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   -> Volume 5, Issue 9


Question: Help Using Non-Haar Wavelets in Code
 
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bhoy@eaw.com (Bill Hoy)
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PostPosted: Wed Oct 30, 1996 10:48 am    
Subject: Question: Help Using Non-Haar Wavelets in Code
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#25 Question: Help Using Non-Haar Wavelets in Code

For my research project at WPI, I am studying denoising methods using
wavelets. My advisor wanted me to write my own algorithms, so
starting with no previous knowledge of wavelets, I set out to learn
how to code the Discrete Wavelet Transform. After a few months of
work, I now can take the DWT of a signal using the Haar wavelet,
denoise it (threshold the DWT), and take the IDWT to see what I have
done to the original signal.

Since I was just starting with wavelets, I used the Haar wavelet. I
can understand how to get the two filter coefficients, use them on 2
input data points, and then slide it over 2 input data points and
repeat. This gives me the "halving" nature of using wavelets ( I see
the averaging and differencing feature).

I now would like to see if I could modify my existing Matlab code so
that I could use something better than a Haar wavelet. I have looked
at these wavelets, and I see that some have 4 or 6 coefficients. How
do I apply these 4 coefficients to my input array? I'm thinking that
I need to apply 4 input data points at a time to the 4 coefficients of
the wavelet. Do I then slide it over 4 points and repeat, or slide it
over 2 points and repeat (then there will be overlap)?

I realize my question is very-very basic and it shows my lack of experience
using wavelets! I've been having a hard time learning wavelets by myself!
Could anyone provide me with some ideas as to the above question, or
perhaps pointers where I could find some more articles for beginners? Is
it considered possible for a beginner to write their own DWT algorithms?
It would also be nice to hear from other people using wavelets to do
denoising!

Thanks,
Bill

bhoy@eaw.com
or
whoy@ee.wpi.edu

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