When working with Mental-Ray, many times we would use final gather almost exclusively. In this tutorial I would like to explore two less commonly used methods of illuminating our scenes, Global Illumination and photometric lighting.Throughout this tutorial we will explore these two methods, and compare their positive versus negative virtues.
Global illumination is a general name for a group of algorithms used in 3D computer graphics that are meant to add more realistic lighting to 3D scenes. Such algorithms take into account not only the light which comes directly from a light source (direct illumination), but also subsequent cases in which light rays from the same source are reflected by other surfaces in the scene, whether reflective or not (indirect illumination).
Photometric stereo is a technique in computer vision for estimating the surface normals of objects by observing that object under different lighting conditions. The technique was originally introduced by Woodham in 1980. The special case where the data is a single image is known as shape from shading, and was analyzed by B. K. P. Horn in 1989.
Credit : Ran Ben Avraham