1. A computer-implemented method comprising: obtaining, a first block including a first boundary pixel and a second block including a second boundary pixel, wherein the first and second boundary pixels are neighboring to each other and separated by a boundary between the first and second blocks; and performing a filtering operation on the boundary between the first and second blocks, wherein the filtering operation includes: obtaining a parameter based on four successive pixels including the first and second boundary pixels, and adjusting each of the first and second boundary pixels using an adjustment value when an absolute value of the parameter is less than a value representing quantization information, and wherein the adjustment value is determined using a difference between the first and second boundary pixels.