Systems and methods for varying quantization parameters

A non-transitory computer-readable storage medium comprising a program stored thereon that, when executed, cause one or more processors of a device for decoding video data to:

• receive level values corresponding to a chroma coding block, wherein:
• the chroma coding block is one of a plurality of chroma coding blocks resulting from partitioning a chroma coding tree block,
• the chroma coding tree block and a corresponding luma coding tree block form a coding tree unit, and
• the corresponding luma coding tree block is partitioned into luma coding blocks and the luma coding blocks are organized into quantization groups such that a plurality of luma quantization parameters are determined for the luma coding tree block;
• identify one of the plurality of luma quantization parameters that is mapped to the chroma coding block;
• derive a predictive quantization parameter for the chroma coding block by using a value derived from the identified luma quantization parameter as an index in a look-up table;
• determine a chroma quantization parameter for the chroma coding block by adding a delta quantization parameter to the predictive parameter, wherein the delta quantization parameter is associated with each of the plurality of chroma coding blocks;
• and
• generate transform coefficient values based on the determined chroma quantization parameter for the chroma coding block.

A device for coding video data, comprising:

• one or more processors;
• and
• a storage device coupled to the one or more processors and storing a program which, when executed by the one or more processors, causes the one or more processors to:
• receive level values corresponding to a chroma coding block, wherein:
• the chroma coding block is one of a plurality of chroma coding blocks resulting from partitioning a chroma coding tree block,
• the chroma coding tree block and a corresponding luma coding tree block form a coding tree unit, and
• the corresponding luma coding tree block is partitioned into luma coding blocks and the luma coding blocks are organized into quantization groups such that a plurality of luma quantization parameters are determined for the luma coding tree block;
• identify one of the plurality of luma quantization parameters that is mapped to the chroma coding block;
• derive a predictive quantization parameter for the chroma coding block by using a value derived from the identified luma quantization parameter as an index in a look-up table;
• determine a chroma quantization parameter for the chroma coding block by adding a delta quantization parameter to the predictive parameter, wherein the delta quantization parameter is associated with each of the plurality of chroma coding blocks;
• and
• generate transform coefficient values based on the determined chroma quantization parameter for the chroma coding block.