A method for decoding a video according to the present invention may comprise: determining an intra prediction mode of a current block, determining, based on the intra prediction mode, a first reference sample of a prediction target sample included in the current block, generating a first prediction sample for the prediction target sample using the first reference sample, and generating a second prediction sample for the prediction target sample using the first prediction sample and a second reference sample located at a position different from the first reference sample.