Polarization - Mitsuba 3
The retargetable design of the Mitsuba 3 rendering system can be leveraged to optionally keep track of the full polarization state of light, meaning that it simulates the oscillations of the light’s electromagnetic wave perpendicular to its direction of travel.
Because humans do not perceive this directly, accounting for it is usually not necessary when rendering images that are intended to look realistic. However, polarization is easily observed using a variety of measurement devices and cameras and it tends to provide a wealth of information about the material and shape of visible objects. For this reason, polarization is a powerful tool for solving inverse problems, and this is one of the reasons why we chose to support it in Mitsuba 3.
Polarized rendering has been studied extensively before. A first (unidirectional) algorithm was proposed by Wilkie and Weidlich [WW12] before it was extended to bidirectional techniques in two later works [MSWK16] , [JA18] by leveraging the general path space formulation [Vea98] .
The first two sections of this document cover the mathematical framework behind polarization that is relevant for rendering (Section Mathematics of polarized light) as well as an in-depth description of the Fresnel equations that are important components of many reflectance models (Section Fresnel equations). Finally, Section Implementation serves as a developer guide and explains how polarization is implemented in Mitsuba 3.
