Indigo is a ray tracer, which means that it renders scenes by firing out rays and letting them bounce around a scene to form ray paths. Different render modes control the way ray paths are constructed. Different render modes have different strengths and weaknesses for different kinds of scenes.
The main render modes are:
- Path tracing
- Bidirectional path tracing
- Path tracing with Metropolis Light Transport (MLT)
- Bidirectional path tracing with MLT
Generally, bidirectional path tracing should be used as it is the best all-round solution.
Metropolis light transport (MLT) can help rendering speeds in tricky scenes, such as scenes with small lights and glass panes, or sunlight reflected off glass or polished surfaces. See this page for more information about MLT.
Here is a diagram describing what they do:
|Path tracing||Rays are fired from the camera, bouncing around the scene until they hit a light.|
|Bidirectional path tracing||Rays are fired from both the camera and light sources. They are then joined together to create many complete light paths.|
|Path tracing with MLT||Rays are fired from the camera, bouncing around the scene until they hit a light.
When a successful light-carrying path is found, another is fired off on a similar direction. Gives good results for caustics.
|Bidirectional path tracing with MLT||Rays are fired from both the camera and the lights, then connected to create many paths.
When a successful light-carrying path is found, another is fired off on a similar direction. Gives good results for caustics and "difficult" scenes generally.
There are also other, more specialised, rendering modes available for use in post-production:
Only shadow catcher materials are rendered to an alpha layer, ready for compositing.
Shadows render mode is Indigo Renderer only and is not available in Indigo RT.