Explain: Lighting Terms

[jeremybirn]

HDRI - High Dynamic Range Images are defined and explained at http://www.debevec.org/ along with examples of their main use in Image Based Lighting. Just scroll down that page and you'll see sections and examples of all of that.

GI (Global Illumination) means lighting on the computer where the renderer calculates bouncing or inter-reflecting light - it's called "Global" because all the objects in the scene can contribute bounced, indirect light to an object. Most renderers traditionally do just "local" illumination, so the only light hitting a surface comes directly from a light source, with no indirect light. Visit http://graphics.ucsd.edu/~henrik/ for lots of related definitions and examples.

Radiosity was one way (used to be about the only way in commercial software) to calculate Global Illumination, now software supports other methods like Photon Mapping to calculate GI. Radiosity was limited to storing amounts of light energy in the vertices of polygon meshes, newer GI methods have a calculation accuracy that can be adjusted independently from the geometry. GI is a broader term than Radiosity - Radiosity only calculated Diffuse reflection of light, GI also makes Caustics possible, which is the specular reflection of light - see http://www.3drender.com/light/caustics.html on my website for an explaination of that.

Fake GI or Fake Radiosity just means lighting in a style that similates bounced light - for example, when sunlight hits a wall, putting an extra light behind the wall to simulate reflected light from that area. Some people use those terms to describe different shaders or plug-ins as well, things that don't really let illumination of one object brighten another, but give a look that is in some way similar.

Hope those links get you started, anyway.

-jeremy

[Oktavian]

If you are new to this stuff, go and buy Jeremy's book. It's not specially focused on these 4 points but contains all the related subjects and it's really worthwhile.

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