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In television, technique for substituting backgrounds. For example, the empty studio behind a newscaster or weather forecaster may be replaced with an outdoor scene or a frame of video footage. This technique is commonly used on news programmes and other shows that feature ‘talking heads’.

A computer analyses the image of the newscaster, who is placed in front of a plain background, usually blue, to identify the exact pixels where the talking figure begins and ends. It can then substitute a new image for just the area specified. The technique allows broadcasters to add visual interest while keeping costs down.