1. A method of decoding an image, the method comprising: constructing an advanced motion vector prediction (AMVP) candidate list using available motion vector candidates of a left motion vector candidate, an above motion vector candidate and a temporal motion vector candidate; selecting a motion vector predictor among motion vector candidates of the AMVP candidate list using an AMVP index; generating a motion vector using the motion vector predictor and a differential motion vector; generating a prediction block using the motion vector and a reference picture index; inversely quantizing a quantized block using a quantization parameter to generate a transformed block and inversely transforming the transformed block to generate a residual block; and generating a reconstructed block using the prediction block and the residual block, wherein the quantization parameter is generated per quantization unit, and a minimum size of the quantization unit is adjusted per picture, wherein the quantization parameter is generated using a differential quantization parameter and a quantization parameter predictor, and the quantization parameter predictor is generated using two available quantization parameter of a left quantization parameter, an above quantization parameter and a previous quantization parameter, wherein an average of the above and previous quantization parameters is set as the quantization parameter predictor when the left quantization parameter is unavailable, wherein a plurality of subsets are generated by inversely scanning quantized coefficient components when a size of the quantized block is larger than a predetermined size, wherein the quantized block is generated by inversely scanning the plurality of subsets in a reverse direction according to a diagonal scan, and wherein an inverse scan pattern for inversely scanning the quantized coefficients components is the same as an inverse scan pattern for inversely scanning the plurality of subsets.