![]() The scattering is often so uniformly chaotic that it can be said to appear the same from all directions – quite different from the case of a mirror! A shader using this approximation really just needs one input: “albedo”, a color which describes the fractions of various colors of light that will scatter back out of a surface. ![]() if an object absorbs most light but scatters blue, it will appear blue). The absorption and scattering of diffuse light are often quite different for different wavelengths of light, which is what gives objects their color (e.g. This is known by many names: “Diffuse Light”, “Diffusion”, “Subsurface Scattering” – all describe the same effect. Some of this scattered light may make its way back out of the surface, then becoming visible once more to eyeballs and cameras. ![]() There it will either be absorbed by the material (usually converting to heat) or scattered internally. Usually some will penetrate into the interior of the illuminated object. Not all light reflects from a surface, however. The word “specular”, often used to describe the effect, is derived from the latin for “mirror” (it seems “specularity” sounds less awkward than “mirrorness”). On a smooth surface this will result in a mirror-like appearance. This behavior is very similar to a ball thrown against the ground or a wall – it will bounce off at the opposite angle. When light hits a surface boundary some of it will reflect – that is, bounce off – from the surface and leave heading in a direction on the opposing side of the surface normal. Most people will be familiar with these ideas on a practical level, but may not know how they are physically distinct. Diffusion & Reflectionĭiffusion and reflection – also known as “diffuse” and “specular” light respectively – are two terms describing the most basic separation of surface/light interactions. You may then want to also check out our own Joe Wilson’s article on creating PBR artwork. We’ll have to start with some of the basics so that they are well defined before we begin to highlight what is new, but if you’ll bear with me through the parts you may already know I think you’ll find it well worth the read. This means both the engineer and the artist should understand the motivations for these changes. Shading capabilities have advanced enough that some of the old approximations can now be safely discarded, and with them some of the old means of producing art. Much of what makes a physically-based shading system different from its predecessors is a more detailed reasoning about the behavior of light and surfaces. This document is intended for non-engineers (artists most likely), and will not present any mathematics or code. The short answer is: “many things”, and “it depends”, which is rather unsatisfying, so I have taken it upon myself to try to explain at some length what PBR represents and how it differs from older rendering methods. The term is bandied about a lot, often generating confusion as to what exactly it means. Physically-based rendering (PBR) is an exciting, if loosely defined, trend in real time rendering lately.
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