Multi-level significance maps for encoding and decoding

• US 8,964,849 B2
• Filed: 11/01/2011
• Issued: 02/24/2015
• Est. Priority Date: 11/01/2011
• Status: Active Grant

• Current Assignee: Velos Media, LLC (Inception Holdings, LLC)
• Original Assignee: Blackberry Limited
• Inventors: Ji, Tianying, He, Dake, Nguyen, Nguyen
• Primary Examiner(s): Kelley, Christopher S
• Assistant Examiner(s): KWAN, MATTHEW K
• Application Number:
  US13/286,336
• Publication Number:
  US 20130107969A1
• Time in Patent Office: 1,211 Days
• Field of Search: 375/240.18
• US Class Current: 375/240.18
• CPC Class Codes: H04N 19/122 Selection of transform size, e.g. 8x8 or 2x4x8 DCT; Selection of sub-band transforms of varying structure or type
• CPC Class Codes: H04N 19/13 Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/136 Incoming video signal characteristics or properties
• CPC Class Codes: H04N 19/157 Assigned coding mode, i.e. the coding mode being predefined or preselected to be further used for selection of another element or parameter
• CPC Class Codes: H04N 19/159 Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
• CPC Class Codes: H04N 19/172 the region being a picture, frame or field
• CPC Class Codes: H04N 19/18 the unit being a set of transform coefficients
• CPC Class Codes: H04N 19/196 being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters processing of motion vectors H04N19/513
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/70 characterised by syntax aspects related to video coding, e.g. related to compression standards
• CPC Class Codes: H04N 19/91 Entropy coding, e.g. variable length coding [VLC] or arithmetic coding

Abstract

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. If there are no non-zero significant-coefficient flags in the group, then the significant-coefficient-group flag is set to zero. The set of significant-coefficient-group flags is encoded in the bitstream. Any significant-coefficient flags that fall within a group that has a significant-coefficient-group flag that is non-zero are encoded in the bitstream, whereas significant-coefficient flags that fall within a group that has a significant-coefficient-group flag that is zero are not encoded in the bitstream.

Claims

1. A method of reconstructing significant-coefficient flags for a transform unit from a bitstream of encoded data, the method comprising:

reconstructing significant-coefficient-group flags, wherein the transform unit is partitioned into non-overlapping blocks, each block containing a respective group of significant-coefficient flags, and wherein each significant-coefficient-group flag corresponds to a respective block and its respective group of significant-coefficient flags; and

reconstructing each significant-coefficient flag by

if the significant-coefficient-flag is at position (0,0) in its group, a corresponding significant-coefficient-group flag is non-zero, the group is not the DC block, and all the previous significant-coefficient flags in that group are zero, then inferring the significant-coefficient-flag at position (0,0) in that group to be 1, and

otherwise

decoding the significant-coefficient flag from the bitstream if that significant-coefficient flag is in a group that has corresponding significant-coefficient-group flag that is non-zero, and

setting the significant-coefficient flag to zero, if that significant-coefficient flag is in a group that has corresponding significant-coefficient-group flag that is zero.

2. The method claimed in claim 1, wherein reconstructing the significant-coefficient-group flags includes decoding at least some of the significant-coefficient-group flags from the encoded data of the bitstream.

3. The method claimed in claim 2, wherein reconstructing the significant-coefficient-group flags further includes inferring a significant-coefficient-group flag to be 1 on the basis that it corresponds to the block containing the significant-coefficient flag for a last-significant coefficient.

4. The method claimed in claim 2, wherein reconstructing the significant-coefficient-group flags further includes inferring a significant-coefficient-group flag to be 1 on the basis that it corresponds to the block containing the significant-coefficient flag for a DC coefficient.

5. The method claimed in claim 2, wherein reconstructing the significant-coefficient-group flags includes inferring a significant-coefficient-group flag to be 1 if that significant-coefficient-group flag corresponds to a group that has two neighbor groups both of which have corresponding significant-coefficient-group flags that have reconstructed values of 1.

6. The method claimed in claim 5, wherein the groups are contiguous blocks, and wherein the two neighbor groups include a right neighbor block and a below neighbor block.

7. The method claimed in claim 1, wherein the transform unit is 16×

16 and wherein each group is a 4×

4 block.

8. The method claimed in claim 1, wherein the transform unit is 32×

32 and wherein each group is an 8×

8 block.

9. The method claimed in claim 1, wherein reconstructing one of the significant-coefficient-group flags includes determining a context for that significant-coefficient-group flag based on the significant-coefficient-group flags reconstructed for two neighbor groups.

10. The method claimed in claim 9, wherein the two neighbor groups include a right neighbor and a below neighbor, and wherein the context is 0 if both of the significant-coefficient-flags for the two neighbor groups are 0, and wherein otherwise the context is 1.

21. A non-transitory processor-readable medium storing processor-executable instructions which, when executed, configures one or more processors to perform the method claimed in claim 1.

