Image decoding method based on chroma quantization parameter data, and apparatus therefor
An image decoding method performed by a decoding apparatus according to the present document comprises the steps of: obtaining a flag indicating whether quantization parameter data for combined chroma coding is present on the basis of a type of chroma; obtaining the quantization parameter data for the combined chroma coding on the basis of the flag; deriving a chroma quantization parameter table on the basis of the quantization parameter data; deriving a quantization parameter for the combined chroma coding on the basis of the chroma quantization parameter table; deriving residual samples on the basis of the quantization parameter; and generating a reconstructed picture on the basis of the residual samples.
1. An image decoding method, performed by a decoding apparatus, comprising:
obtaining a flag representing whether quantization parameter data for combined chroma coding is present based on a chroma type;
obtaining the quantization parameter data for the combined chroma coding based on the flag;
deriving a chroma quantization parameter table based on the quantization parameter data;
deriving a quantization parameter for the combined chroma coding based on the chroma quantization parameter table;
deriving residual samples based on the quantization parameter; and
generating a reconstructed picture based on the residual samples,
wherein the quantization parameter data includes a syntax element for a starting quantization parameter of the chroma quantization parameter table and a syntax element for a number of quantization parameters in the chroma quantization parameter table.
2. The image decoding method of claim 1 , wherein when a value of the flag is 1, the flag represents that the quantization parameter data for the combined chroma coding is present.
3. The image decoding method of claim 1 , wherein the flag is signaled through a sequence parameter set (SPS).
4. The image decoding method of claim 1 , wherein the quantization parameter data includes syntax elements for quantization parameter values of indices of the chroma quantization parameter table.
5. The image decoding method of claim 1 , wherein a value of the chroma type is not 0.
6. The image decoding method of claim 1 , wherein the quantization parameter for the combined chroma coding is derived based on a quantization parameter for an index identical with an index of a quantization parameter for a luma component corresponding to the current chroma block.
7. The image decoding method of claim 1 , wherein the quantization parameter data includes a syntax element representing an offset for deriving the quantization parameter for the combined chroma coding.
8. The image decoding method of claim 7 , wherein the flag is signaled through a picture parameter set (PPS).
9. 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.
10. The image encoding method of claim 9 , wherein when a value of the flag is 1, the flag represents that the quantization parameter data for the combined chroma coding is present.
11. The image encoding method of claim 9 , wherein the flag is signaled through a sequence parameter set (SPS).
12. The image encoding method of claim 9 , wherein the quantization parameter data includes syntax elements for quantization parameter values of indices of the chroma quantization parameter table.
13. The image encoding method of claim 12 , wherein the chroma quantization parameter table for the combined chroma coding is derived based on the quantization parameter data,
wherein a quantization parameter for the combined chroma coding is derived based on the chroma quantization parameter table.
14. The image encoding method of claim 9 , wherein the quantization parameter data includes a syntax element representing an offset for deriving the quantization parameter for the combined chroma coding.
15. 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.