Chroma key can make a low-budget production look expensive.
Special effects have become important in the marketability of modern film. Independent filmmakers have to find a way to compete with the larger studios by being creative with special effects. The chroma key process, often called "blue screen" or "green screen," can help create scenes that a struggling filmmaker couldn't otherwise afford on a shoestring budget.
History
In the 1930s, RKO Radio Pictures developed a primitive blue screen method for the movies "Flying Down to Rio" and "The Thief of Baghdad" to include scenes the company couldn't afford to shoot. Larry Butler won an Academy Award for special effects for the latter in 1940. In 1958, in the Spencer Tracy movie "The Old Man and the Sea," Arthur Widmer used blue screen technology as modern society knows it to record a background, then record the actors in front of a blue screen. The separate photos were rephotographed through red and green filters before being merged together.
Process
Blue or green backgrounds are usually used while the actor is being filmed performing an action. A second image, usually a background scene, is phased into the image with the actors during the editing phase. A keying process matches the background color with the alternate background. All greens or blues will show as the second image. Richard Harrington advises against using digital video for chroma key because it compresses the images and therefore often leaves head or foot space.
Clothing
Any clothing an actor wears that matches the background color will blend into the background image during the keying process. To avoid this, the actor must wear colors that are as far away from the background color as possible. Blending colors is used as a technique when the actors are supposed to be invisible or part of their body is supposed to be missing. In the book "DV Filmmaking," Ian David Aronson says shaggy clothes, fuzzy sweaters and dangling jewelry should be avoided because compression in digital cameras can cause spotting with fusing the images.
Backgrounds
Blue was the first color used in this process because it is said to generate less grain in film. It promotes better detail than other colors. Green requires less light and so do digital cameras. Digital camera users more commonly choose green for backgrounds because the detail quality matches better with the device, as film cameras do with blue backgrounds. For software chroma key, magenta has become the background color of choice.
Lighting
Lighting is critical to avoid shadows. Shadows can make the greens and blues darker. During the keying process, the software used to key may not identify the darker color. The background image could be blotched and look inauthentic. All lighting must be even for the process to be effective.
Tags: background color, blue screen, keying process, background image, digital cameras, green backgrounds, greens blues