Primary and Secondary Method (CineRender Global Illumination)

The Primary Method calculates the effect of Diffuse Depth 1, which is
The Secondary Method calculates the brightness of surfaces (that do not have to lie in the camera’s field of view) that are brightened by multiple light reflections.
The Primary Method is most important method for the render quality and therefore higher-quality methods such as QMC or IR should be used. These also take correspondingly longer to render! For light that is reflected back-and-forth, methods can be used that are of “lesser quality” and render faster (such as Radiosity).
Tip: The two-part GI calculation already existed in previous versions: With Mode set to IR and Sampling set to Radiosity Maps, this corresponds to the current Irradiance Cache Primary Method and Radiosity Maps Secondary Method.
Quasi-Monte Carlo (QMC): QMC is the most precise but slowest method. Animations are flicker-free (if not free of noise) when QMC+QMC is used.
Irradiance Cache: A simplified, fast method of ascertaining the most important areas of a given project, calculating GI at these locations, and interpolating. Animations tend to flicker if the values are too low.
Irradiance Cache (Legacy): This is the Irradiance Cache from CineRender versions prior to V20. It has been maintained so older Projects can be rendered with the same render results.
Quasi-Monte Carlo (QMC): QMC as a Secondary Method is best when used as IR+QMC for exterior scenes, and most precise – and slowest – as QMC+QMC.
Irradiance Cache: IC as Secondary Method works well for interior spaces with small lights defined as GI area lights or GI portal lights. Make sure to reduce the Samples value in combination with QMC+IR. Internally, a much greater number of QMC samples is used for IR, which can increase render times very dramatically.
Radiosity Maps: Radiosity Maps as Secondary Method are well-suited for fast preview renderings because of their low Diffuse Depth (less reflected light).
None: Disables the secondary GI calculation. This represents a Diffuse Depth of 1.
Color saturations can also be modified for surfaces (see also Illumination (CineRender Surface Channel)). Both saturation parameters represent a global, project-wide saturation setting.
Note that gamma correction can, within limits, be used to compensate for lower Diffuse Depth values.
Tip: When “real” light sources are used, indirect illumination can already be achieved with a Diffuse Depth value of 1 because the objects illuminated by the light source will be recognized as a luminous object.
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