Method and apparatus for encoding an image

1. A method of encoding an image, comprising:

determining an intra prediction mode and generating one or more prediction blocks using the intra prediction mode;

determining motion information and generating a prediction block using the motion information;

transforming residual signals generated using an original block and the prediction block to generate a transformed block;

determining a quantization parameter and quantizing the transformed block using a quantization matrix and the quantization parameter to generate a quantized block;

determining a scan pattern and applying the scan pattern to the quantized block to generate one-dimensional coefficient information; and

entropy-coding the one-dimensional coefficient information, information on the intra prediction mode, the motion information, and a differential quantization parameter,

wherein the differential quantization parameter is generated by subtracting a quantization parameter predictor from the quantization parameter,

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, an average of first two available quantization parameters determined according to a predetermined order 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 of the current coding unit, the only one available quantization parameter is set as the quantization parameter predictor,

wherein a transform type for transforming the residual signals is selected among a DCT-based integer transform and a DST-based integer transform depending on a prediction mode and a size of a transform unit, and

wherein when a size of the quantized block is larger than 4×4, the quantized block is divided into plural subsets, each subset is scanned respectively according to the determined scan pattern, and the subsets are scanned according to the determined scan pattern.

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

3. The method 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 method of claim 1 , wherein if the left quantization parameter is not available and the above quantization parameter and the previous quantization parameter are available, an average of the above quantization parameter and the previous quantization parameter is set as the quantization parameter predictor.

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

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

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

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

9. The method of claim 8 , 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.