A Generic Framework for Physical Light Transport

Steinberg, S., Yan, L.

ACM Transactions on Graphics (Proceedings of SIGGRAPH 2021)
To Appear

The ability of a light beam to produce observable wave interference phenomena evolves globally: A small but powerful white LED source (marked by a yellow circle) illuminates a scene. The light falls upon the head of a desk lamp made of brushed aluminum, however (a) no diffractive effects are visible because the lamp is close to the source. The light beam is then incident upon a Venus de Milo statue made of scratched bronze. The illumination of the upper part of the statue is dominated by direct incident light, and (b) visible interference patterns arise. On the other hand, light reaching the lower parts of the statue is diffused by a large decorative vase filled with water, altering the coherence properties of the light and (c) diminishing the observable diffraction effects. Rendering is done using a bi-directional path tracer that propagates coherence information, under our formalism, from the light sources.


Physically accurate rendering often calls for taking the wave nature of light into consideration. In computer graphics, this is done almost exclusively locally, i.e. on a micrometre scale where the diffractive phenomena arise. However, the statistical properties of light, that dictate its coherence characteristics and its capacity to give rise to wave interference effects evolve globally: these properties change on, e.g., interaction with a surface, diffusion by participating media and simply by propagation. In this paper, we derive the first global light transport framework that is able to account for these properties of light and, therefore, is fully consistent with Maxwell's electromagnetic theory. We show that our framework is a generalization of the classical, radiometry-based light transport—prominent in computer graphics—and retains some of its attractive properties. Finally, as a proof of concept, we apply the presented framework to a few practical problems in rendering and validate against well-studied methods in optics.


To be presented at SIGGRAPH 2021