ABSTRACT
Participating media model the interaction of light as photons penetrate through a given material, and are used to simulate a wide variety of elements in the natural world. Examples include many organic and inorganic translucent solids, whose visual appearance is mostly affected by subsurface scattering, such as marble, wax, leaves, fruits and skin. Similar phenomena are observed in various liquids, including milk and water in its various phases (e.g., flowing fluid as in oceans, ice crystals responsible for halos, snow flakes, droplets forming clouds and fog or producing rainbows), while the non-linear propagation of light through refractive media is responsible for mirages due to temperature gradients in air layers. Their scope also encompasses light absorption in fumes as well as scattering in many gases and aerosols, such as smoke, dust particles, haze and the earth’s atmosphere causing the common variations in sky color and the blue coating of our planet when seen from space. Finally, participating media are used to model several emissive volumes, either due to thermal radiation or luminescence, including fire, fluorescent gases and plasmas such as lightning, auroras, stars and nebulae.
