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 data stream representing an encoded video, the apparatus comprising:
a decoder configured to extract, from a data stream based on context-adaptive entropy decoding, first-type syntax elements and second-type syntax elements both syntax element types related to a transform coefficient block, wherein each of the first-type syntax elements indicates whether at a respective position of the first-type syntax element within the transform coefficient block a significant transform coefficient is present, and each of the second-type syntax elements relates to a value of the significant transform coefficient at a respective position of the second-type syntax element within the transform coefficient block; and
an associator configured to associate the first-type syntax elements to the respective positions within the transform coefficient block,
wherein the decoder is configured to use, in context-adaptive entropy decoding the first-type syntax elements, contexts which are selected for each of the first-type syntax elements, wherein the context for a current first-type syntax element being decoded is selected in accordance with a transform block size and a number of positions of the significant transform coefficients within the transform coefficient block related to previously extracted first-type syntax elements in a neighborhood of the current first-type syntax element.
2. The apparatus according to claim 1 , wherein the neighborhood comprises a position within the transform coefficient block adjacent to the position of the current first-type syntax element.
3. The apparatus according to claim 1 , wherein the neighborhood comprises a position within the transform coefficient block separated from the position of the current first-type syntax element by a position in vertical direction and/or a position in the horizontal direction.
4. The apparatus according to claim 1 , wherein the decoder is further configured to map the number of positions to a context index of a set of possible context indices.
5. The apparatus according to claim 1 , wherein the associator is configured to associate the first-type syntax elements to the respective positions within the transform coefficient block in accordance with a scan order determined from among a plurality of scan orders.
6. The apparatus according to claim 5 , wherein the plurality of scan orders includes a diagonal scan order.
7. The apparatus according to claim 1 , wherein the data stream comprises at least a portion associated with color samples.
8. The apparatus according to claim 1 , wherein the data stream comprises at least a portion associated with depth values related to a depth map.
9. An apparatus for encoding a video into a data stream, the apparatus comprising:
an encoder configured to encode, based on context-adaptive entropy encoding, first-type syntax elements and second-type syntax elements both syntax element types related to a transform coefficient block, wherein each of the first-type syntax elements indicates whether at a respective position of the first-type syntax element within the transform coefficient block a significant transform coefficient is present, and each of the second-type syntax elements relates to a value of the significant transform coefficient at a respective position of the second-type syntax element within the transform coefficient block;
wherein the encoder is configured to, in context-adaptive entropy encoding each of the first-type syntax elements, use contexts selected for the first-type syntax elements, wherein the context for a current first-type syntax element being encoded is selected in accordance with a transform block size and a number of positions of the significant transform coefficients within the transform coefficient block related to previously extracted first-type syntax elements in a neighborhood of the current first-type syntax element.
10. The apparatus according to claim 9 , wherein the neighborhood comprises a position within the transform coefficient block adjacent to the position of the current first-type syntax element.
11. The apparatus according to claim 9 , wherein the neighborhood comprises a position within the transform coefficient block separated from the position of the current first-type syntax element by a position in vertical direction and/or a position in the horizontal direction.
12. The apparatus according to claim 9 , wherein the encoder is further configured to map the number of positions to a context index of a set of possible context indices.
13. The apparatus according to claim 9 , wherein the encoder is configured to encode the first-type syntax elements in accordance with a scan order determined from among a plurality of scan orders.
14. The apparatus according to claim 13 , wherein the plurality of scan orders includes a diagonal scan order.
15. The apparatus according to claim 9 , wherein the data stream comprises at least a portion associated with color samples.
16. The apparatus according to claim 9 , wherein the data stream comprises at least a portion associated with depth values related to a depth map.
17. A method for decoding a data stream representing an encoded video, the method comprising:
extracting, from a data stream based on context-adaptive entropy decoding, first-type syntax elements and second-type syntax elements both syntax element types related to a transform coefficient block, wherein each of the first-type syntax elements indicates whether at a respective position associated with the first-type syntax element within the transform coefficient block a significant transform coefficient is present, and each of the second-type syntax elements relates to a value of the significant transform coefficient at a respective position associated with the second-type syntax element within the transform coefficient block; and
associating the first-type syntax elements to the respective positions within the transform coefficient block,
wherein the context-adaptive entropy decoding the first-type syntax elements includes using contexts which are selected for each of the first-type syntax elements, wherein the context for a current first-type syntax element being decoded is selected in accordance with a transform block size and a number of positions of the significant transform coefficients within the transform coefficient block related to previously extracted first-type syntax elements in a neighborhood of the current first-type syntax element.
18. The method according to claim 17 , wherein the neighborhood comprises a position within the transform coefficient block adjacent to the position of the current first-type syntax element.
19. The method according to claim 17 , wherein the neighborhood comprises a position within the transform coefficient block separated from the position of the current first-type syntax element by a position in vertical direction and/or a position in the horizontal direction.
20. The method according to claim 17 , further comprising mapping the number of positions to a context index of a set of possible context indices.
21. The method according to claim 17 , wherein the associating comprises associating the first-type syntax elements to the respective positions within the transform coefficient block in accordance with a scan order determined from among a plurality of scan orders.
22. The method according to claim 21 , wherein the plurality of scan orders includes a diagonal scan order.
23. The method according to claim 17 , wherein the data stream comprises at least a portion associated with color samples.
24. The method according to claim 17 , wherein the data stream comprises at least a portion associated with depth values related to a depth map.
25. 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 first-type syntax elements and second-type syntax elements both syntax element types related to a transform coefficient block, wherein each of the first-type syntax elements indicates whether at a respective position associated with the first-type syntax element within the transform coefficient block a significant transform coefficient is present, and each of the second-type syntax elements relates to a value of the significant transform coefficient at a respective position associated with the second-type syntax element within the transform coefficient block,
wherein the first-type syntax elements are decoded based on context-adaptive entropy decoding using contexts which are selected for each of the first-type syntax elements, wherein the context for a current first-type syntax element being decoded is selected in accordance with a transform block size and a number of positions of the significant transform coefficients within the transform coefficient block related to previously extracted first-type syntax elements in a neighborhood of the current first-type syntax element.
26. The computer-readable medium according to claim 25 , wherein the neighborhood comprises a position within the transform coefficient block adjacent to the position of the current first-type syntax element.
27. The computer-readable medium according to claim 25 , wherein the neighborhood comprises a position within the transform coefficient block separated from the position of the current first-type syntax element by a position in vertical direction and/or a position in the horizontal direction.
28. The computer-readable medium according to claim 25 , wherein the first-type syntax elements are associated to the respective positions within the transform coefficient block in accordance with a scan order determined from among a plurality of scan orders.
29. The computer-readable medium according to claim 25 , wherein the data stream comprises at least a portion associated with color samples.
30. The computer-readable medium according to claim 25 , wherein the data stream comprises at least a portion associated with depth values related to a depth map.