10 Production Tips for Better Green Screen Keys
Chroma keying software has made huge strides in recent years, but that’s no excuse for sloppy production work. Here are a few tips to keep up with the software advancements:
1) Resolution and Framing
Let’s start with the obvious. You’re going to want as much visual information as possible. This means shooting at as high a res as possible and providing 4:4:4 files without color compression to your post team. In terms of framing don’t be afraid to shoot portrait or otherwise ignore every composition instinct you have- just make sure everything you want to see is in the frame- it can all be moved in post.
2) Green vs. Blue Screens
In recent years it seems blue screens have fallen almost entirely out of style. While the green channel has the highest luminance and camera sensors are most sensitive to green, blue screens still have a place in production. The old adage ‘Blondes on Blue’ is still true (blonde hair can turn reddish after removing green), green is twice as reflective as blue so it has a greater risk of spill and blue spill is less unsightly than green. Evaluate your situation and understand the benefits of each.
3) Depth of Field
Keep a shallow DOF to provide a visual separation between your foreground and the green screen. This will help keying accuracy and by physically separating the talent from the background you can help avoid light spill.
4) Don’t Over Expose
Your background requires less light than you think, so it’s really easy to overexpose. Since green is so reflective, blowing out your shot also contributes to spill.
5) Deal with Those Split Ends
If you’ve ever keyed something out, you know the worst enemy of a clean key is a frayed edge, usually someone’s hair. The easiest solution is to deal with the frayed edge in production. Beware of costumes and props with frayed edges and keep the moose handy.
6) Pay Attention to What Your Talent is Holding and Wearing
It should be common sense that you can’t have people wearing green in front of a green screen, but colors with a lot of green in them, such as certain browns, are also risky. Additionally, beware of any surfaces that reflect light, like metal jewelry, shiny plastic props, or glass, because they are at risk of suddenly vanishing when they catch the light.
7) Preview on Set
The best method of getting a good chroma key is to check it during production. Have your DIT or an on set editor provide a rough key with a few early shots to make sure all of your ducks are in a row.
8) Keep an Eye on Shadows
Shadows should be relatively easy to avoid, if you’re spacing your subject far enough away from your background. If they’re left unchecked, shadows can require multiple keys or even manual masking or rotoscoping.
9) Don’t Sharpen
Turn off your in-camera sharpening features. Counterintuitively, these settings make it harder for software to separate foreground from background.
10) Fix it in Production, Not Post
Every time a producer says ‘We’ll fix it in post’ an editor somewhere weeps softly into their keyboard. Take care of all the production issues you can, especially with technically demanding shoots like green screen, and you’ll save your clients money and your editor an endless amount of frustration.
Photo Credit: Eelke, Nelson Minar