Abstract: Matrix Radiance Transfer
Precomputed Radiance Transfer allows interactive rendering of
objects illuminated by low-frequency environment maps, including
self-shadowing and interreflections. The expensive integration of
incident lighting is partially precomputed and stored as matrices.
Incorporating anisotropic, glossy BRDFs into precomputed radiance
transfer has been previously shown to be possible, but none
of the previous methods offer real-time performance. We propose
a new method, matrix radiance transfer, which signcantly speeds
up exit radiance computation and allows anisotropic BRDFs. We
generalize the previous radiance transfer methods to work with a
matrix representation of the BRDF and optimize exit radiance computation
by expressing the exit radiance in a new, directionally locally
supported basis set instead of the spherical harmonics. To
determine exit radiance, our method performs four dot products per
vertex in contrast to previous methods, where a full matrix-vector
multiply is required. Image quality can be controlled by adapting
the number of basis functions. We compress our radiance transfer
matrices through principal component analysis (PCA). We show
that it is possible to render directly from the PCA representation,
which also enables the user to trade interactively between quality
and speed.