Keying and Rotoscoping
- L K
- Apr 22, 2022
- 1 min read
Rotoscoping and/or keying are two of the principle ways to separate filmed elements onto a transparent plate to help composite into other footage.
Rotoscoping is the act of painting out the subject frame by frame - with the term "rotoscoping" coming from the earliest form of film where images would be physically traced. Companies like Disney used the process to trace reference footage of people performing actions like dancing that the animators could then use for the cartoon characters.
I've sourced some footage of how traditional rotoscoping used a dance by Cab Calloway as the source for their animation.
Although used differently in visual effects today, the principle remains, but tools exist to remove a lot of the manual frame by frame work involved.
Chroma keying uses colour or luminance to remove a specific range of colours or luminance while retaining the rest of the spectrum. A greenscreen is commonly used, but any colour that is different to your target can be used; blue and white background screens are both commonly used too.
This technique also has a long history in use with traditional film stock, where some colours - primarily blue - could be chemically removed during the developing process. The first bluescreen shot in cinema is of the genie in The Thief of Baghdad.
The process of chroma or colour keying remains today, except there are no physical limitations from doing the process chemically.
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