A Fuzzy View on k-Means Based Signal Quantization with Application in   Iris Segmentation
  This paper shows that the k-means quantization of a signal can be interpreted both as a crisp indicator function and as a fuzzy membership assignment describing fuzzy clusters and fuzzy boundaries. Combined crisp and fuzzy indicator functions are defined here as natural generalizations of the ordinary crisp and fuzzy indicator functions, respectively. An application to iris segmentation is presented together with a demo program. 
Nicolaie Popescu-Bodorin
cs.CV