Green Screen Technology

Green Screening is a simple term for a technique called Chroma key compositing, or chroma keying. This  is a visual effects / post-production technique for layering two images or video streams together based on color hues (chroma range). The technique has been used heavily in many fields to remove a background from the subject of a photo or video – particularly the newscasting, motion picture and video game industries. A color range in the foreground footage is made transparent, allowing separately filmed background footage or a static image to be inserted into the scene. The chroma keying technique is commonly used in video production and post-production. Chroma keying can be done with backgrounds of any color that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from most human skin colors. No part of the subject being filmed or photographed may duplicate the color used as the backing.
Adapted from https://en.wikipedia.org/wiki/Chroma_key

Chroma Key (Wikipedia)

How does green screen work?
A comprehensive guide, with videos, on how green screening works

How does a green screen work? (Wonderopolis)

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