1. An apparatus for generating a residual block, comprising: an entropy decoding unit configured to decode residual signals to generate quantized coefficient components; an inverse scanning unit configured to determine an inverse scan pattern and generate a quantized block using the inverse scan pattern; an inverse quantization unit configured to derive a quantization parameter and inversely quantize the quantized block using the quantization parameter to generate a transformed block; and an inverse transform unit configured to inversely transform the transformed block to generate a residual block, wherein when the quantization parameter is a chroma quantization parameter, the chroma quantization parameter is generated using a luma quantization parameter and an offset parameter indicating a relationship between the luma quantization parameter and the chroma quantization parameter, the luma quantization parameter is derived using a differential quantization parameter and a quantization parameter predictor, the differential quantization parameter is generated by entropy decoding, if two or more quantization parameters are available among a left quantization parameter, an above quantization parameter and a previous quantization parameter of a current coding unit, the quantization parameter predictor is generated using two available quantization parameters determined according a predetermined order, and if only one quantization parameter is available, the available quantization parameter is set as the quantization parameter predictor.