Image decoding method based on chroma quantization parameter data, and apparatus therefor

An image encoding method, performed by an encoding apparatus, comprising:

• deriving residual samples for a chroma component;
• generating quantization parameter data for combined chroma coding of the residual samples based on a chroma type of the chroma component;
• generating a flag representing whether the quantization parameter data for the combined chroma coding is present;
• and
• encoding the quantization parameter data and the flag,
• wherein the quantization parameter data includes a syntax element for a starting quantization parameter of a chroma quantization parameter table and a syntax element for a number of quantization parameters in the chroma quantization parameter table.

A non-transitory computer-readable storage medium storing a bitstream generated by a method, the method comprising:

• deriving residual samples for a chroma component;
• generating quantization parameter data for combined chroma coding of the residual samples based on a chroma type of the chroma component;
• generating a flag representing whether the quantization parameter data for the combined chroma coding is present;
• encoding the quantization parameter data and the flag;
• and
• generating the bitstream including the quantization parameter data and the flag,
• wherein the quantization parameter data includes a syntax element for a starting quantization parameter of a chroma quantization parameter table and a syntax element for a number of quantization parameters in the chroma quantization parameter table.