Method of deriving quantization parameter with differential and predicted quantization parameters
A method for encoding an image using intra prediction can include determining an intra prediction mode of a current block, generating a mode group indicator and a prediction mode index specifying the intra prediction mode of the current block, constructing a most probable mode (MPM) group including three intra prediction modes determined using a left and an above intra prediction mode of the current block. The method can further include generating a prediction block based on the intra prediction mode of the current block specified by the mode group indicator and the prediction mode index, generating a residual block of the current block, generating a quantization block by transforming and quantizing the residual block. The method can include scanning the quantized block using a scan pattern determined based on the intra prediction mode and the size of a transform unit, and entropy-encoding the scanned information of the quantized block.
1. A method for encoding an image using intra prediction, the method comprising:
determining an intra prediction mode of a current block;
generating a mode group indicator and a prediction mode index, wherein the mode group indicator and the prediction mode index specify the intra prediction mode of the current block;
constructing a most probable mode (MPM) group including three intra prediction modes determined using a left intra prediction mode and an above intra prediction mode of the current block;
generating a prediction block based on the intra prediction mode of the current block specified by the mode group indicator and the prediction mode index;
generating a residual block of the current block using the prediction block;
generating a quantization block by transforming and quantizing the residual block;
scanning the quantized block using a scan pattern determined based on the intra prediction mode and the size of a transform unit; and
entropy-encoding the scanned information of the quantized block,
wherein when only one of a left intra prediction mode and an above intra prediction mode is available, the MPM group includes the available intra prediction mode and two additional intra prediction modes, and if the available intra prediction mode is one of two non-directional intra prediction modes, the two additional intra prediction modes are the other of the two non-directional intra prediction modes and a vertical mode, and if the available intra prediction mode is one of directional intra prediction modes, the two additional intra prediction modes are two non-directional intra prediction modes and
wherein when both of the left intra prediction mode and the above intra prediction mode are unavailable, the MPM group includes a DC mode, a Planar mode and the vertical mode.
2. The method of claim 1 , wherein when the left intra prediction mode is equal to the above intra prediction mode and the left intra prediction mode is a non-directional intra prediction mode, the MPM group includes the two non-directional intra prediction modes and a vertical mode.
3. The method of claim 1 , wherein if the size of the current block is 4×4, the reference pixels are not filtered, and if the size of the current block is larger than 4×4, the number of intra prediction mode where the reference pixels are filtered increases as the size of the current block becomes larger.
4. The method of claim 1 , wherein in the vertical mode, the prediction pixels of the prediction block which are adjacent to the left reference pixels are generated by using a vertical reference pixel and a variance between a corner pixel and a left neighboring pixel.
5. The method of claim 1 , wherein when the intra prediction mode of the current block is not belong to the MPM group, the mode group indicator does not indicate the MPM group, and the prediction mode index is constructed such that the intra prediction mode of the current block is specified by performing the ordered steps of:
increasing a value of the prediction mode index by one if the prediction mode index is equal to or greater than a first intra prediction mode of the MPM group;
increasing the value of the prediction mode index by one if the prediction mode index is equal to or greater than a second intra prediction mode of the MPM group;
increasing the value of the prediction mode index by one if the prediction mode index is equal to or greater than a third intra prediction mode of the MPM group; and
specifying the value of the prediction mode index as the mode number of the intra prediction mode of the current block.
6. The method of claim 5 , wherein the first intra prediction mode is an intra prediction mode having lowest mode number, the second intra prediction mode is an intra prediction mode having middle mode number and the third intra prediction mode is an intra prediction mode having highest mode number, and wherein the three intra prediction modes are reordered in the order of mode number to determine the first intra prediction mode, the second intra prediction mode and the third intra prediction mode.
7. The method of claim 1 , wherein the two non-directional intra prediction modes are the DC mode and the planar mode.