Editing Chroma key (section)

===Predecessors===

Prior to the introduction of [[Matte (filmmaking)|travelling mattes]] and [[optical printer|optical printing]], [[double exposure]] was used to introduce elements into a scene which were not present in the initial exposure. This was done using black draping where a green screen would be used today. [[George Albert Smith (film pioneer)|George Albert Smith]] first used this approach in 1898. In 1903, ''[[The Great Train Robbery (1903 film)|The Great Train Robbery]]'' by [[Edwin Stanton Porter|Edwin S. Porter]] used double exposure to add background scenes to windows which were black when filmed on set, using a [[garbage matte]] to expose only the window areas.<ref>{{cite book | title=Experimental Filmmaking: Break the Machine | first=Kathryn | last=Ramey | page=70 | url=https://books.google.com/books?id=XYRICgAAQBAJ&pg=PA70| isbn=9781136071508 | date=2015-07-30 | publisher=CRC Press }}</ref>

[[File:travelling_matte.svg|thumb|upright=1.5|Simplified principle of travelling mattes]]
In order to have figures in one exposure actually move in front of a substituted background in the other, a travelling matte was needed, to occlude the correct portion of the background in each frame. In 1918 [[Frank D. Williams (cinematographer)|Frank Williams]] patented a travelling matte technique, again based on using a black background. This was used in many films, such as ''[[The Invisible Man (1933 film)|The Invisible Man]]''.<ref name=Foster />{{rp|4}}

In the 1920s, [[Walt Disney]] used a white backdrop to include human actors with cartoon characters and backgrounds in his ''[[Alice Comedies]]''.<ref name=Foster />{{rp|5}}