Global illumination refers to lighting in a scene/environment that comes from light bouncing around and off objects (or the environment itself). Global Illumination (or GI) refers to the computation of this effect through computer graphics. For more details, please see the Indirect Illumination Reference section.
V-Ray implements several approaches (called engines) for computing indirect illumination with different trade-offs between quality and speed. Additional rollouts become available depending on the engine(s) specified for Primary and Secondary Rays:
UI path: ||V-Ray Asset Editor|| > Settings > Global Illumination
Indirect Illumination (GI) Parameters
With Interactive turned off shows the most commonly used options needed for a rendering.
With Interactive turned on shows the most commonly used options needed for an Interactive rendering.
Enabled – Turns indirect illumination on and off.
Primary Rays – Specifies the GI method to use for primary bounces.
Irradiance map – Causes V-Ray to use an irradiance map for primary diffuse bounces. See the Irradiance Map Settings section for more information.
Brute force – Specifies direct computation for primary diffuse bounces. See the Brute Force Settings section for more information.
Light cache – Specifies the light cache for primary diffuse bounces. See the Light Cache Settings section for more information.
Secondary Rays – Specifies the GI method to use for secondary bounces.
None – No secondary bounces will be computed. Use this option to produce skylit images without indirect color bleeding.
Brute force – Specifies direct computation for secondary diffuse bounces. See the Brute Force Settings section for more information.
Light cache – Specifies the light cache for secondary diffuse bounces. See the Light Cache Settings section for more information.
These controls allow an ambient occlusion term to be added the global illumination solution.
Enabled – Turns ambient occlusion on or off.
Radius – Determines the amount of area (in Scene units) where the ambient occlusion effect is produced.
Occlusion Amount – Specifies the amount of ambient occlusion. A value of 0.0 will produce no ambient occlusion.
Example: Ambient Occlusion
Note: the scene in this example is from Evermotion. ( http://www.evermotion.org/)
This example demonstrates the effect of the global ambient occlusion options.
The first image to the right is rendered with the Light cache for both primary and secondary bounces, Fixed Filter type for the light cache, and Store direct light off. The second image in the center is rendered with the same light cache settings, but with global ambient occlusion enabled. The third image to the right is rendered without ambient occlusion, with Brute force GI engine for primary bounces, and the Light cache as a secondary engine with Nearest Filter type . The render times include the time for calculating the light cache. Note how ambient occlusion can produce a feeling of a more detailed image, even though the result is not entirely correct.
Ambient occlusion is off - lighting is good, but there is a lack of detail
Ambient occlusion is on - details are much more defined
Brute force GI, no ambient occlusion - details are fine, but render times is longer.
Example: Light Bounces
This examples shows the effect of the number of light bounces on an image:
Direct lighting only: GI is off.
1 bounce: irradiance map, no secondary GI engine.
2 bounces: irradiance map + brute force GI with 1 secondary bounce.
4 bounces: irradiance map + brute force GI with 3 secondary bounces
8 bounces: irradiance map + brute force GI with 7 secondary bounces
Unlimited bounces (complete diffuse lighting solution): irradiance map + light cache