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In this paper, a new approach of images coding by Shapiro algorithm (Embedded Zerotree Wavelet algorithm or EZW) is proposed. This approach, the modified EZW (MEZW), distributes entropy differently than Shapiro's and also optimizes the coding. This can produce results that are a significant improvement on the PSNR and compression ratio obtained by Shapiro, without affecting the computing time. These results are also comparable with those obtained using the SPIHT and SPECK algorithms. The EZW, Spiht or Speck algorithms are based on the Wavelet transform. The principle ofwavelet transform is to decompose hierarchically the input image into a series ofsuccessively lower resolution reference images and detail images which contain the information needed to be reconstructed back to the next higher resolution level. The sub-band images resulting from wavelet transform are not ofequal significance. Some sub-bands contain more information than others (example the baseband sub band).

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