Each lens is a shape that has a fill color which is an operator...http://www.google.com.au/patents/US6072501?utm_source=gb-gplus-sharePatent US6072501 - Method and apparatus for composing layered synthetic graphics filtersAdvanced Patent SearchPublication numberUS6072501 APublication typeGrantApplication numberUS 08/883,845Publication date6 Jun 2000Filing date27 Jun 1997Priority date27 Jun 1997Fee