[Help-gsl] Daubechies and images

[Humberto Luiz Razente]

Hello,

I applied Daubechies on a gray scale 256*256 pixels image.
Considering pixels[][] is a matrix where each value is the
color of a pixel, the source code is:

============
    gsl_wavelet *w = gsl_wavelet_alloc (gsl_wavelet_daubechies_centered, 4);
    gsl_wavelet_workspace *work = gsl_wavelet_workspace_alloc (width *
height);
    double *data = malloc (width * height * sizeof (double));
    for (i = 0; i < width; i++)
        for (j = 0; j < height; j++)
            data[i * width + j] = pixels[i][j];
    gsl_wavelet2d_nstransform (w, data, width, width, height, +1, work);
============

After running gsl_wavelet2d_nstransform, the data vector contains
the transformed data, but the values varies from -1466.34 to 8443.58
I tried to normalize the data using:

============
    for (i = 0; i < width*height; i++)
        data[i] = ((data[i] - lowestvalue) / (greatestvalue -
lowestvalue)) * 255;
============

and the result and original images can be seen in:

http://gbdi.icmc.usp.br/~humberto/daubechies.png

Does anybody have an idea of what am I doing wrong?

Thanks,

Humberto Razente


Brian Gough wrote:
===========================================================
Date: Mon, 18 Dec 2006 17:50:27 +0000
From: Brian Gough <address@hidden>
Subject: Re: [Help-gsl] Daubechies and images and CBIR
To: Humberto Luiz Razente <address@hidden>
Cc: address@hidden
Message-ID: <address@hidden>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Humberto Luiz Razente wrote:
> I'd like to extract Daubechies features from
> medical images for content based image retrieval (CBIR).
> Does anybody have an example using gsl?
> I couldn't understand how to do this in the reference manual
> and I couldn't adapt the example for images.
> Should I have read other documentation?
> I already opened the images and I have a matrix containing
> colors of the pixels.

I didn't see any replies on the list, but if anyone does have an example
of that I'd be glad to add it to the manual.

-- 
Brian Gough
(GSL Maintainer)
===========================================================