Apparatus for encoding an image

Abstract

Provided is an apparatus for encoding and decoding an image that adaptively filters reference pixels according to an intra prediction mode and a size of a prediction block, and generates the prediction block according to the intra prediction mode. When the reference pixels for a second directional intra prediction mode are filtered, the reference pixels for a first directional intra prediction mode, that is closer to an intra prediction mode having a direction of 45° with reference to a horizontal mode than the second directional intra prediction mode is, are also filtered. The first and the second intra prediction modes exist between the horizontal mode and the intra prediction mode having the direction of 45° with reference to the horizontal mode. The number of intra prediction modes in which the filter is applied increases as the size of the prediction block increases.

The invention claimed is: 
     
       1. An apparatus for decoding an image, the apparatus comprising:
 an entropy decoder configured to restore quantized residual coefficients and intra prediction information;   a prediction mode decoder configured to restore an intra prediction mode based on the intra prediction information;   a residual signal decoder configured to convert the quantized residual coefficients into a residual block;   a reference pixel generator configured to generate reference pixels when one or more unavailable reference pixels exist, and to adaptively filter the reference pixels according to the intra prediction mode and a size of a prediction block;   a prediction block generator configured to generate the prediction block using reference pixels determined by the intra prediction mode;   a prediction block filter configured to adaptively filter a part of the prediction block using the intra prediction mode; and   an image constructor configured to generate a reconstructed image using the prediction block and the residual block,   wherein the reference pixel generator adaptively filters the reference pixels according to the size of the prediction block for intra prediction modes existing between a horizontal mode and an intra prediction mode having a direction of 45° with reference to the horizontal mode,   wherein, when the reference pixel generator filters the reference pixels for a second directional intra prediction mode, the reference pixel generator also filters the reference pixels for a first directional intra prediction mode that is closer to the intra prediction mode having the direction of 45° with reference to the horizontal mode than the second directional intra prediction mode is,   wherein the second and the first directional intra prediction modes exist between the horizontal mode and the intra prediction mode having the direction of 45° with reference to the horizontal mode,   wherein the number of intra prediction modes in which the filter is applied increases as the size of the prediction block increases, and   wherein, when the intra prediction mode is a vertical mode, the reference pixel generator does not filter the reference pixels.   
     
     
       2. The apparatus of  claim 1 , wherein the reference pixel generator does not filter the reference pixels when the size of the prediction block is smaller than a predetermined block size. 
     
     
       3. The apparatus of  claim 1 , wherein, when the intra prediction mode is a planar mode, the prediction block generator generates the prediction block using a corner reference pixel, a left reference pixel and an upper reference pixel. 
     
     
       4. An apparatus for encoding an image, the apparatus comprising:
 an intra predictor configured to generate a prediction block using reference pixels according to an intra prediction mode of a current block;   a transformer configured to generate a transformed block by transforming a residual block obtained by subtracting the current block and the prediction block;   a quantizer configured to generate a quantized block by quantizing the transformed block; and   an entropy-coder configured to scan coefficients of the quantized block and entropy-code the scanned coefficients,   wherein the intra predictor generates reference pixels when one or more unavailable reference pixels exist, and adaptively filters the reference pixels, and   wherein the reference pixels are not filtered for the prediction block of which size is smaller than a predetermined size.    
     
     
       5. The apparatus of claim 4, wherein the intra predictor filters the reference pixels with a filter selected out of two filters.