Method of generating reconstructed block

An image decoding method comprising:

• deriving an intra prediction mode using three intra prediction modes which are determined by left and above intra prediction modes of a current prediction unit;
• generating a prediction block according to the intra prediction mode;
• generating a residual block using the intra prediction mode;
• and
• generating a reconstructed block using the prediction block and the residual block,
• wherein the size of the prediction block is determined by transform size information,
• wherein the residual block is generated by inversely scanning the quantized coefficient information using an inverse scan pattern which is determined according to the intra prediction mode and the transform size information to generate a quantized block, by inversely quantizing the quantized block using a quantization parameter to generate a transformed block, and by inversely transforming the transformed block using an inverse transform matrix, and
• wherein a type of the inverse transform matrix is determined by a size of the transform unit.