Image coding method and device on basis of wide-angle intra prediction and transform

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

• deriving an intra prediction mode for a current block;
• deriving a modified intra prediction mode through intra prediction mode remapping based on whether wide-angle intra prediction is applied to the current block;
• deriving prediction samples based on the modified intra prediction mode;
• deriving residual samples for the current block based on the prediction samples;
• determining a low frequency non-separable transform (LFNST) set among four LFNST sets, the LFNST set comprising LFNST matrices based on the modified intra prediction mode;
• deriving transform coefficients for the current block based on the residual samples, the determined LFNST set, and the LFNST matrices;
• and
• encoding image information comprising the intra prediction mode and an LFNST index indicating the LFNST matrices,
• wherein the intra prediction mode information indicates any one of a planar mode (0), a DC mode (1), and directional modes 2 to 66,
• wherein the modified intra prediction mode is derived to range from 67 to 80 based on the width of the current block being greater than the height of the current block,
• wherein the modified intra prediction mode is derived to range from −1 to −14 based on the height of the current block being greater than the width of the current block, and
• wherein an LFNST set in a case where the modified intra prediction mode ranges from 67 to 80 and an LFNST set in a case where the modified intra prediction mode ranges from −1 to −14 are the same, and
• a first LFNST set of the four LFNST sets is used for the intra prediction mode ranging from 0 to 1, a second LFNST set of the four LFNST sets is used for the modified intra prediction mode ranging from −1 to −14 and 67-80, and the intra prediction mode ranging from 2 to 12 and 56-66, a third LFNST set of the four LFNST sets is used for the intra prediction mode ranging from 13 to 23 and ranging from 45 to 55, a fourth LFNST set of the four LFNST sets is used for the intra prediction mode ranges from 24 to 44.

A non-transitory computer-readable digital storage medium that stores a bitstream generated by a method, the method comprising:

• deriving an intra prediction mode for a current block;
• deriving a modified intra prediction mode through intra prediction mode remapping based on whether wide-angle intra prediction is applied to the current block;
• deriving prediction samples based on the modified intra prediction mode;
• deriving residual samples for the current block based on the prediction samples;
• determining a low frequency non-separable transform (LFNST) set among four LFNST sets, the LFNST set comprising LFNST matrices based on the modified intra prediction mode;
• deriving transform coefficients for the current block based on the residual samples, the determined LFNST set, and the LFNST matrices;
• and
• encoding image information comprising the intra prediction mode and an LFNST index indicating the LFNST matrices to generate the bitstream,
• wherein the intra prediction mode information indicates any one of a planar mode (0), a DC mode (1), and directional modes 2 to 66,
• wherein the modified intra prediction mode is derived to range from 67 to 80 based on the width of the current block being greater than the height of the current block,
• wherein the modified intra prediction mode is derived to range from −1 to −14 based on the height of the current block being greater than the width of the current block, and
• wherein an LFNST set in a case where the modified intra prediction mode ranges from 67 to 80 and an LFNST set in a case where the modified intra prediction mode ranges from −1 to −14 are the same, and
• a first LFNST set of the four LFNST sets is used for the intra prediction mode ranging from 0 to 1, a second LFNST set of the four LFNST sets is used for the modified intra prediction mode ranging from −1 to −14 and 67-80, and the intra prediction mode ranging from 2 to 12 and 56-66, a third LFNST set of the four LFNST sets is used for the intra prediction mode ranging from 13 to 23 and ranging from 45 to 55, a fourth LFNST set of the four LFNST sets is used for the intra prediction mode ranges from 24 to 44.