means detects the coded data as an error.  
     
     
         18 . A variable length decoding system as set forth in  claim 16 , wherein when the bit number of the decoded coded data is not coincident with the bit number of transmitted coded data, at lease one of said forward decoding means and said backward decoding means detects as an error.  
     
     
         19 . A variable length decoding system as set forth in  claim 16 , wherein when a decoded value obtained by decoding coded data is inadequate, at least one of said forward decoding means and said backward decoding means detects as an error of decoding processing.  
     
     
         20 . A variable length decoding system as set forth in  claim 16 , wherein when an error is detected by at least one of said forward decoding means and said backward decoding means, said decoded-value determining means uses a decoded result, which is presumed to be correct, of decoded results of said forward decoding means and said backward decoding means, and abandons a portion which is not able to be decoded in both of the decoded results.  
     
     
         21 . A variable length decoding system as set forth in  claim 16 , wherein said decoded-value determining means: 
 (a) uses, as decoded values, only decoded values, in which no error is detected, when said error is detected in both of said forward decoding means and said backward decoding means and when the ways to the error detected positions do not overlap with each other;    (b) uses forward decoded results as decoded values for code words immediately before a position, at which said error is found by said forward decoding means, and uses backward decoded results as decoded values for code words after the position, when errors have been detected both in said forward decoding means and said backward decoding means and when the ways to error detected positions overlap with each other;    (c) uses forward decoded results as coded values for code words immediately before a position, at which said error is detected, and uses backward decoded results as decoded values for code words after the position, when said error has been detected by only one of said forward decoding means and said backward decoding means; and    (d) abandons decoded values for code words at the position, at which said error has been decoded, and uses backward decoded results as decoded values for code words after the position, when said error has been detected for the same code word by said forward decoding means and said backward decoding means.    
     
     
         22 . A variable length decoding system as set forth in  claim 16 , wherein said decoded-value determining means abandons all the decoded results, in which there is a probability that an error may exist, when said error has been detected by at least one of said forward decoding means and said backward decoding means.  
     
     
         23 . A variable length decoding means as set forth in  claim 16 , wherein said synchronization interval detecting means detects the bit number of said coded data by decoding said stuffing codes in the backward direction.  
     
     
         24 . A variable length decoding system for decoding coded data every predetermined synchronization interval, said coded data comprising variable length codes, which are of code words containing code words capable of being decoded both in forward and backward directions, and said coded data being prepared by code words corresponding to layered source symbols to be multiplexed, said variable length decoding system comprising: 
 dividing means for dividing said multiplexed coded data into respective layers;    synchronization interval detecting means for detecting a synchronization interval of said coded data divided by said dividing means;    forward decoding means for decoding, in the forward direction, the coded data in the synchronization interval detected by said synchronization interval detecting means;    backward decoding means for decoding, in the backward direction, the data in the synchronization interval detected by said synchronization interval detecting means; and    synthesizing means for synthesizing decoded results of respective layers obtained by said forward decoding means and said backward decoding means.    
     
     
         25 . A variable length decoding system as set forth in  claim 24 , wherein when a code word, which does not exist in a code-word table of a variable length code, appears in the coded data, at least one of said forward decoding means and said backward decoding means detects the coded data as an error.  
     
     
         26 . A variable length decoding system as set forth in  claim 24 , wherein when the bit number of the decoded coded data is not coincident with the bit number of transmitted coded data, at lease one of said forward decoding means and said backward decoding means detects as an error.  
     
     
         27 . A variable length decoding system as set forth in  claim 24 , wherein when a decoded value obtained by decoding coded data is inadequate, at least one of said forward decoding means and said backward decoding means detects as an error of decoding processing.  
     
     
         28 . A variable length decoding system for decoding coded data every predetermined synchronization interval, said coded data comprising variable length codes, which are of code words containing code words capable of being decoded both in forward and backward directions, and said coded data being prepared by code words corresponding to layered source symbols to be multiplexed, said variable length decoding system comprising: 
 dividing means for dividing said multiplexed coded data into respective layers;    synchronization interval detecting means for detecting a synchronization interval of said coded data divided by said dividing means;    forward decoding means for decoding, in the forward direction, the coded data in the synchronization interval detected by said synchronization interval detecting means;    backward decoding means for decoding, in the backward direction, the data in the synchronization interval detected by said synchronization interval detecting means;    decoded-value determining means for determining decoded values on the basis of decoded results of respective layers obtained by said forward decoding means and said backward decoding means, to output final decoded results; and    synthesizing means for synthesizing final decoded results of respective layers obtained by said decoded-value determining means.    
     
