``Extended Camera Specification for Image Synthesis''
  Eduard Groeller, Helwig Loeffelmann

Published
  1994, Machine Graphics and Vision 3(3), pp. 514-530.
  
Abstract
  typically a rather simple definition of the viewing parameters (e.g., per-
  spective projection)  is used  for ray tracing,  which is one of the most
  powerful rendering  techniques for  generating realistic images.  in this
  paper this  simple camera model  is extended in several ways  to increase
  user flexibility.  a sequence of mappings  defines a more general way  to
  assign 3d rays  for each pixel of the final raster image.  these rays are
  then taken as primary rays in the following ray tracing step. an extended
  camera specification,  for example,  allows the projection  of the object
  scene onto more general projection surfaces (quadrics, free form surfaces).
  different views  of the same object scene m ay be incorporated within one
  single image.  a test implementation and sample images show the feasibili-
  ty of the approach.  the extended camera specification enables more elabo-
  rate  viewing  techniques which  may be used,  e.g.,  for virtual reality,
  arts and special effects. 

The full paper is available as gzipped postscript file per www:
  http://www.cg.tuwien.ac.at/~helwig/some_personal_details/GrLo94Paper.ps.gz

If you have any questions, please contact the authors per email:
  groeller@cg.tuwien.ac.at
  helwig@cg.tuwien.ac.at

If you are interested in a printed version, please write an email to:
  Helwig Loeffelmann, helwig@cg.tuwien.ac.at