12 Tips For Getting a Better Green Screen Key

Since we're about a month away from the 2015 NAB Show, I thought it would be timely to look back at some of the useful information I came away with from last year's sessions.

In this post, I want to talk about green screen workflows. Those of you who have worked on green screen shoots before (and that's probably a majority of you) know how important it is to properly light your green screen and light and place your talent. Otherwise, the edges of your key will be blotchy and your talent will have a green glow.

I had the opportunity to attend Jeff Foster's class, in which he provided some extremely valuable information for setting up, lighting, and shooting green screens. By adhering to his tips, you can get a nice, clean key in post-production.

Scopes are incredibly important when lighting both the green screen and the talent. You will want to reference both a Vectorscope and a Waveform monitor to ensure that the green screen is both evenly lit and at the proper exposure. Two iPhone/iPad apps Jeff recommends for this purpose is Cine Meter and Green Screener.

Now, on to some general guidelines:

  • The type of camera you are using is secondary to how you set up and light your green screen.
  • It's important to know ahead of time what your back plate will look like. That way you can light your talent so that he/she matches the back plate and the composite looks more natural.
  • Light the green screen first, then your talent.
  • Make sure you light enough of the green screen to completely cover the background of your talent.
  • Avoid shiny props. Anything reflective will reflect the green color cast of the screen.
  • Keep your talent at least 6 feet away from the green screen to avoid green color cast on your talent.
  • Warm up the talent if you notice any green on the edges.
  • Your camera's f-stop should be between 5.6 and 8.0.

Next, how to use your scopes for green screen work:

  • When looking at a properly lit green screen on a vectorscope, the line will run diagonally from the center to the bottom left, exactly in the middle between green and red (see the picture above). If necessary, you can use green gels on your lights to help with color accuracy and saturation.
  • On a waveform monitor, the green screen should sit at about 70 IRE. If it isn't, you can make the proper adjustments in-camera rather than adding more light to the screen.
  • The waveform line should be straight across from left to right. Any curvature in the line means that the screen isn't lit evenly.
  • The waveform line should be as thin as possible. The thinner, the better.

In another post, I'll go over some of Jeff's tips for compositing in After Effects. Meanwhile, enjoy this brief video on how green screen worked before computers came along and made everything so easy. For further reading, check out the article Hollywood's History of Faking It.