26. The method claimed in claim 1, wherein the transform unit is 32×

32 and wherein each group is a 4×

4 block.

11. A decoder for decoding a bitstream of encoded data to reconstruct significant-coefficient flags for a transform unit, the decoder comprising:

a processor;

a memory; and

a decoding application stored in memory and containing instructions for configuring the processor to

reconstructing significant-coefficient-group flags, wherein the transform unit is partitioned into non-overlapping blocks, each block containing a respective group of significant-coefficient flags, and wherein each significant-coefficient-group flag corresponds to a respective block and its respective group of significant-coefficient flags; and

reconstruct each significant-coefficient flag by

if the significant-coefficient-flag is at position (0,0) in its group, a corresponding significant-coefficient-group flag is non-zero, the group is not the DC block, and all the previous significant-coefficient flags in that group are zero, then inferring the significant-coefficient-flag at position (0,0) in that group to be 1, and

otherwise

decoding the significant-coefficient flag from the bitstream if that significant-coefficient flag is in a group that has corresponding significant-coefficient-group flag that is non-zero, and

setting the significant-coefficient flag to zero, if that significant-coefficient flag is in a group that has corresponding significant-coefficient-group flag that is zero.

12. The decoder claimed in claim 11, wherein the processor is configured to reconstruct the significant-coefficient-group flags by decoding at least some of the significant-coefficient-group flags from the encoded data of the bitstream.

13. The decoder claimed in claim 12, wherein the processor is further configured to reconstruct significant-coefficient-group flags by inferring a significant-coefficient-group flag to be 1 on the basis that it corresponds to the block containing the significant-coefficient flag for a last-significant coefficient.

14. The decoder claimed in claim 12, wherein the processor is further configured to reconstruct the significant-coefficient-group flags by inferring a significant-coefficient-group flag to be 1 on the basis that it corresponds to the block containing the significant-coefficient flag for a DC coefficient.

15. The decoder claimed in claim 12, wherein the processor is further configured to reconstruct the significant-coefficient-group flags by inferring a significant-coefficient-group flag to be 1 if that significant-coefficient-group flag corresponds to a group that has two neighbor groups both of which have corresponding significant-coefficient-group flags that have reconstructed values of 1.

16. The decoder claimed in claim 15, wherein the groups are contiguous blocks, and wherein the two neighbor groups include a right neighbor block and a below neighbor block.

17. The decoder claimed in claim 11, wherein the transform unit is 16×

16 and wherein each group is a 4×

4 block.

18. The decoder claimed in claim 11, wherein the transform unit is 32×

32 and wherein each group is an 8×

8 block.

19. The decoder claimed in claim 11, wherein the processor is further configured to reconstruct one of the significant-coefficient-group flags by determining a context for that significant-coefficient-group flag based on the significant-coefficient-group flags reconstructed for two neighbor groups.

20. The decoder claimed in claim 19, wherein the two neighbor groups include a right neighbor and a below neighbor, and wherein the context is 0 if both of the significant-coefficient-flags for the two neighbor groups are 0, and wherein otherwise the context is 1.

27. The decoder claimed in claim 11, wherein the transform unit is 32×

32 and wherein each group is a 4×

4 block.

22. A method for encoding significant-coefficient flags for a transform unit, the method comprising:

encoding significant-coefficient-group flags, wherein the transform unit is partitioned into non-overlapping blocks, each block containing a respective group of significant-coefficient flags, and wherein each significant-coefficient-group flag corresponds to a respective block containing its respective group of significant-coefficient flags, and wherein the significant-coefficient-group flag is set to zero to indicate that that corresponding group contains no non-zero significant-coefficient flags; and

for each of the significant-coefficient flags,

encoding the significant-coefficient flag if that significant-coefficient flag is in one of the groups for which its corresponding significant-coefficient-group flag is non-zero, and

not encoding the significant-coefficient flag if

that significant-coefficient flag is in one of the groups for which the corresponding significant-coefficient-group flag is zero, or

that significant-coefficient-flag is at position (0,0) in its group, the corresponding significant-coefficient-group flag is non-zero, the group is not the DC block, and all the previous significant-coefficient flags in that group are zero.

23. The encoder claimed in claim 22, further including a two-stage rate-distortion optimized quantization process, wherein a second stage of the two-stage rate-distortion optimized quantization process includes determining whether to set any of the significant-coefficient-group flags and their corresponding significant-coefficient flags and coefficients to zero based on a rate-distortion analysis.

24. An encoder for encoding significant-coefficient flags for a transform unit, the encoder comprising:

a processor;

a memory storing the significance map; and

an encoding application stored in memory and containing instructions for configuring the processor to perform the method claimed in claim 22.

25. A non-transitory processor-readable medium storing processor-executable instructions which, when executed, configures one or more processors to perform the method claimed in claim 22.