This page provides information on the GI tab of the V-Ray Renderer parameters.
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 controls in V-Ray are divided into two large sections: primary diffuse bounces and secondary diffuse bounces.
- 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.
For detailed information on the Brute Force, Light Cache and Irradiance Map settings, please go to their respective page:
||Renderer tab|| > Global Illumination tab
(with the V-Ray Renderer node selected)
On – Enables/disables indirect illumination.
Reflective 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. This option is disabled by default because reflective GI caustics usually contribute little to the final illumination, while often they produce undesirable subtle noise.
Note: 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 Tab 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.
Refractive 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.
Primary/Secondary Bounces Engine – Specifies the method to be used for primary diffuse bounces.
Multiplier – Determines the degree to which primary/secondary diffuse bounces contribute to the final image's illumination. Note that the default value of 1.0 produces a physically accurate image. Other values are possible, but not physically accurate.
Advanced – Enables advanced global illumination controls
Saturation – Controls the saturation of the GI. A value of 0.0 means that all color is removed from the GI solution and the result 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 – This parameter works together with Contrast base to boost the contrast of the GI solution. When Contrast is 0.0, the GI solution uses the value defined by Contrast base. A value of 1.0 means the solution remains unmodified. Values higher than 1.0 boost the contrast.
Contrast Base – Determines the base for the contrast boost. It determines which GI values in the image remain unchanged during contrast calculations, and which are shifted. The default value of 0.5 values leaves the medium grey values in the GI solution unmodified. When a low Contrast Base value is used in conjunction with a raised Contrast value, the image brightens. When a higher Contrast Base is used with a higher Contrast value, the image darkens.
The previous three post-processing parameters allow additional modification of the indirect illumination before it is added to the final rendering. The default values ensure a physically accurate result, but values can be changed to modify the way GI looks for artistic purposes.
When V-Ray GPU is chosen as a rendering engine, all unsupported options are hidden from the parameters.
Example: GI Caustics
This example shows GI caustics generated by a self-illuminated object:
Example: Light Bounces
This example shows the effect of the number of light bounces on an image: