CGI Acronyms & Terminology
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- Physically Based Rendering - A physically accurate system for reasoning about the behavior of light and surfaces. Physically based rendering respects the rules of thermodynamics, i.e. the brightness of a reflection can never be brighter than the source it is reflecting, because all surfaces absorb some percentage of light energy.
- Bidirectional Reflectance Distribution Function - A mathematical model for describing the behavior of light when interacting with a surface. Blinn, Phong, Lambert are all BRDFs.
- Index of Refraction - When light waves pass through a material, they slow down. IOR describes how fast light travels. An IOR value of 1.33 (water) means that light travels 1.33 times slower through water than it does the empty vacuum of space. Every material has a different IOR. Creating realistic materials often depends on using the correct value, so look up material IOR values online when creating shaders.
- Sub-Surface Scattering - In many partially translucent materials like human skin, light not only strikes the surface and reflects into our eyes but a percentage of penetrates the surface, bounces around inside the object then exits the object, carrying with it the interior color back to your eye.
- In the CGI industry, Albedo is roughly synonymous with "diffuse". Albedo refers to the percentage of diffuse light energy that an object reflects. Black materials appear black because much light energy is absorbed, light objects are bright because they reflect more light than they absorb.
- To make an Albedo texture, follow the same steps required for a diffuse texture, but take extra care to remove any direction light, shadow, or ambient occlusion. Albedo should be based on real-world values, easily found online.
- Fresnel refers to variation in reflectivity in relation to a surface's facing ratio. In nature, light is more likely to reflect when striking an object at glancing angles.
- Anisotropy refers to the property of something being directionally dependent. For example, wood grain has a "direction" in which it flows, so it can be said to be anisotropic. In the CGI industry, anisotropy commonly refers to the "directional shine" found on many metallic materials.
- In mathematics, interpolation is the act of extracting/constructing points between multiple known data points. In animation we find the word interpolation in a number of contexts, but generally referring to "blending between". In a graph editor for example, different interpolation methods can be utilized to blend between keyframes (i.e. linear, smooth, etc).
- In digital imaging, a channel is a greyscale image representing a set of values between 0 (black) and 255 (white). When viewed on a computer screen, all images are made of three channels: red green and blue, corresponding to red green and blue light emitters in your LCD screen. These three colors, when seen in combination produce an image with full color range.
- Images can also contain an alpha channel. Like the red green and blue channels, an alpha channel is a greyscale image representing transparency values between 0 (transparent) and 255 (opaque).