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DWT to compress a signal

Module by: Mark Eastaway. E-mail the author

Summary: Explains how the discrete wavelet transform can be used to compress a signal. Explains the use of the code r_compression.m

Module content for matlab program Wcompression.m

Introduction:

Wcompression.m is a basic program that uses the wavelet transform to compress a signal using the wavelet transform. The following module will briefly describe how to use Wcompression.m to perform and to understand a compression wavelet method.

For some background on how the Discrete Wavelet Transform (DWT) works, click here.

How does wavelet compression work?

Compression in wavelet theory is very similar to de-noising. First, the wavelet transform is performed on the input signal. Second, the low coefficients are changed to zero. Then the coefficients are stored or transmitted without the zeros. Additionally, but not covered in this program, quantization and entropy encoding techniques, such as Huffman coding can be applied to the coefficients.

How to use our code

To use our Wavelet compression code: after downloading our .m files, including the program OurDWT.m, type the following line in Matlab:

[reducedwsig, compressedsig] = R_compression(signal, compperc, plotoption)

Filling in your actual information for these inputs:

signal = signal input to be compressed

compperc = percentage of compression (0-100)

plotoption = option to plot, set equal to 1 to plot; all else will not plot

The outputs:

compressedsig = signal that has been compressed by DWT

reducedwsig = wavelet transform of compressed signal

An Example:

Use the following lines of code in Matlab to see how this program works and visually see how wavelet compression works. We will create a signal, then compress the coefficients by 75% and show the results.

  1. signal = sin(0:8*pi/100:8*pi-8*pi/100)
  2. [reducedwsig, comrpessedsig] = R_compression(signal,75,1)

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