1. An image decoding method comprising: decoding image data including information on a quantization parameter for each macroblock in a bitstream; and determining respective quantization parameters based on a location of each macroblock and inverse-quantizing each macroblock using the respectively determined quantization parameter, wherein macroblocks located on a boundary of a region are inverse-quantized using a second quantization parameter obtained based on a first quantization parameter, with all other macroblocks of the region being inverse-quantized using the first quantization parameter decoded from the bitstream for macroblocks of the region.