Successive coefficient refinement for embedded lossless image compression

We consider here a new approach to successive coefficient refinement which speeds up embedded image compression and decompression. Such speedups are especially useful when lossless or near lossless image compression is required because so many refinement bits must be transmitted. Rather than sending a binary refinement symbol typical of existing embedded coders, our algorithm uses a ternary refinement symbol, allowing the encoder to tell the decoder when its current approximation of a given wavelet coefficient is exact. Thus, both encoder and decoder operate faster because they process fewer refinement symbols, yet the fundamental structure of the refinement process remains unchanged-something that is not true if a non-binary refinement tree is used instead. To implement a complete encoder, we combine the proposed refinement process with Shapiro´s embedded zerotree wavelet (EZW) algorithm. By optimizing this process, speed increases of between 13 and 16% can be realized on the set of test images