When you’re shooting against a chromakey backdrop, good lighting can be the difference between being able to pull a really clean key from your final image and shooting something that’s mostly noise and falls apart as soon as you attempt to do anything to it in post (shooting in 4:2:2 will also help). Here are a few things you’re going to want to keep in mind…
1. Aim for soft, even, overhead lighting
To pull the cleanest possible key from anything shot against a chroma wall, you need your backdrop to be evenly lit, with no obvious of areas of highlight and shadow (any variation will translate to noise in your image, and make it far harder to get usable footage. The easiest way to do this is to light your chromakey backdrop from above, as this will reduce overlap, using a soft light like a KinoFlo or Ianiro 5502 (we actually put together an Ianiro kit specifically for chromakey lighting)
2. Position your subject carefully
You want to keep your subject about two metres away from your chromakey backdrop, because you don’t want their shadow to mess up your carefully balanced backdrop lighting. If you’re working on an infinity curve (a curved green, blue or white backdrop that has no corners and so can be used to give the impression that the space behind your subject goes on forever), you might want to hide their shadow there, too. Using something like a fresnal should help with this – just be careful not to give them bright and shiny legs, as that will look strange.
3. Remember the inverse-square law
There’s a scientific explanation of this that you’re welcome to go and Google, but it practical terms it means that the closer your subject is to your lighting, the brighter their face will be and the darker the backdrop will be, as you have to expose for the subject. The brighter and more headache-inducing your chromakey backdrop is, the easier you’ll find pulling your key, so try and light your subject from as far away as possible without splashing your subject lights over your green screen and creating hotspots.
4. Backlight your subject from above, key from 45 degrees above the eyes and fill from 20 degrees below the eyeline
Like your chromawall, you want to try and light your subject from above. As well as helping you get enough shadow to avoid their face looking completely flat (for classic portrait lighting you want one side of their face to be a stop darker than the other), this will also make it easier to avoid having your subject lighting affect your nice, even backdrop. You can now get flexible lamp arms that will allow you to position your light directly above someone (Dedo’s DSTFX stand is a safe bet), but a ¾ light will do if you don’t have the budget for extra kit. In chroma your back light serves two purposes: cutting down on green fringes (if you’re shooting with a less than ideal camera for chroma) and separating the subject from the background.