receiving a bitstream;

determining, based on index information decoded from the bitstream, a reference line index for a current block,

wherein the reference line index indicates one of a plurality of reference line candidates including a neighboring reference line and non-neighboring reference lines, and

wherein the non-neighboring reference lines include at least one of a first non-neighboring reference line adjacent to the neighboring reference line or a second non-neighboring reference line adjacent to the first non-neighboring reference line;

determining an intra prediction mode of the current block among pre-defined intra prediction modes; and

performing intra prediction of the current block based on the reference line index and the intra prediction mode,

wherein determining the intra prediction mode of the current block comprises:

determining, based on an MPM (Most Probable Mode) flag, whether there exists an MPM candidate that identical to the intra prediction mode the current block in an MPM candidate list including one or more MPM candidates, and

wherein the MPM flag is decoded from the bitstream only when the index information indicates the neighboring reference line among the plurality of reference line candidates.