Imaging decoding apparatus
An image decoding device is provided which includes an intra prediction module for reconstructing an intra prediction mode and creating a prediction block of a current block or a sub block, an inverse scanning module for converting residual signals into a quantization block, an inverse quantization module for inversely quantizing the quantization block, and an inverse transform module for inversely-transforming the inversely-quantized block. A quantization parameter predictor for deriving the quantization parameter is created using quantization parameters of a left coding unit and a top coding unit of a current coding unit. 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 to reduce the number of bits required for transmitting the quantization parameter.
1. An image decoding device comprising:
a processor; and
a non-transitory computer-readable medium having stored thereon instructions that, when executed, cause the processor to perform a method, the method comprising:
reconstructing a prediction mode and creating a prediction block with the reconstructed prediction mode;
converting residual signals into a two-dimensional quantization block;
inversely quantizing the quantization block using a quantization parameter; and
inversely-transforming the inversely-quantized block,
wherein the quantization parameter is derived using a received residual quantization parameter and a quantization parameter predictor, and the quantization parameter predictor used for deriving the quantization parameter is created using a quantization parameter of a left coding unit of a current coding unit and a quantization parameter of a top coding unit of the current coding unit,
wherein a size of the prediction block is determined based on transform size information,
wherein the prediction mode is reconstructed using a first intra prediction mode group consisting of three intra prediction modes among 34 intra prediction modes, an intra prediction mode group indicator and a prediction mode index,
wherein the three intra prediction modes of the first intra prediction mode group are determined using intra prediction modes of a left block and a top block of a current block,
wherein the three intra prediction modes of the first intra prediction mode group are determined as a DC mode, a planar mode and a vertical mode among the 34 intra prediction modes when the intra prediction modes of the left block and the top block are not unavailable,
wherein the prediction mode is set as an intra prediction mode indicated by the prediction mode index in the first intra prediction mode group when the intra prediction mode group indicator indicates the first intra prediction mode group, and
wherein the prediction mode is set as an intra prediction mode indicated by the prediction mode index in a second intra prediction mode group consisting of 31 intra prediction modes besides the three intra prediction modes of the first intra prediction mode group when the intra prediction mode group indicator indicates the second intra prediction mode group.
2. The image decoding device according to claim 1 , wherein the quantization parameter is reconstructed by adding the quantization parameter predictor to the received residual quantization parameter.
3. The image decoding device according to claim 1 , wherein the quantization parameter predictor is set as an average value of the quantization parameter of the left coding unit and the quantization parameter of the top coding unit.
4. The image decoding device according to claim 1 , wherein when the intra prediction modes of the left block and the top block are not equal to each other and are directional intra prediction modes, the three intra prediction modes in the first intra prediction mode group are the intra prediction modes of the left block and the top block and a planar mode.
5. The image decoding device according to claim 1 , wherein when the intra prediction modes of the left block and the top block are not equal to each other and are non-directional intra prediction modes, the three intra prediction modes in the first intra prediction mode group are the intra prediction modes of the left block and the top block and a vertical mode.
6. The image decoding device according to claim 5 , wherein the non-directional intra prediction modes are a planar mode and a DC mode, and a mode number 0 is assigned to the planar mode and a mode number 1 is assigned to the DC mode.