Apparatus for encoding 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 encoding an image, comprising:
a transform unit configured to transform a residual block obtained by calculating difference between an original block and the prediction block to generate a transform block;
a quantization unit configured to quantize the transform block to generate a quantized transform block;
a scanning unit configured to scans quantized transform coefficients of the quantized transform block to generate one dimensional (1D) coefficient sequence, wherein the quantized transform coefficients are divided into a plurality of sub-blocks if it is determined that a size of the transform block is equal to 8×8;
an entropy coder configured to entropy-code the 1D coefficient sequence; and
an intra predictor configured to generate a prediction block according to an intra prediction mode of a current prediction block,
wherein the intra predictor includes:
a prediction mode determiner configured to determine the intra prediction mode of the current prediction block; and
a prediction mode coder configured to generate 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 and encode information indicating the intra prediction mode group and an intra prediction mode index corresponding to the intra prediction mode of the current prediction block when the intra prediction mode of the current prediction block is included in the intra prediction mode group,
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 and the one available intra prediction mode is a non-directional intra prediction mode, the intra prediction mode group includes a DC mode and a vertical mode,
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 and the one available intra prediction mode is a directional intra prediction mode, the intra prediction mode group includes the one available intra prediction mode, and two intra prediction modes closest to the one available intra prediction mode, one on each side, and
wherein the plurality of sub-blocks are scanned and non-zero coefficients of each sub-block are scanned according to a scan pattern, wherein said scan pattern for scanning the plurality of sub-blocks and for scanning the non-zero coefficients of each sub-block is determined according to the intra prediction mode of the current prediction block.
2. The apparatus of claim 1 , wherein, when the one available intra prediction mode is a DC mode, another non-directional intra prediction mode is a planar mode.
3. The apparatus of claim 1 , wherein the scanning unit scans the non-zero coefficients of each sub-block in a reverse direction from a last non-zero coefficient of each sub-block using one of a plurality of scan patterns.