Editing Chroma key (section)

=== From bluescreen to greenscreen ===
The blue screen method was developed in the 1930s at [[RKO Radio Pictures]].  At RKO, [[Linwood Dunn]] used an early version of the [[Matte (filmmaking)|travelling matte]] to create "wipes" – where there were transitions like a windshield wiper in films such as ''[[Flying Down to Rio]]'' (1933). Credited to [[Lawrence W. Butler|Larry Butler]], a scene featuring a genie escaping from a bottle was the first use of a proper bluescreen process to create a travelling matte for ''[[The Thief of Bagdad (1940 film)|The Thief of Bagdad]]'' (1940), which won the [[Academy Award for Best Visual Effects|Academy Award for Best Special Effects]] that year. In 1950, [[Warner Brothers]] employee and ex-[[Kodak]] researcher [[Arthur Widmer]] began working on an [[ultraviolet]] travelling matte process. He also began developing bluescreen techniques: one of the first films to use them was the [[The Old Man and the Sea (1958 film)|1958 adaptation]] of the [[Ernest Hemingway]] novella, ''[[The Old Man and the Sea]]'', starring [[Spencer Tracy]].<ref name="cri">{{cite web|url=http://en.chinabroadcast.cn/2246/2005-2-14/90@206385.htm|title=Illusions Take Home First Oscars|date=14 February 2005|publisher=[[China Radio International|CRI English]]|access-date=21 January 2009|archive-url=https://web.archive.org/web/20050315004609/http://en.chinabroadcast.cn/2246/2005-2-14/90%40206385.htm|archive-date=15 March 2005|url-status=dead|df=dmy-all}}</ref>

The name "Chroma-Key" was [[RCA]]'s trade name for the process, as used on its [[NBC]] television broadcasts, incorporating patents granted to RCA's Albert N. Goldsmith.<ref>"Studio: The World--NBC Introduces 'Chroma-Key' to Extend Scope of TV Settings." Electronic Age, January 1958, 8.</ref> A very early broadcast use was NBC's George Gobel Show in fall 1957.<ref>Johnson, Erskine. "Video's Special Effects Men Becoming Master Magicians of Hollywood; Many Tricks." (NEA syndicated article) Gloversville (NY) Leader-Herald, 6 December 1957.</ref>

[[Petro Vlahos]] was awarded an Academy Award for his refinement of these techniques in 1964. His technique exploits the fact that most objects in real-world scenes have a colour whose blue-colour component is similar in intensity to their green-colour component. [[Zbigniew Rybczyński]] also contributed to bluescreen technology. An [[optical printer]] with two projectors, a film camera and a "beam splitter", was used to combine the actor in front of a blue screen together with the background footage, one frame at a time. In the early 1970s, American and British television networks began using green backdrops instead of blue for their newscasts. During the 1980s, [[minicomputer]]s were used to control the optical printer. For the film ''[[The Empire Strikes Back]]'', [[Richard Edlund]] created a "quad optical printer" that accelerated the process considerably and saved money. He received a special [[Academy Awards|Academy Award]] for his innovation.

For decades, travelling matte shots had to be done "locked-down", so that neither the matted subject nor the background could shift their camera perspective at all. Later, computer-timed, [[Motion control photography|motion-control]] cameras alleviated this problem, as both the foreground and background could be filmed with the same camera moves.

Meteorologists on television often use a field monitor, to the side of the screen, to see where they are putting their hands against the background images. A newer technique is to project a faint image onto the screen.

Some films make heavy use of chroma key to add backgrounds that are constructed entirely using [[computer-generated imagery]] (CGI). Performances from different takes can be composited together, which allows actors to be filmed separately and then placed together in the same scene. Chroma key allows performers to appear to be in any location without leaving the studio.

Advances in computer technology have simplified the [[camera tracking|incorporation of motion]] into composited shots, even when using handheld cameras. Reference points such as a painted grid, X's marked with tape, or equally spaced tennis balls attached to the wall, can be placed onto the coloured background to serve as markers. In post-production, a computer can use these markers to compute the camera's position and thus render an image that matches the perspective and movement of the foreground perfectly. Modern advances in software and computational power have eliminated the need to accurately place the markers ⁠— ⁠the software figures out their position in space; a potential disadvantage of this is that it requires camera movement, possibly contributing to modern [[Cinematography|cinematographic]] techniques whereby the camera is always in motion.