     
         29 . A variable length decoding system as set forth in  claim 28 , wherein when a code word, which does not exist in a code-word table of a variable length code, appears in the coded data, at least one of said forward decoding means and said backward decoding means detects the coded data as an error.  
     
     
         30 . A variable length decoding system as set forth in  claim 28 , wherein when the bit number of the decoded coded data is not coincident with the bit number of transmitted coded data, at lease one of said forward decoding means and said backward decoding means detects as an error.  
     
     
         31 . A variable length decoding system as set forth in  claim 28 , wherein when a decoded value obtained by decoding coded data is inadequate, at least one of said forward and backward decoding means detects as an error of decoding processing.  
     
     
         32 . A variable length decoding system as set forth in  claim 28 , wherein when an error is detected by at least one of said forward decoding means and said backward decoding means, said decoded-value determining means uses a decoded result, which is presumed to be correct, of decoded results of said forward decoding means and said backward decoding means, and abandons a portion which is not able to be decoded in both of the decoded results.  
     
     
         33 . A variable length decoding system as set forth in  claim 28 , wherein said decoded-value determining means: 
 (a) uses, as decoded values, only decoded values, in which no error has been detected, when said error is detected in both of said forward decoding means and said backward decoding means and when the ways to the error detected positions do not overlap with each other;    (b) uses forward decoded results as decoded values for code words immediately before a position, at which said error is found by said forward decoding means, and uses backward decoded results as decoded values for code words after the position, when errors are detected both in said forward decoding means and said backward decoding means and when the ways to error detected positions overlap with each other;    (c) uses forward decoded results as coded values for code words immediately before a position, at which said error is detected, and uses backward decoded results as decoded values for code words after the position, when said error is detected by only one of said forward decoding means and said backward decoding means; and    (d) abandons decoded values for code words at the position, at which said error has been decoded, and uses backward decoded results as decoded values for code words after the position, when said error is detected for the same code word by said forward decoding means and said backward decoding means.    
     
     
         34 . A variable length decoding system as set forth in  claim 16 , wherein said decoded-value determining means abandons all the decoded results, in which there is a probability that an error may exist, when said error is detected by at least one of said forward decoding means and said backward decoding means.  
     
     
         35 . A variable length decoding system for decoding coded data, which are of variable length codes of code words containing code words capable of being decoded both in forward and backward directions and into which stuffing codes capable of being decoded in a backward direction are inserted every predetermined synchronization interval, said variable length decoding system comprising: 
 synchronization interval detecting means for detecting a synchronization interval of said coded data; and    bidirectional decoding means for decoding, both in forward and backward directions, the coded data in the synchronization interval detected by said synchronization interval detecting means.    
     
     
         36 . A variable length decoding system as set forth in  claim 35 , wherein said synchronization interval detecting means detects the bit number of said coded data by decoding said stuffing code in the backward direction.  
     
     
         37 . A variable length decoding system as set forth in  claim 35 , wherein when a code word, which does not exist in a code-word table of a variable length code, appears in the coded data in at least one of said forward and backward decoding processes, said bidirectional decoding means detects said code word as an error.  
     
     
         38 . A variable length decoding system as set forth in  claim 35 , wherein when the bit number of the decoded coded data is not coincident with the bit number of transmitted coded data in at lease one of said forward and backward decoding processes, said bidirectional decoding means detects as an error.  
     
     
         39 . A variable length decoding system as set forth in  claim 35 , wherein when a decoded value obtained by decoding coded data is inadequate in at least one of said forward and backward decoding processes, said bidirectional decoding means detects as an error of decoding processing.  
     
     
         40 . A variable length decoding system as set forth in  claim 39 , wherein said bidirectional decoding means carries out the backward decoding process from the suffix of said coded data after carrying out the forward decoding process.  
     
