MULTI-LEVEL SIGNIFICANCE MAPS FOR ENCODING AND DECODING

• US 20130107969A1
• Filed: 11/01/2011
• Published: 05/02/2013
• Est. Priority Date: 11/01/2011
• Status: Active Grant

• Current Assignee: Velos Media, LLC (Inception Holdings, LLC)
• Original Assignee: Blackberry Limited
• Inventors: NGUYEN, Nguyen, He, Dake, Ji, Tianying
• Granted Patent: US 8,964,849 B2
• Time in Patent Office: Days
• 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 each significant-coefficient-group flag corresponds to a respective group of significant-coefficient flags; and

reconstructing each significant-coefficient flag by

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 setting the significant-coefficient-group flag for the group containing the significant-coefficient flag for a last-significant coefficient to 1.

4. The method claimed in claim 2, wherein reconstructing the significant-coefficient-group flags further includes setting the significant-coefficient-group flag for the group containing the significant-coefficient flag for a DC coefficient to 1.

5. The method claimed in claim 2, wherein reconstructing the significant-coefficient-group flags includes setting a significant-coefficient-group flag to 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.

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

reconstruct significant-coefficient-group flags, wherein each significant-coefficient-group flag corresponds to a respective group of significant-coefficient flags; and

reconstruct each significant-coefficient flag by

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 setting the significant-coefficient-group flag for the group containing the significant-coefficient flag for a last-significant coefficient to 1.

14. The decoder claimed in claim 12, wherein the processor is further configured to reconstruct the significant-coefficient-group flags by setting the significant-coefficient-group flag for the group containing the significant-coefficient flag for a DC coefficient to 1.

15. The decoder claimed in claim 12, wherein the processor is further configured to reconstruct the significant-coefficient-group flags by setting a significant-coefficient-group flag to 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.

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

encoding significant-coefficient-group flags, wherein each significant-coefficient-group flag corresponds to a 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.

23. The encoded 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.