<P> 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 . Computer development also made it easier to incorporate motion into composited shots, even when using handheld cameras . Reference - points can be placed onto the colored background (usually as a painted grid, X's marked with tape, or equally spaced tennis balls attached to the wall). In post-production, a computer can use the references 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 disadvantage of this is that it requires a large camera movement, possibly encouraging modern film techniques where the camera is always in motion). </P> <P> The principal subject is filmed or photographed against a background consisting of a single colour or a relatively narrow range of colours, usually blue or green because these colours are considered to be the farthest away from skin tone . The portions of the video which match the pre-selected color are replaced by the alternate background video . This process is commonly known as "keying", "keying out" or simply a "key". </P> <P> Green is used as a backdrop for TV and electronic cinematography more than any other colour because television weathermen tended to wear blue suits . When chroma keying first came into use in television production, the blue screen that was then the norm in the movie industry was used out of habit, until other practical considerations caused the television industry to move from blue to green screens . Broadcast quality color television cameras use separate red, green and blue image sensors, and early analog TV chroma keyers required RGB component video to work reliably . From a technological perspective it was equally possible to use the blue or green channel, but because blue clothing was an ongoing challenge, the green screen came into common use . Newscasters sometimes forget the chroma key dress code, and when the key is applied to clothing of the same color as the background, the person would seem to disappear into the key . Because green clothing is less common than blue, it soon became apparent that it was easier to use a green matte screen than it was to constantly police the clothing choices of on - air talent . Also, because the human eye is more sensitive to green wavelengths, which lie in the middle of the visible light spectrum, the green analog video channel typically carried more signal strength, giving a better signal to noise ratio compared to the other component video channels, so green screen keys could produce the cleanest key . In the digital television and cinema age, much of the tweaking that was required to make a good quality key has been automated . However, the one constant that remains is some level of color coordination to keep foreground subjects from being keyed out . </P> <P> Before electronic chroma keying, compositing was done on (chemical) film . The camera colour negative was printed onto high - contrast black and white film, using either a filter or the colour sensitivity of the black and white film to limit it to the blue channel . Assuming this film was a negative it produced clear where the blue matte screen was, black elsewhere, except it also produced clear for any white objects (since they also contained blue). Removing these spots could be done by a suitable double - exposure with the colour positive, and many other techniques . The end result was a clear background with an opaque shape of the subject in the middle . This is called a female matte, similar to an alpha matte in digital keying . Copying this film onto another high - contrast negative produced the opposite' male matte' . The background negative was then packed with the female matte and exposed onto a final strip of film, then the camera negative was packed with the male matte was double - printed onto this same film . These two images combined together creates the final effect . </P>

Can you wear blue on a green screen