2. Mask Out the Parameter
If your green screen came up a little short and/or uneven (as ours did), use a matte filter to remove non-green sections of the background before applying the color key. Doing so will save you lots of time futzing with the Color Picker and will result in a cleaner, better-looking composite. Double-click the foreground track in the Timeline to load the clip into Final Cut’s Viewer window.
Now click the Browser window’s Effects tab and scroll down to the Matte section - we used the Eight-Point Garbage Matte. Click and drag the effect’s icon onto the clip (either in the Timeline or Viewer window, both ways work) and press the Viewer window’s Filters tab to access the Matte controls. Click the plus-sign icon for Point 1 and use the resulting crosshair cursor to drag the onscreen point 1 (in the Canvas window), and repeat for all eight points to block out the rough edges. Don’t forget to scrub through the entire clip to make sure the matte fits.
If you have too much background garbage to fit in an 8-point matte, you can always add more matte filters.
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3. Key Out the Color
Knocking out the green background is done with Final Cut’s Chroma Keyer. Double-click your foreground clip in the Timeline to load it into the Viewer window. Now scroll down in the Effects Browser window to the Key Effects and drag the Chroma Keyer icon onto the clip in the Viewer window or in the Timeline. Open the Viewer window’s Filters tab and find the Chroma Keyer’s configurator. Click the button labeled Visual to get to the magic Eyedropper - click its icon and then click on the color (in the Canvas window) that you want to remove.
Missed some? Press the Shift key while clicking some of the remaining background color with the Eyedropper to add to your already selected color (a non-Shift-click will pick a new color instead). Then fiddle with the sliders to adjust the edge’s thickness and sharpness, and if you still don’t like the results, click the Numeric button. As with any video effect, you’ll want to play or scrub through the clip to make sure the background is gone throughout - lighting changes in the clip can tweak the color enough to thwart the Chroma Keyer, but you can add the colors to the key out by returning to the configurator and Shift-clicking color scraps with the Eyedropper.
You can adjust the Color, Saturation, and Luminance bars for a perfect match - or use the Shift-click Eyedropper to auto-match every drop.
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