ImageUtils tresholding images

git-svn-id: http://lire.googlecode.com/svn/trunk@114 f280a053-6817-128d-8a7e-cdf98506035a
Changes in LireFeature interface

git-svn-id: http://lire.googlecode.com/svn/trunk@115 f280a053-6817-128d-8a7e-cdf98506035a