Lighting a large chroma key drop is not very difficult with a little attention to detail and a few studio multi-source instruments. Chroma keying requires a lot of work and practice to achieve believable results, but the effort is rewarding. With a fundamental chroma key technique and proper lighting, you will stand a much better chance of getting the shot you want.
Lighting the Background
Successful chroma keying requires a lot of light for an even glow the blue screen with absolutely no shadows. Start with two large lights, such as 650 ARRI'S. Set them up high enough on either side of the screen so they cannot interfere too much with the subject.
This setup can remain fairly constant from shoot to shoot; you can find a set up you like and use it every time you have a chroma key shoot. Factors such as interference from foreground lights can cause problems with this lighting, but these adjustments can be fixed easily.
When setting up lights, also consider the reflection of your blue screen. Too much light can cause color bleeding, which occurs when the blue background reflects onto the subject. The easiest way to reduce the reflective properties of the blue screen is by diffusing lights with amber gels.
Lighting the Foreground
Lighting the subject properly can make the difference between a seemingly natural or artificial shot. Once your subject is positioned, place the key light. Know what your planned background will be, including the direction of the principal light. The shadows in the background image and the key light on the subject must correspond.
Also, maintain the separation of the subject lighting and background lighting. Just as key light cannot interfere with blue screen lighting, backdrop lighting cannot interfere with the foreground shot. This can be accomplished by first moving the subject away from the background. Start at least three feet away, and try to create as much distance as possible between the background and blue screen.
Now incorporate the most crucial elements: a back light and a kicker. As they would in a normal shot, these help separate the subject from the background and bring out the detail that may be lost otherwise. They also serve the additional function of minimizing spill.
The most effective way to learn about chroma key is through experimentation. After finding your ideal setup, begin rearranging and readjusting. Try different lights, bounce cards and gels. Play with the key light and background light to come up with new or interesting combinations. Above all, develop a foundation of patience and preciseness.
Contributed by: Mike Karmolinski, Director of Photography, Metro Productions