You’ve probably seen a lot of those funny green screen behind the scenes pictures of Daenerys Targaryan riding a green machine, instead of a badass dragon, or Gandalf standing in front of a green screen instead of a breathtaking out-of-this-world waterfall. Well, yes, a lot of our dear movie scenes have been shot in a studio in front of a green screen and the process is called Chroma Keying. In this process, the green colour captured by the camera can be completely removed by a video editing program thus making space for any kind of background you’d want. Now, the question is, why is green preferred on these occasions? Let’s find out!
Why are green screens green?
Green screens are green because people are not, modern digital cameras are more sensitive to green than to any other color and also green is an uncommon clothing color and thus prevents any Chrome Keying errors. However, green screens don’t actually need to be green. The idea is that in video editing, there is a tool called Chrome Key which enables you to remove any color you’d like. Green is preferred because it’s the exact opposite of our skin tone and it makes it all much easier. Also, blue can be used as well since it also resides on the opposite side of the color spectrum than our skin color.
However, the process can be performed with any color. The most important thing that that color does not resemble your skin tone because if that happens, your skin would just disappear in the video background. So, actors, newscasters or weathermen really need to be careful what color their outfit is or otherwise, they can disappear in the background. In the post-production process, the green colors are filtered out of the video so if your shoes are green, then you would no longer have feet in the final video if you know what I’m saying. If your t-shirt has a few green dots on it, you might appear like having holes in yourself on the final videos. Yes, it might sound morbid, but this can happen if you don’t play right with Chroma Keying.
Green Screens were originally blue
Well, yes and there still are some blue screens today as well. They serve the same purpose as green screens. Blue and green are really opposite colors to our skin tone. Chroma Keying was first used in 1940 by Larry Butler in the movie “The Thief of Baghdad” and he actually won an Academy Award for special effects for that. However, it seems green has become more common these days. Maybe it’s because people don’t usually wear green clothes, while green shirts, t-shirts are everywhere out there. Well, maybe except for the Queen of England. Remember that Chrome Key green suit she wore? Everybody tried their hands at changing the green color with something more…poetic.
Cameras mimic the human eye.
First of all, from a color science perspective, our skin is orange. Ok, having said that, let’s move on to how the human eye perceives color. We have three types of color-sensitive cells in the retinas of our eyes, they can recept red, green and blue. Sometimes their sensitivities overlap and we get to see yellow, blue-ish, green and blue. And since cameras were made by the human eye, they can also detect red, green and blue as the primary colors. Furthermore, our eyes do not only perceive these colors, but also their brightness and other colors. Most video cameras convert these inputs into separate background and color information called luma and chroma. Luma is the brightness, while chroma is a saturation color circle.
Digital TVs today still encode luma and chroma separately, as did the “ancient” black and white TVs and this enables us to play tricks with green screens. The Chroma Key tool analyzes the whole chroma data and recognizes the pixels centered on the green hue, then replaces them with pixels from the desired background, like a weather map or something more complicated, like a dragon.
So, the bottom line is, green is a color very far-away from our skin color and that helps with removing it without any damage to our “bodies” on the video recording. And that is really cool!