A method of generating a reconstructed block is provided. A mode group indicator and a prediction mode index are entropy-decoded. A quantized block is inversely quantized using a quantization parameter and a quantization matrix to generate a transform block. The transform block is inversely transformed to generate a residual block. A Most Probable Mode (MPM) group including three intra prediction modes is constructed using a left intra prediction mode and an above intra prediction mode of a current prediction unit. An intra prediction mode of the current prediction unit is derived using the mode group indicator and the prediction mode index. Reference pixels of a current block are adaptively filtered according to a size of a transform unit and the intra prediction mode. The prediction block is generated according to the intra prediction mode. The reconstructed block is generated using the prediction block and the residual block.