FCP X: Create a Chroma-key

Posted on by Larry

I’ve covered chroma-keying (also called green-screen keys) in my FCP X video training, but haven’t written about it. So, time to fix that lack.

This article looks at how to chroma-key using Final Cut Pro X. (This article shows how to chroma-key using Final Cut Pro 7.)

GETTING STARTED

First, the best thing you can do to improve the quality of your keys is to improve how you shoot them. Here are seven basic production rules:

  1. Actors should be at least 10 feet in front of the green screen. This avoids light from the background “spilling” around their body or shoulders.
  2. In general, don’t cast shadows on the green screen. Be very careful shooting feet.
  3. The green background should be as smooth as possible. Paint is always better than fabric; avoid wrinkles and folds.
  4. The green background should be lit smoothly, both from side to side and top to bottom. I try to have the green background display between 40-50% level on the waveform monitor.
  5. There is NO relationship between how the background is lit and how your actors are lit. This example will illustrate that.
  6. Light your background for smoothness. Light your actors for drama.
  7. Don’t worry about having the green background fill the frame. It only needs to completely surround the edges of your actors. Garbage mattes are used to get rid of the junk.

SETTING UP THE KEY

The green screen image is always placed above the background. You can place either the green screen or background image into the Primary Storyline. I find it easier to put the background in the Primary Storyline, because it makes editing the green screen image easier. But this is purely personal choice.

Select the green screen clip.

From the Effects Browser > Keying category, double-click the Keyer effect, which applies it to the selected clip. (You can also drag the effect on top of the clip, if you forgot to select the green-screen clip first.)

Don’t panic if your image looks weird – we will fix it.

Click the Sample Color icon. This allows fine-tuning the selection of the background color.

In the green-screen image, drag to select a representative section of the background. I try to get close to the face, but not so close that I accidentally select loose hair or skin.

Your key should look better immediately. Most of the time, you can probably stop here. But there are three other adjustments that can make your key look even better:

* Cleaning up the matte
* Edge adjustments
* Light wrap

Click the Matte button to display your key as a white foreground on a black background.

Your goal is the make the foreground solid white, which means opaque, and the background solid black, which means transparent. Adjust the Fill Holes and Edge Distance sliders until your key looks solid. (For REALLY bad keys, you’ll need to also adjust Color Selection, mentioned below.)

If an edge is too pronounced, or needs help, click the Edges icon.

Then, click and drag a line from the foreground to the background in the Canvas. Drag the midpoint slider (where my cursor is) until the edge looks the best it can. Different video formats make this easy (ProRes), while others (HDV, AVCHD) make this much harder. Perfection is impossible – do the best you can.

New with the 10.0.3 release are four additional tweaks at the bottom of the keyer filter:

* Color Selection
* Matte Tools
* Spill Suppression
* Light Wrap

The first three are designed to clean up poorly shot keys – read the FCP X Help files to learn how these work. (I used the Color Selection tools to clean up the key I show later in this article.)

Light wrap, though, is aesthetic. What it does is blend colors from the background into the edges of the foreground, to make the entire key look more “organic,” as if the foreground and background were actually in the same space.

This is a subtle effect, but very cool.

Twirl down Light Wrap and adjust the Amount slider and watch what happens. Drag the other sliders around and see what happens. The nice thing about this setting is that when it looks good to you, it is good. The amount of the effect is totally up to you.

Remember, Light Wrap only affects the edges of the foreground and should be used subtly.

When you are done, you have a great looking key!


GARBAGE MASK

Sometimes, however, you don’t have, um, perhaps, the best green-screen image to work with. Here, for example, there are lighting instruments in the foreground, with a completely inadequately lit green screen in the background. (Sigh… just awful.)

Once you pull the key – which is film-speak for creating a green-screen shot, as I described above – and get it looking as good as possible, there’s one more step: adding a garbage matte to get rid of all the garbage.

Once you get your key looking as good as you can – which in this case isn’t all that good – drag the Mask effect (Effects > Keying > Mask) on top of the green-screen clip.

NOTE: The Mask effect should always be added after the Keying effect, so that the Mask is below the Keyer in the Inspector.

Then, drag each of the four circles to create a shape such that your foreground image is contained inside it, and everything you want to exclude is outside. Here, for instance, we removed the light stand and the tearing around the top of the image. I’ve found this Mask effect works best when applied to a connected clip, though Apple cleaned up a bug that prevented it from working when applied to a clip in the Primary Storyline.

