Setting up a green screen for chroma-keying

If you're new to working with chroma-keyed shots, understand that having a proper "green screen" setup, especially one with even lighting, is the best thing that you can do for professional-looking results (not to mention the fewest post-production fixes later).

Generally, these things are most critical:

• Choosing the proper background material: You need a background texture that works with your lighting efforts—not against them. A matte surface is best.
• Creating smooth, even lighting: Providing smooth, even lighting for the shot's background is the most important thing that you can do—although even lighting doesn't necessarily mean bright lighting.
• Minimizing problems with your subject: Avoiding and/or eliminating certain problem areas with your subject during production is far better than spending time on post-production fixes later (assuming the problems can be fixed).
• Choosing the shot's action carefully: In some cases it's best to plan out the actor/subject's movement ahead of time.

Here's more information about these key points.

CHOOSING A PROPER BACKGROUND MATERIAL

Your choice of background material can either help you—or add considerably to your headaches.

Choose a background image color that isn't present in your actor/subject, unless you're trying for a special effect. For example, bright green is often chosen because it's a color that doesn't appear naturally on people, thereby minimizing the chance of chroma-key color conflicts. A blue screen could cause overrun of the chroma-keyed image if, for example, your human subject has blue eyes. On the other hand, if your primary image includes plant with bright green leaves, then a blue background might be a better choice. The color choice depends on your shot's needs.

The surface itself should be as smooth as possible and have a matte finish, rather than a glossy one.

A common choice for green screen use is a painted wall. If the surface has a flat luster and is smooth (such as wallboard instead of plaster, which can be uneven) then it could work well. If you want to create a painted background for regular use, there are paints available that are formulated for chroma-key background surfaces.

Many creators like to work with backgrounds made from foam fabric, which is light absorbent and eliminates reflections. Felt-type fabric can work too, although it can sometimes be tough to get it completely smooth and wrinkle-free (which is essential).

Paper backgrounds can work as long as the finish is matte, and not shiny in any way.

CREATING SMOOTH, EVEN LIGHTING

This is one of the most important areas for you to focus on. For the chroma-keying process to work smoothly, SlingStudio Console needs a background with color that is as even as possible—otherwise you might have to lose some portions of the background by trying to smooth out lighting imperfections. In the long run, it's much easier to spend some time getting the lighting right while you can ... not after the shooting is done.

Darker or lighter areas on the background surface can appear to SlingStudio Console as different colors (colors other than the one you've chosen as a chroma-key color). This can cause the chroma-key feature to refuse to apply the secondary image to these lighter or darker areas. You then have to do a lot of tweaking and adjusting to get a satisfactory image (and you may not entirely succeed).

It's much better to spend the time necessary to create an evenly and softly-lighted background. Many successful video creators employ as many as five or six lights when they're using a chroma-keyed shot:

• Two, or even three soft, evenly-distributed lights for the green screen in the background.
• Backlight ("hair light") for the actor/subject, diffused for best results.
• Key (main) light on actor/subject, diffused for best results.
• Fill light on actor/subject, to balance the key light—but also allow for a bit of contrast on the actor/subject.

IMPORTANT: While a number of lights are used, note that you don't want bright lighting—you want even lighting. Avoid overlighting the set; less light can be better than more light, as long as it's even. If possible, the background should be slightly darker than the actor/subject.

MINIMIZING PROBLEMS WITH YOUR SUBJECT

Look out for these potential problems when you're planning your shot, as well as when you're actually setting it up. It's much easier to fix these things during production than afterward:

• Shadows—Since even lighting on the background is critical, it's very important to avoid having your actor/subject throw shadows onto the green screen. Try moving your subject further away from the background, even as far as 8 to 10 feet. If you can't manage that, then do the best that you can. The farther your actor/subject is from the background, the better effect you'll get from having the background a bit darker.
• Reflections—Reflections from shiny or metallic objects are a real potential difficulty, even without chroma-keying. With it, they could ruin the effect. Try to spot such items (clothing, jewelry, wristwatches, eyeglasses, etc.) ahead of time.
• Hair—The upper outline of a subject's head can present a real problem. That's because certain types of hair create fine outlines that don't chroma-key well (especially if the hair is lighter in color). Just be aware of this situation and look out for it.

CHOOSING THE SHOT'S ACTION CAREFULLY

This may seem obvious, but it's still something to bear in mind: If your subject/actor somehow manages to move outside of the green screen, the shot is likely ruined. This kind of error cannot be fixed.

So it pays to do a dry run ahead of time, planning out any movements (and limits to movement) to avoid this kind of problem.