Tuesday, April 26, 2011

Green Screen For Photographers

Chris Borgman is a New York-based photographer with a knack for crafting wild and whimsical images.
By William Sawalich, Photography By Chris Borgman Published in Shooting
"What's the difference between masking and keying? Think of it this way: You mask the background, and key the subject. The same thing is happening in both instances; it's just semantics, I guess."
"What's the difference between masking and keying? Think of it this way: You mask the background, and key the subject. The same thing is happening in both instances; it's just semantics, I guess."

"When someone says, 'We're gonna green-screen it,' when referring to a still shoot, they're just saying, 'We're gonna mask out the studio background and drop in something else.'"

"When chroma-keying video," Borgman says, "the use of green, and previously blue, is for the simple reason that most people never wear those exact colors, and programs like Final Cut and After Effects know exactly what they are. But a still photographer using Photoshop can use any color. I try to use a background that closely matches the image I'm dropping in. In a shoot I did for Lipton Tea, I used gray on the floor and blue on the background. I used gray because I was going to create a stone patio, and when models or props are close to the seamless paper, gray neutralizes the color spill. Although it's what I use, chroma seamless paper isn't ideal for true plug-in-driven masking. Fabric and paint do a much better job. Paper actually reflects colored light back onto your subject—aka color spill. Fabric and paint help to absorb the spill."

Once the studio is prepped appropriately, it's time to light. Borgman approximates lighting type and direction to match a background image, but he doesn't have to limit the way he lights the subject. Hard or soft light, flat or directional, the quality of light on the subject doesn't really matter. What does matter is the separation between subject and background. Cross-contamination won't work.

"The lighting is simple," Borgman says, "but you need more room. You have to light the background separately and evenly, no matter what light is on your subject. Shadows on your background will create difficulties for the masking program. It's a good idea to place large pieces of foam core between your background lights and your subject, just to make sure there's no unwanted light. And the farther away your subject is from the background, the better. It lessens the chance of color spill and further separates the two different lightings."

Aside from more studio space to create separation, Borgman says you'll probably need more lights, too—especially if you want to rely on Photoshop plug-ins for the heavy lifting of the mask. If you're careful, though, you can get away with more rudimentary lighting and a less-than-ideal background.

"If you're low on lights," he says, "and you have only white seamless and are lighting the model pretty flat, you can get away with using white seamless. Just don't light it, and make sure your background is one to two stops under your subject. Overexposing the background leads to color spill, and that could contaminate your subject's light and color balance."

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