1. A method of decoding a video signal with a decoding apparatus, the method comprising: determining an intra prediction mode of a current block based on an intra prediction mode of a neighboring block adjacent to the current block; deriving reference samples for intra prediction of the current block based on at least one of neighboring samples adjacent to the current block; obtaining a prediction sample of the current block by performing the intra prediction for a target prediction position of the current block based on a top reference sample having a same x-coordinate as the target prediction position and a variation relating to the reference samples, wherein the variation relating to the reference samples is representative of a difference value between a reconstructed value of a top-left reference sample whose a location is fixed regardless of a coordinate of the target prediction position and a reconstructed value of a left reference sample whose a location is determined dependent on the coordinate of the target prediction position, the left reference sample having a same y-coordinate as the target prediction position; and deriving a reconstruction sample of the current block by adding the prediction sample and a residual sample corresponding to the prediction sample.