Here’s a chroma-key effect that uses two different colors to allow us to change backgrounds during the same clip.
NOTE: This effect is created the same way in all versions of Final Cut Pro X.
SECOND NOTE: Here’s an article that describes how to create this same effect using Adobe Premiere Pro CC.
There are many stock footage clips that use this two-color effect. This is an especially clever technique to use when you can shoot the background clip with a camera; for example a hand unwrapping a present to first reveal the blue layer, then peel that off to reveal the green layer. This gives the effect of unwrapping a present to first reveal the box, then the contents of the box.
In this example, I’m using blue and green, but any two different colors can be used to create this effect.
Here’s the first layer: A paper layer that page-peels to reveal a chroma-key blue background.
NOTE: Yes, I know. It’s a page peel. But I need to illustrate movement while using still image screen captures. You can substitute a more interesting transition when you do this for yourself.
Here’s the second layer: A blue background peeling back to reveal green.
And here’s our goal: insert one background clip into the blue layer and a second clip into the green layer; while retaining the top, paper, layer and all effects.
REMOVE THE FIRST COLOR
First, while it does not make any difference which clip is in the Primary Storyline, I’m going to start by putting the clip with the color backgrounds, the “chroma-key clip” into the Primary Storyline.
Next, put the first background clip below the chroma-key clip; in this example, its the “Grand Canyon Sunset” clip. Chroma-key backgrounds always go below the clip containing the key color.
From the Effects Browser (shortcut: Cmd+5), drag the Keyer effect, in the Keying category, on top of the chroma-key (top) clip.
The keyer may, or may not, properly select the first color. Assuming that it does not:
Position the Playhead in the chroma-key clip so that is in the middle of the first color you want to remove. Depending upon the Keyer settings, you may, or may not, see the color in the Viewer.
Click the Sample Color box, immediately above the Strength slider, to select it.
Then, in the Viewer, drag a selection rectangle to select the first background color. You should immediately see a clean key. Be careful to only include the background color.
NOTE: FCP always selects colors based upon the source media, not the effected media in the Viewer. Color correcting a chroma-key clip is not necessary, as FCP X ignores the color correction, as well.
Verify you have a solid key by clicking the Matte icon (middle), to switch the Viewer to display the alpha channel (transparency) of the chroma-key clip.
The foreground (paper) should be fully white (opaque), while the background (sunset) should be fully black. If there are holes in the foreground, remove them by dragging the Fill Holes slider, just below the Matte icon, until the foreground is solid white; as illustrated here.
Reset the Viewer display by clicking the Composite icon on the left of the three icons.
KEY THE SECOND COLOR
To create the key for the second color, select both the chroma-key and background clips in the Timeline, then choose File > New > Compound Clip (shortcut: Option + G).
Give the compound clip a name and click OK.
In the Timeline, the two clips are coalesced into a single compound clip.
Edit the second background below the compound clip. You can trim it so that it starts just before the effect, if you want, but the trimming is not required; I do it here to illustrate the difference between the compound clip and the new background clip.
Drag the Keyer effect from the Effects Browser on top of the Compound clip.
It should automatically sense the correct color; in this case, green. If it doesn’t, repeat the process of sliding Strength to 0 and sampling a new color, representing the green background in the second half of the clip.
Verify your key by selecting the Matte icon, again. Remember, solid white is opaque and solid black is transparent.
This technique can be used to create a wide variety of very interesting effects, either shot in-camera or created using Motion or After Effects.
The key is to create the first key in the Timeline, then create the second key using a compound clip.
2 Responses to FCP X: Two Color Chroma-key
If the keyer in FCPX ignores any color correction, can you shoot green/blue screen in a flattened format/codec like c-log, s-log or Black Magic Film Gamma
Maybe, but I’m not sure. FCP X keys using RGB color space. It may work with log files, but I haven’t tested this.