This page gives an overview and explanation of Indirect Illumination.
Overview
Indirect Illumination is the illumination in a scene that effectively comes from reflected (or bounced) light as opposed to coming directly from a light source. There are a few different approaches for computing indirect light within V-Ray, however using a combination of Brute Force and Light Cache for interior scenes or Brute Force and Brute Force for exterior scenes is recommended in most circumstances for the Primary and Secondary Bounces respectively.
The Primary Bounces in V-Ray are always calculated with the Brute Force GI engine.
Image courtesy of Spencer Fitch
Primary and Secondary Bounces
The indirect illumination controls in V-Ray concern the 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. It is always calculated with the Brute Force GI engine. A secondary bounce occurs when a shaded point is used in GI calculations.
Approaches to Indirect Illumination
V-Ray implements several approaches for computing indirect illumination with different trade-offs between quality and speed:
Brute Force – This is the simplest approach; indirect illumination is computed independently for each shaded surface point by tracing a number of rays in different directions on the hemisphere above that point.
Advantages:
– This approach preserves all the detail (e.g. small and sharp shadows) in the indirect lighting.
– It is free from defects like flickering in animations.
– No additional memory is required.
– Indirect illumination in the case of motion-blurred moving objects is computed correctly.
Disadvantages :
– Might be slow for complex images
Light Cache – Light caching (or light mapping) is a technique for approximating the global illumination in a scene. The light map is built by tracing many, many eye paths from the camera. Each of the bounces in the path stores the illumination from the rest of the path in a 3D structure. The light map is a universal GI solution that can be used for both interior or exterior scenes.
Advantages:
– In many cases the light cache can be used as-is for direct visualization of very fast and smooth previews of the lighting in the scene.
Disadvantages:
– The resulting light cache is view-dependent and is generated for a particular position of the camera. However, it generates an approximation for indirectly visible parts of the scene as well. For example, one light cache can approximate all the GI in a closed room.
– Lighting involving motion-blurred moving objects is not entirely correct, but is very smooth since the light cache blurs GI in time as well (as opposed to the irradiance map (deprecated), where each sample is computed at a particular instant of time).
– Requires additional memory.
The choice of method to use depends on the task at hand. See the examples below.
For more information about the render settings and parameters for GI and Bounce Engines, please check the GI pages.
Example: Comparisons of Different GI Methods
These examples show the effect of the different 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