Green screen is a video special effect that allows you to place your subject in any location you have a visual for. If you have a still picture of Mars, then you can put your subject on Mars using green screen without leaving Earth. (Or even leaving your living room.)

Green Screen is a nick name; the technique is actually called CHROMA KEY. Chroma means color. In video, to “key” is to put two separate images together. So chroma key literally means to replace any one color in your image with a different image.

In other words, you take your subject and video them in front of a lime green background. Then, you can take out the lime green background and replace it with anything you want, a picture of Mars for example. This makes it look as if your subject was originally photographed with Mars in the background.

You see green screen on TV all the time. The most common example of green screen is the weather report. The weather-guesser stands in front of a lime green background and the different weather maps are chroma-keyed in behind him. This way, the weather-guesser looks like he is in front of a US map one second and a local map the next second. In reality, he is in front of neither; he is is front of a lime green background and the maps are merely video images chroma-keyed in.