1. An image decoding apparatus comprising: an inter prediction unit configured to generate a merge candidate list using available spatial and temporal merge candidates, obtain motion information using a merge index and the merge candidate list, and generate a prediction block using the motion information; an inverse quantization unit configured to inverse-quantize a quantized block using a quantization parameter to generate a transform block; an inverse transform unit configured to inverse-transform the transform block to generate a residual block; and an adder configured to generate a reconstructed block using the prediction block and the residual block, wherein if a current prediction unit is a second prediction unit partitioned by asymmetric partitioning, the spatial merge candidate corresponding to a first prediction unit partitioned by the asymmetric partitioning is set as unavailable, and wherein the quantization parameter is generated using a quantization parameter predictor and a differential quantization parameter, and the quantization parameter predictor is generated by averaging two quantization parameters of a left quantization parameter, an above quantization parameter and a previous quantization parameter if two or more quantization parameters are available.
8. The apparatus of claim 1 , wherein a motion vector of the temporal merge candidate is a motion vector of a temporal merge candidate block within a temporal merge candidate picture, and a position of the temporal merge candidate block is determined depending on a position of the current prediction unit within an LCU.