Method and apparatus for CAVLC decoding
A CAVLC decoding method and apparatus is provided. In the method for decoding a coded bitstream using a CAVLC length table and a CAVLC value table, CAVLC length tables are re-sorted in an order of a codeword length and the coded bitstream is decoded using the re-sorted length table. Therefore, since data on a bitstream is sequentially read as much as a length suggested by the re-sorted table of the present invention, a memory access time is reduced and calculation complexity for comparing the CAVLC codewords is reduced.
1. A CAVLC (context-based adaptive variable length coding) decoding method for decoding a coded bitstream using CAVLC length tables and CAVLC value tables, the method comprising the steps of:
re-sorting the CAVLC Length tables in an order of a codeword length; and
decoding the coded bitstream using the re-sorted length tables;
wherein the step of re-sorting the CAVLC length tables is performed for each table of CAVLC variables, and each table comprises a Total_Zeros variable table including a Total_Coeff, a Total_Zeros variable table including a Total_Coeff for a Chroma DC, a run_before variable table of a CAVLC, a Total_Coeff and TrailingOnes variable tables, a Total_Coeff for a Chroma and TrailingOnes variable tables.
2. The method of claim 1 , wherein the step of re-sorting the CAVLC length tables uses a binary tree.
3. The method of claim 2 , wherein the binary tree has a symmetric structure and has ‘1’ assigned to its left branch and ‘0’ assigned to its right branch.
4. The method of claim 2 , wherein the step of re-sorting is so performed as to compare a codeword length last if the codeword length consisting of zero within the same column of the CAVLC length table is not a lowermost level of the binary tree.
5. The method of claim 1 , wherein the step of re-sorting the CAVLC length tables in the order of the codeword length is performed in such an order that a short codeword length is sorted first, namely, a codeword length having a high possibility of generation is sorted first.
6. The method of claim 1 , wherein the step of decoding the coded bitstream comprises the steps of
selecting a table that corresponds to a variable desired to be decoded among the re-sorted tables;
reading the bitstream as much as the codeword length sequentially starting from a first codeword length in a reference column within the selected table;
comparing a value of the read bitstream with a value on the CAVLC value table, held by a codeword length that coincides with the read codeword length in a column that coincides with the reference column within the CAVLC length table; and
if the value of the bitstream value coincides with the value on the CAVLC value table as a result of the comparison, storing a variable value at that point.
7. The method of claim 6 , wherein the reference column is a column selected from information included in a header part of a packet enclosing the bitstream and information of a decoded adjacent block.
8. The method of claim 6 , wherein if the read bitstream value is zero, the bitstream is read as much as a codeword length that corresponds to a value next to a value compared in the reference column on the re-sorted table.
9. The method of claim 8 , wherein if a codeword value that corresponds to a codeword length for the next value is zero, a process is terminated.
10. The method of claim 6 , wherein if the bitstream value does not coincide with the value on the CAVLC value table as a result of the comparison, the bitstream is read as much as a codeword length that corresponds to a value next to a value compared in the reference column on the re-sorted table.
11. A CAVLC (context-based adaptive variable length coding) decoding method for decoding a coded bitstream using CAVLC length tables and CAVLC value tables, the method comprising the steps of:
selecting a table that corresponds to a variable desired to be decoded among tables in which the CAVLC length tables set and inputted in advance are re-sorted based on an order of a codeword length;
reading the bitstream as much as the codeword length sequentially starting from a first codeword length in a reference column within the selected table;
comparing the read bitstream value with a value on the CAVLC value table, held by a codeword length that coincides with the read codeword length in a column that coincides with the reference column within the CAVLC length table; and
if the bitstream value coincides with the value on the CAVLC value table as a result of the comparison, storing a variable value at that point;
wherein the CAVLC length table comprises a Total_Zeros variable table including a Total_Coeff, a Total_Zeros variable table including a Total_Coeff for a Chroma DC, a run_before variable table of a CAVLC, a Total_Coeff and TrailingOnes variable tables, a Total_Coeff for a Chroma and TrailingOnes variable tables.
12. The method of claim 11 , wherein the re-sorted table is a table organized by re-sorting the CAVLC codeword length tables in an order of the codeword length.
