Interpolation-directed transform domain downward conversion for block-based image compression

In this paper, we design an interpolation-directed transform domain downward conversion (ITDDC) to build up a new block-based image compression scheme. This ITDDC is derived from our proposed 2-D padding and performed on each 16×16 macro-block of pixels to convert it into an 8×8 coefficient block, leading to a downward image conversion in the transform domain. More interestingly, the further compression is just performed on the down-sized coefficient block and the reconstruction for an entire macro-block is achieved via the interpolation by using the decoded pixels only locating in some specific positions of it. To make the interpolation more efficient, the pixels participating in the interpolation will be optimized before the compression. The ITDDC-based coding is used competitively with the JPEG baseline coding to compress each macro-block in our proposed compression scheme according to a simple but efficient rate-distortion optimization based criterion. Experimental results demonstrate that our proposed method gets a remarkable quality gain over the existing approaches.