Chroma Key (commonly referred to as "Greenscreen" or "Bluescreen") is the process of layering videos by removing a colored background in a video. It was pioneered by Larry Butler in the film The Thief of Baghdad in 1940. The Chroma Key method is used frequently for special effects in feature films, but also on a day to day basis in television studios, to see meteorologists along with weather information, or other small scale uses.
In recent years, most all Chroma Key work has been done digitally, by using computers to remove pixels of the exact color of the background. Computers that process these images in real time enable television studios to underlay images, such as weather maps, during a live news broadcast.
The early concept of Chroma Key was accomplished by different methods of chemically processing the film to render the background transparent.