Photographic effects have been used to manipulate and enhance audience experience since the advent of motion pictures. An early technique was the use of static wood or cardboard cut-outs called matts. The matts worked by blocking certain areas of the film emulsion, and exposing the stock multiple times to selectively control which areas were exposed. The use of matts became increasingly sophisticated. Complex special-effects scenes could include dozens of discrete image elements, requiring elaborate uses of mattes, layering one upon another to form a single image.
Such processes were the forerunner to today’s blue and green screen technologies.
By the 1940’s a far simpler process saw development. Called “keying” or “keying out,” the principal subject is photographed against a background consisting of a narrow range of colors, either green or blue. These were originally chosen because they are the furthest from skin tones. With computers, the portions of the film which match the preselected color are replaced rather easily by alternate background images.
In theory, almost any color can be used, but the most common are the Digital and Chroma blues and greens.
The Chroma colors are a slightly different tint than digital.
The most commonly used textiles consist of tempo or poly-pro fabric. There is no discernable difference in color between the two fabrics, but there are some differences:
Tempo material has a black backing to block most light, has a nappy texture, and accepts Velcro.
Poly Pro compresses more, is somewhat more resistant to dirt and wrinkles, and will sometimes require a light-blocking backing material when used outside.
While location, set design, actor wardrobe, and placement and quality of light can play a part in selection, the choice of which to use can be a matter of personal preference, and may be due to familiarity.
Today, “green screen technology” continues to push artists and audiences to the limits of our imaginations.
L.A. Rag House