Video or image coding applying adaptive loop filter

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

• deriving prediction samples for a current block in a current picture;
• deriving residual samples for the current block based on the prediction samples;
• generating residual information and reconstructed samples 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 ALF information, the residual information and index information of an alternative filter of the chroma component of the current block,
• wherein the ALF information includes alternative filter information for a chroma component of the current block,
• wherein the alternative filter information indicates an alternative filter for deriving modified reconstructed samples for the chroma component of the current block,
• wherein the alternative filter information includes information on a number of alternative filters for the chroma component of the current block, absolute value information of coefficients included in the 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 for a current block in a current picture;
• deriving residual samples for the current block based on the prediction samples;
• generating residual information and reconstructed samples 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 ALF information, the residual information and index information of an alternative filter of the chroma component of the current block to output the bitstream,
• wherein the ALF information includes alternative filter information for a chroma component of the current block,
• wherein the alternative filter information indicates an alternative filter for deriving modified reconstructed samples for the chroma component of the current block,
• wherein the alternative filter information includes information on a number of alternative filters for the chroma component of the current block, absolute value information of coefficients included in the 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.