Method of decoding motion vector

A method of decoding an image, comprising:

• constructing an advanced motion vector predication (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 candidates list using an AMVP index, and 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,
• 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 parameters of a left quantization parameter, an above quantization parameter and a previous quantization parameter according to an order of the left quantization parameter, the above quantization parameter and the previous quantization parameter, and
• wherein when the left quantization parameter is unavailable, an average of the above and previous quantization parameters is set as the quantization parameter predictor.