William A. Stokes, James A. Ferwerda, Bruce Walter, and Donald P. Greenberg.
 <b>Perceptual illumination components: a new approach to
  efficient, high quality global illumination rendering</b>.
 In <em>Proceedings of ACM SIGGRAPH</em>, pages 742--749, 2004.
  <a href="http://vis.cs.brown.edu/docs/pdf/bib/g/Stokes-2004-PIC.pdf.html">(pdf)</a>
  <a href="http://vis.cs.brown.edu/results/bibtex/Stokes-2004-PIC.bib">(bibtex:
  Stokes-2004-PIC)</a>.