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

1. 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.

2. The apparatus of claim 1 , wherein a size of the prediction block generated by the intra predictor is equal to a size of a transform unit, and plural prediction blocks are generated by the intra predictor using the intra prediction mode if a size of the current prediction unit is larger than the size of the transform unit.

3. The apparatus of claim 1 , wherein if the left and above quantization parameters are available, an average of the left and above quantization parameters is set as the quantization parameter predictor.

4. The apparatus of claim 1 , wherein the quantization parameter is generated per quantization unit, and a minimum size of the quantization unit is adjusted per picture.

5. The apparatus of claim 1 , wherein the quantizer has a size of a coding unit equal to or larger than a reference size, and the reference size is a minimum size of a quantization unit.

6. The apparatus of claim 5 , wherein the minimum size of the quantization unit is one of allowable sizes of the coding unit.

7. The apparatus of claim 1 , wherein the scan pattern is determined by the intra prediction mode and the size of the transform unit in intra prediction.

8. The apparatus of claim 7 , wherein if the size of the transform unit is larger than 4×4, the quantized block is divided into a plurality of subsets, the scan pattern is applied to the plurality of subsets, and non-zero subset flags are determined and encoded.

9. The apparatus of claim 8 , wherein the non-zero subset flag indicates whether the subset contains non-zero coefficients or not.