Multi-level significance map scanning
Methods of encoding and decoding for video data are described in which multi-level significance maps are used in the encoding and decoding processes. The significant-coefficient flags that form the significance map are grouped into contiguous groups, and a significant-coefficient-group flag signifies for each group whether that group contains no non-zero significant-coefficient flags. A multi-level scan order may be used in which significant-coefficient flags are scanned group-by-group. The group scan order specifies the order in which the groups are processed, and the scan order specifies the order in which individual significant-coefficient flags within the group are processed. The bitstream may interleave the significant-coefficient-group flags and their corresponding significant-coefficient flags, if any.
1. A method for encoding significant-coefficient flags for a transform unit, each of the significant coefficient flags belonging to a respective group of significant-coefficient flags and each respective group having a corresponding significant-coefficient-group flag, the method comprising:
for each respective group of significant-coefficient flags in a group reverse scan order, the group reverse scan order starting with the group containing the significant-coefficient flag for a last-significant coefficient indicating the location of the last non-zero significant coefficient in the transform unit, and working back through the groups in reverse direction until the group containing the DC position in the transform unit is reached:
encoding a significant-coefficient-group flag for the group, except when the group contains the last-significant coefficient and except when the group contains the DC position, wherein encoding comprises setting the corresponding significant-coefficient-group flag to one if the group contains at least one non-zero significant-coefficient flag and setting the corresponding significant-coefficient-group flag to be zero otherwise, and
when the group contains the DC position,
encoding the significant-coefficient flags in the group in a reverse scan order,
otherwise when the significant-coefficient-group flag for the group is one or the group contains the last-significant coefficient:
encoding each significant-coefficient flag in the group in a reverse scan order, except for the significant-coefficient-flag at position (0,0) in the group when all the previous significant-coefficient flags in the group are zero.
2. The method claimed in claim 1 , wherein the group reverse scan order is a prescribed order in which the respective groups of significant-coefficient flags are to be reconstructed.
3. The method claimed in claim 1 , wherein the group reverse scan order is one of a horizontal, vertical, or diagonal order.
4. The method claimed in claim 1 , wherein the reverse scan order is one of a horizontal, vertical, or diagonal order.
5. The method claimed in claim 1 , wherein the group reverse scan order and the reverse scan order are the same.
6. The method claimed in claim 1 , wherein each group corresponds to a contiguous square block of the transform unit.
7. The method claimed in claim 1 , wherein each group corresponds to a non-square rectangular block.
8. An encoder for encoding significant-coefficient flags for a transform unit, each of the significant coefficient flags belonging to a respective group of significant-coefficient flags and each respective group having a corresponding significant-coefficient-group flag, the encoder comprising:
a processor;
a memory; and
an encoding application stored in memory and containing instructions for configuring the processor to:
for each respective group of significant-coefficient flags in a group reverse scan order, the group reverse scan order starting with the group containing the significant-coefficient flag for a last-significant coefficient indicating the location of the last non-zero significant coefficient in the transform unit, and working back through the groups in reverse direction until the group containing the DC position in the transform unit is reached:
encode a significant-coefficient-group flag for the group, except when the group contains the last-significant coefficient and except when the group contains the DC position, wherein encoding the significant-coefficient-group flag for the group comprises instructions for configuring the processor to set the corresponding significant-coefficient-group flag to one if the group contains at least one non-zero significant-coefficient flag and set the corresponding significant-coefficient-group flag to be zero otherwise, and
when the group contains the DC position,
encoding the significant-coefficient flags in the group in a reverse scan order,
otherwise when the significant-coefficient-group flag for the group is one or the group contains the last-significant coefficient:
encode each significant-coefficient flag in the group in a reverse scan order, except for the significant-coefficient-flag at position (0,0) in the group when all the previous significant-coefficient flags in the group are zero.
9. The encoder claimed in claim 8 , wherein the group reverse scan order is a prescribed order in which the respective groups of significant-coefficient flags are to be reconstructed.
10. The encoder claimed in claim 8 , wherein the group reverse scan order is one of a horizontal, vertical, or diagonal order.
11. The encoder claimed in claim 8 , wherein the reverse scan order is one of a horizontal, vertical, or diagonal order.
12. The encoder claimed in claim 8 , wherein the group reverse scan order and the reverse scan order are the same.
13. The encoder claimed in claim 8 , wherein each group corresponds to a contiguous square block of the transform unit.
14. The encoder claimed in claim 8 , wherein each group corresponds to a non-square rectangular block.
15. A non-transitory processor-readable medium storing processor-executable instructions which, when executed, configures one or more processors to:
for each respective group of significant-coefficient flags in a group reverse scan order, the group reverse scan order starting with the group containing the significant-coefficient flag for a last-significant coefficient indicating the location of the last non-zero significant coefficient in the transform unit, and working back through the groups in reverse direction until the group containing the DC position in the transform unit is reached:
encode a significant-coefficient-group flag for the group, except when the group contains the last-significant coefficient and except when the group contains the DC position, wherein encoding the significant-coefficient-group flag for the group comprises instructions for configuring the processor to set the corresponding significant-coefficient-group flag to one if the group contains at least one non-zero significant-coefficient flag and set the corresponding significant-coefficient-group flag to be zero otherwise, and
when the group contains the DC position,
encoding the significant-coefficient flags in the group in a reverse scan order,
otherwise when the significant-coefficient-group flag for the group is one or the group contains the last-significant coefficient:
encode each significant-coefficient flag in the group in a reverse scan order, except for the significant-coefficient-flag at position (0,0) in the group when all the previous significant-coefficient flags in the group are zero.
16. The non-transitory processor-readable medium claimed in claim 15 , wherein the group reverse scan order is one of a horizontal, vertical, or diagonal order.
17. The non-transitory processor-readable medium claimed in claim 15 , wherein the reverse scan order is one of a horizontal, vertical, or diagonal order.
18. The non-transitory processor-readable medium claimed in claim 15 , wherein the group reverse scan order and the reverse scan order are the same.
19. The non-transitory processor-readable medium claimed in claim 15 , wherein each group corresponds to a contiguous square block of the transform unit.
20. The non-transitory processor-readable medium claimed in claim 15 , wherein each group corresponds to a non-square rectangular block.