Vignetting (CineRender Effect)

This effect is available in the Detailed view of PhotoRendering Settings for the CineRender engine.

Vignetting is the effect of darkening an image to its edges (light that hits the lens axis at an angle does not fill the shutter opening entirely, due to the way the shutter is constructed).

https://helpcenter.graphisoft.com/wp-content/uploads/archicad-24-reference-guide/132_cinerenderdetailed/Vignetting_illus.png 

See also Defining Color and Brightness Values and Adjusting Gradient Parameters.