Once upon a time, to make a movie, you had to create realistic looking sets or find special places to film that looked exactly like the background you wanted for your story.
Now a technique called Chroma Keying with a green or blue screen is widely used. As a movie maker, you film live action in front of a screen of one color. Then you can take that live action and add any background you like - either still or moving, real or computer generated.
If you have seen a live action movie, you have almost certainly seen chroma keying being used. With it, you can create some very clever special effects which would not otherwise have been possible.
For example, think of Harry Potter flying around playing Quidditch on his broomstick. This picture shows how the background was added to make the actor look like he was flying high in the air. He had to act and move as though the scene was really happening, so when using a green screen the ability of the actors to look realistic is very important, even if they feel a bit silly.
Picture courtesy of @BehindScenesPic/Twitter
Here's a picture of green screen being used to make characters balance impossibly in a movie called The Matrix. You can see that the people helping the characters move are also dressed in the same colored green as the screen. They will seem to disappear when the new background is added.
Picture courtesy of @thegtd_/Twitter
Chroma keying can also be used to create smaller special effects on a traditional movie set. In the scene from Harry Potter and the Order of the Phoenix pictured below, the books magically put themselves away as Hermoine Granger holds them towards the shelves. You can see how it was done by the green hands of the crew members hidden behind the set. These hands were edited out of the final movie, creating the magic.
Picture courtesy of @BehindScenesPic/Twitter
The best way to fully appreciate work done with a green screen is to see before and after video. This video shows scenes from a movie called The Great Gatsby which was set in America in the 1920's. It shows how the movie looked when it was shot with the green screens, as well as how it looked when the backgrounds were added. It really is amazing what can be done.
Would you like to have a try at creating your own green screen special effects? You can make your own green screen quite easily using green cardboard and green tape. With Chroma Key editing software (that you can find free online) you can start making movies that you never thought would be possible. Very cool!
