Bidirectional Rendering of Vector Light Transport

Abstract

On the foundations of many rendering algorithms it is the symmetry between the path traversed by light and its adjoint path starting from the camera. However, several effects, including polarization or fluorescence, break that symmetry, and are defined only on the direction of light propagation. This reduces the applicability of bidirectional methods that exploit this symmetry for simulating effectively light transport. In this work, we focus on how to include these non‐symmetric effects within a bidirectional rendering algorithm. We generalize the path integral to support the constraints imposed by non‐symmetric light transport. Based on this theoretical framework, we propose modifications on two bidirectional methods, namely bidirectional path tracing and photon mapping, extending them to support polarization and fluorescence, in both steady and transient state.

Image-based acquisition and modeling of polarimetric reflectance

“…Several works in the field of computer graphics have proposed rendering algorithms that track the polarization state of light via the Stokes/Mueller calculus. Wilkie and Weidlich [2012] were the first to propose a undirectional method, and two later works build on the path integral formulation [Jarabo and Arellano 2018;Mojzik et al 2016] to enable bidirectional connection strategies [Veach 1998]. Recently, Nimier-David et al [2019] have proposed an open-source renderer, Mitsuba 2, that supports forward and inverse rendering with polarimetric light simulation.…”

“…Rendered images shown in this paper were produced using a polarized Monte Carlo renderer based on Jarabo and Arellano's [2018] path integral formulation of light transport implemented on Mitsuba 2 [Nimier-David et al 2019]. In particular, the Stokes vector of a rendered pixel is computed using an unbiased estimate of the path integral…”

Monte Carlo Methods for Volumetric Light Transport Simulation

“…This ignores effects like fluorescence and phosphorescence, and means that the transport at one wavelength can be simulated independently of other wavelengths. It is possible to incorporate all of these effects using anisotropic [JAM * 10], refractive [ABW14], and multienergy or vector [JA18] forms of the resulting transport equations. We encourage the interested reader to consult these works to fully comprehend the mathematics of light transport under these more general conditions.…”

“…Note that these equations do not account for crosstalk between wavelengths, i.e. fluorescence [JA18].…”

Progressive Transient Photon Beams

“…In particular, most previous work on transient rendering has focused on simulating surfaces transport: Klein et al [KPM*16]. extended Smiths' transient radiosity [SSD08] for second bounce diffuse illumination, while other work has used more general methods based on transient extensions of Monte Carlo (bidirectional) path tracing [Jar12, JMM*14, PBSC14, JA18] and photon mapping [MNJK13, OHX*14]. Several works have also dealt with time‐resolved transport on the field of neutron transport [CPH53, BG70, Wil71, DM79].…”