chroma key

The practicality of green-screen compositing is demonstrated by actor Iman Crosson in a self-produced video.Top panel: A frame in a full-motion video shot in the actor's living room.Bottom panel: The corresponding frame in the final version in which the actor impersonates Barack Obama "appearing" outside the White House's East Room.

Chroma key compositing, or chroma keying, is a visual-effects and post-production technique for compositing (layering) two or more images or video streams together based on colour hues (chroma range). The technique has been used in many fields to remove a background from the subject of a photo or video — particularly the newscasting, motion picture, and video game industries. A colour range in the foreground footage is made transparent, allowing separately filmed background footage or a static image to be inserted into the scene. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as colour keying, colour separation overlay (CSO; primarily by the BBC), or by various terms for specific colour-related variants such as green screen or blue screen; chroma keying can be done with backgrounds of any colour that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from any human skin colour. No part of the subject being filmed or photographed may duplicate the colour used as the backing, or the part may be erroneously identified as part of the backing.