Method and apparatus for generating reconstructed block
A reconstructed block creating method is provided which includes decoding an intra prediction mode using an intra prediction mode group indicator and a prediction mode index, constructing a prediction block, inversely quantizing a received residual signal using a quantization parameter and adaptively inversely transforming the residual signal using the intra prediction mode to create a residual block, and adding the prediction block and the residual block to create a reconstructed block. The quantization parameter is reconstructed using a minimum quantization CU size, and the minimum quantization CU size is determined by a parameter transmitted from a picture parameter set. Therefore, it is possible to improve image quality by adaptively adjusting a quantization parameter of a current block depending on the size of a coding unit and enhance compression efficiency of an image by effectively encoding/decoding the quantization parameter.
1. A reconstructed block creating method comprising:
decoding an intra prediction mode of a current block using an intra prediction mode group indicator, a prediction mode index and a MPM group, wherein the MPM group is generated using intra prediction modes of left and top blocks of the current block, and includes three intra prediction modes;
constructing a prediction block using the intra prediction mode;
inversely quantizing a received residual signal using a quantization parameter to create an inversely quantized block and inversely transforming the inversely quantized block to create a residual block; and
adding the prediction block and the residual block to create a reconstructed block,
wherein the quantization parameter is reconstructed using received information indicating a minimum quantization coding unit (CU) size and the information indicating the minimum quantization CU size is determined by a parameter transmitted from a picture parameter set,
wherein the intra prediction mode of the current block is set equal to an intra prediction mode indicated by the prediction mode index in the MPM group when the intra prediction mode group indicator indicates the MPM group, and the intra prediction mode of the current block is determined out of intra prediction modes other than the three intra prediction modes in the MPM group using the three intra prediction modes in the MPM group and the prediction mode index when the intra prediction mode group indicator does not indicate the MPM group, and
wherein when the intra prediction modes of the left and top blocks are not equal to each other and non-directional intra prediction modes, the MPM group includes the intra prediction modes of the left and top blocks and a vertical mode.
2. The reconstructed block creating method according to claim 1 , wherein the quantization parameter is reconstructed by adding a created quantization parameter predictor to a received residual quantization parameter.
3. The reconstructed block creating method according to claim 2 , wherein the quantization parameter predictor is determined by a quantization parameter of a left coding unit of a current block and a quantization parameter of a top coding unit.
4. The reconstructed block creating method according to claim 1 , wherein the information indicating the minimum quantization CU size and being transmitted from the picture parameter set represents whether the quantization parameter is changed in a unit smaller than a largest coding unit (LCU).
5. The reconstructed block creating method according to claim 3 , wherein the quantization parameter predictor is an average value of the quantization parameter of the left coding unit and the quantization parameter of the top coding unit.
6. The reconstructed block creating method according to claim 1 , wherein when the intra prediction modes of the left and top blocks are not equal to each other and directional intra prediction modes, the MPM group includes the intra prediction modes of the left and top blocks and a planar mode.
7. The reconstructed block creating method according to claim 1 , wherein the non-directional intra prediction mode are a planar mode and a DC mode, and the mode number 0 is assigned to the planar mode and the mode number 1 is assigned to the DC mode.
8. The reconstructed block creating method according to claim 1 , wherein a method of entropy-encoding the prediction mode index varies depending on whether the intra prediction mode belongs to the MPM group or not.