Diffusion and Multiple Anisotropic Scattering for Global Illumination in Clouds

Nelson Max

Lawrence Livermore National Lab.
Mail Stop L-560
7000 East Avenue
USA 94550 Livermore CA

Greg Schussman
Stanford Linear Accelerator Ctr.
Mail Stop 26
2575 Sand Hill Road
USA 94025 Menlo Park CA

Ryo Miyazaki, Kei Iwasaki,  and Tomoyuki Nishita

University of Tokyo
7-3-1 Hongo, Bunkyo-ku
Japan 113-0033 Tokyo

{ryomiya, kei-i, nis}@nis-lab.is.s.u-tokyo.ac.jp


The diffusion method is a good approximation inside the dense core of a cloud, but not at the more tenuous boundary regions. Also, it breaks down in regions where the density of scattering droplets is zero. We have enhanced it by using hardware cell projection volume rendering at cloud border voxels to account for the straight line light transport across these empty regions. We have also used this hardware volume rendering at key voxels in the low-density boundary regions to account for the multiple anisotropic scattering of the environment.


Diffusion approximation, multiple anisotropic scattering, global illumination, participating media, clouds.