CPC H04N 19/124 (2014.11) [H04N 19/176 (2014.11); H04N 19/186 (2014.11); H04N 19/70 (2014.11)] | 10 Claims |
1. A picture decoding method performed by a decoding apparatus, comprising:
obtaining image information including information related to a quantization parameter (QP) from a bitstream, wherein the information related to the QP includes information related to a luma QP, and the information related to the luma QP includes information on an absolute value of a QP delta value and information on a sign of the QP delta value;
deriving the luma QP based on the information related to the luma QP;
deriving chroma QPs based on a chroma QP mapping table, wherein the chroma QPs include a first chroma QP for a Cb component and a second chroma QP for a Cr component; and
generating a reconstructed picture including reconstructed samples based on the luma QP, the first chroma QP for the Cb component and the second chroma QP for the Cr component,
wherein deriving the luma QP based on the information related to the luma QP comprises:
deriving a predicted luma QP based on a first luma QP of a coding unit containing a luma coding block covering (xQg−1, yQg) and a second luma QP of a coding unit containing a luma coding block covering (xQg, yQg−1), wherein (xQg, yQg) represents a top-left sample position of a current quantization group;
deriving the QP delta value based on the information on the absolute value of the QP delta value and the information on the sign of the QP delta value; and
deriving the luma QP based on the predicted luma QP and the QP delta value,
wherein the chroma QP mapping table for the chroma QPs is divided into a first chroma QP mapping table for the Cb component and a second chroma QP mapping table for the Cr component,
wherein the first chroma QP mapping table for the Cb component is a separate mapping table from the second chroma QP mapping table for the Cr component,
wherein deriving the chroma QPs comprises:
deriving the first chroma QP for the Cb component based on the luma QP and the first chroma QP mapping table for the Cb component; and
deriving the second chroma QP for the Cr component based on the luma QP and the second chroma QP mapping table for the Cr component, and
wherein both an input of the first chroma QP mapping table and an input of the second chroma mapping table are based on the luma QP.
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