     
         41 . A variable length decoding system as set forth in  claim 40 , wherein said bidirectional decoding means stops the forward decoding process and carries out the backward decoding process from the suffix of the coded data, when an error is detected in the forward decoding process.  
     
     
         42 . A variable length coding system as set forth in  claim 40 , wherein said bidirectional decoding means carries out the backward decoding process from the suffix of the coded data after carrying out the forward decoding process.  
     
     
         43 . A variable length decoding system as set forth in  claim 40 , wherein when an error is detected in the forward decoding process, said bidirectional decoding means resumes the forward decoding process from a position apart from the position of the error by a predetermined distance.  
     
     
         44 . A variable length decoding system as set forth in  claim 40 , wherein when an error is detected in the forward decoding process, said bidirectional decoding means carries out the backward decoding process from a position apart from the position of the error by a predetermined distance to the position of the error.  
     
     
         45 . A variable length decoding system as set forth in  claim 35 , wherein said bidirectional decoding means carries out the backward decoding process from the suffix of said coded data after carrying out the forward decoding process.  
     
     
         46 . A variable length decoding system as set forth in  claim 45 , wherein when an error is detected in the forward decoding process, said bidirectional decoding means carries out the backward decoding process from a position apart from the position of the error by a predetermined distance to the position of the error.  
     
     
         47 . A variable length decoding system as set forth in  claim 45 , wherein said bidirectional decoding means carries out the backward decoding process only when an error is detected in the suffix of the coded data in the forward decoding process.  
     
     
         48 . A recording medium for having recorded therein data for use in a variable length coding and/or decoding system, said recording medium having recorded therein variable length coded data capable of being inputted and outputted by the variable length coding and/or decoding system, said recording medium recording therein: 
 coded data including code words, which are capable of being decoded both in forward and backward direction and which are formed so that the delimiters of the code words are identified by a predetermined weight of the code words; and    data, in which stuffing codes capable of being decoded in the backward direction every predetermined synchronization interval are inserted into said coded data.    
     
     
         49 . A recording medium for having recorded therein data for use in a variable length coding and/or decoding system, said recording medium having recorded therein transform coefficient data capable of being produced by orthogonal transforming every block in an image coding and/or decoding system, said recording medium recording therein: 
 said transform coefficient data, wherein a plurality of code words capable of being decoded both in forward and backward directions correspond to orthogonal transform coefficients having high appearance frequencies other than the last orthogonal transform coefficients of the block, for each of a plurality of coded modes of said image coding and/or decoding system;    data, wherein a plurality of code words capable of being decoded both in the forward and backward directions are commonly provided for a plurality of coded modes of said image coding and/or decoding system and correspond to orthogonal transform coefficients having high appearance frequencies of the last orthogonal transform coefficients of the block;    data, wherein transform coefficient data having a low appearance frequency are described by fixed length codes, and code words capable of being decoded both in forward and backward directions are added to the prefix and suffix thereof; and    data, wherein stuffing codes capable of being decoded in the backward direction are inserted in the coded data every predetermined synchronization interval.    
     
     
         50 . A recording medium having recorded therein a program for use in a variable length coding system, which assigns, to a plurality of source symbols, code words having a code length according to occurrence probability of the source symbols, to output code words corresponding to inputted source symbols as coded data, said recording medium including at least the steps of: 
 storing a code-word table, wherein a plurality of code words including code words, which are capable of being decoded both in forward and backward directions and which are formed so that the delimiters of the code words are capable of being identified by a predetermined weight of the code words, correspond to source symbols;    selecting code words corresponding to said inputted source symbols from said code-word table; and    preparing coded data every synchronization interval by using the code words selected by said code-word selecting step, and setting a synchronization interval to said code words by inserting stuffing codes capable of being decoded in the backward direction.    
     
     
         51 . A recording medium having recorded therein a program for use in a variable length decoding system for decoding coded data, which are of variable length codes of code words including code words capable of being decoded both in forward and backward directions and into which stuffing codes capable of being decoded in the backward direction are inserted every predetermined synchronization interval, said recording medium including at least the steps of: 
 detecting a synchronization interval of said coded data;    decoding the coded data in the synchronization interval detected by said synchronization interval detecting step in the forward direction; and    decoding the coded data in the synchronization interval detected by said synchronization interval detecting step in the backward direction.