How does a green screen work, and why is it green? Those are two very basic questions with both short and long answers. Whether you work in photography or video production, it pays to have a green screen. You can either have one painted on your studio wall, or have a portable green screen kit stored and ready to use for smaller-scale shoots. Beyond being useful in producing special effects and other eye-catching tricks in your videos and photos, green screens can serve other purposes as well. Here’s a selection of tips and trivia that will help you better understand why you need a green screen in your professional life.
It’s Easy Being Green
Let’s address the second question first. Why are green screens green? The answer is so simple it might surprise you. At base, the reason green screens are green is because human beings aren’t green. Green is a tone that rarely turns up in a human being’s skin, outside of the metaphorical “looking a little green” when people are feeling nauseated. That leaves a lot of freedom to replace the bright green of the screen with, well, just about anything. Blue screens are also available, and other neutral colors like white, grey, and black can also be employed. But a green screen is both handy and accommodating. Unless your talent shows up in a green suit and has green hair, it’s unlikely anything they wear will interfere with the green screen effect. That’s why green screens are green; now, here’s the why of how it all works.
The green screen process goes by a more technical term: chroma key. Chroma key is short for chroma key compositing, which involves the layering (or compositing) of two images of videos based on color. Chroma key is a function of digital cameras and editing software that allows you to remove a color—in this case, green—and replace it with anything you imagine. If you want to make a subject look as big as a giant or as small as an ant or have rocket ships and unicorns flying in the background, the green screen allows it. It can also perform more practical and sensible effects like embedding branding information or providing text and visual information like an electronic billboard. While that’s all fine and dandy, there’s more to it than just that.
Going Green Pre-Production
Chroma key requires work on both ends of the production process. As mentioned, you can paint a wall with chroma-key paint or set up a portable green screen kit behind your subject or talent. But that’s not all you need to do. Lighting is especially important to the green screen process. The screen must be evenly lit so there are no shadows or hotspots that can interfere with drawing a proper key. If the screen isn’t well lit, then you run the possibility of shooting poor footage that looks spotty. Once it reaches the post-production process, you may have footage that looks spotty or dim and fails to embed the new footage. People can see what’s behind (or in this case before) the curtain, revealing how the green screen “magic” happens. Positioning of the subject or talent is also important, since either can cast shadows, move improperly, or engage in other actions that can interfere with drawing a good key.
Post-production is what happens after the cameras are shut off and the set is put away. This phase involves the technical aspects of chroma keying, when the digital “film” of the shoot is run through the software. The production equipment looks at the video as a series of electronic signals, especially the coding that covers color, and as such can alter them. You may be familiar with the term pixel, referring to a point illuminated on a digital screen. Now, imagine a page filled with thousands of dots, and it’s your job to fill in all the green ones with another color or colors until a different image appears. In simplest terms, that’s how chroma key works. It also explains why green clothes are forbidden during green screen productions, because the green in the clothing will be replaced with the new image.
While post-production is technically a time to correct mistakes made during the shoot, you should keep in mind that a bad shoot makes the post-production team’s job more difficult. Not only that, but it will also likely cost more if you use an outside production company in terms of money and time, as well as to fix mistakes in lighting.
How Green Was My Screen?
If you’re pondering the question, “How does a green screen work and why is it green?” it’s important to know that green screens come in all shapes, sizes, and materials. As mentioned, a green screen can be painted, or it can be a piece of fabric. Professionally-made green screens tend to be made of spandex or similar stretchy material that aids in preventing shadows. However, a piece of felt or similar material colored the same brilliant an eye-catching green may do as well. But again, the surface of the fabric needs to be free from wrinkles, holes, and the like. Otherwise, drawing a key will be a fruitless exercise.
Paints that provide the proper green are also available, but you will need to choose your wall carefully. Pitted and otherwise uneven surfaces will make it impossible to light the wall well enough to avoid shadows. Stick with a flat surface, or even better, with a cyclorama wall setup. Cycloramas are slightly curved to give the impression of a much larger room when you zoom in. They’re also perfect for covering with chroma-key paint, as they show none of the imperfections of other types of walls.
Lean Green Screen Machine!
Is a green screen a good investment for a fledgling video producer? Even if you start out small with a portable green screen kit, it will help enhance and add excitement to your commercials, presentations, interviews, conferences, and more. Green screens not only help you think outside the box, but they can also take you out of the boring “box” formed by a TV or computer screen!