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; they are merely video images chroma-keyed in.

WHY USE GREEN?

Green is commonly used because it is the exact OPPOSITE color of skin tone. Then, when you remove the green, you will not remove any face along with it. Using a color opposite of skin tone gets you the best results; on a technical level, any color can be used.

If you want to green screen a little green Martian, you might want to actually do a brown screen instead.

Lime green and bright turquoise blue have been shown to function best when you are chroma-keying skin tones.

WHAT EQUIPMENT DO I NEED?

In order to do color-key, you have to have the right equipment. Generally, this would be a sophisticated video editing software program, like Final Cut. Simple, basic editing programs like Windows Movie Maker or iMovie do NOT allow you to color key.

You can also color key using a video switcher if you have a video studio.

To see a demonstration of me doing a green screen for the Stephen Colbert Show, watch this free video editing tutorial.

Green screen is very easy if you have the proper tools.

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