Apparatus for decoding an image
Provided is a method that de-multiplexes a bit stream to extract intra prediction mode information and residual signals, restores an intra prediction mode of a current prediction unit using the intra prediction information and intra prediction modes of prediction units adjacent to the current prediction unit, generates reference pixels using one or more available reference pixel if there exist unavailable reference pixels of the prediction unit, adaptively filters the reference pixels based on the restored intra prediction mode, generates a prediction block using the restored intra prediction mode and the reference pixels, decodes the residual signal to generating a residual block, and generates a reconstructed block using the prediction block and the residual block. Accordingly, additional bits resulted from increase of a number of intra prediction mode are effectively reduced. Also, an image compression ratio can be improved by generating a prediction block similar to an original block.
1. An apparatus for decoding an image, comprising:
an entropy decoder configured to derive intra prediction information and quantized coefficient information from a bit stream;
an inverse scanning unit configured to generate a quantized transform block by inversely scanning the quantized coefficient information;
an inverse quantization unit configured to generate a transform block by inversely quantizing the quantized transform block;
an inverse transform unit configured to generate a residual block by inversely transforming the transform block;
an intra predictor configured to restore an intra prediction mode of a current prediction block based on the intra prediction information and to generate a prediction block according to the intra prediction mode; and
an adder configured to generate an original block by adding the prediction block and the residual block,
wherein, if it is determined that a size of the transform block is equal to 8×8, the inverse scanning unit inversely scans the quantized coefficient information in the unit of sub-block using a first scan pattern determined according to the intra prediction mode to generate a plurality of sub-blocks and inversely scans the plurality of sub-blocks using a second scan pattern determined according to the intra prediction mode to generate the quantized transform block, wherein the first scan pattern is the same as the second scan pattern,
wherein the intra predictor restores an intra prediction mode group indicator and a prediction mode index of a current prediction block from the intra prediction information, generates an intra prediction mode group using available intra prediction modes of a left prediction block and an above prediction block neighboring the current prediction block, wherein the number of intra prediction modes belonging to the intra prediction mode group is fixed to three, and determines an intra prediction mode which is included in the intra prediction mode group and indicated by the intra prediction mode index as the intra prediction mode of the current prediction block when the intra prediction mode group indicator indicates the intra prediction mode group, and
wherein, when only one intra prediction mode out of the intra prediction modes of the left prediction unit and the above prediction unit is available, the intra prediction mode group includes the one available intra prediction mode of the respective prediction units and two additional intra prediction modes that are determined such that when the one available intra prediction mode is a non-directional intra prediction mode, the two additional intra prediction modes include another non-directional intra prediction mode and a vertical mode.
2. The apparatus of claim 1 , wherein the inverse scanning unit inversely scans non-zero coefficients of each sub-block in a reverse direction from a last non-zero coefficient of each sub-block using the first scan pattern.
3. The apparatus of claim 1 , wherein, when the one available intra prediction mode is a DC mode, the two additional intra prediction modes include a planar mode and the vertical mode.
4. The apparatus of claim 1 , wherein, when the one available intra prediction mode is a planar mode, the two additional intra prediction modes include a DC mode and the vertical mode.