Apple Final Cut Pro 5 - Manual (Page 1193)

406 Part II Project Interchange
6 You can also adjust the Choke and Feather sliders.
The Choke slider adjusts the overall size of the matte, without changing the shape; the
Feather slider blurs the edges of the matte.
The parameters of the Garbage Matte filters can be keyframed, just like any other filter.
This can come in handy if you need to use one of the Garbage Matte filters to crop out
the outside edge of a green screen in a shot where the camera is panning.
Example: Keyframing Garbage Mattes
In the following example, two sets of keyframes are created to compensate for a simple
pan in the clip being keyed.
1 With the playhead on the first frame of the clip being matted, apply and adjust the
Four-Point Garbage Matte filter.
2 Once you’ve created the proper shape for the first frame of the clip, click the keyframe
buttons for the Point 1, Point 2, Point 3, and Point 4 crosshair controls.
3 Move the playhead to the last frame of the clip, and readjust the Point 1, Point 2, Point
3, and Point 4 crosshair controls to fit the new position of the green screen.
The finished matte image
Create keyframes for
all four points.
The four points are
adjusted again.