Disclosed herein is a method of decoding an image including deriving intra prediction mode of a current block using an intra prediction mode of a neighbor block adjacent to the current block, constructing a reference sample of the current block, and performing intra prediction with respect to the current block using the intra prediction mode of the current block and the reference sample. The deriving of the intra prediction mode of the current block includes constructing a most probable mode (MPM) list based on whether the intra prediction mode of the current block is a Planar mode.