Attempt to replicate what the eye sees rather than a camera, to get the best onboard view for driving rather than create photo-real external screenshots. Also happens to be less demanding on the GPU than the default filters. No chromatic aberration, lens flares or wacky autoexposure.
For those of us that have been struggling with the "darkness" when the weather changes this mod might help.
Found here on Racedepartment http://www.racedepartment.com/downloads/natural-graphics-mod.4551/
and here in the Assetto Corsa Forums