Video or image coding based on mapping of luma samples and scaling of chroma samples
According to the disclosure of the present document, it is possible for various LMCS application cases to apply an LMCS procedure to a block having a dual tree structure. In addition, the coding performance of the block can be improved. According to the disclosure of the present document, resources required for the LMCS procedure can be reduced. Therefore, the complexity of the LMCS can be reduced and the video/image coding efficiency can be increased.
1. An image decoding method performed by a decoding apparatus, the method comprising:
obtaining image information including prediction information, residual information and information on luma mapping with chroma scaling (LMCS) data from a bitstream;
deriving an inter prediction mode for a current block in a current picture based on the prediction information;
deriving motion information for the current block based on the inter prediction mode;
generating predicted luma samples based on the motion information;
deriving LMCS codewords based on the information on the LMCS data;
generating mapped predicted luma samples based on the predicted luma samples and the LMCS codewords;
deriving residual samples based on the residual information, wherein the residual samples includes residual luma samples and residual chroma samples;
generating reconstructed luma samples based on the mapped predicted luma samples and the residual luma samples; and
generating modified reconstructed luma samples based on the reconstructed luma samples and the LMCS codewords,
wherein the image information includes LMCS adaptation parameter sets (APSs),
wherein an LMCS APS includes type information indicating that the LMCS APS is an APS including an LMCS data field,
wherein the LMCS APS includes the LMCS data field based on the type information,
wherein the LMCS data field includes the information on the LMCS data,
wherein a maximum number of the LMCS APS is a specific value,
wherein the specific value is 4,
wherein the method further comprises:
deriving a chroma residual scaling factor based on a piece wise index; and
generating scaled residual chroma samples based on the residual chroma samples and the chroma residual scaling factor,
wherein the piecewise index is identified based on the information on the LMCS data.
2. An image encoding method performed by an encoding apparatus, the method comprising:
deriving an inter prediction mode for a current block in a current picture;
generating motion information based on the inter prediction mode;
generating predicted samples based on the motion information, wherein the predicted samples include predicted luma samples and predicted chroma samples;
deriving luma mapping with chroma scaling (LMCS) codewords and bins for luma mapping;
generating mapped predicted luma samples based on the LMCS codewords and the bins for the luma mapping;
generating reconstructed luma samples based on the mapped predicted luma samples;
generating modified reconstructed luma samples based on the reconstructed luma samples, the LMCS codewords, and the bins for the luma mapping;
deriving information on LMCS data based on the LMCS codewords and the bins for the luma mapping;
generating residual luma samples based on the mapped predicted luma samples;
generating residual information based on the residual luma samples;
generating residual chroma samples based on the predicted chroma samples; and
encoding image information including the residual information and the information on the LMCS data,
wherein the image information includes LMCS adaptation parameter sets (APSs),
wherein an LMCS APS includes type information indicating that the LMCA APS is an AP including an LMCS data field,
wherein the LMCS APS includes the LMCS data field based on the type information;
wherein the LMCS data field includes the information on the LMCS data,
wherein a maximum number of the LMCS APS is a specific value,
wherein the specific value is 4,
wherein the method further comprises:
deriving a chroma residual scaling factor based on a piecewise index; and
generating scaled residual chroma samples based on the residual chroma samples and the chroma residual scaling factor,
wherein the piecewise index is identified based on the information on the LMCS data.
3. A transmission method of data for an image, the method comprising:
obtaining a bitstream of the image, wherein the bitstream is generated based on deriving an inter prediction mode for a current block in a current picture, generating motion information based on the inter prediction mode, generating predicted samples based on the motion information, wherein the predicted samples include predicted luma samples and predicted chroma samples, deriving luma mapping with chroma scaling (LMCS) codewords and bins for luma mapping, generating mapped predicted luma samples based on the LMCS codewords and the bins for the luma mapping, generating reconstructed luma samples based on the mapped predicted luma samples, generating modified reconstructed luma samples based on the reconstructed luma samples, the LMCS codewords, and the bins for the luma mapping, deriving information on LMCS data based on the LMCS codewords and the bins for the luma mapping, generating residual luma samples based on the mapped predicted luma samples, generating residual information based on the residual luma samples, generating residual chroma samples based on the predicted chroma samples, and encoding image information including the residual information and the information on the LMCS data; and
transmitting the data comprising the bitstream,
wherein the image information includes LMCS adaptation parameter sets (APSs),
wherein an LMCS APS includes type information indicating that the LMCA APS is an AP including an LMCS data field,
wherein the LMCS APS includes the LMCS data field based on the type information;
wherein the LMCS data field includes the information on the LMCS data,
wherein a maximum number of the LMCS APS is a specific value,
wherein the specific value is 4,
wherein the method further comprises:
deriving a chroma residual scaling factor based on a piecewise index; and
generating scaled residual chroma samples based on the residual chroma samples and the chroma residual scaling factor,
wherein the piecewise index is identified based on the information on the LMCS data.