auto-binarize a fingerprint

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Jean-Edouard Simonin
Hi, I am a French student and i'm working on a minutia recognition project. My work is based on this application : http://www.mathworks.com/matlabcentral/fileexchange/16728-fingerprint-application It works with the joined picture but a problem comes with the binarization (if the pixel is a stria -> 0, else -> 1). Indeed, the limit between white and black is manually fixed to 160. I am looking for ideas to make it automatically. Maybe, find the average intensity of the stria... Can someone help me ?

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Jean-Edouard Simonin
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Sean de Wolski
Sean de Wolski 2011-3-30
Perhaps use:
graythresh
to determine a suitable threshold.
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Sean de Wolski
Sean de Wolski 2011-3-30
How are the stria too close? graythresh uses a histogram so location doesn't matter. What class is your data?
Jean-Edouard Simonin
Jean-Edouard Simonin 2011-3-30
It's maybe beacause of the difference of intensity between stria and valley which is not too much strong...

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Jean-Edouard Simonin
I have an idea but I don't know how to do it. If we draw a histogram of the picture, we can see two Gaussians. To determine the limit between white and black, I have to find the min between these two Gaussians. How could I do that ?
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Sean de Wolski
Sean de Wolski 2011-4-4
It's called the minimum valley method.
Basically find the peaks; it's the bottom of the valley between the two peaks. You could use the histc function and some basic numerical derivatives to find it.

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