@PhdThesis{krivanek05radiance_phd,
 author = "Jaroslav K\v{r}iv\'anek",
 title  = "Radiance Caching for Global Illumination Computation on Glossy Surfaces",
 school = "Universit\'e de Rennes 1 and Czech Technical University in Prague",
 type   = "Ph.D. Thesis",
 year   = "2005",
 month  = "December",
 url    = "http://www.cgg.cvut.cz/~havran/dissertation/index.htm",
 annote = "Computation of global illumination is an important means in the
pursuit of photorealism of computer-generated images. It is of
particular importance in scenes with glossy surfaces, since it
conditions correct perception of glossy material characteristics.
This dissertation focuses on efficient computation of global
illumination in presence of glossy surfaces with low-frequency
reflectance functions. Computing global illumination on those
surfaces is difficult with pure Monte Carlo sampling because of the
sheer number of rays required to get a good estimate of indirect
illumination. We propose radiance caching, a ray tracing-based
algorithm for computing indirect illumination on glossy surfaces
with low-frequency reflectance functions. The algorithm takes
advantage of the shading smoothness on these surfaces by
interpolating indirect illumination from a set of sparsely
distributed, cached values. We discuss all the components necessary
for an implementation of radiance caching: (1) an automatic choice
of surfaces on which radiance caching is used; (2) compact
representation for the cached illumination by spherical harmonics;
(3) efficient spherical harmonics rotation that makes interpolation
possible; (4) computation of translational gradient for smooth
interpolation; and (5) an adaptive criterion for distributing the
cached illumination values on surfaces. Radiance caching delivers
high quality images in a shorter time compared to existing ray
tracing-based methods. It can be used for final gathering in
two-pass global illumination methods or as a stand-alone global
illumination algorithm."
}