I have to shoot a scene similar to the progressive "the heist" commercial.
The problem I'm trying to work out is this: I will have an 8' x 8' platform with a hole cut into it. The platform will be painted green with a green sceen hung behind the actors. In the commercial, the enviroment is in a semi-dark air duct. This is what I'm trying to reproduce. I have a virtual set modeled in 3DS MAX and will render that out.
My question is how do I light the actors? The painted set that the actors will be kneeling on needs to be lit brightly enough to be recognized when keying in Adobe Premier. If I light the scene that bright, the actors will be over lit.
The first trick to low-key lighting for chroma key is that anything the actors come into contact with should be real. That way the lighting on the talent does not have to be flat in order to get a good key. An example would be a promo I did for a planned condo development in Las Vegas. In order to pre-sell units even before they were built, my client rendered a young women into a virtual set of the finished condominium to illustrate what life would be like.
The story followed the young women from the time she came home after work to the time she went to work the next morning. When it came time for her go to bed and get up the next morning, the director wanted to create a time lapse effect from the time the room lights go out till the sun comes up the next morning. In the pictures attached the only thing that is real is the bed.
For low-key chroma keying it is also important to separate the lighting for the background from the lighting for the talent in the foreground. To do that you need a good size studio. We shot this promo on a 40'x60' stage which was just big enough to separate the two. Separation also helps to get a cleaner key because it greatly reduces the reflection of green light off the walls and into the shadowed parts of your talent's face. It also helps to use large solids to further reduce the reflection of green light off the walls.
The typical approach to lighting for Chroma Key, using Space Lights, is not ideal for low-key keying because they are too hard to control. We used cyc lights to light the cyc walls and then smaller Fresnels to reverse key or just edge light the talent. We then filled the talent with a cooler soft light source (pictured here is a Chimera soft bank with 4x4 Kinos with 5500K tubes inside.)
Guy Holt, Gaffer, ScreenLight & Grip, Lighting Rental and Sales in Boston