Why are green screens green?
In: Technology
(This is going to be a gross oversimplification, so feel free to correct me or add more detail)
In olden days, when you wanted to do bluscreen effects, like in Star Wars, you’d shoot the model in black and white with a blue filter, then a red. Combined, it would have a dark spot in the middle in the exact shape of your blue screened subject. Then you put the footage of the actor/object/whatever underneath those layers, and he shows up through the black silhouette. Do the opposite for the footage in the background. This is why with older movies you can often see a black outline around a subject, where the matte is either slightly off or there was a bit of light bleed. Or the film grain doesn’t match up. There’s a bunch of reasons. But it’s all done so you have a single piece of film combined from multiple elements.
So, blue and green were chosen because they were each one of the three colors that made up a color print.
The reason still holds up today. Red Green and Blue are still the colors we use to make images on most of our screens, and they’re the channels most cameras record. So it’s easy to tell a computer to cut out anything on those channels, provided the subject isn’t one of those colors.
Also, fun fact, the moving ships in Star Wars aren’t actually moving. They’re fixed, stationary, and the camera moves around them and films them against the bluescreens. When comped against a moving background element, it gives the illusion of a moving object. It’s the first example of motion controlled cameras used in compositing, and let them have movement in the scene instead of a locked off camera and background.
If you ever want to learn about an even more insane type of this technique, look up sodium vapor process/’yellow’ screen. It’s magical.
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