Here we have explored the use of Displacement, Final Gathering and Global Illumination with Maya and Mental Ray.
Displacement maps can add additional detail to basic geometry. Where black areas of the map are 'lowered' and white areas are 'raised' off the object mesh, 'Mid-Greys' are the baseline value where no displacement will occur.
For displacement maps to work properly, its important to determine the Mid-Grey value of the map by adjusting the 'Alpha Gain' and 'Alpha Offset' accordingly.
Below are further examples of displacement, using a non-subdivision setup for unsmoothed objects, a subdivision setup for smoothed surfaces as well as a nurb surface displacement.
Final Gather works by projecting 'Final Gather Rays' into a scene which scatter upon contact of an object's surface. This effectively calculates 'bounced light and colour' which can be used to light a scene independently or in conjunction with Global Illumination.
Global Illumination makes use of the photons being projected into a scene. The photons are absorbed and reflected throughout the scene where colour inheritance can occur to bounce or bleed as it moves between different surfaces and their respective material. As such, global illumination can mimic real-world lighting conditions as the photons carries wavelengths of the colour spectrum. Final Gather can also be used to smooth the photons out.