This page provides an overview of the GI Render Settings.

 

Section Contents

Page Contents

 

Overview


Indirect 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 section.

 


 

 UI Paths:

V-Ray Menu > Render Settings -> GI

||V-Ray Toolbar|| > V-Ray GI render settings button

 

 

 

 

||V-Ray Toolbox|| > GI render settings button

 

||Shading viewport|| > Shader Tree mode > right click Render item > Properties > V-Ray GI tab


 

GI Rollouts


  • Environment Importance Sampling - A rendering optimization that reduces noise when sampling blurry effects (glossy reflections, GI, soft shadows, etc.) and calculating photon maps.
  • Global Illumination - General controls for GI. Also specifies the Primary and Secondary GI engines.
  • Irradiance Map Settings - Controls aspects of the irrandiance map when it is specified as a GI engine.
  • Photon Map Settings - Controls aspects of the photon map when it is specified as a GI engine.
  • Brute Force Settings - Controls various aspects of brute force GI computing when it is specified as a GI engine.
  • Light Cache Settings -  Controls aspects of the light cache when it is specified as a GI engine.
  • Caustics - Enables and controls aspects of caustic effects in the scene.

 

 

Global Illumination Parameters



   

 

On Turns indirect illumination on and off.

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. See the Irradiance Map page for more information.
Photon map
 – Causes V-Ray to use a photon map for primary diffuse bounces. This mode is useful when setting up the parameters of the global photon map. Usually it does not produce good enough results for final renderings when used as a primary GI engine. See the Photon map 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 the light cache as the primary GI engine. See the Light Cache Settings page for more information.

Secondary Engine – Specifies the method to be used for secondary diffuse bounces.

None – No secondary bounces will be computed. Use this option to produce sky-lit images without indirect color bleeding.
Photon map
 – V-Ray uses a photon map for secondary diffuse bounces. The number of bounces is set by the Bounces parameter. See the Photon map page for more information.
Brute force
 – V-Ray uses direct computation for secondary diffuse bounces. The number of bounces is set by the Depth parameter. See the Brute force Settings page for more information.
Light cache
 – Uses light cache as the secondary GI engine. The number of bounces is not set by a specific parameter, but rather by outside limitations such as light source cutoff values, global settings, etc. See the Light Cache page for more information.

 

 



Example: Light Bounces


This example shows the effect of the number of light bounces on an image. The Primary Engine for global illumination accounts for the first bounce, then the Secondary Engine creates additional bounces.  


 

GI is off, direct lighting only
(total bounces = 0)

 

Primary Engine = Irradiance map
Secondary Engine = None
(total bounces = 1)

 

Primary Engine = Irradiance map 
 Secondary Engine = Brute force, Depth = 1
(total bounces: 2)

 

 

 


Primary Engine = Irradiance map 
 Secondary Engine = Brute force, Depth = 3
(total bounces = 4)

 

Primary Engine = Irradiance map 
 Secondary Engine = Brute force, Depth = 7
(total bounces = 8)

 

Primary Engine = Irradiance map 
 Secondary Engine = Light cache
Unlimited bounces (complete diffuse lighting solution)

 

 

 


 

Global Illumination - Advanced Parameters


GI caustics represent light that has gone through one diffuse, and one or several specular reflections (or refractions). For example, GI caustics can be generated by skylight or self-illuminated objects. 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 might introduce noise in the GI solution.




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. Reflective GI caustics usually contribute little to the final illumination, while often they produce undesired subtle noise.
For more information, see Example: GI Caustics.

 
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; however, the user may want to modify the way GI looks for artistic purposes.  

Primary Multiplier – Determines how much the primary diffuse bounces contribute to the final image illumination. Note that the default value of 1.0 produces a physically accurate image. Other values are possible, but not physically plausible. For more information, see the Multiplier example below.

Secondary Multiplier – Determines the effect of secondary diffuse bounces on the scene illumination. Values close to 1.0 can wash out a scene, while values around 0.0 may 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 plausible.

Saturation – Controls the saturation of the GI; a value of 0.0 means that all color will be removed from the GI solution and 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 – 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 that 1.0 boost the contrast.

Contrast base – Determines the base for the contrast boost. It defines the GI values that remain unchanged during the contrast calculations. 

 

The options in this group allow you to limit the distance traveled by each GI ray in order to optimize and speed up the rendering.

Ray Distance On – Activates the Ray Distance limit.

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

 

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

Ambient Occlusion On – Enables or disables ambient occlusion. For more information, see Example: Ambient Occlusion

AO Multiplier – Controls the amount of ambient occlusion. A value of 0.0 will produce no ambient occlusion, while higher values will make the ambient occlusion effect more prominent.

AO Radius – The distance between two objects that will be calculated in the ambient occlusion effect.

AO Subdivs – Determines the number of samples used for calculating ambient occlusion. Lower values will render faster, but might introduce noise.

 

 



Example: GI Caustics


The following examples show GI caustics generated by a self-illuminated object.


 


GI Caustics Enabled

 


GI Caustics Disabled

 

 

 

 


 

Example: Multiplier

 

 

 


Primary Multiplier: 0.5

 


Primary Multiplier: 1.0

 


Primary Multiplier: 5.0

 

 

 

 

 

 


 

Example: Ambient Occlusion


This example demonstrates the effect of the global ambient occlusion options.

Note how ambient occlusion can produce a feeling of a more detailed image when using light cache even though the result is not entirely physically correct.  In the examples shown below the Primary Engine was set to Irradiance Map and the Secondary Engine was set to Light Cache.

 

 

Irraidiance Map + Light Cache
Ambient Occlusion On is disabled. Lighting is good, but there is a lack of detail.

 

Irraidiance Map + Light Cache
Ambient Occlusion On is enabled. Details are much more defined.

 

 

 


 

Notes


  • Physically accurate lighting can be achieved if both the primary and secondary GI multipliers are set to their default value of 1.0. While other values are possible, they will not produce a physically accurate result.
  • The GI Settings drop-down has a circular button in the top right corner which, when toggled, detaches the window from the UI so it can be moved wherever needed. Click this button once more to close the window.