Significance map encoding and decoding using partition selection
View Patent ↗Methods of encoding and decoding for video data are describe in which significance maps are encoded and decoded using non-spatially-uniform partitioning of the map into parts, wherein the bit positions within each part are associated with a given context. Example partition sets and processes for selecting from amongst predetermined partition sets and communicating the selection to the decoder are described.
1. A method of decoding a bitstream of encoded data to reconstruct a significance map for a transform unit, the method comprising:
for each bit position in the significance map having a significant coefficient flag that is to be decoded using context-adaptive decoding,
determining a context for that bit position based upon a partition set,
decoding the encoded data based on the determined context to reconstruct a bit value, and
updating the context based on that reconstructed bit value,
wherein the reconstructed bit values form the decoded significance map;
wherein the transform unit is sized 4×4;
and wherein the partition set assigns contexts to bit positions within the transform unit such that
a different context is assigned to each bit position in an upper left quadrant of the transform unit,
contexts are shared by groups of two in an upper right and lower left quadrant of the transform unit, and
a single context is shared by all bit positions in the lower right quadrant.
2. The method claimed in claim 1 , further comprising selecting the partition set from among a plurality of partition sets.
3. The method claimed in claim 2 , wherein the selecting comprises selecting based upon text type.
4. The method claimed in claim 3 , wherein the text type is luma.
5. The method claimed in claim 3 , wherein the text type is chroma.
6. The method claimed in claim 2 , wherein the selecting comprises determining for each transform unit whether an encoded slice size to that point has exceeded a threshold value and, if so, switching from the partition set to a refined partition set for reconstruction of subsequent significance maps within the slice, wherein the partition set is a subset of the refined partition set.
7. The method claimed in claim 2 , wherein the selecting comprises selecting based upon the transform unit size.
8. A decoder for decoding a bitstream of encoded data to reconstruct a significance map for a transform unit, the decoder comprising:
a processor;
a memory; and
a decoding application stored in memory and containing instructions that, when executed, cause the processor to
for each bit position in the significance map having a significant coefficient flag that is to be decoded using context-adaptive decoding,
determine a context for that bit position based upon a partition set,
decode the encoded data based on the determined context to reconstruct a bit value, and
update the context based on that reconstructed bit value;
wherein the reconstructed bit values form the decoded significance map;
wherein the transform unit is sized 4×4;
and wherein the partition set assigns contexts to bit positions within the transform unit such that
a different context is assigned to each bit position in an upper left quadrant of the transform unit,
contexts are shared by groups of two in an upper right and lower left quadrant of the transform unit, and
a single context is shared by all bit positions in the lower right quadrant.
9. The decoder claimed in claim 8 , wherein the instructions further cause the processor to select the partition set from among a plurality of partition sets.
10. The decoder claimed in claim 9 , wherein the processor selects the partition set based upon text type.
11. The decoder claimed in claim 10 , wherein the text type is luma.
12. The decoder claimed in claim 10 , wherein the text type is chroma.
13. The decoder claimed in claim 9 , wherein the instructions further cause the processor to determine for each transform unit whether an encoded slice size to that point has exceeded a threshold value and, if so, switch from the partition set to a refined partition set for reconstruction of subsequent significance maps within the slice, wherein the partition set is a subset of the refined partition set.
14. The decoder claimed in claim 9 , wherein the instructions further cause the processor to select the partition set based upon the transform unit size.
15. A non-transitory processor-readable medium storing processor-executable instructions which, when executed, cause one or more processors to decode a bitstream of encoded data to reconstruct a significance map for a transform unit by:
for each bit position in the significance map having a significant coefficient flag that is to be decoded using context-adaptive decoding,
determining a context for that bit position based upon a partition set,
decoding the encoded data based on the determined context to reconstruct a bit value, and
updating the context based on that reconstructed bit value,
wherein the reconstructed bit values form the decoded significance map;
wherein the transform unit is sized 4×4;
and wherein the partition set assigns contexts to bit positions within the transform unit such that
a different context is assigned to each bit position in an upper left quadrant of the transform unit,
contexts are shared by groups of two in an upper right and lower left quadrant of the transform unit, and
a single context is shared by all bit positions in the lower right quadrant.
16. The non-transitory processor-readable medium claimed in claim 15 , wherein the instructions further cause the one or more processors to select the partition set from among a plurality of partition sets.
17. The non-transitory processor-readable medium claimed in claim 16 , wherein the selecting comprises selecting based upon text type.
18. The non-transitory processor-readable medium claimed in claim 17 , wherein the text type is luma.
19. The non-transitory processor-readable medium claimed in claim 17 , wherein the text type is chroma.
20. The non-transitory processor-readable medium claimed in claim 16 , wherein the selecting comprises determining for each transform unit whether an encoded slice size to that point has exceeded a threshold value and, if so, switching from the partition set to a refined partition set for reconstruction of subsequent significance maps within the slice, wherein the partition set is a subset of the refined partition set.
21. The non-transitory processor-readable medium claimed in claim 16 , wherein the selecting comprises selecting based upon the transform unit size.