GI-related options

The GI data computed by REDsdk contain a lot of useful information about the scene, not only the indirect illumination distribution. Two engine options exist to take into account this information during rendering to enhance the quality of lighting and glossiness.

GI for lighting

The RED::OPTIONS_RAY_GI_FOR_LIGHTING option enables the engine to use the GI data to better sample the lights in each shading point. It requires a GI cache with sufficient quality in order to work properly (a GI cache computed with the default engine options should suffice).

The GI cache contains additional information about where the light is coming in every location in the scene. Knowing that, the engine can concentrate the light sampling on lights which actually lit the current shading location. It means that for approximatively the same amount of computation, the noise is really reduced when the option is turned on.

Differences in quality between the option disabled (above the red line) and enabled (below the red line) for the same rendering time.

GI for glossiness

Just the same way the GI cache was used to enhance the sampling of lights (GI for lighting), it can be used to approximate glossiness reflections/refractions through the RED::OPTIONS_RAY_GI_FOR_GLOSSINESS option. This time, the option is about speed, not quality. When turned on, the engine, instead of computing exact costly glossiness, approximates the result of the computation based on the GI cache. This saves a lot of computation but can produce small variations compared to the ground-truth image.

The option value is related to the error introduced by using it and is unit less. A 0 value means no error tolerated and resolves to the exact computation of glossiness. Any other positive value turns the option on.

From left to right option=0, option=4 (speed up=x1.05), option=8 (speed up=x1.22), option=16 (speed up=x1.47).