Chroma Key/Green Screen Tutorial
Posted by: San Francisco Film Society
Chroma keying is a special effects/post-production technique for layering two images or video streams together based on color hues. Mainly used in newscasting, chroma key is also used in the motion picture and videogame industry to remove a background from the subject of a photo or video by making the color range transparent and revealing another image.
The principal subject is filmed or photographed against a background consisting of a single color or a relatively narrow range of colors (like a “green screen”). While any color with a uniform hue can be used, chroma key usually entails using blue or green screens because these colors are considered to be the furthest away from human skin tones.
A chroma key subject must avoid wearing clothes which are similar in color to the chroma key color, because the clothing may be replaced with the background video. An intentional use of this common mistake is the filming of Harry Potter’s invisibility cloak.
Today, chroma key is easy to use in your own classroom. Just set up a backdrop made of green or blue paper, and get to work! Thanks to tools like iMovie, FinalCut Pro, and Adobe After Effects, anyone can use green screen technology to make more complex films easily and cheaply.