However, the big limitation of the Mask effect is that you only have four points to work with. That’s where a free effect comes in, which allows you to create far more flexible shapes with it.

It’s written by Alex Gollner and is available on his website – alex4d.wordpress.com/fcpx/ – I recommend his effects highly.

Apple totally rewrote the chroma-key filter in FCP X — it is far better than the filter supplied with FCP 7 — which allows us to create some amazing effects. Have fun playing with it.

LEARN MORE: Want to learn more about chroma-keying, and luma keying, in FCP X? Check out this chapter of my FCP X video training.


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12 Responses to FCP X: Create a Chroma-key

  1. Pingback: FCP 7: Green-screen or Chroma-key with Primatte « GLJ Media Group

  2. Brent says:

    I’m trying out this tutorial with a video of me holding an iPhone and kind of going through some of the screens. However, everything that is green on the iPhone screen is filtered/masked out just like the background green screen. I put a white background on it and the green colors on the iPhone screen turn white/grayish.

    Any suggestions on how to fix this?

  3. Pingback: Larry Jordan FCP X: Chroma-key Advanced Features | Robin Lewis

  4. Petre Nicolescu says:

    Thank you for this very informative material.
    Still, the guys from Apple didn’t really think it through when they implemented the spill suppressor. If I am allowed to choose any color for background then the spill supressor should compensate for ANY color as well, not only for the complement of either green or blue. This is really silly. I tried to cut out a blue flower (which of course has a lot of green, blue and some white). Although the result was ok-ish, I can imagine other situations and color combination in which the magenta spill added by the supressor can render awkward results.

    Thank you for your lessons.
    Regards.

  5. Benito says:

    Hi,
    Thanks for the tutorial, it works perfectly for me.

    I’m doing a green chroma key, and I’m trying to change the background to pure white.
    I’m using a custom generator in the background, but the result is not pure white, but a little bit grayish.

    Do you have any suggestions in what to do?

    thanks in advance.

  6. chase sumner says:

    gaaaaayyyy

  7. Michal Mrhy says:

    Hello, I would like to ask you for a favour.
    I ve tried to make keying via final cut 10. And I have problem, I ve changed background no problem by Keyer, but, I when I do dit, so unfurtunately automatic changed also the colour of body human (it very going to white color).

    Can you help me pls? What I should to do? thank U very much!

  8. Mike Beanland says:

    HI Larry,
    After reading your greenscreen piece I just spent 2 weeks (actually a bit longer, about 150 hours) on a 45 minute green screen training video. It was 45 minutes of me in front of a green screen. I put 45 minutes of ocean waves as a background, on the primary storyline, the talking head with the greenscreen above it – and edited away.
    Literally thousands of carefully timed and attached clips later and edits and titles etc etc , and I have just realised that every single attached clip is attached to the background, which is the ocean and not the talking head. They have all been timed in sequence with words and actions of the talking person in the green screen layer, but not linked to these clips. So if I want to move anything of the talking head does, or cut or adjust anything that the talking head does, not a single other thing will be correct, as it is all linked to the ocean background.
    Aaargh, what a disaster.
    That is a huge negative of putting the background on the primary storyline.
    I realise that the most important story must be the storyline.
    Is there a solution?
    Can I move all attachments to the talking head clips? Or change the primary storyline away from ocean to the greenscreen talking head?
    Any ideas Larry?

    • Larry says:

      Mike:

      You make some good points. Fortunately, there’s an easy solution to this: it is very easy to edit a selected connected clip into the Timeline. All you’ll need to do is replace your ocean wave background.

      First AS A TEST!! select the first talking head clip in your project. Only use one – if it doesn’t work, you can easily Undo.

      With the talking head clip selected, choose Edit > Overwrite to Primary Storyline. This will drop the connected clip precisely down to the Timeline, where it will overwrite (replace) your background waves clip. This move will include all effects and trims so that everything remains just as you had it.

      Then, add the background waves as a connected clip BELOW the green screen clip in the Primary Storyline. (Yes, below seems like heresy, but it works perfectly fine.)

      Once you see how this works for one clip, select all your talking head clips and overwrite them all at once.

      Problem solved.

      Larry

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