Chroma key compositing, or
chroma keying, is a
special effects /
post-production technique for
compositing (layering) two
images or
video streams together based on color hues (
chroma range). The technique has been used heavily in many fields to remove a from the subject of a photo or video – particularly the
newscasting,
motion picture and
videogame industries. A color range in the top layer is made transparent, revealing another image behind. The chroma keying technique is commonly used in
video production and post-production. This technique is also referred to as
color keying,
colour-separation overlay (
CSO; primarily by the
BBC), or by various terms for specific color-related variants such as
green screen, and
blue screen – chroma keying can be done with backgrounds of any color that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from most
human skin colors. No part of the subject being filmed or photographed may duplicate a color used in the background.