MATLAB Answers


Regarding Wavelets and DWT.

Asked by Sriram G on 25 Mar 2013

Hi everybody,

Since am a Dummie for image processing,I need to know about Multiresolution analysis with "WAVELETS" and

How does "Wavelet Transform" differs from fourier transform ?

And how to apply DWT to an image using MATLAB ?

what does the four subbands LL, LH, HL, HH meant for ?

Thanks a lot. Give your hand to my ignorance :-D


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1 Answer

Answer by Carlos
on 25 Mar 2013
 Accepted Answer

Basically the wavelet transform is similar to the STFT(Short time Fourier Transform), because it links the frecuency of a signal to the time instant where that specific frecuency is happening.

However, the Wavelet transform has different resolutions depending on the frecuency.At high frecuency it has a high resolution, whereas at low frecuency it has low resolution. The STFT has a constant time resolution, that depends on the selected window length.

The DWT algorithm decomposes the image into 4 subband (subimage) ie,LL,LH,HL,HH. LL is the low frequency subband so it is used for further decomposition process.. LH subband extracts the horizontal features of original image. HL subband gives vertical features HH subband gives diagonal features.

However type doc cwt, for further details

Hope it helps

  1 Comment

Hey Carlos !

I do understand :-D

Thanks a lot ! If some doubts come, I will ask :-D

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