The Green Screen

Green/blue screens are a fascinating tool used to produce our favorite films like Star Wars, Lord of the Rings, Batman, etc. They make you feel as if you're really there and the actors/actresses are actually in danger. A green screen uses one of two methods. Either a static or traveling matte. Static mattes work using a double-exposure matte. The cameraman would shoot the actors in a specific landscape. When the shot is created a piece of black paper or tape is used on the lens so the area of the top of the shot is masked out and left unexposed on the film. The scene is shot normally, but the film is exposed on only one half of the frame. The the cameraman rewinds the film in the camera, and films the top half of the shot(whatever they need it to be) They could use a computer generated top half of the film Or use a technique called optical compositing where the two scenes might be short separately on two pieces of film and then brought into the special effects department to be combined onto a third piece of film.

The scene could also use traveling mattes. This technique lets you combine two or more pieces of film into one piece that looks real. You first must film the background plate. Then you film the actor/actress preforming some sort of daring feat and behind them you would have the background screen displaying the background plate. In the special effects department you can easily use special filters to form two mattes from the shot of the actor/actress.

My favorite use of the screen is the use in action films like Batman, Die Hard, Taken, Salt, Law Abiding Citizen, etc. When the hero does a something impossible against the villain and they look as if they are even more of a hero when they complete it because it looks as if they actually did the thing. Such as when the Batman tumbler collided with the police car. A green screen was used to make it look as if there was a nasty crash in a small parking garage. This was particularly captivating because you're already on the edge of your seat rooting for Batman, and then a massive crash pulls you even further into the movie.