Provided is a video decoding method including obtaining, from a bitstream, information about a prediction mode of a current block; when the prediction mode of the current block is an intra mode, obtaining information about an intra prediction mode of the current block; obtaining a predicted sample value of the current block by using at least one sample that is from among samples included in an adjacent reference region of a plurality of lines and is located, from the current block, in an intra prediction direction indicated by an intra prediction mode. The adjacent reference region of the plurality of lines may include a plurality of lines that are in a vertical direction and located at a left side of the current block, or a plurality of lines that are in a horizontal direction and located at an upper side of the current block.