Image coding using adaptive resizing in the block-DCT domain

In this paper, we propose an image coding scheme using adaptive resizing algorithm to obtain more compact coefficient representation in the block-DCT domain. Standard coding systems, e.g. JPEG baseline, utilize the block-DCT transform to reduce spatial correlation and to represent the image information with a small number of visually significant transform coefficients. Because the neighboring coefficient blocks may include only a few low-frequency coefficients, we can use downsizing operation to combine the information of two neighboring blocks into a single block. Fast and elegant image resizing methods operating in transform domain have been introduced previously. In this paper, we introduce a way to use these algorithms to reduce the number of coefficient blocks that need to be encoded. At the encoder, the downsizing operation should be performed delicately to gain compression efficiency. The information of neighboring blocks can be efficiently combined if the blocks do not contain significant high-frequency components and if the blocks share similar characteristics. Based on our experiments, the proposed method can offer from 0 to 4 dB PSNR gain for block-DCT based coding processes. Best performance can be expected for large images containing smooth homogenous areas.