We look at green screen technology almost everyday without realizing it. From weather reports to movie trailers, green screen technology has become so synonymous with digital video that we accept it without question. Most of us probably have a much better understanding of how Photoshop works, but it’s worth knowing a few facts about the technology that led to Photoshop in the first place.
Green screen technology, or “chroma-keying”, has been around in one form or another since the 1940s, and was actually invented to create the PowerPoint-like “wipe” transitions in movies made during the Golden Age of Hollywood. Eventually the technology became sophisticated enough to replace the background behind an actor entirely, and modern green screens were born.
The way chroma-keying works is actually very simple in theory. The monocolor (i.e. “chroma”) of the background is erased in a computer program like Adobe After Effects or Final Cut Pro and replaced with another image or video (think weather maps). Of course, there’s a caveat – the targeted color will be erased entirely. That’s why you never see weathermen wearing green…except for that one guy who didn’t get the memo.
This begs the question of how to “greenscreen” anyone who happens to be wearing green. Let’s say you wanted to make Godzilla trample through NYC. Would you be out of luck?
Not exactly. Chroma-keying can be done with any color as the backdrop, but green is the safest choice because it isn’t found in human skin tones. In fact, blue used to be the color of choice until it was largely phased out by green after digital keying became commonplace. Video resolution is highest in the green channel, and green backdrops require less lighting than blue ones due to the human eye’s natural sensitivity to green. But blue backdrops still have their place in certain productions because blue is furthest from the predominant pigment in human skin: red.
So, now we know why everyone uses green. But how do you actually shoot footage of a green screen? What, exactly, is the green screen even made of?
The answer may disappoint you. There’s nothing special about the green background at all – it can be as simple as a piece of fabric from Walmart. The challenge is to make sure that piece of green fabric is evenly lit. Shadows and hot spots will distort the even tone and cause unwanted problems when keying to transparency in production software.
The best way to make sure the green screen is evenly lit is with 3 lights set 45 degrees apart from one another in front of the subject. Another important consideration? Making sure the primary actor or subject is no more than 3 inches from the background. Anything more than that is going to result in unwanted shadows.
Understanding how green screen technology works is important because Hollywood makes it seem so inaccessible. Really, nothing could be further from the truth. If you understand the concept of “layers” and know your way around Photoshop, you can easily pick up green screen technology and post-production software.
Moral of the story? Keep chroma-keying in mind the next time you feel like shooting a video. Imagine the possibilities.