Method and apparatus for signaling of mapping function of chroma quantization parameter

A decoder comprising:

• one or more electronic circuits or processors configured to:
• receive a bitstream;
• parse the bitstream to obtain a luminance quantization parameter (QP) and information of a chroma QP mapping table which associates a QP index (QPi) to a chrominance QP (QPc);
• obtain a QPi based at least in part on the obtained luminance QP;
• obtain the chroma QP mapping table based on the obtained information of the chroma QP mapping table;
• obtain a first QPc based on the obtained chroma QP mapping table and the obtained QPi;
• and
• obtain a second QPc based on the first QPc.

A non-transitory computer-readable medium having instructions stored therein, which when executed by a processor, cause a decoder to:

• receive a bitstream;
• parse the bitstream to obtain a luminance quantization parameter (QP) and information of a chroma QP mapping table which associates a QP index (QPi) to a chrominance QP (QPc);
• obtain a QPi based at least in part on the obtained luminance QP;
• obtain a chroma QP mapping table based on the obtained information of the chroma QP mapping table;
• obtain a first QPc based on the obtained chroma QP mapping table and the obtained QPi;
• and
• obtain a second QPc based on the first QPc.