Method and apparatus for chrominance quantization parameters signalling

An encoding method comprising:

• encoding a joint chrominance component residual (JCCR) control flag into a sequence parameter set (SPS) level syntax;
• encoding, based on the JCCR control flag, chrominance mapping information into the SPS level syntax;
• encoding, based on the JCCR control flag, a chrominance quantization parameter (QP) offset into a slice level syntax;
• obtaining quantized coefficients of a picture block;
• and
• obtaining a bitstream including the SPS level syntax, the slice level syntax, and the quantized coefficients.

A non-transitory computer readable medium storing a bitstream and one or more instructions executable by at least one processor to perform operations of decoding of the bitstream, the operations comprising:

• receiving the bitstream including a sequence parameter set (SPS) level syntax and a slice level syntax, wherein the SPS level syntax includes a joint chrominance component residual (JCCR) control flag and chrominance mapping information, wherein the slice level syntax includes a chrominance quantization parameter (QP) offset;
• obtaining the JCCR control flag from the SPS level syntax;
• obtaining, based on the JCCR control flag, the chrominance mapping information from the SPS level syntax;
• obtaining, based on the JCCR control flag, a chrominance QP offset from the slice level syntax;
• obtaining a QP value for a current chrominance block based on the chrominance mapping information and the chrominance QP offset;
• performing, based on the QP value, inverse quantization on the current chrominance block to obtain a reconstructed residual block;
• obtaining a reconstructed block based on the reconstructed residual block;
• and
• obtaining a decoded picture based on the reconstructed block.