Metropolis light transport for participating media

In this paper we show how Metropolis Light Transport can be extended both in the underlying theoretical framework and the algorithmic implementation to incorporate volumetric scattering. We present a generalization of the path integral formulation that handles anisotropic scattering in non-homogeneous media. Based on this framework we introduce a new mutation strategy that is specifically designed for participating media. Our algorithm includes effects such as volume caustics and multiple volume scattering, is not restricted to certain classes of geometry and scattering models and has minimal memory requirements. Furthermore, it is unbiased and robust, in the sense that it produces satisfactory results for a wide range of input scenes and lighting situations within acceptable time bounds.