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 transform coefficient blocks encoded in a data stream, comprising:
a decoder configured to extract, from the data stream, last significant syntax elements by context-adaptive entropy decoding, each of the last significant syntax elements being associated with a respective position within a corresponding transform coefficient block and indicating whether a transform coefficient at the respective position is the last significant transform coefficient according to a scan order in the corresponding transform coefficient block; and
an associator configured to associate each of the last significant syntax elements with a respective position of the corresponding transform coefficient block in the scan order,
wherein the decoder is configured to use, in context-adaptive entropy decoding the last significant syntax elements, a context for a current last significant syntax element associated with a current transform coefficient block, wherein the context is chosen from among a plurality of available contexts for the current last significant syntax element in accordance with a combination of at least the position of the current last significant syntax element within the current transform coefficient block, a corner coordinate of the current transform coefficient block, a size of the current transform coefficient block, and information regarding prior significant transform coefficients previously extracted from a neighborhood of the position of the current last significant syntax element, the neighborhood including a position above and a position to the left of the position of the current last significant syntax element.
2. The apparatus according to claim 1 , wherein the information regarding the prior significant transform coefficients previously extracted from the neighborhood relates to values of the prior significant transform coefficients.
3. The apparatus according to claim 1 , wherein the information regarding the prior significant transform coefficients previously extracted from the neighborhood relates to a number of positions at of the prior significant transform coefficients.
4. The apparatus according to claim 3 , wherein the number of positions corresponds to a context index pointing to a set of possible context indices.
5. The apparatus according to claim 1 , wherein the context for the current last significant syntax element is chosen further based on a color plane type associated with the current transform coefficient block.
6. The apparatus according to claim 1 , wherein the context for the current last significant syntax element is chosen further based on the scan order.
7. The apparatus according to claim 1 , wherein the neighborhood comprises one position adjacent to the position of the current last significant syntax element.
8. The apparatus according to claim 7 , wherein the neighborhood comprises one position horizontally adjacent to the current last significant syntax element.
9. The apparatus according to claim 7 , wherein the neighborhood comprises one position vertically adjacent to the current last significant syntax element.
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 transform coefficient blocks into a data stream, the apparatus being configured to code, into the data stream, last significant syntax elements via context-adaptive entropy encoding, each of the last significant syntax elements being associated with a respective position within a corresponding transform coefficient block and indicating whether a transform coefficient at the respective position is the last significant transform coefficient according to a scan order in the corresponding transform coefficient block,
wherein the apparatus is configured to code the last significant syntax elements into the data stream in the scan order,
wherein the apparatus is configured to use, in context-adaptive entropy encoding the last significant syntax elements, a context for a current last significant syntax element associated with a current transform coefficient block, wherein the context is chosen from among a plurality of available contexts for the current last significant syntax element in accordance with a combination of at least the position of the current last significant syntax element within the current transform coefficient block, a corner coordinate of the current transform coefficient block, a size of the current transform coefficient block, and information regarding prior significant transform coefficients previously encoded from a neighborhood of the position of the current last significant syntax element, the neighborhood including a position above and a position to the left of the position of the current last significant syntax element.
12. The apparatus according to claim 11 , wherein the information regarding the prior significant transform coefficients previously encoded from the neighborhood relates to values of the prior significant transform coefficients.
13. The apparatus according to claim 11 , wherein the information regarding the prior significant transform coefficients previously encoded from the neighborhood relates to a number of positions of the prior significant transform coefficients.
14. The apparatus according to claim 13 , wherein the number of positions corresponds to a context index pointing to a set of possible context indices.
15. The apparatus according to claim 11 , wherein the context for the current last significant syntax element is chosen further based on a color plane type associated with the current transform coefficient block.
16. The apparatus according to claim 11 , wherein the context for the current last significant syntax element is chosen further based on the scan order.
17. The apparatus according to claim 11 , wherein the neighborhood comprises one position adjacent to the position of the current last significant syntax element.
18. The apparatus according to claim 17 , wherein the neighborhood comprises one position horizontally adjacent to the current last significant syntax element.
19. The apparatus according to claim 17 , wherein the neighborhood comprises one position vertically adjacent to the current last significant syntax element.
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 for storing data associated with a video, comprising:
a data stream stored in the non-transitory computer-readable medium, the data stream comprising information related to transform coefficient blocks including encoded last significant syntax elements, each of the last significant syntax elements being associated with a respective position within a corresponding transform coefficient block and indicating whether a transform coefficient at the respective position is the last significant transform coefficient according to a scan order in the corresponding transform coefficient block,
wherein the last significant syntax elements are coded into the data stream in the scan order, and are context-adaptive entropy encoded using a context for a current last significant syntax element associated with a current transform coefficient block, wherein the context is chosen from among a plurality of available contexts for the current last significant syntax element in accordance with a combination of at least the position of the current last significant syntax element within the current transform coefficient block, a corner coordinate of the current transform coefficient block, a size of the current transform coefficient block, and information regarding prior significant transform coefficients previously extracted from a neighborhood of the position of the current last significant syntax element, the neighborhood including a position above and a position to the left of the position of the current last significant syntax element.
22. The computer-readable medium according to claim 21 , wherein the information regarding the prior significant transform coefficients previously encoded from the neighborhood relates to values of the prior significant transform coefficients.
23. The computer-readable medium according to claim 21 , wherein the information regarding the prior significant transform coefficients previously encoded from the neighborhood relates to a number of positions of the prior significant transform coefficients.
24. A method for decoding a transform coefficient block encoded in a data stream, comprising:
extracting, from the data stream, last significant syntax elements by context-adaptive entropy decoding, each of the last significant syntax elements being associated with a respective position within a corresponding transform coefficient block and indicating whether a transform coefficient at the respective position is the last significant transform coefficient according to a scan order in the corresponding transform coefficient block;
associating each of the last significant syntax elements with a respective position of the corresponding transform coefficient block in the scan order; and
using, in context-adaptive entropy decoding the last significant syntax elements, a context for a current last significant syntax element associated with a current transform coefficient block, wherein the context is chosen from among a plurality of available contexts for the current last significant syntax element in accordance with a combination of at least the position of the current last significant syntax element within the current transform coefficient block, a corner coordinate of the current transform coefficient block, a size of the current transform coefficient block, and information regarding prior significant transform coefficients previously extracted from a neighborhood of the position of the current last significant syntax element, the neighborhood including a position above and a position to the left of the position of the current last significant syntax element.
25. The method according to claim 24 , wherein the information regarding the prior significant transform coefficients previously extracted from the neighborhood relates to values of the prior significant transform coefficients.
26. The method according to claim 24 , wherein the information regarding the prior significant transform coefficients previously extracted from the neighborhood relates to a number of positions of the prior significant transform coefficients.
27. The method according to claim 24 , wherein the context for the current last significant syntax element is chosen further based on a color plane type associated with the current transform coefficient block.
28. The method according to claim 24 , wherein the context for the current last significant syntax element is chosen further based on the scan order.
29. The method according to claim 24 , wherein the neighborhood comprises one position adjacent to the position of the current last significant syntax element.
30. The method according to claim 24 , wherein the data stream comprises at least a portion associated with color samples.