The Challenges of Building Chroma Key Sets
Chroma key sets are where green screen effects are shot. These effects allow movies to go places that otherwise might not have been possible such as space, a volcano or a heavily stylized black and white city. The effect works by shooting actors in front of a green screen. The green is then chroma keyed out in post production which turns it transparent. Then replace that empty video with the background of your choosing. In order for this effect to work the green screen needs to be the right size for the shot and the light needs to be perfect. Both of these factors present challenges in building a chroma key set.
A chroma key set needs to be built in a large area that can incorporate the green screen, the actors and action and the lighting. If one of these things is compromised then the effect is going to be ruined.
The green screen needs to be large enough to cover the action in the shot. If the shot is just one person you can get away with a green screen that's 8 feet by 8 feet but if you're going to be shooting a lot of scenes with multiple actors then the set should at least be 20 feet by 20 feet. The screen should also be stretched over the floor so that it looks infinite instead of having corners. The set also needs to be large enough so that you can get all of the shots you envisioned.
Plus, you need to have room to set up lights and store other equipment necessary for the shoot. That can eat up a lot of real estate.
Another reason the set needs to be large is because lighting a green screen can get complicated. For the effect to be properly pulled off the green screen must be evenly lit so that the entire thing is one color. If it is unevenly lit then you're going to have multiple shades of green to key out which can turn into a huge headache. This is why you don't want any corners on your green screen. Corners will create shadows.
Creating the Green Screen
How you create the green screen largely depends on where your set is and how long you will be there. There are two ways to build the proper green screen. One is to rent or buy green screens that you can rig up. If you're only going to be shooting on a green screen for a day and the work is fairly small then this might be an attractive option. The other choice you have is to paint your own green screen on a wall in the studio. If you're going to do this then make sure you use real chroma key paint. This paint will not reflect light and will remain even and flat in its tone.