A method for decoding an image, the method including decoding base block size information on a size of a base block from a bitstream, decoding residual presence information of a decoding object unit from the bitstream, the residual presence information indicating whether the decoding object unit has residual signal or not, when the residual presence information indicates that the decoding object unit has the residual signal, decoding a residual quantization parameter of the decoding object unit from the bitstream, determining a quantization parameter of the decoding object unit based on the residual quantization parameter of the decoding object unit, and performing inverse quantization for the decoding object unit based on the quantization parameter.