Physically Based Rendering

Physically Based Rendering is an extremely important concept in 3D Design and should be researched thoroughly to achieve realistic results in your final renders. I recommend checking the links out at the bottom of the page to learn more.

So… what is Physically Based Rendering?

Physically Based Rendering or PBR is the creation of materials that interact with the physical environment realistically. PBR mainly uses two workflows:
Metal/Rough
Specular/Gloss1
Different parts of workflow define what parts of the materials reflect colour and which part absorb colour and ultimately how they interact with the environment and light.

How Does Colour Work?

Colour is often the frequency of light reflected by a material after the material has been hit by light. A red apple for example reflects red light, but all other light is absorbed. White light (fluorescent/LED) contains all frequencies of colours, however in Yellow (Halogen) light you will have a harder time reflecting blues and purples.

PBR uses different materials and dynamic shaders (like Metal and Gloss) to realistically reflect and dynamically change based on the environment.

Objects are divided into 3 different categories when it comes to PBR. Dielectric, Metal and Iridescent.

Dielectric - Anything that's not a metal or certain types of precious rocks/gems (this means Rust, Painted metal, plastic, wood). Dielectric materials interact with light differently to Metal or Iridescent materials, they don't reflect all of their light, and instead diffuse it (scatter light).

Metal - Metals (like copper, iron, cobalt, platinum) reflect ALL light, and don't absorb any.

Iridescents - Pearls, Opals. These aren't possible with PBR, because of the nature of the shader, custom shading is necessary to create good looking iridescent.

What are the workflows?

Metal/Rough and Spec/Gloss are different ways of achieving almost the same thing, they define what materials you use and give basic rules per workflow.

Different packages have different preferences for each workflow, many programs like Substance Painter and Unreal prefer the Metal/Rough Workflow, but they (like most high end programs) implement both.
Metalness/Roughness is used in most industry programs however and is generally easier to produce because of this.

+Metalness/Roughness

The workflow is relatively simple

You would generally have one colour map.
Base colour Map - This defines colour for both dielectric and metal surfaces, when creating metal surfaces try and use real world values page 13 of the PBR encyclopedia gives you very good reference for different metal values (steel, copper, iron, etc.)

The following are grayscale maps used in the Metal/Rough workflow, grayscale maps are used to quickly define values on a UV map, 1 being white, 0 being black and values between 0 and 1 being defined by greys.

Metal Map - How much of the material is metal (often denoted by white colour or number 1) or how dielectric is it (often denoted by black colour or number 0). As a general rule nothing is a little bit metal and a little bit dielectric, so grey's and numbers between 0 and 1 are never used to denote metalness.

Roughness map - refers to how rough a surface is, rough surfaces (denoted by lighter colours) or smooth surfaces (denoted by darker colours). The rougher a surface the more the white light will appear to dissipate and get larger, the less rough a surface the more tight and intense the reflected light will be. Metal surfaces will reflect the environment more clearly the less rough they are.
PBR has some disadvantages, namely the difficulties of creating realistic pearlescent or iridescent materials, as they don't support coloured specular workflows.

Bibliography
: How we see colour: https://www.pantone.com/how-do-we-see-color
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