Global Illumination (or GI) is the illumination in a scene that effectively comes from reflected (or bounced) light as opposed to coming directly from a light source. This enables more naturalistic and accurate lighting solutions.
The indirect illumination rollout in V-Ray controls the secondary diffuse bounces. The primary diffuse bounces are always calculated with Brute Force.
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A primary diffuse bounce occurs when a shaded point is directly visible by the camera, or through specular reflective or refractive surfaces.
A secondary bounce occurs when a shaded point is used in GI calculations.
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UI Path: ||Render Settings window|| > GI tab> GI rollout
UI Path: ||Render Settings window|| > GI tab > GI rollout
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On– Enables/disables indirect illumination.
Reflective and Refractive Caustics
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When the render engine is V-Ray GPU, the Reflective/Refractive Caustics options are always enabled and are hidden from the UI.
GI caustics represent light that has gone through one diffuse, and one or several specular reflections (or refractions). GI caustics can be generated by skylight, or self-illuminated objects, for example. However, caustics caused by direct lights cannot be simulated in this way. You must use the separate Caustics section to control direct light caustics. Note that GI caustics are usually hard to sample and may introduce noise in the GI solution. For more information, see the GI Caustics example below.
Reflective GI caustics – Allows indirect light to be reflected from specular objects (mirrors etc). Note that this is not the same as Caustics, which represent direct light going through specular surfaces.
Refractive GI caustics – Allows indirect lighting to pass through transparent objects (glass etc). Note that this is not the same as Caustics, which represent direct light going through transparent objects. You need refractive GI caustics to get skylight through windows, for example.
Engine – Specifies the method to be used for the secondary diffuse bounces.
None – No secondary bounces will be computed. Use this option to produce skylit images without indirect color bleeding. Brute force– Selects the brute force method (direct computation) for secondary diffuse bounces. See the Brute Force Settingssection for more information. Light cache – Selects the light cache method as the secondary GI engine. See the Light Cache Settings section for more information.
