<P> 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 cameras alleviated this problem, as both the foreground and background could be filmed with the same camera moves . </P> <P> 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 . </P> <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 . The comedy show Tosh. 0 in particular is known for filming entirely with green - screen and then cutting the image being produced by the computer to show Daniel Tosh standing directly on the purely green set . This is always done at the very end of the show . </P> <P> 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>

What is use of green cloth in vfx