After Effects background animation - green screen effect,br in film and video techniques such as chromakey) a green background in front of which moving subjects are filmed and which allows a separately filmed background to be added to the final image.br a digital technique by which a block of a particular colour (often blue or green) in a film or video image can be replaced by another colour or image, enabling, for example, a weather forecaster to appear against a background of a computer-generated weather map.