Maya: Mental Ray: Global Illumination, Final Gathering, and Photon Intensity

What is the relationship between normal light illumination, global illumination (GI), final gathering (FG), and photon intensity? The tables below attempts to answer that question for a fixed illumination intensity (1000 with quadratic falloff). The first table demonstrates photons only scenes with no specular/diffuse lighting turned off, while the second table turns on lighting.

On the surface, it seems that FG is linked to photon intensity only when both FG and GI are on. Note, when FG (and the light) is on, it predominates. Thus suggests workflow should start with FG only, tune slightly dark, then turn on GI to soften the areas in darkness. This is exacly what everyone does. Well, draw your own conclusions.

Note: Maya standard shaders only - no DGS material and DGS photon shaders used.

Photon Intensity	Table 1: Light (diffuse/specular) off, photons only
	GI on FG on	GI on FG off	GI off FG on
0 (emitt off)
4000
8000
16000
32000
64000
128000

Photon Intensity	Table 2: Light (diffuse/specular) on with photons
	GI on FG on	GI on FG off	GI off FG on	GI off FG off
0 (emitt off)
4000
8000
16000
32000
64000
128000

Scene Description

nurbs sphere, scale 2
lambert (.8, 0, 0) red
polygon cube, scale 10, front face missing
lambert (.8, .8, 0) yellow

point light, translate 20 in X, quadradic, intensity 900, ray traced shadow, default 10000 globillums

mental ray, ray trace on

camera enviornment background color 50% gray (0.5, 0.5, 0.5)

Final gather rays reduced from 1000 to 300 to shorten rendering times

Global Illumination uses defaults

Maya 6.01