Coding of significance maps and transform coefficient blocks
A higher coding efficiency for coding a significance map indicating positions of significant transform coefficients within a transform coefficient block is achieved by the scan order by which the sequentially extracted syntax elements indicating, for associated positions within the transform coefficient block, as to whether at the respective position a significant or insignificant transform coefficient is situated, are sequentially associated to the positions of the transform coefficient block, among the positions of the transform coefficient block depends on the positions of the significant transform coefficients indicated by previously associated syntax elements. Alternatively, the first-type elements may be context-adaptively entropy decoded using contexts which are individually selected for each of the syntax elements dependent on a number of significant transform coefficients in a neighborhood of the respective syntax element, indicated as being significant by any of the preceding syntax elements.
1. An apparatus for decoding a transform coefficient block encoded in a data stream, comprising a processor, which when executes computer-readable code, is configured to:
extract, from the data stream, syntax elements via context-based entropy decoding, wherein each of the syntax elements indicates whether a significant transform coefficient is present at a corresponding position within the transform coefficient block; and
use, for context-based entropy decoding of at least one syntax element of the syntax elements, a context which is selected for the at least one syntax element based on a size of the transform coefficient block and a position of the at least one syntax element within the transform coefficient block, wherein contexts for different syntax elements are selected based on different combinations of the size of the transform coefficient block and the position of the respective syntax element.
2. The apparatus according to claim 1 , wherein the context for the at least one syntax element is selected further based on information regarding prior syntax elements previously extracted from a neighborhood of the position of the at least one syntax element.
3. The apparatus according to claim 2 , wherein the information regarding the prior syntax elements previously extracted from the neighborhood relates to values of the prior syntax elements.
4. The apparatus according to claim 2 , wherein the information regarding the prior syntax elements previously extracted from the neighborhood relates to a number of positions at which prior syntax elements indicating presence of significant transform coefficients.
5. The apparatus according to claim 4 , wherein the number of positions corresponds to a context index pointing to a set of possible context indices.
6. The apparatus according to claim 2 , wherein the neighborhood comprises at least one position adjacent to the position of the at least one syntax element.
7. The apparatus according to claim 6 , wherein the neighborhood comprises at least one position horizontally adjacent to the position of the at least one syntax element or at least one position vertically adjacent to the position of the at least one syntax element.
8. The apparatus according to claim 1 , wherein the context for the at least one syntax element is selected further based on a scan order.
9. The apparatus according to claim 1 , further configured to extract information indicating values of significant transform coefficients within the transform coefficient block.
10. The apparatus according to claim 1 , wherein the data stream comprises at least a portion associated with color samples.
11. An apparatus for encoding a transform coefficient block into a data stream, the apparatus comprising a processor, which when executes computer-readable code, is configured to:
encode, into the data stream, syntax elements via context-based entropy encoding, with each of the syntax elements indicating whether a significant transform coefficient is present at a corresponding position within the transform coefficient block; and
use, in context-based entropy encoding at least one of the syntax elements, a context which is selected for the at least one syntax element based at least on a size of the transform coefficient block and a position of the at least one syntax element within the transform coefficient block, wherein contexts for different syntax elements are selected based on different combinations of the size of the transform coefficient block and the position of the respective syntax element.
12. The apparatus according to claim 11 , wherein the context for the at least one syntax element is selected further based on information regarding prior syntax elements previously extracted from a neighborhood of the position of the at least one syntax element.
13. The apparatus according to claim 12 , wherein the information regarding the prior syntax elements previously encoded from the neighborhood relates to values of the prior syntax elements.
14. The apparatus according to claim 12 , wherein the information regarding the prior syntax elements previously encoded from the neighborhood relates to a number of positions at which prior syntax elements indicate presence of significant transform coefficients.
15. The apparatus according to claim 14 , wherein the number of positions corresponds to a context index pointing to a set of possible context indices.
16. The apparatus according to claim 12 , wherein the neighborhood comprises at least one position adjacent to the position of the at least one syntax element.
17. The apparatus according to claim 16 , wherein the neighborhood comprises at least one position horizontally adjacent to the position of the at least one syntax element or at least one position vertically adjacent to the position of the at least one syntax element.
18. The apparatus according to claim 11 , wherein the context for the at least one syntax element is selected further based on a scan order.
19. The apparatus according to claim 11 , further configured to encode information indicating values of significant transform coefficients within the transform coefficient block.
20. The apparatus according to claim 11 , wherein the data stream comprises at least a portion associated with color samples.
21. A non-transitory computer-readable medium comprising computer-readable code, which when executed by a processor, generates
a data stream comprising information related to a transform coefficient block, the computer-readable code including instructions for:
encoding, using via context-based entropy encoding, syntax elements each of which indicates whether a significant transform coefficient is present at a corresponding position within the transform coefficient block; and
using, in context-based entropy encoding at least one of the syntax elements, a context is selected based at least on a size of the transform coefficient block and a position of the at least one syntax element within the transform coefficient block, wherein contexts for different syntax elements are selected based on different combinations of the size of the transform coefficient block and the position of the respective syntax element.
22. The computer-readable medium according to claim 21 , wherein the context for the at least one syntax element is selected further based on information regarding prior syntax elements previously encoded from a neighborhood of the position of the at least one syntax element.
23. The computer-readable medium according to claim 21 , wherein the data stream further comprises information related to values of significant transform coefficients.
24. A method for decoding a transform coefficient block encoded in a data stream, comprising:
extracting, from the data stream, syntax elements via context-based entropy decoding, wherein each of the syntax elements indicates whether a significant transform coefficient is present at a corresponding position within the transform coefficient block; and
using, for context-based entropy decoding of at least one syntax element of the syntax elements, a context which is selected for the at least one syntax element based on a size of the transform coefficient block, a position of the at least one syntax element within the transform coefficient block and a position of the at least one syntax element within the transform coefficient block, wherein contexts for different syntax elements are selected based on different combinations of the size of the transform coefficient block and the position of the respective syntax element.
25. The method according to claim 24 , wherein the context for the at least one syntax element is selected further based on information regarding prior syntax elements previously extracted from a neighborhood of the position of the at least one syntax element.
26. The method according to claim 25 , wherein the information regarding the prior syntax elements previously extracted from the neighborhood relates to values of the prior syntax elements.
27. The method according to claim 25 , wherein the information regarding the prior syntax elements previously extracted from the neighborhood relates to a number of positions at which prior syntax elements indicating presence of significant transform coefficients.
28. The method according to claim 24 , wherein the context for the at least one syntax element is selected further based on a scan order.
29. The method according to claim 24 , further comprising extracting information indicating values of significant transform coefficient.
30. The method according to claim 24 , wherein the data stream comprises at least a portion associated with color samples.