obtaining specific mode value information, intra prediction mode information and a Low-Frequency Non-Separable Transform (LFNST) index from a bitstream;

remapping an intra prediction mode of the current block to a wide angle intra prediction mode based on the specific mode value information when an Intra Sub-Partitions (ISP) mode is applied to a current block;

performing prediction on the current block based on the wide angle intra prediction mode;

remapping the intra prediction mode of the current block to a wide angle intra prediction mode based on the specific mode value information and determining an LFNST set including LFNST matrices based on the wide angle intra prediction mode; and

deriving transform coefficients for the current block based on the LFNST index and an LFNST matrix derived from the LFNST set,

wherein the specific mode value information specifies whether a first mode is used or a second mode is used for an operating mode of a wide angle intra prediction mode process,

wherein the current block includes a coding block,

wherein the coding block is divided to a plurality of partition blocks based on the ISP mode, and

wherein, based on the specific mode value information specifying the first mode, the wide angle intra prediction mode is remapped based on a width and height of the coding block and the LFNST set is determined based on the wide angle intra prediction mode that is remapped based on the width and height of the coding block, and

based on the specific mode value information specifying the second mode, the wide angle intra prediction mode is remapped based on a width and height of a partition block and the LFNST set is determined based on the wide angle intra prediction mode that is remapped based on the width and height of the partition block.