Appears in ACM TOG 33(4) (SIGGRAPH 2014). Unifying Points, Beams, and Paths in Volumetric Light Transport Simulation

Figure 1: We present a new rendering algorithm, unified points, beams, and paths (UPBP), for light transport simulation in participating media. UPBP combines a number of volumetric estimators based on points and beams with Monte Carlo path sampling techniques, all of which have complementary strengths and weaknesses. The bottom row shows the contributions of the various volumetric transport techniques to the final image at the top. As shown in Fig. 2, UPBP excels at rendering scenes with different kinds of media, where previous specialized techniques each fail in complementary ways. (Scene inspired by Gkioulekas et al. [2013].) Efficiently computing light transport in participating media in a man-ner that is robust to variations in media density, scattering albedo, and anisotropy is a difficult and important problem in realistic im-age synthesis. While many specialized rendering techniques can efficiently resolve subsets of transport in specific media, no single approach can robustly handle all types of effects. To address this problem we unify volumetric density estimation, using point and beam estimators, and Monte Carlo solutions to the path integral formulation of the rendering and radiative transport equations. We extend multiple importance sampling to correctly handle combina-tions of these fundamentally different classes of estimators. This, in turn, allows us to develop a single rendering algorithm that correctly combines the benefits and mediates the limitations of these powerful volume rendering techniques