The foundational elements for shooting all green screen setups are the materials used and the lighting of the background and the foreground subjects, including how these elements are positioned in relation to each other. Using the right combination of background materials, lighting, and positioning will save you hours of time during the keying or matte extraction process. The information in the book, The Green Screen Handbook: Real-World Production Techniques, 2nd Edition from which this excerpt was taken from, will guide you through these processes in various situations and production circumstances; but the basics, covered below, are always much the same.
Basic Setups for Shooting Green Screen
You first need to understand the various setups required for the kind of keying you’re going to do. For example, if you’re doing a straight head shot or upper-torso shot of an actor that will get keyed out, then you don’t need to worry about covering and lighting the floor in your green screen studio. If your actor will come in contact with the green background, then you need to approach the lighting entirely differently.
To grasp the basic concept of shooting green screen video, you must first understand how the camera sees the different elements in the shot. The green background must be evenly lit, or shadowed areas will be harder to key out. This is especially true for backgrounds behind fine hair or transparent items such as glass or liquids. The subject you’re keying out needs to be far away from the green screen so you don’t get spill from the reflective light off the screen onto your subject. In addition, the subject in the foreground must be lit separately so you have control over the exposure and direction of the light source(s) you require for your scene.
The diagram above shows a starting setup for a project when you’re trying to get a clean key with no shadows or interaction with the green screen. Of course, you need to add more lights if you can’t get sufficient coverage on the screen or if you need to create a specific lighting of your subject to match the background onto which you’re compositing.
Notice that two lights are dedicated to lighting the green screen in this example setup. If you’re using four-bank Kino Flo fluorescent lights (www.kinoflo.com), such as the Diva 400s (or equivalent), you should have enough coverage for a standard 10 x 10 background screen, provided you can move your subject a minimum of 8 feet away from the screen to avoid reflective spill off the brightly lit screen. Some setups even use green colored bulbs to control the color temperature of the screen and reduce the amount of light needed to illuminate the backdrop, thus making it possible to get the subject even closer to the screen if there’s no green light spill from the lights.
You use model lights to light your subject. These are the same as typical lighting used in still photography or video interviews. The three essential lights are the key light, the fill light, and the back light. If you’re doing simple interviews or a talking-head shot in a studio, the layout of these three lights as shown in the image above, will probably be sufficient and pleasing to the viewer, because it’s most flattering for your model or subject.
The key light is your main light. This is the predominant light source on your model and should be positioned to match the direction of the strongest light source in the background to which you’re compositing. For instance, if your subject will be composited into an outdoor scene with strong sunlight, you need to match your key light to the direction the sun is shining in your background footage. Matching the color temperature and intensity is equally important. If you’re compositing your subject onto a scene that’s supposed to be under a streetlamp on a dark corner, then the same concepts apply, but the direction and intensity of the light source should be much different. For instance, the subject in the below image appears to be underlit until you see the environment she is to be composited into. The key light source was positioned above and to the right to match the spot light at the bar.
The fill light is just as its name suggests: it fills in light throughout the scene. The position and intensity of this light (or several lights) give the illusion of creating available ambient light in a scene. To use the previous examples, a bright outdoor setting requires much more fill light than a dark scene under a streetlamp. Matching color temperature is equally important in the fill light and can be controlled with colored gels. You may opt for several fill lights, silks and or reflectors to achieve the proper lighting of your subject to match the final background plate you’ll be compositing onto.
The back light is mostly used for studio settings; it creates a soft halo effect on the subject’s hair. This gives a bit more definition from the background but isn’t necessarily good for compositing into a background scene where you need to match lighting. In that case, you should have several fill lights to help provide even lighting.
In any case, be sure your subject is far enough from the green screen and the screen lights so that you have the most control over your foreground lighting and to avoid spill as much as possible. Below shows a couple different live green screen setups using both Kino Flo fluorescent lighting and Fiilex Spectral LED lights (www.fi ilex.com).
Another popular, simple setup uses the model lights to light both the screen and the subject. The subject is close to the screen and the key light is predominantly strong, causing a shadow on the back wall. To compensate for the reflective spill, side spill suppressor lights on either side of the subject warm up and wash out the spill, creating a clean key in the studio (below).
This setup is most popular for the purpose of interacting with the back wall surface, such as live TV weather forecasters who make contact with the screen and want to retain shadows on the wall (see below).
Directors may use a blue screen in this case if they want subtle shadows and aren’t worried about reflective spill. Note that your lighting may not be as even in this setup, because you use the available model lights to illuminate both the background and the foreground elements.
Yet another technique used in some larger green screen stages where the actors are on the green surface with a cyc wall, is to use what’s referred to as a “China Ball” light that is a large diffused light source that doesn’t cast heavy shadows. An example below shows several China Ball lights on a set, along with some large silks that help illuminate a big area. There are several DIY China Ball light videos you can explore on YouTube.
Excerpt from The Green Screen Handbook: Real-World The Green Screen Handbook:Real-World Production Techniques, 2nd Edition Techniques, 2nd Edition by Jeff Foster ©2015 Taylor and Francis Group. All Rights Reserved.