Green Screen in FCP X

posted Jan 5, 2012, 12:57 PM by Frank Maggi   [ updated Jan 6, 2012, 12:50 PM ]
Green screening is a strong suit of FCP X. The built in keyer is robust and does a very good job. 

To apply a green screen effect, go to the Effects Browser, choose Keying and then the Keyer Effect. Simply drag that effect onto the clip you want to key. Usually, that's it. It does a terrific job without any help from you. But, unlike iMovie, you do have options, such as:
  •  You can put either the green screen clip or the background clip on the primary storyline; when you're ready, the missing clip is added above or below (yes, you can add clips under the primary storyline)
  • You can use Auditions with either the green screen clip or the background clip (or both) to preview different options
  • If you click on the green screen clip and hit the "i" button [for Inspector], you'll see the options to the left for refining your work (although you may not need to use them)
  • You can fine tune your key with the tools described below 

Green Screen Controls

Below is a brief explanation of the controls you have. A good way to get a sense how they work is to just play with them and watch how it affects your work. They can make a real difference.
  •  Reset Arrow—Curved arrow in the top right corner; if you screw everything up, click this to go back to defaults
  • Refine Key
    • Sample Color would be used if there were some green "crumbs" still left behind. Click on this and then draw a rectangle with the tool over the crumbs
    • Edges would be used if the keyed clip is having a hard time picking up the edge. Click on the tool and drag a line over the edge where there is trouble. The idea is to get one circle just on the outside, one circle just on the inside, and the line directly over the edge. Can be tricky to use.
  • Strength—Almost always you want this at 100%
  • Jump to Sample—If you used the tools above, use these arrows to go back/forward to where the tool was used
  • View—This can be really useful; three choices:
    • Final—All the green is gone and you see the background
    • Matte—Anything white will be visible, black will be hidden, grey will be semi-transparent. Your goal is to get solid black/white (unless there are things you're supposed to see through; then some grey is OK). The edge between black and white should be slightly blurred (see Edge Distance below).
    • Original—No effect applied
  • Fill Holes—If your white parts have some bleed-through, this may be able to get rid of it. As you drag to the right the holes will fill in (it increases matte density). Obviously, you don't want to go too far. Use judgement.
  • Edge Distance—Basically, this blurs the edge to get rid of stair-steps and make the edge more believable.
  • Invert—Flips the matte so what was hidden is shown and what was shown is hidden.
  • Mix—Here, too, you always want it to the far right (1.0) unless you have very special needs.