Chroma keying is a technique used for combining two frames or images by replacing a color or a color range in one frame with that from the another frame. It is often used in film industry to replace a scene's background by using a blue or green screen as the initial background and placing the actor in the foreground. The principle behind chroma keying is that the color blue is the opposite color of skin tone, so a distinction between the two is very clear, making it easier to select the color without worrying about any part of the actor being included in the selection. The whole blue selection is then replaced with another frame as the background.

Chroma keying is used in movies to replace a blue or green background with computer-generated or separately-shot scenes during the post-production stage. The selection of blue or green back ground mainly depends on the effect required and what colors the actors are wearing. This makes it easier to separate the actor from the background. The final result is that the film is made to look like the actor is somewhere other than a studio.

The chroma key process is widely used because it is cheaper to do this than to shoot in expensive or inaccessible locations. It can also be done in real time, making it ideal for weather report or entertainment shows.

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