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