A New Image Coding Technique with Low Entropy Using a Flexible Zerotree

Sanghyun JOO
Hisakazu KIKUCHI
Shigenobu SASAKI
Jaeho SHIN

IEICE TRANSACTIONS on Communications   Vol.E81-B       pp.2528-2535
Publication Date: 1998/12/25
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: Category: Source Encoding
image compression,  wavelet transform,  zerotree coding,  entropy coding,  

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A zerotree image-coding scheme is introduced that effectively exploits the inter-scale self-similarities found in the octave decomposition by a wavelet transform. A zerotree is useful for efficiently coding wavelet coefficients; its efficiency was proved by Shapiro's EZW. In the EZW coder, wavelet coefficients are symbolized, then entropy-coded for further compression. In this paper, we analyze the symbols produced by the EZW coder and discuss the entropy for a symbol. We modify the procedure used for symbol-stream generation to produce lower entropy. First, we modify the fixed relation between a parent and children used in the EZW coder to raise the probability that a significant parent has significant children. The modified relation is flexibly modified again based on the observation that a significant coefficient is more likely to have significant coefficients in its neighborhood. The three relations are compared in terms of the number of symbols they produce.