The present invention relates to a method for decoding an image. The method comprises: determining whether or not to perform filtering on signals reconstructed earlier than decoding object signals based on a block size and an intra prediction mode related to the decoding object signals within decoding object images; performing filtering on signals reconstructed earlier than decoding object signals at the time of performing intra prediction based on the determining; generating prediction signals of the decoding object signals using the filtered reconstructed signals; and reconstructing the decoding object signals based on the prediction signals and a residual signal, wherein the tap size of a filter to be used when performing filtering is determined variably.