Green screens and blue screens are commonly used by photographers and videographers with a process known as “Chroma Key.” The idea behind Chroma Key is to place someone in front of a solid background, then remove it, replacing it with whatever you want. For example, you could take a photo of two people in a studio, then make it look like they're in front of Niagara Falls. There are some differences between the two screen types--blue and green--aside from the color.
The most obvious difference between green and blue screens, of course, is the color. This makes a difference regarding clothing and other foreground items. The reason that green and blue color screens were chosen for Chroma Key is that neither color naturally appears in human skin pigmentation. This makes it easier to wipe away the color and replace it with something else. If the subject happens to wear a blue or green outfit in front of the screen, however, the outfit would disappear as well, since the computer cannot tell the difference between the two greens or blues. Therefore, the primary issue when choosing between a blue or green screen is the color of other items in the shot.
According to Steven Bradford, a professional photographer and videographer from Seattle, one advantage green has over blue--and a reason some photographers and videographers choose green screens instead of blue--is the reflectivity of the color. Green allows for better matting of the foreground (matting in this context means that a second item will show up against the first item, so if our subject is wearing an orange jumpsuit, for example, it shows up more clearly because the green provides a better contrast to the foreground than blue might --again, according to Bradford) so it will be easier to remove later on the computer. Bradford also points out that video cameras tend to be very sensitive to the green color channel, making it easier to remove green from the scene being photographed.
Contrast with Flesh Tone
Bradford suggests that blue is a better contrast color with flesh tone, allowing for a more natural look when filming people against a blue background. This is important since videographers and photographers try to make a scene that uses green or blue screens appear as natural as possible.
Chroma spill is a phenomenon where an outline remains from the background color, either blue or green used in the Chroma Key technology. Bradford and Jonas Hummelstrand, another videography and photography professional from Sweden, hold the opinion that blue chroma spillover is less noticeable than green, thus making it potentially more attractive to professionals.
- old camera 2 image by James Lemmon from Fotolia.com