A new low memory wavelet zerotree coder for image

Zerotree coding technique is computationally simple and efficient for image compression and progressive transmission, however high working memory is its main drawback. This paper presents a new low memory zerotree coder (NLMZC) which abandons the use of lists and defines a compact flag map to save the memory requirement. A new heuristic depth finding strategy in the sorting pass is developed for its compact structure. The compact flag map stores the status of coefficients and the heuristic depth finding strategy searches the significant descendant coefficients in tree branches. Comparison of NLMZC with set partitioning in hierarchical trees (SPIHT) shows that NLMZC saves at least 1.085 Mbytes of memory but only reduces minor peak signal-to-noise ratio (PSNR) values for coding a 512 × 512 gray image. In addition, NLMZC outperforms another low memory coder (LZC) in both PSNR value and memory requirement.