An image decoding method performed by a decoding apparatus comprises: deriving a first intra prediction mode based on a left neighboring block (1130) of a current block (1110); deriving a second intra prediction mode based on an upper neighboring block (1140) of the current block (1110); receiving intra prediction mode information; determining an intra prediction mode for the current block (1110) based on the intra prediction mode information, the first intra prediction mode and the second intra prediction mode; and generating prediction samples on the current block (1110) based on the determined intra prediction mode. When the upper neighboring block (1140) is not located in a current largest coding unit, LCU, in which the current block (1110) is located, the second intra prediction mode is set equal to an intra DC mode.