Chroma-key photography or video uses a solid background, usually green, as a backdrop. In postproduction -- the processing of the digital files after the shooting -- the backdrop is replaced with another image. This creates an image in which it appears the main subjects are in front of a setting instead of a green screen. Proper lighting is critical to make the illusion work.
Background lighting
The most important technique of chroma-key lighting is balanced lighting of the background. Any variation in light intensity can keep the postproduction software from recognizing the background. The chroma-key background also should be brightly lit in order for the cameral to register the color accurately. Start with two large lights, one on each side of the set. Check for bright or hot spots on the chroma-key backdrop. Take test shots, if the lights are too bright, the backdrop may appear white.
Subject Lighting
Place lights aimed at the subjects high enough so that shadows do not fall from them on the chroma-key background. Check the color cast of the subjects. A green cast usually mean the subject is too close to the backdrop and the reflected light is coloring the subject. Additional lighting techniques include adding an orange filter on the lights pointed at the subject to counteract the green reflection.
Diffusing Lights
Hot spots on the backdrop can be created by either the backdrop lighting or the subject lighting. In either case, placing diffusers on the lights will spread the light over a wider area and reduces the hot spots. Commercial diffusers, such as soft boxes, are available but the same thing can be accomplished by placing bubble wrap over the lights.
Tags: chroma-key background