In one embodiment, the method includes obtaining quantization information related to at least one of a first block and an adjacent second block, comparing the quantization information with a predefined constant value, and performing a filtering process based on the comparing step when both of the first block and the second block are intra-coded blocks according to obtained block type information. The filtering process includes calculating a value of at least one pixel in the first block based on pixel values of at least two pixels in the first block, and calculating a value of at least one pixel in the second block based on pixel values of at least two pixels in the second block. The at least two pixels in the first block and the at least two pixels in the second block are successive pixels across a block boundary between the first block and the second block.