Why are green screens green?
In: Technology
This is what an editor dude told me it’s because the human skin don’t have that color, green and blue are the most used because of that I am sure there’s more detailed explanation and other reasons (maybe) but ELI5 easy cheese
It’s a color that stands out and isn’t usually a part of the actors wardrobe etc. so that you can tell the computer that that specific shade of green is what needs to be replaced with CGI.
In modern times it’s just because it’s the furthest away from human skin tones. Technology wise there’s nothing special about it, and it just works as a nice solid color for the computer to basically just do a “paint bucket,” style fill/erase like you would in MS paint.
[Back in the day before computers](https://youtu.be/msPCQgRPPjI) though, they would use the color blue (one of the primary colors) and run the footage through filters in order to get a black and white “matte,” they could use for blending the foreground and the background together.
You can make them any color. Blue used to be the most popular color (and still is, when green can’t be used), and yellow has also bee used in the past.
The thing is, the technology that they use for this isn’t smart enough to tell the screen apart from anything in front of it. What effects softwarw *really* does is take out everything of a particular color, which you usually set to be the color of the screen. But if anything in front of the screen is the same color, it will vanish too.
Sometimes you *want* that to happen. For example, if you’re working with puppets, you can dress the puppeteers in full-body suits the same color as the screen. Then the puppeteers will be cut out along with the background, and the puppet will look like it’s moving on its own. But if I stand in front of a blue screen wearing a blue shirt and jeans, then moat of my body will vanish and I’ll look like a floating head. That’s usually *not* what you want.
So most of the time, they pick an ugly eye-bleeding color that nobody wears, like that bright green. That way, there’a not much risk of the screen taking out things it shouldn’t. And *if* it still does, you can find another color.
The color green they use doesn’t occur often in the subject matter they shoot (film).
Modern Green screen works by keying on a specific color and then programmatically removing that color (I.e. making it transparent.)
Additionally, the color leaves an edge that blends well with whatever image they put behind the Green-Screened footage
So, they use that green because it’s rare. If they used, say a skin tone, then people would look partially transparent after the color-keying removal is done
There is a really good explanation of this by captain disillusion. This is one of his more entertaining videos in my opinion, and he goes on to cover multiple aspects of green/blue screen technology and what tools and software does in motion pictures. https://youtu.be/aO3JgPUJ6iQ
(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.
Blue used to be the go to choice and this was because on colour film (actual film) blue really stood out. Colour film was more sensitive to blue. This made the blue screen really obvious and easy to work with so you could remove it and replace it with your SFX.
Today digital cameras are normally used and they are especially good at picking up the colour green. This makes green stand out the best and so it’s easier to pick out the green screen and remove it for the SFX/CGI/whatever.
However, if you need green in your shot, say an actor’s costume, or trees, etc then a blue screen is still used. In fact, the sky is a natural blue screen and has been used in movies to add another sky.
There is another reason to choose one or the other. Because green registers so well there is a higher chance that the green screen when brightly lit will spill onto things that you don’t want to remove. For instance, actors may get a green tinge and that’ll either ruin the shot or make it a lot harder to cleanly edit.
Originally, in film days, it was blue screens that were used. This is because it was often the background like that sky that was being replaced. In film, they literally used the blue part of the film strip and replaced it with whatever they wanted to. Oh, and this required cutting things out *by hand*.
In digital, we can use whatever. You just need the colour to be nice and constant, and to be unique in the shot. Having it constant makes sure the computer can spot it all. Having it unique means the computer doesn’t start replacing things it shouldn’t. Green is a good colour to use because humans are very not green.
Not an expert but, generally green/blue screens are used in the industry. Computer softwares are designed to remove the green colors from the video/image and specifically green because we don’t have green on our skin. But in cases where we have green on our clothes, we use blue.
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