Primatte chromakey technology

Primatte is a brand of chroma key software used in motion picture, television and photographic host applications to remove solid colored backgrounds (greenscreen or bluescreen usually) and replace them with transparency to facilitate ‘background replacement’. It uses a unique algorithm based on three multi-faceted polyhedrons floating in RGB colorspace that are used to isolate color regions in the foreground image.

Source: Wikipedia — Primatte chromakey technology (CC BY-SA 4.0)