Editing Chroma key (section)

{{short description|Compositing technique, also known as green screen}}
{{redirect|Green screen}}
{{for-multi|the electronic music project|Chroma Key|musical tonality depending on key|Key (music)}}
{{Use British English|date=May 2020}}
{{Use dmy dates|date=November 2017}}
[[File:Green screens compare with Iman Crosson 20110524.png|thumb|upright=1.3|The practicality of green-screen compositing is demonstrated by actor [[Iman Crosson]] in a self-produced video.<br>'''Top panel:''' A frame in a full-motion video shot in the actor's living room.<ref>From YouTube video [https://www.youtube.com/watch?v=_U9HzHqMGi0 "President Obama on Death of Osama SPOOF- '''BEHIND THE SCENES'''"] posted to Crosson's secondary YouTube channel "Iman" on 8 May 2011.</ref><br>'''Bottom panel:''' The corresponding frame in the final version in which the actor impersonates [[Barack Obama]] "appearing" outside the White House's East Room.<ref name="SPOOFvid">The final (composite) video [https://www.youtube.com/watch?v=xlOIy6QEbes "President Obama on Death of Osama bin Laden '''(SPOOF)'''"] posted to Crosson's YouTube channel "Alphacat" on 4 May 2011.</ref>]]

'''Chroma key compositing''', or '''chroma keying''', is a [[Visual effects|visual-effects]] and [[post-production]] technique for [[compositing]] (layering) two or more [[image]]s or [[video]] streams together based on colour hues ([[colorfulness|chroma]] range). The technique has been used in many fields to [[background subtraction|remove a background]] from the subject of a photo or video – particularly the [[newscast]]ing, [[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]]<ref name="What is Chroma Key?">{{cite web |url=http://lumeo.com.au/chroma-key/ |title=What is Chroma Key?|publisher=Lumeo |access-date=3 July 2014}}</ref>), 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.<ref name="BorisFX" />

It is commonly used for live [[weather forecasting|weather forecast]] [[broadcasts]] in which a [[news presenter]] is seen standing in front of a [[Computer-generated imagery|CGI]] map instead of a large blue or green background. Chroma keying is also common in the entertainment industry for visual effects in [[movies]] and video games. [[Rotoscopy]] may instead be carried out on subjects that are not in front of a green (or blue) screen. [[Match moving|Motion tracking]] can also be used in conjunction with chroma keying, such as to move the background as the subject moves.