Provided is an image decoding method including: generating an intra prediction value of a current sample based on a position of the current sample in a current block and an intra prediction mode of the current block; determining, based on the position of the current sample in the current block, a sample value of at least one filtering reference sample to be filtered and a first weight with respect to the filtering reference sample and a second weight with respect to the intra prediction value of the current sample; generating a filtered prediction sample value of the current sample based on the determined sample value of the filtering reference sample to be filtered, the intra prediction value of the current sample, the first weight with respect to the filtering reference sample, and the second weight with respect to the intra prediction value of the current sample; and generating a prediction block of the current block, the prediction block including the filtered prediction sample value of the current sample.