obtaining most probable mode (MPM) flag information related to whether an intra prediction mode for a current block is derived based on MPM candidates for the current block and multi-reference line (MRL) index information for at least one reference sample line for intra prediction of the current block from a bitstream;

deriving the intra prediction mode for the current block, based on the MPM flag information and the MRL index information;

deriving prediction samples for the current, block based on the intra prediction mode for the current block; and

generating a reconstructed picture, based on the prediction samples,

wherein based on a value of the MPM flag information being equal to 1 and a value of the MRL index information being equal to 0, planar flag information indicating whether the intra prediction mode for the current block is a planar mode is obtained from the bitstream, and

wherein the intra prediction mode of the current block is derived based on a value of the planar flag information.