A green screen creates visual effects that enable subjects to appear in different locations by imposing images behind them. In a live-action production, shooting on green screen employs a technique called "chroma key compositing." The compositing process makes it possible to integrate separate visual elements, so that they become part of one scene. The idea is that the green screen gets replaced by other visual elements during postproduction, or even during live streaming or live broadcast.
Weather Maps
TV news stations use green screen effects in weather forecasts. In these broadcasts, a weatherperson or meteorologist stands in front of a green screen backdrop and looks at the video monitor on one side where the screen has been replaced by the weather map. This allows the weatherperson to point to the right spots over the map during the forecast -- even if the weatherperson is actually standing on a plain green screen.
Virtual Sets on TV Shows
Virtual sets for news broadcasts and talk shows allow for the shooting of both live and taped shows using partly or completely virtual sets. This means that certain portions or the entire production background are actually green screen effects. For live broadcasts, this is done in real time. For taped shows, this can be done during taping or during postproduction. Unlike green screen effects used in weather forecasts, virtual sets are set in a 3-D space.
Motion Pictures
Filmmakers may mix live characters with computer-generated images, especially in epic, fantasy, horror and action movies. Usually, an actor is shot on a green screen background, whereby the blank green screen is replaced with a striking image, for example, a scenic vista, a fairy land, deep space or an apocalyptic environment. In some cases an actor in a fight scene wears a harness to give the illusion of flight and motion that defies gravity. The green screen camouflages the harness's wires and makes the scene look real.
Motion Control Photography
Motion control photography is a technique that uses still or motion photography to acquire precise control over camera movements, and create visual effects that cannot be produced when only using a single camera. This involves shooting the subject over green screen for better control of the images and their movement. The process requires shooting several elements using the same camera motion, then compositing them into one frame during postproduction.
