1. An image decoding method comprising: receiving a bitstream; obtaining a first quantization parameter for a first plurality of blocks from the bitstream, where the first plurality of blocks are not located on a boundary of a picture; calculating a second quantization parameter for a second plurality of blocks in a predetermined manner, where the second plurality of blocks are located on the boundary of the picture; and inverse-quantizing the first plurality of blocks of the picture using the first quantization parameter and the second plurality of blocks of the picture using the second quantization parameter, respectively.