Image encoding apparatus adaptively determining a scan pattern according to an intra prediction mode

1. An image encoding apparatus, comprising:

an intra predictor configured to generate a prediction block corresponding to a current prediction block according to an intra prediction mode selected out of a plurality of intra prediction modes;

a subtracter configured to generate a residual block by calculating a difference between the prediction block and an original block;

a transformer configured to transform the residual block to generate a transform block;

a quantizer configured to quantize the transform block using a quantization step size to generate a quantized transform block;

a scanner configured to scan the quantized transform block to generate one-dimensional (1D) quantized coefficients; and

an entropy coder configured to entropy-code the 1D quantized coefficients,

wherein, when a size of the transform block is 8×8, the quantized transform block is divided into a plurality of sub-blocks after the quantization of the transform block,

wherein the scanner scans the plurality of sub-blocks using a first scan pattern determined according to the selected intra prediction mode and scans coefficients of each sub-block using a second scan pattern determined according to the selected intra prediction mode,

wherein the first scan pattern is a scan order applied to the plurality of sub-blocks, and the second scan pattern is a scan order applied to the coefficients of each sub-block,

wherein the first scan pattern is the same as the second scan pattern,

wherein, when the selected intra prediction mode is a horizontal mode, the scan pattern is a vertical scan,

wherein the selected intra prediction mode is coded using both an intra prediction mode of an above block neighboring the current prediction block and an intra prediction mode of a left block neighboring the current prediction block, and

wherein the intra predictor includes:

a reference pixel generator configured to generate reference pixels using available reference pixels of the current prediction block when reference pixels do not exist;

a reference pixel filter configured to adaptively filter reference pixels adjacent to the current prediction block based on the selected intra prediction mode and size information of the current prediction block; and

a prediction block generator configured to generate the prediction block corresponding to the current prediction block according to the selected intra prediction mode.

2. The apparatus of claim 1 , wherein, when the selected intra prediction mode is one out of a predetermined number of intra prediction modes adjacent to the horizontal mode, the scan pattern is the vertical scan.

3. The apparatus of claim 1 , wherein the plurality of sub-blocks are scanned in a reverse direction.

4. The apparatus of claim 1 , wherein, when the intra prediction mode of the above block is unavailable, the intra prediction mode of the above block is set to a DC mode.

5. The apparatus of claim 1 , wherein the quantization step size is determined per coding unit of a predetermined size.