1. Embedded Image coding using zero-trees of Wavelet Transform Authors: Harish Rajagopal Brett Buehl

2. Project Overview • Purpose: create a software implementation of EZW coder for image compression • Overall process flow-chart:

3. Step 1: Wavelet Transform • Step 1a: Replace each image row with its 1D DWT • Step 1b: Replace each image column with its 1D DWT • Step 1c: Repeat steps (1) and (2) on the lowest subband to create the next scale • Step 1d: Repeat step (3) until the desired number of scales has been created Original Image Discrete Wavelet Transform

4. Step 2: EZW Coding • Flow-chart for EZW encoding: (See next slide for more details)

5. EZW Coding Cont’d • The EZW consists of two algorithms: 1. Dominant Pass Flow-Chart 2. Subordinate Pass Flow-Chart

6. Step 3: Arithmetic Encoding • Uses symbol probabilities for lossless compression • Added to EZW implementation to increase compression • Encodes output from EZW encoder • P,N,T,Z,E or 0,1,E Symbol Probabilities & subintervals Process of encoding a1a2a3a4

7. Results: • Compression ratios similar to JPEG image compression • Demonstration image results: • cameraman.bmp – 16.8:1 compression ratio • lena.bmp – 7.5:1 compression ratio • barbara.bmp – 7.5:1 compression ratio

8. Compression Comparisons:

9. Image Demonstration: Original Image Reconstructed image Difference Image Initial DWT Reconstructed DWT