Methods and devices for context modeling to enable modular processing

Abstract

Methods of encoding and decoding for video data are described for encoding or decoding coefficients for a transform unit. In particular, the significant-coefficient flags for a coefficient group are encoded and decoded based upon a context determination, and the context is determined based upon the values of neighboring flags. The neighborhood used to determine the context varies depending on whether the significant-coefficient flag to be encoded or decoded is in the right column or bottom row of the coefficient group or not. If it is in the right column or bottom row one of the alternative context neighborhoods is used to avoid relying on significant-coefficient flags in other coefficient groups except for the flags immediately adjacent the right border and bottom border of the coefficient group, and the flag diagonally to the lower-right.

What is claimed is: 
     
         1 . A method of decoding a bitstream of encoded video by reconstructing significant-coefficient flags for a transform unit, the transform unit comprising a sequence of block-based coefficient groups, each coefficient group corresponding to a significant-coefficient-group flag and a set of significant-coefficient flags encoded in the bitstream, the method comprising:
 determining a coefficient group for which the corresponding significant-coefficient-group flag is set;   determining a context for each significant-coefficient flag in the set of significant-coefficient flags corresponding to said coefficient group, based on the respective significant-coefficient-group flags of one or more coefficient groups neighboring that coefficient group;   and decoding each significant-coefficient flag of the set of significant-coefficient flags corresponding to that coefficient group, using the determined context.   
     
     
         2 . The method of  claim 1 , wherein the one or more coefficient groups neighboring that coefficient group comprise at least one of: a coefficient group to the right of that coefficient group, a coefficient group below that coefficient group, and a coefficient group diagonally to the lower-right of that coefficient group. 
     
     
         3 . The method of  claim 1 , wherein determining the context for each significant-coefficient flag in the set of significant-coefficient flags corresponding to that coefficient group is further based on the position, in that coefficient group, of the coefficient corresponding to the significant-coefficient flag. 
     
     
         4 . The method of  claim 1 , wherein the coefficient group flags of the one or more neighboring coefficient groups were previously decoded. 
     
     
         5 . The method of  claim 1 , further comprising selecting a context set for use in decoding the set of significant-coefficient flags corresponding to that coefficient group. 
     
     
         6 . The method of  claim 5 , wherein selecting a context set is based on a size of the transform unit. 
     
     
         7 . The method of  claim 5 , wherein selecting a context set is based on a color component index for the transform unit. 
     
     
         8 . The method of  claim 1 , wherein decoding the significant-coefficient flags of the set of significant-coefficient flags corresponding to that coefficient group further comprises using a DC-specific context for the significant-coefficient flag in the DC position. 
     
     
         9 . The method of  claim 1 , wherein the coefficient groups each have a square shape, and wherein the transform unit has size 16×16. 
     
     
         10 . The method of  claim 1 , wherein determining a context further comprises selecting a context for one of the significant-coefficient flags in the right-most column of that coefficient group, and wherein that context is only available for selection for that significant-coefficient if the significant-coefficient-group flag reconstructed for a coefficient group to the right of that coefficient group is non-zero. 
     
     
         11 . The method of  claim 1 , wherein determining a context further comprises selecting a context for one of the significant-coefficient flags in the bottom row of that coefficient group, and wherein that context is only available for selection for that significant-coefficient if the significant-coefficient-group flag reconstructed for a coefficient group below that coefficient group is non-zero. 
     
     
         12 . A video decoder for decoding a bitstream of encoded video by reconstructing significant-coefficient flags for a transform unit, the transform unit comprising a sequence of block-based coefficient groups, each coefficient group corresponding to a significant-coefficient-group flag and a set of significant-coefficient flags encoded in the bitstream, the video decoder comprising:
 a processor;   memory;   a video decoding application containing processor-executable instructions that, when executed, cause the processor to:
 determine a coefficient group for which the corresponding significant-coefficient-group flag is set; 
 determine a context for each significant-coefficient flag in the set of significant-coefficient flags corresponding to said coefficient group, based on the respective significant-coefficient-group flags of one or more coefficient groups neighboring that coefficient group; 
 and decode each significant-coefficient flag of the set of significant-coefficient flags corresponding to that coefficient group, using the determined context. 
   
     
     
         13 . The video decoder of  claim 12 , wherein the one or more coefficient groups neighboring that coefficient group comprise at least one of: a coefficient group to the right of that coefficient group, a coefficient group below that coefficient group, and a coefficient group diagonally to the lower-right of that coefficient group. 
     
     
         14 . The video decoder of  claim 12 , wherein the processor determines the context for each significant-coefficient flag in the set of significant-coefficient flags corresponding to that coefficient group based on the position, in that coefficient group, of the coefficient corresponding to the significant-coefficient flag. 
     
     
         15 . The video decoder of  claim 12 , wherein the coefficient group flags of the one or more neighboring coefficient groups were previously decoded. 
     
     
         16 . The video decoder of  claim 12 , wherein the instructions, when executed, further cause the processor to select a context set for use in decoding the set of significant-coefficient flags corresponding to that coefficient group. 
     
     
         17 . The video decoder of  claim 16 , wherein selecting a context set is based on a size of the transform unit. 
     
     
         18 . The video decoder of  claim 16 , wherein selecting a context set is based on a color component index for the transform unit. 
     
     
         19 . The video decoder of  claim 12 , wherein the processor decodes the significant-coefficient flags of the set of significant-coefficient flags corresponding to that coefficient group using a DC-specific context for the significant-coefficient flag in the DC position. 
     
     
         20 . The video decoder of  claim 12 , wherein the coefficient groups each have a square shape, and wherein the transform unit has size 16×16. 
     
     
         21 . The video decoder of  claim 12 , wherein the instructions further cause the processor to selecting a context for one of the significant-coefficient flags in the right-most column of that coefficient group, and wherein that context is only available for selection for that significant-coefficient if the significant-coefficient-group flag reconstructed for a coefficient group to the right of that coefficient group is non-zero. 
     
     
         22 . The video decoder of  claim 12 , wherein the instructions further cause the processor to selecting a context for one of the significant-coefficient flags in the bottom row of that coefficient group, and wherein that context is only available for selection for that significant-coefficient if the significant-coefficient-group flag reconstructed for a coefficient group below that coefficient group is non-zero. 
     
     
         23 . A non-transitory processor-readable medium storing processor-executable instructions which, when executed, configure one or more processors to perform the method claimed in  claim 1 .