Chroma quantization in video coding
AssigneeApple Inc.
InventorsAlexandros Tourapis, Guy Cote
Life of this patent
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Abstract
A method of signaling additional chroma QP offset values that are specific to quantization groups is provided, in which each quantization group explicitly specifies its own set of chroma QP offset values. Alternatively, a table of possible sets of chroma QP offset values is specified in the header area of the picture, and each quantization group uses an index to select an entry from the table for determining its own set of chroma QP offset values. The quantization group specific chroma QP offset values are then used to determine the chroma QP values for blocks within the quantization group in addition to chroma QP offset values already specified for higher levels of the video coding hierarchy.
Claims11
A non-transitory machine-readable medium storing instructions that, when executed, are configured to cause one or more processing units to perform operations comprising:
- receiving, in a bitstream, an encoded group of video pictures, including an encoded first video picture with a hierarchical coding structure having at least a first coding level, a second coding level and a third coding level, the encoded first video picture comprising two or more sets of chroma quantization parameter (QP) offset values at the first coding level and the second coding level, each set of chroma QP offset values providing information about chroma QPs of video units encompassed by one level of the hierarchical coding structure, the encoded first video picture further comprising one or more chroma quantization groups (QGs) at the third coding level;
- for a particular chroma QG of the one or more chroma QGs at the third coding level, identifying an additional set of chroma QP offsets, the identifying comprising:
- determining, based on information included in the first coding level or the second coding level, a parameter specifying the maximum length of a binary string in the bitstream, and
- identifying the additional set of chroma QP offsets using the parameter;
- and
- decoding the encoded first video picture by computing chroma QP values corresponding to the one or more chroma QGs of the encoded first video picture, the decoding comprising, for the particular chroma QG:
- selecting the identified additional set of chroma QP offsets, and
- computing the chroma QP values corresponding to the particular chroma QG using the selected set of the chroma QP offsets.
Dependencies are inferred from the claim text.