If you’ve watched any behind-the-scenes videos of superhero or sci-fi films, you’ve likely seen actors working in front of a large green backdrop called a green screen. It was maybe being used to set the characters in space or a fantastical location, but green screens can also be used for places that exist in our world. Maybe you don’t have access to a particular location or it’s not a practical setting for filming so it’s easier to film the actors in a controlled studio and add the background afterward.
For example, instead of filming these two in an actual cabin in front of a fire, we placed a green screen behind them and added the setting after. We filmed the backdrop separately so we didn’t have to bring the two subjects five hours north to the location.
So how do green screens actually work?
If you’ve ever used a “remove background” function on a photo, you’ll understand the helpfulness of a green screen. If there’s a tree in the background, the program may think that’s a part of your clothing and not know to remove that. So you end up with a tree sticking out of your head. Or it removes half of your hair, thinking that’s a part of the background, and you have a slice taken out of you. Imagine then if you and the background were moving, how hard it would be for the program to recognize what is the background and what is the intended object in the foreground.
The green screen is what helps differentiate what to keep and what to remove.
Chroma keying is the technical term for removing the backdrop in post-production. Essentially you’re telling your computer to remove anything green and replace it with transparency. Then all you’re left with is your actor or object to place in front of whatever background you require.
In theory, any colour backdrop will work, as long as it is very different from your subject. Otherwise, your computer program will have a hard time differentiating the subject from the background and may turn the wrong parts transparent. This is why green has become a standard. It is the furthest away from human skin tones and therefore runs the least risk of error. Just make sure you don’t wear anything green or that part of you will disappear too!
Green screens are used every day in news stations, weather forecasts, commercials, content creation and of course the film industry.