This page provides information on the Global Illumination rollout under the GI tab in V-Ray's Render Settings.
Overview
The Global Illumination rollout appears under the GI tab. It controls various settings related to GI and specifies the Primary engine and Secondary engine.
For additional information on the different GI engines and how they compare with each other, see the Indirect Illumination page.
UI Path
||Properties Editor|| > Render > GI tab > Global Illumination rollout
Parameters
GI Presets – Allows for the saving and loading of global illumination presets.
Reflect – 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. This is off by default, because reflective GI caustics usually contribute little to the final illumination, while often they produce undesired subtle noise.
Refract – 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. See the GI Caustics example below for more information.
Saturation – Controls the saturation of the GI. A value of 0.0 means that all color is removed from the GI solution and is in shades of grey only. The default value of 1.0 means the GI solution remains unmodified. Values above 1.0 boost the colors in the GI solution.
Contrast - Works together with Contrast base to boost the contrast of the GI solution. When Contrast is 0.0, the GI solution becomes completely uniform with the value defined by Contrast base. A value of 1.0 means the solution remains unmodified. Values higher than 1.0 boost the contrast.
Contr. Base – Determines the base for the contrast boost. It defines the GI values that remain unchanged during the contrast calculations.
Primary engine – Specifies the method to be used for primary diffuse bounces.
Irradiance map – Causes V-Ray to use an irradiance map for primary diffuse bounces. This option is not available for V-Ray GPU. See the Irradiance Map Settings page for more information.
Brute force – Causes V-Ray to use direct computation for primary diffuse bounces. See the Brute force Settings page for more information.
Light cache – Sets light cache as the primary GI engine. See the Light Cache Settings page for more information.
Secondary engine – Determines how V-Ray calculates secondary diffuse bounces.
None – No secondary bounces are computed. Use this option to produce skylit images without indirect color bleeding.
Brute force – Causes V-Ray to use direct computation for secondary diffuse bounces. See the Brute force Settings page for more information.
Light cache – Sets light cache as the secondary GI engine. See the Light Cache Settings page for more information.
Ambient occlusion – Enables or disables ambient occlusion. The multiplier controls the amount of ambient occlusion. A value of 0.0 produces no ambient occlusion, while higher values make the ambient occlusion effect more prominent. See the ambient occlusion example below for more information on how this works.
Radius – The ambient occlusion radius.
Subdivs – Determines the number of samples used for calculating ambient occlusion. Lower values will render faster, but might introduce noise.
Ray Distance – Enables the limiting of GI ray distance.
Max. Ray Dis. – Specifies the maximum distance each GI ray travel.
Example: Light Bounces
These examples show the effect of the different primary and secondary engines. Note that by default Brute Force has 3 light bounces and Light Cache works with 100 light bounces. All the examples are set to their default values.
GI is disabled
GI is set to Brute Force/None
GI is set to Brute Force/Brute Force
GI is set to Brute Force/Light Cache
GI is set to Light Cache/None
GI is set to Light Cache/Light Cache
GI is set to Light Cache/Brute Force
Example: GI Caustics
This example shows GI caustics generated by a self-illuminated object.
Example: Ambient Occlusion
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.