Bluescreen is a special effects process used in film, television, video and more recently, the world of computers. Bluescreen, greenscreent, or bluescreen imaging, is used to create the illusion of a background that isn't actually there when filming takes place. Hollywood blockbusters such as Star Wars and the Harry Potter films use bluescreen to transport the actors into exciting worlds that had previously only existed in the imagination.
To create a bluescreen image, the actor is photographed or filmed in front of an evenly lit, pure blue background. The image is then usually transferred to computer and the blue background is replaced with another image. This is known as the background plate. Bluescreen images can be made optically for movies or still photos, digitally for computer images or electronically for video.
The reason blue is favored for this process is that the most common color in scenes is peach shades; blue is the most complementary color to peach. As blue is the opposite color to peach, it is easier to avoid conflict between the colors. Red and green have also been used, but cameras and film are more sensitive to blue light.
Another term for the bluescreen process is Chroma-Key. This is a television process only, and is based on the Luminance key. It works by setting a brightness level for the image and then cutting out anything that is over or under the set brightness. Think of it as a keyhole where all that is left is the foreground image and everything else is darkness. This is usually used for creating titles on television.
Bluescreen has become such a sophisticated technique that it is now virtually impossible to tell the difference between special effects and real film locations. The process can transport actors anywhere in the world, or out of this world, without actually leaving the studio. It can take you to prehistoric times or transport you to outer space.
Interactive computer games are increasingly utilizing bluescreen technology. Hollywood actors are using video games to include film clips from their latest films, and with the bluescreen imaging process, the actors can actually appear in the games themselves. It is thought that in the future, these games will become indistinguishable from movies -- the only difference being that you will be able to control the actors. Thanks to bluescreen technology, it shouldn't be too long before we are able to appear in our own film or game with our favorite actors.