At its most basic level, a green screen is a tool utilized by media content creators to remove the background of video content. Then, depending on the content being created, the background is either replaced with CG (Computer Graphics) or some other form of media. This is the modern use case of a green screen, but its origins are far more humble.
Sometimes this tool is referred to as a Chromakey filter, and the reason for this is that you aren’t restricted to using the color green. It can really be any color you want, but the two most commonly used colors are green and blue. I’ll explain in more detail below why if you’re curious, but I want to tell you a little bit about the history of how green screens came to be.
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A Brief History of the Origin of Green Screens
The first use of a green screen in film-making was “The Great Train Robbery“, created in 1903 to superimpose a clip of a moving train over a window to make it look like it was leaving the station.
However, the screen used back then was nothing more than a black cloth. See, background removal back then was accomplished using a very different technique. Rather than having a digital processor pick out everything that matched a certain color, people had to be creative. After all, it was only recently that technology had advanced to a point where the modern chromakey filter became possible.
The effect was accomplished by cranking the contrast way up to cause the black cloth to “Virtually Disappear.” Then, the editor overlayed a second layer of film and exposed the film to introduce the desired picture-in-picture effect.
Of course, there are imperfections with this method, which resulted in easily noticeable artifacts on the screen, particularly in the area that had the film overlaid. The screenshot shows a few of those imperfections, and I’ve pointed them out for you.
Alas, the goal of this article isn’t the history of a Green screen and its origins. For that, you can learn more about the history of green screen technology from “The Evolution of Green Screens“.
Not Just Green – Other Colors Work Too!
Despite the word “green” being in the name, the screen doesn’t actually have to be green – it can also be blue, magenta, or really any other color you like.
However, since human skin contains a lot of red, that isn’t a very popular key color. As a result, it can be difficult to find – you may need to look into something like a red presentation board rather than something designed for chromakey purposes.
Green is simply the most common type of Chromakey screen. This is due to the fact that blue screens, the other popular chromakey alternative, require better lighting to achieve a comparable result. The reason for this tidbit is that camera sensors are more sensitive to green than blue and red, thanks to the Bayer Array utilized to create color images.
Why You Might Use Different Color Green Screens
As to why you would want a different color chromakey surface, that has to do with your actors. For example, if you have actors with blue eyes, a green screen is a good choice, and blue is a poor one.
However, if you have actors who have green eyes, their eyes might actually get keyed out with a green room. These days, fixing the eyes being removed is somewhat easy to accomplish in the editing process, but if you had a lot of green vegetation props, it would be a good idea to utilize a blue screen instead to minimize editing work.
The Modern Approach: Traditional Green Screens VS. AI Background Removal
Traditionally, a green screen is an actual physical medium that has a unified color across its surface, but there have been fairly recent technological advancements that allow image processing and AI to work together to “key out” (remove) the backgrounds. These processing methods are, however, significantly less effective than their physical counterparts, and often remove foreground elements that you actually want in addition to the background elements.
A good example of this is the NVIDIA Broadcast app for those of you who own an RTX 2000+ series video card, which actually does a decent job of removing the background elements without the assistance of a green screen. Again, the removal process is an imperfect one, and you will find that with poor lighting of your subject, the errors in the key will be more pronounced on the digital processing removal vs a physical green screen.
However, for low-budget or amateur production in tight recording conditions, it can be a useful tool to utilize.
Programs that Can Make Use of a Green Screen
The next step is to find computer software that is able to implement the chromakey filter. Traditionally, this is accomplished using video editing software, such as Adobe Premiere Pro. However, some programs that have a focus on creating live content (like OBS Studio) allow you to take advantage of this feature for live productions.