Patent ID: 9584812
Date: 2017-02-28
CPC Classifications: H04N

Claim:
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 blocks in a scan order, the bitstream encoding sets of significant-coefficient flags, each set corresponding to a respective block, each block having an associated significant-coefficient-group flag that indicates whether the significant-coefficient flags corresponding to that block are to be decoded from the bitstream or may be inferred to be zero, the method comprising: (i) for a set of significant-coefficient flags corresponding to a first block with an associated non-zero significant-coefficient-group flag, selecting a context set from a plurality of context sets for use in decoding significant-coefficient flags of that set based on a significant-coefficient-group flag associated with a block to the right of the first block and a significant-coefficient-group flag associated with a block below the first block, wherein the context sets identify the contexts to be used in context-adaptively decoding the significant-coefficient flags of that set of significant-coefficient flags, and wherein selecting includes selecting a first context set if both of the significant-coefficient-group flags are non-zero, and, otherwise, selecting a different, mutually exclusive context set; (ii) entropy decoding the significant-coefficient flags of that set using the selected context set by, for each significant-coefficient flag, selecting a context from within the selected context set for context-adaptively decoding that significant-coefficient flag; and (iii) moving to the next block in the scan order and returning to operation (i), wherein each significant-coefficient-group flag indicates whether its associated block is presumed to contain at least one non-zero significant-coefficient flag, wherein for each block in the sequence of blocks that has an associated significant coefficient-group flag that is decoded to be zero, there are no non-zero significant-coefficient flags in that block, and for each block in the sequence of blocks that has an associated significant-coefficient-group flag that is decoded to be non-zero, there is at least one non-zero significant-coefficient flag in that block, and wherein for each block in the sequence of blocks that has an associated significant-coefficient-group flag that is zero, all of the significant-coefficient flags in that block are set to zero instead of performing the selecting operation and the entropy decoding operation.