Method and apparatus for image encoding and image decoding

Abstract

Provided are a method and apparatus for image encoding which improves encoding efficiency in accordance with image characteristics by performing prediction in lines and performing a one-dimensional transformation in lines on an input image, and a method and apparatus for image decoding. Encoding efficiency of an image may be improved by generating a prediction sub residual block using neighboring residues and performing a one-dimensional discrete cosine transformation (DCT) on a difference residual block which is a difference between an original sub residual block and the prediction sub residual block.

What is claimed is: 
     
         1 . A method of image encoding, the method comprising:
 dividing a residual block into a plurality of sub residual blocks having different sizes according to division mode;   transforming, quantizing and entropy encoding the sub residual blocks;   comparing costs of bitstreams generated by transforming, quantizing and entropy encoding the sub residual blocks; and   determining the division mode based on the result of the comparing,   wherein, if a size of the residual block is N×N, where N is a positive number equal to or greater than 2, the residual block is divided into the sub residual blocks which have a size of a×a according to the division mode, where a is a natural number smaller than N.   
     
     
         2 . The method of  claim 1 , wherein the division mode further comprises modes which divides the residual block into one of the sub residual blocks which have a size of one of N×1 and 1×N. 
     
     
         3 . The method of  claim 2 , wherein transforming the sub residual blocks comprises performing a one-dimensional transformation on the first plurality of the sub residual blocks. 
     
     
         4 . The method of  claim 1 , further comprising:
 generating prediction sub residual blocks of a plurality of sub residual blocks of the residual block by using residues of previously processed neighboring sub residual blocks; and   generating difference sub residual blocks by calculating differences between the prediction sub residual blocks and the first plurality of sub residual blocks.   
     
     
         5 . A method of image decoding, the method comprising:
 dividing a residual block into a plurality of sub residual blocks having different sizes by using information on a division mode of the residual block included in a received bitstream;   entropy decoding, inverse quantizing and inverse transforming the sub residual blocks; and   restoring the sub residual blocks,   wherein, if a size of the residual block is N×N, where N is a positive number equal to or greater than 2, the residual block is divided into the sub residual blocks which have a size of a×a according to the division mode, where a is a natural number smaller than N.   
     
     
         6 . The method of  claim 5 , wherein, the division mode further comprises modes which divides the residual block into one of the sub residual blocks which have a size of one of N×1 and 1×N. 
     
     
         7 . The method of  claim 6 , wherein inverse transforming the sub residual blocks comprises performing a one-dimensional inverse transformation on the first plurality of the sub residual blocks. 
     
     
         8 . The method of  claim 5 , wherein the restoring comprising:
 generating prediction sub residual blocks of a plurality of sub residual blocks of the residual block by using residues of previously processed neighboring sub residual blocks; and   restoring difference residues that are differences between the prediction sub residual blocks and the plurality of the sub residual blocks.