The world we inhabit is made of so many different things, both natural and human-created, along with light from our sun, fire, or artificial light. The number of particulates in the atmosphere (and type) and, of course, weather, all affect how we perceive what it is that we see in our environment. When we capture imagery, we do so through glass lens elements and onto our digital devices or photographic film. The type of lenses we use, or the digital sensors or film will affect the final outcome even more. OctaneRender® will mimic these factors through synthetic cameras and lenses, lights and materials. As a spectral rendering, unbiased path tracer, Of course, Octane is most concerned with light and how light interacts within the environment and objects of a scene. Materials are used to define the appearance of given objects, and can get to be rather sophisticated. In fact, actually creating materials amounts to a good portion of the typical Octane experience. 


Rendering, by the simplest definition, mimics how light photons hit the surface of an object and react according to the properties of that surface defined by the material itself. The appearance that we perceive of a surface is actually determined by the structural (chemical/organic/metallic) and optical texture (smooth/rough) of the surface itself, as well as anything that may be riding above the surface (liquid/dirt particles/coating). These factors determine how a given light ray will interact with a surface. When a light ray hits a surface, three types of interaction occur: 


1- Light can be Absorbed by the surface.

2- Light can be Transmitted to the other side of the surface.

3- Light can be Reflected from the surface.



Some materials absorb certain wavelengths of light and may also reflect some wavelengths and even emit light when absorbing radiation (an effect known as fluorescence, viewable under ultraviolet radiation). As always, the interaction of radiant energy (electromagnetic radiation, AKA light) with the surface material follows the Law of Energy Conservation: the sum of the energies absorbed, transmitted and reflected by a surface equals the sum of the energies coming to the surface. This rule applies separately for each wavelength of light throughout the spectrum whose quantities are determined in ratio to the incoming energy (i.e., relative). These ratios are different for each material and surface geometry and seem to be more related to matter structure. Accordingly, for a material surface, these ratios are called transmittance, absorbance, and reflectance, respectively.