This page provides information on the GI tab and GI rollout of the Render Settings.

 

Page Contents ×

 

Overview


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.

 

UI Path


 

||Render Settings window|| > GI tab > GI rollout



 

 

GI Rollout Parameters


 

 

On – Enables/disables indirect illumination.

Reflective and Refractive Caustics

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. 

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.
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. This option is disabled by default because reflective GI caustics usually contribute little to the final illumination, while often they produce undesirable subtle noise.

When the render engine is set to CUDA, the Reflective/Refractive Caustics options are always enabled and are hidden from the UI.

 

Primary Bounces

Primary Engine – Specifies the method to be used for primary diffuse bounces.

Irradiance map – Selects the Irradiance map method for primary diffuse bounces. See the Irradiance Map Settings section for more information on the feature's functionality.
Brute force – Selects the brute force method (direct computation) for primary diffuse bounces. See the  Brute Force GI  section for more information on functionality.
Light cache – Selects the light cache method as the primary GI engine. See the  Light Cache Settings  section for more information on functionality. 

Multiplier – Determines the degree to which primary 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.

Secondary Bounces

Secondary 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 Settings section for more information.
Light cache – Selects the light cache method as the secondary GI engine. See the Light Cache Settings section for more information.

Multiplier – Determines the effect of secondary diffuse bounces on the scene illumination. Values close to 1.0 might wash out the scene, while values around 0.0 might produce a dark image. Note that the default value of 1.0 produces physically accurate results. While other values are possible, they are not physically accurate.

 

When the renderer is set to CUDA, the Primary GI engine is always set to Brute Force. You can select between Brute Force and Light Cache for Secondary bounces.

Note that the Irradiance Map is not supported with the GPU renderer.

 



Example: GI Caustics


This example shows GI caustics generated by a self-illuminated object:






 

Example: Primary and Secondary 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

 

 

 

GI Advanced Parameters


 

 

Post-Processing

These controls 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.

Saturation – Controls the saturation of the GI. A value of 0.0 means that all color will be removed from the GI solution and the result will be 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 unmodifiedWhen 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.

Ambient Occlusion

These controls add an ambient occlusion term to the global illumination solution.

On – Enables the ambient occlusion pass.

Multiplier – Multiplies the effect of the ambient occlusion.

Radius – Determines the amount of area (in scene units) where the ambient occlusion effect is produced.

Subdivs – Controls the number of samples that V-Ray takes to calculate the ambient occlusion effect. Lower values render faster but produce a more noisy result.

Ray Distance

The options in this group limit the distance traveled by each GI ray in order to optimize rendering time.

On – Enables the Ray Distance limit.

Ray Distance – Specifies the maximum distance each GI ray will travel.