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Directional zerotrees image coding

This paper investigates new zerotree structures for image compression. The objective of this research is to make the tree structures flexible enough to fit themselves to any significant coefficients within image subbands. In this fashion, a higher compression ratio can be achieved. The approach discussed utilizes predetermined tree structures corresponding to the natural directionality of the separable wavelet transformation. Without increasing the coder's complexity and side rate, the set partitioning in a hierarchical trees (SPIHT) codec proposed by Said and Pearlman (see IEEE Transactions on Circuits and Systems for Video Technology, vol.6, no.3, p.243-50, 1996) is modified for testing these structures. The results demonstrate some significant improvement especially for highly horizontal and vertical texture images.