13. The method of claim 12 , wherein the re-sorting of the CAVLC codeword length tables is performed using a binary tree.
14. The method of claim 12 , wherein the re-sorting of the CAVLC codeword length tables is so performed as to compare a codeword length last if the codeword length consisting of zero within the same column of the CAVLC length table is not a lowermost level of the binary tree.
15. The method of claim 12 , wherein the re-sorting of the CAVLC codeword length tables is performed in such an order that a short codeword length is sorted first, namely, a codeword length having a high possibility of generation is sorted first.
16. The method of claim 11 , wherein the reference column is a column selected from information included in a header part of a packet enclosing the bitstream and information of a decoded adjacent block.
17. The method of claim 11 , wherein if the read bitstream value is zero, or if the bitstream value does not coincide with the value on the CAVLC value table as a result of the comparison, the bitstream is read as much as a codeword length that corresponds to a value next to a value compared in the reference column on the re-sorted table.
18. A CAVLC (context-based adaptive variable length coding) decoding apparatus for decoding a coded bitstream using (DAVLC length tables and CAVLC value tables, the apparatus comprising:
a memory in which the CAVLC length tables and the CAVLC value tables are stored;
a memory in which the CAVLC length tables are re-sorted in an order of a codeword length if the codeword length consisting of zero within the same column of the CAVLC length table is not a lowermost row of the CAVLC length table, and the CAVLC length tables are stored; and
a CAVLC parser for receiving the bitstream to parse relevant variables using the re-sorted length tables, the CAVLC length tables, and the CAVLC value tables.
19. The apparatus of claim 18 , further comprising a stream controller for delivering an inputted bitstream to the CAVLC parser according to a sorted order of the re-sorted table.
20. The apparatus of claim 18 , wherein the re-sorted table is a table organized by re-sorting the CAVLC codeword length tables in an order of the codeword length.
21. The apparatus of claim 20 , wherein the re-sorting of the CAVLC codeword length tables in the order of the codeword length is performed in such an order that a short codeword length is sorted first, namely, a codeword length having a high possibility of generation is sorted first.
22. A CAVLC (context-based adaptive variable length coding) decoding method for decoding a coded bitstream using CAVLC length tables and CAVLC value tables, the method comprising the steps of:
re-sorting the CAVLC length tables in an order of a codeword length; and
decoding the coded bitstream using the re-sorted length tables,
wherein the step of re-sorting the CAVLC length tables uses a binary tree, and wherein the step of re-sorting is so performed as to compare a codeword length last if the codeword length consisting of zero within the same column of the CAVLC length table is not a lowermost level of the binary tree.
23. The method of claim 22 , wherein the step of re-sorting comprises comparing a codeword length last if the codeword length consisting of zero within the same column of the CAVLC length table is not a lowermost level of the binary tree.
24. The method of claim 22 , wherein the step of re-sorting comprises sorting a short codeword length having a high possibility of generation first.
25. The method of claim 22 , wherein the step of decoding the coded bitstream comprises the steps of:
selecting a table that corresponds to a variable desired to be decoded among the re-sorted tables;
reading the bitstream as much as the codeword length sequentially starting from a first codeword length in a reference column within the selected table;
comparing a value of the read bitstream with a value in the CAVLC value table, the value held by a codeword length that coincides with the read codeword length in a column that coincides with the reference column within the CAVLC length table; and
storing a variable value if the value of the read bitstream coincides with the value in the CAVLC value table.
26. The method of claim 25 , wherein the reference column is a column selected from information included in a header part of a packet enclosing the bitstream and information of a decoded adjacent block.
27. The method of claim 25 , wherein if the read bitstream value is zero, the bitstream is read as much as a codeword length that corresponds to a value next to a value compared in the reference column on the re-sorted table.
28. The method of claim 27 , wherein a process is terminated if a codeword value that corresponds to a codeword length for the next value is zero.
29. The method of claim 25 , wherein if the bitstream value does not coincide with the value in the CAVLC value table, the bitstream is read as much as a codeword length that corresponds to a value next to a value compared in the reference column on the re-sorted table.