Method of decoding video data
Provided is a method derives a reference picture index and a motion vector of a current prediction unit, generates a prediction block of the current prediction unit using the reference picture index and the motion vector, generating a residual block by inverse-scan, inverse-quantization and inverse transform, and generates reconstructed pixels using the prediction block and the residual block. Prediction pixels of the prediction block is generated using an interpolation filter selected based on the motion vector. Accordingly, the coding efficiency of the motion information is improved by including various merge candidates. Also, the computational complexity of an encoder and a decoder is reduced by selecting different filter according to location of the prediction pixels determined by the motion vector.
1. A method of decoding video data in uni-directional prediction, the method comprising:
deriving a reference picture index and a motion vector of a current prediction unit;
generating a prediction block of the current prediction unit using the reference picture index and the motion vector;
generating a quantized block by inverse-scanning quantized coefficient components;
generating a transformed block by inverse-quantizing the quantized block using a quantization parameter;
generating a residual block by inverse-transforming the transformed block; and
generating a reconstructed pixels using the prediction block and the residual block,
wherein prediction pixels of the prediction block are generated using an interpolation filter selected based on the motion vector, the interpolation filter is a 7-tap asymmetry filter if the motion vector indicates a quarter pixel position, and the interpolation filter is a 8-tap filter if the motion vector indicates a half pixel position, and
wherein the quantization parameter is generated using a quantization parameter predictor and a differential quantization parameter, and the quantization parameter predictor is generated by averaging two quantization parameters of a left quantization parameter, an above quantization parameter and a previous quantization parameter if two or more quantization parameters are available.
2. The method of claim 1 , wherein if only one of the left quantization parameter and the above quantization parameter is available, the quantization parameter predictor is an average of the previous quantization parameter and the available one of the left quantization parameter and the above quantization parameter.
3. The method of claim 1 , wherein the quantization parameter is derived per a quantization unit, and a size of the quantization unit is one of allowable sizes of a coding unit.
4. The method of claim 1 , wherein a number of taps of the interpolation filter is determined by the prediction pixel position indicated by the motion vector.
5. The method of claim 1 , wherein the reference picture index and the motion vector of the current prediction unit are a reference picture index and a motion vector of a spatial or temporal merge candidate specified by a merge index, and
if the current block is a second prediction unit partitioned by asymmetric partitioning, a spatial merge candidate corresponding to a first prediction unit partitioned by the asymmetric partitioning is set as unavailable.
6. The method of claim 5 , wherein if the size of the current prediction unit is (3/2)N×2N, a left spatial merge candidate is set as unavailable.
7. The method of claim 5 , wherein a motion vector of the temporal merge candidate is a motion vector of a temporal merge candidate block within a temporal merge candidate picture, and a position of the temporal merge candidate block is determined depending on a position of the current block within an LCU (largest coding unit).
8. The method of claim 1 , wherein if both of the left quantization parameter and the above quantization parameter are unavailable, the quantization parameter predictor is set as the previous quantization parameter.