G. Borgefors.
  <b>Distance transformation in digital images </b>.
  <i>Computer Vision, Graphics, and Image Processing</i>,
  34(3):344-371, 1986.
  published
  <A HREF="http://vis.cs.brown.edu/results/bibtex/Borgefors-1986-DTI.bib">(bibtex:
  Borgefors-1986-DTI)</A>.<br />