| CPC H04N 19/132 (2014.11) [H04N 19/159 (2014.11); H04N 19/176 (2014.11); H04N 19/186 (2014.11); H04N 19/134 (2014.11); H04N 19/189 (2014.11); H04N 19/61 (2014.11)] | 13 Claims |
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1. An image decoding method performed by a decoding apparatus, the method comprising:
obtaining prediction mode information from a bitstream;
deriving a prediction mode of a current block based on the prediction mode information;
deriving luma prediction sample values of the current block based on the prediction mode of the current block;
determining whether reshaping is performed for the luma prediction sample values;
deriving a chroma residual scaling index based on the determination on whether reshaping is performed;
deriving chroma residual samples based on the chroma residual scaling index; and
deriving chroma reconstructed samples based on the chroma residual samples,
wherein whether reshaping is performed is determined based on a determination on whether the current block belongs to a reshaped domain, or the prediction mode of the current block,
wherein the chroma residual scaling index is derived based on an average luma value of the luma prediction sample values, forward-reshaped luma prediction sample values or inverse-reshaped luma prediction sample values, and
wherein based on a determination that the current block does not belong to the reshaped domain:
the average luma value of the luma prediction sample values is derived,
reshaping is performed for the derived average luma value as forward reshaping, and
the chroma residual scaling index is derived based on the forward-reshaped average luma value.
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