Blue like... a bluescreen

The video bluescreen (or chroma keying) visual effect is often used in television: it allows us to remove the blue background the weather presenter stands in front of and to replace it with another image, such as the national weather map. The process works thanks to the detection of a luminance level, in other words a luminous intensity, corresponding to a very specific color. This makes it possible to isolate it from the other colors in order to replace it by a video image. This visual effect works well with basic tints but can create holes in very detailed outlines (hair, fur, veils, etc.) when the nuances of skin and clothes are too close to the background color. The Ultimatte process, created in the 80s, is able to precisely bring out all these details, as well as handling shadows, smoke or transparent objects. Nowadays, the composite shots for Star Wars 's films are realized on the computer on the basis of this principle.