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

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

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 ImageDiscrete Wavelet Transform

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

EZW Coding Cont’d The EZW consists of two algorithms: 1. Dominant Pass Flow-Chart2. Subordinate Pass Flow-Chart

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 Process of encoding a 1 a 2 a 3 a 4 Symbol Probabilities & subintervals

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

Compression Comparisons:

Image Demonstration: Original Image Initial DWT Reconstructed imageDifference Image Reconstructed DWT