A novel adaptive decimation/interpolation algorithm

which can be applied in all kinds of blocking image coding algorithm

is proposed. The image is first divided into non-overlapping blocks. Then the horizontal and the vertical gradients of each block are calculated. According to the two gradient values

the image blocks are classified into four groups

namely smooth block

horizontal-contour block

vertical-contour block and high-detail block. Then different decimation methods are applied to different class of blocks to reduce the original data quantity. Experimental results show

compared to other decimation/interpolation algorithms

the proposed algorithm can well preserve the contour and other detail information

thus substantially improve the quality of the reconstructed images

especially the subjective quality. The proposed method increases thePSNRby 3.9 dB while keeping comparable compression ratio for high-detailed images. For low-detailed images

compression ratio and PSNRare all slightly improved.