Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!iuvax!uxc.cso.uiuc.edu!tank!james@rover.bsd.uchicago.edu
From: james@rover.bsd.uchicago.edu
Newsgroups: comp.graphics
Subject: Re: Fingerprint enhancement
Message-ID: <4344@tank.uchicago.edu>
Date: 8 Jul 89 19:56:49 GMT
Sender: news@tank.uchicago.edu
Organization: University of Chicago - Dept. Rad. Onc. and Med. Physics
Lines: 19

In article <1269@servax0.essex.ac.uk>, nigel@ese.essex.ac.uk (Nigel S.H. Brooks) writes...
>I'm working on a project to analyse finger prints and I need
>an algorithm to thin the lines down to single pixel width to
>aid recognition of the features.

One possibility is to take an unsharp mask of the image:

	For each pixel, add a factor times the difference between the pixel
value and that of its neighbors to a distance of r pixels away in all 
directions. R will be determined by the current line width.  The resulting
image will not be monochrome, but a threshold can be taken at which the most
central lines are generally above.

	If the image is currently noisy, an appropriate high frequency mask
or lowpass filter may be used first.

James Balter
james@rover.uchicago.edu
"If the hat fits, slice it!"