Video or image coding applying adaptive loop filter

An image encoding method performed by an encoding apparatus, the method comprising:

• deriving prediction samples of a current block;
• deriving residual samples of the current block based on the prediction samples;
• generating reconstructed samples based on the prediction samples and the residual samples
• generating residual information based on the residual samples;
• deriving filter coefficients for an adaptive loop filter (ALF) for the reconstructed samples;
• generating ALF information based on the filter coefficients;
• and
• encoding image information including the residual information and the ALF information,
• wherein the image information includes index information of an alternative filter for a chroma component of the current block,
• wherein the ALF information includes alternative filter information for the chroma component of the current block including information on a number of alternative filters for the chroma component of the current block,
• wherein based on the information on the number of the alternative filters for the chroma component of the current block, the alternative filter information includes absolute value information of coefficients included in alternative filters for the chroma component of the current block and sign information of coefficients included in the alternative filters for the chroma component of the current block,
• wherein the index information of the alternative filter is based on truncated rice binarization,
• wherein bins of a bin string for the index information of the alternative filter are entropy-encoded based on a context model,
• wherein the context model for the bins of the bin string related to the index information of the alternative filter is determined based on a context index increment for the bins, and
• wherein the context index increment is determined based on the chroma component of the current block.

A non-transitory computer-readable storage medium storing a bitstream generated by a method, wherein the method comprises:

• \
• deriving prediction samples of a current block;
• deriving residual samples of the current block based on the prediction samples;
• generating reconstructed samples based on the prediction samples and the residual samples
• generating residual information based on the residual samples;
• deriving filter coefficients for an adaptive loop filter (ALF) for the reconstructed samples;
• generating ALF information based on the filter coefficients;
• and
• encoding image information including the residual information and the ALF information,
• wherein the image information includes index information of an alternative filter for a chroma component of the current block,
• wherein the ALF information includes alternative filter information for the chroma component of the current block including information on a number of alternative filters for the chroma component of the current block,
• wherein based on the information on the number of the alternative filters for the chroma component of the current block, the alternative filter information includes absolute value information of coefficients included in alternative filters for the chroma component of the current block and sign information of coefficients included in the alternative filters for the chroma component of the current block,
• wherein the index information of the alternative filter is based on truncated rice binarization,
• wherein bins of a bin string for the index information of the alternative filter are entropy-encoded based on a context model,
• wherein the context model for the bins of the bin string related to the index information of the alternative filter is determined based on a context index increment for the bins, and
• wherein the context index increment is determined based on the chroma component of the current block.