We propose an extension of the path integral formulation amenable to the expression of volumetric light transport with photon beam estimates. Our main contribution is a generalization of Hachisuka et al.'s [2012] extended path space formulation to light transport in participating media. Our formulation supports various point- and beam-based volumetric density estimators, unifying them with path integration in the spirit of the work by Křivánek et al. [2014]. One unique and useful property of our formulation is that it recasts beam-based density estimation as Monte Carlo path vertex sampling in a higher-dimensional space, rather than beam merging in a lower-dimensional space, which enables a practical algorithm for beam estimators with 3D-blur kernels. We thus establish a complementary theoretical foundation for the development of rendering algorithms using points, beams, and paths in participating media.
@inproceedings{hachisuka17extended,
author = {Hachisuka, Toshiya and Georgiev, Iliyan and Jarosz, Wojciech and K\v riv\'anek, Jaroslav and
Nowrouzezahrai, Derek},
title = {Extended Path Integral Formulation for Volumetric Transport},
booktitle = {Proceedings of EGSR (Experimental Ideas \\& Implementations)},
year = {2017},
month = jun,
publisher = {The Eurographics Association},
doi = {10/gfznb3}
}