In today's technologically advanced world, if you have the dream, the drive and a green screen, anything is possible. You want to deliver a Shakespearean monologue in Paris while monsters are attacking the city? Easy.
Green screen, or “chroma key compositing,” is a popular special-effects technique used to strip the background of a subject on video or film and replace it with another. The effect is achieved by filming a subject in front of a uniformly colored background that editing software can recognize and remove, allowing editors to slide in a different background.
One of the simplest and most common examples of green-screen effects is your local TV news weather report. The weatherperson is not actually delivering the forecast in front of a large map of the country or region. They're actually standing in front of a blank green screen and waving their hands at nothing.
Whether you're an actor, a filmmaker, or a broadcaster, you can use green screen effects to make magic onscreen—easily and inexpensively. Here are a few tips to help you get started.
1. Find a suitable space to shoot. You will need a bit of space to set up a studio. To maximize the effect, the subject you are shooting should be at least a few feet away from the green-screen background. The green screen also needs to be flat and well lit, so there should be space for lights and rigging.
2. Choose a background. Why does it have to be green? Because green is one of the cool colors on the spectrum most distinct from the warm hues of human skin. Technically, you can use any color (blue screens are also fairly common) so long as that color contrasts with the color of the subject you are filming. If it doesn't completely contrast, the subject will “disappear.” (That's how floating heads are possible!)
You can set up a green background easily using green poster board and clear tape or green paint on a flat surface like a wall or table. If you are willing to spend a little more money, you can buy professional grade green screens made of paper or cloth and rigging to set them up.
3. Dress the subject. Again, the subject has to be distinct from the green background or it will disappear. Actors should dress in warm colors (reds, oranges, yellows, browns, pinks and reddish purples). Avoid any shades of green, and try to avoid blue and bluish purple outfits if possible.
4. Lights! To get the best results in post-production, your green screen has to be uniformly lit. This helps to distinguish it more clearly from the subject, so your editing software won't get confused. If there's too little separation, the subject can appear blurred and the effect can look fake. You'll need at least two lights aimed at and positioned evenly on either side of the background. More is better, so if you have access to more lights, use two, lower-wattage lights positioned on the floor, one aimed up at the green screen and one backlighting your subject from the top. And don't forget to light your subject from the front and/or side with a separate light(s) as well!
5. Post-Production. This is where the magic happens. The keystrokes to accomplish the chroma key effect will vary depending on the editing software you use, but the basic principal is to use the program's chroma key function to strip everything in the footage that matches the green color of the background. Then, layer the desired background image or video underneath your footage of the subject.
Once you're satisfied with how it looks (you can play with color correction in your editing software), compress and export your clip. Then, prepare to wow viewers with your fantastic special effects!