What is a Green Screen and how can I use one?

Known as “chroma keying”, green screens allow filmmakers to place their subject in outer space, in front of a weather forecast, or anywhere else that they can dream up. Today, the effect is widespread in movies, TV news broadcasts, sports commentary, and videogames. With a colored sheet, some well-placed lighting, and a laptop, anyone can harness this technique for their next production.


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How does a green screen work?
The reason behind the name “chroma keying” is simple, but brilliant. In video editing software, you can select a particular color (or “key”) and it will be removed from your footage. Then, you can replace that color with another layer of video. When done right, it can simulate a realistic backdrop and make your actors look like they’re in another world. 
 
Are they always green?
Technically, the chroma key process can be done with any color background, but bright green and blue are the most popular. Since these colors are totally distinct from a human’s skin tone, there is little risk that body parts will be cropped (or “keyed”) out. Digital video cameras are also sensitive to green, so less editing and lighting prowess is needed for a clean key. On the other hand, blue screens are better suited for film cameras, because the film’s negative can be limited to the blue channel. This results in a clear background, which can then be copied onto another negative to achieve the final effect.
 
Blue and green may get all the credit, but colors like magenta and red have also been used to make objects disappear or replace a background.  
 
Who invented the technology?
Developed in the 1930s, RKO Pictures first used blue screens to create elaborate transitions, such as a windshield wiper that actually wiped away a previous scene. By 1940, blue screen technology was being used for visual effects in film storylines. These early forays in chroma keying had far more limitations than the green screens we see today. At the beginning, cameras needed to be stationary for the effect to work, and actors couldn’t shift their perspective either.
 
By the 1980s, computers had advanced enough that they could control the optical printing process needed to combine actors and background images. Today, it can be done with a laptop at the push of a button, and sites like Shutterstock allow moviemakers to add green-screened visuals to their work without recording a single frame. Elephants, airplanes, and giant crowds can be dropped into a scene, instantly.
 
How can I use a green screen in my next production?
Here’s what you’ll need to get started:

  1. Background: There are plenty of ways to build a suitable backdrop for chroma keying. Don’t be afraid to take a trip to a local hobby shop and see if they have brightly colored fabric. You can also buy some green paint at the hardware store, if you have smooth walls or paneling in your studio. As long as the background fills your entire camera frame and doesn’t cast shadows, you’re good to go.

  2. Proper Lighting: Apart from your screen, good lighting is the most essential element in creating a believable effect. Using soft light, you should spread it evenly across the background, while lighting your subject separately to minimize shadows and reflections. To help with this process, move your subject a few feet in front of the screen and then light them using a three-point system (i.e. two angled lights on either side, forming a triangle with the subject).

  3. Tripod: Motion tracking software is out of reach for most indie filmmakers, so your best bet is to lock the camera down. Even the slightest jiggle of the camera can cause your subject to “bounce” in their green-screened background, so just press record and step away.

  4. Video Editing Software: If you’ve handled the first three steps well, keying the background should be easy. First, import your green screen clips into the software, place a background visual on a second track, and then turn on the chromakey filter. If there’s still a bit of visible green or graininess, you can adjust the color settings further. 

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