Patent ID: 11909997
Assignee: LG ELECTRONICS INC.
Field: Audio-visual technology (Electrical engineering)
Classification: CPC H | IPC H

Claim 0:
1. An image decoding method, performed by a decoding apparatus, comprising:
obtaining image information including prediction information and residual information for a current chroma block, and 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;
obtaining quantization parameter data for a chroma cb component and quantization parameter data for a chroma cr component;
deriving a chroma quantization parameter mapping table for the combined chroma coding based on the quantization parameter data for the combined chroma coding;
deriving a chroma quantization parameter mapping table for the chroma cb component and a chroma quantization parameter mapping table for the chroma cr component based on the quantization parameter data for the chroma cb component and the quantization parameter data for the chroma cr component;
deriving a quantization parameter for the combined chroma coding based on the chroma quantization parameter mapping table for the combined chroma coding;
deriving a quantization parameter for the chroma cb component and a quantization parameter for the chroma cr component based on the chroma quantization parameter mapping table for the chroma cb component and the chroma quantization parameter mapping table for the chroma cr component;
deriving prediction samples of the current chroma block based on the prediction information;
deriving transform coefficients of the current chroma block based on the residual information;
deriving residual samples by dequantizing the transform coefficients based on a quantization parameter related to the current chroma block among the quantization parameter for the combined chroma coding, the quantization parameter for the chroma cb component and the quantization parameter for the chroma cr component; and
generating a reconstructed picture based on the prediction samples and the residual samples,
wherein the quantization parameter data for the combined chroma coding includes a syntax element for a starting quantization parameter of the chroma quantization parameter mapping table for the combined chroma coding and a syntax element for a number of quantization parameters in the chroma quantization parameter mapping table for the combined chroma coding,
wherein the quantization parameter for the combined chroma coding is derived based on a quantization parameter corresponding to a quantization parameter of a luma component in the chroma quantization parameter mapping table for the combined chroma coding,
wherein the flag is included in a Sequence Parameter Set (SPS), and
wherein a parsing order of the syntax element for the starting quantization parameter of the chroma quantization parameter mapping table for the combined chroma coding is prior to a parsing order of the syntax element for the number of quantization parameters in the chroma quantization parameter mapping table for the combined chroma coding.