A radiative transfer framework for non-exponential media

Authors: Benedikt Bitterli, Srinath Ravichandran, Thomas Müller, Magnus Wrenninge, Jan Novák, Steve Marschner, Wojciech Jarosz

A collaborative research project between Dartmouth College (Benedikt Bitterli, Srinath Ravichandran, Wojciech Jarosz), Disney Research (Thomas Müller, Jan Novák), ETH Zurich (Thomas Müller), Pixar Animation Studios (Magnus Wrenninge), and Cornell University (Steve Marschner) will be presented at SIGGRAPH Asia next month in Tokyo, Japan.

The motivation for this project came from observing the real-world behavior of light-scattering media composed of tiny particles, such as fog or clouds. When simulating such media in computer graphics, one typically assumes that the scattering particles are independent, or randomly distributed, in space. However, research in other fields has shown that these particles can exhibit a number of other spatial distributions, from uniform to clumped. Based on experiments detailed in the new paper, we now know that the spatial relationship between particles affects the transmission of light through the medium, and by extension, its appearance.

The paper derives a new model for light transport in a scene that does not assume independence between scattering particles. This means particles can now exhibit any number of spatial relationships, including blue noise and fractal patterns. A natural consequence is that light decay through scattering media is no longer limited to exponential decay (which follows from the independence assumption), and can be described in any number of ways, as illustrated in the paper. This will allow for a much greater degree of freedom in controlling the appearance of any scattering medium.

For more information, check out the project page.