Apparatus and method for chrominance quantization parameter derivation

A decoder, comprising:

• a non-transitory memory configured to store instructions;
• and
• a processor coupled to the non-transitory memory and configured to execute the instructions to facilitate the following being performed by the decoder:
• parsing a bitstream to obtain a differential quantization parameter value for a current block of a chrominance component of a picture;
• determining a quantization parameter value for the current block of the chrominance component as a predetermined function of:
• the obtained differential quantization parameter value;
• and
• quantization parameter values of a coding unit of a luminance component collocated to the current block, at least one neighboring block of the current block of the chrominance component, and at least one coding unit of a luminance component that is collocated to the at least one neighboring block;
• performing inverse quantization on the current block of the chrominance component by using the determined quantization parameter value, to obtain a dequantized coefficient of the current block;
• and
• obtaining a reconstructed picture at least based on the dequantized coefficient.

A non-transitory computer-readable medium having instructions stored thereon, wherein the instructions, when executed by a processor, facilitate:

• parsing a bitstream to obtain a differential quantization parameter value for a current block of a chrominance component of a picture;
• determining a quantization parameter value for the current block of the chrominance component as a predetermined function of:
• the obtained differential quantization parameter value;
• and
• quantization parameter values of a coding unit of a luminance component collocated to the current block, at least one neighboring block of the current block of the chrominance component, and at least one coding unit of a luminance component that is collocated to the at least one neighboring block;
• performing inverse quantization on the current block of the chrominance component by using the determined quantization parameter value, to obtain a dequantized coefficient of the current block;
• and
• obtaining a reconstructed picture at least based on the dequantized coefficient.