Improved decoder for transform coding with application to the JPEGbaseline system

Transform coding, a simple yet efficient image coding technique, has been adopted by the Joint Photographic Experts Group (JPEG) as the basis for an emerging coding standard for compression of still images. However, for any given transform encoder, the conventional inverse transform decoder is suboptimal. Better performance can be obtained by a nonlinear interpolative decoder that performs table lookups to reconstruct the image blocks from the code indexes. Each received code index of an image block addresses a particular codebook to fetch a component vector. The image block can be reconstructed as the sum of the component vectors for that block. An iterative algorithm for designing a set of locally optimal codebooks is developed. Computer simulation results demonstrate that this improved decoding technique can be applied in the JPEG baseline system to decode enhanced quality pictures from the bit stream generated by the standard encoding scheme