Method of removing deblocking artifacts

1. A method for decoding image data, the method comprising:

generating a prediction block based on a prediction mode;

generating a quantization block by inversely scanning quantization coefficient information;

generating a transform block by inversely quantizing the quantization block using a quantization parameter;

generating a residual block by inversely transforming the transform block;

generating a reconstructed picture by using the prediction block and the residual block; and

applying a deblocking filter on the reconstructed picture,

wherein it is determined whether the deblocking filtering is applied between two adjacent blocks P and Q containing samples p0 and q0 respectively by using a boundary quantization parameter when a boundary strength is not zero,

wherein the boundary quantization parameter is set to an average value of a quantization parameter of block P and a quantization parameter of block Q, and the quantization parameter is derived by adding a residual quantization parameter and a quantization parameter predictor, and

wherein the quantization parameter predictor is an average of two available quantization parameters among a left quantization parameter, an above quantization parameter, and a previous quantization parameter.

2. The method of claim 1 , wherein the average of the two quantization parameter is rounded off.

3. The method of claim 1 , wherein when at least two of the left quantization parameter, the above quantization parameter and the previous quantization parameter are available, an average of two available quantization parameters selected in a predetermined order is set as the quantization parameter predictor.

4. The method of claim 3 , wherein the predetermined order is the order of the left quantization parameter, the above quantization parameter and the previous quantization parameter.

5. The method of claim 1 , wherein the previous quantization parameter is set as the quantization parameter predictor when both of the left quantization parameter and the above quantization parameter are unavailable.

6. The method of claim 1 , wherein the deblocking filter to be applied is selected by using the boundary quantization parameter.

7. The method of claim 1 , wherein the quantization parameter predictor is derived per quantization unit which includes at least one coding unit.

8. The method of claim 1 , wherein the transform block is inversely transformed by using transform matrix determined according to a size of a transform unit.

9. A method for encoding image data, the method comprising:

determining a prediction mode;

generating a prediction block based on the prediction mode;

generating a transformed block by transforming a residual block generated using the prediction block;

generating a quantized block by quantizing the transformed block using a quantization parameter;

inversely quantizing the quantized block using the quantization parameter;

inversely transforming the inversely quantized block;

generating a reconstructed picture using the prediction block and the inversely transformed block; and

applying a deblocking filter on the reconstructed picture,

wherein it is determined whether the deblocking filtering is applied between two adjacent blocks P and Q containing samples p0 and q0 respectively by using a boundary quantization parameter when a boundary strength is not zero,

wherein the boundary quantization parameter is set to an average value of a quantization parameter of block P and a quantization parameter of block Q, and the quantization parameter is derived by adding a residual quantization parameter and a quantization parameter predictor, and

wherein the quantization parameter predictor is an average of two available quantization parameters among a left quantization parameter, an above quantization parameter, and a previous quantization parameter.

10. A non-transitory computer-readable storage medium storing encoded video information, comprising:

a bit stream stored in the medium, the bit stream including entropy-encoded information on a quantized coefficients and a prediction mode for a current prediction unit,

wherein a residual block is generated by inversely quantizing and inversely transforming the quantized coefficients, a prediction block is generated using the prediction mode for a current prediction unit, and the residual block and the prediction block are added to generate a reconstructed picture,

wherein, for the reconstructed picture, it is determined whether the deblocking filtering is applied between two adjacent blocks P and Q containing samples p0 and q0 respectively by using a boundary quantization parameter when a boundary strength is not zero,

wherein the boundary quantization parameter is set to an average value of a quantization parameter of block P and a quantization parameter of block Q, and the quantization parameter is derived by adding a residual quantization parameter and a quantization parameter predictor, and

wherein the quantization parameter predictor is an average of two available quantization parameters among a left quantization parameter, an above quantization parameter, and a previous quantization parameter.