Abstract: A simple‚fast and efficient still image compression algorithm based on the embedded zero-tree wavelet （EZW） algorithm is presented to meet the demands of high speed and great efficiency of network transmission．The improved fast algorithm has three distinguishing features： （1） Introducing the conceptions of significant subband and insignificant subband‚which reduces the repetition scan times of coefficient‚and quickens the compression speed；（2） Using two thresholds in one coding scan‚and combining two iterations of the original EZW algorithm into one‚which not only reduces the time complexity‚but also improves the compression rate and the power signa-l to-noise ratio；（3） Coding the lowest frequency subband separately from other high frequency subbands．The experimental result shows that the improved algorithm has higher compression rate and faster coding speed than Shapiro’s．

Key words: zero-tree coding, image compression, significant subband, wavelet transform, iteration combination