Chroma key compositing, or chroma keying, is a special effects / post-production technique for compositing (layering) two imagesor video streams together based on color hues (chroma range). The technique has been used heavily in many fields to remove abackground from the subject of a photo or video – particularly the newscasting, motion picture and videogame industries. A color rangein 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^[2]), 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.^[3]

It is commonly used for weather forecast broadcasts, wherein a news presenter is usually seen standing in front of a large CGI map during live television newscasts, though in actuality it is a large blue or green background. When using a blue screen, different weather maps are added on the parts of the image where the color is blue. If the news presenter wears blue clothes, his or her clothes will also be replaced with the background video. A complementary system is used for green screens. Chroma keying is also used in the entertainment industry for special effects in movies and videogames. The advanced state of the technology and much commercially available computer software, such as Autodesk Smoke, Final Cut Pro, Pinnacle Studio, Adobe After Effects, and dozens of othercomputer programs, makes it possible and relatively easy for the average home computer user to create videos using the "chromakey" function with easily affordable green screen or blue screen kits