Method and apparatus of deriving intra prediction mode using most probable mode group

An image encoding apparatus comprising:

• an intra predictor to determine an intra prediction mode of a current prediction unit and generate a prediction block using the intra prediction mode;
• an inter predictor to determine motion information and generate a prediction block;
• a transformer to transform residual signals generated by using an original block and the prediction block to generate a transformed block;
• a quantizer to determine a quantization parameter and quantize the transformed block using a quantization matrix and the quantization parameter to generate a quantized block;
• a scanner to determine a scan pattern and apply the scan pattern to significant coefficients, sign flags and levels of the quantized block;
• an entropy coder to entropy-code one-dimensional coefficient information received from the scanner, intra prediction information received from the intra predictor, and motion information received from the inter predictor;
• an inverse quantizer to inversely quantize the quantized block;
• an inverse transformer to inversely transform the inversely quantized block to generate a residual block;
• an adder to generate a reconstructed block by adding the residual block and the prediction block;
• and
• a post-processor to remove blocking artifact in a reconstructed picture,
• wherein a differential quantization parameter is generated by subtracting a quantization parameter predictor from the quantization parameter, and is entropy-coded,
• wherein,
• 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 among the left quantization parameter, the above quantization parameter and the previous quantization parameter,
• if the left quantization parameter is not available among the left quantization parameter, the above quantization parameter and the previous quantization parameter, an average of the above quantization parameter and the previous quantization parameter is set as the quantization parameter predictor, and
• if only one quantization parameter is available among the left quantization parameter, the above quantization parameter and the previous quantization parameter, the available quantization parameter is set as the quantization parameter predictor, and
• wherein a transform type for inversely transforming the residual signals is selected among a discrete cosine transform (DCT)-based integer transform and a discrete sine transform (DST)-based integer transform based on a prediction mode and a size of a transform unit.