Apple Final Cut Express HD - Manual (Page 682)

682 Part IX Effects
Matte Filters
Matte filters can be used by themselves to mask out areas of a clip, or to create alpha
channel information for a clip to make a transparent border so that the clip can be
composited against other layers. Matte filters can also be used to make further
adjustments to layers with keying filters applied to them. For detailed information, see
“
Using Mattes to Add or Modify Alpha Channels ” on page 822.
Filter Result
Eight-Point Garbage Matte Generates an eight-point polygon you can use to crop out portions
of a clip. Eight-point controls allow you to define the polygonal
matte. The Smooth slider rounds off the corners of the polygon to
create rounder mattes. The Choke slider allows you to expand or
contract the matte, and the Feather slider allows you to blur the
edges of the matte. The Invert checkbox reverses what’s matted
and what’s transparent, and the Hide Labels checkbox hides the
number labels, which indicate which point of the matte
corresponds to which point control of the filter.
Extract Produces a matte around the clip, similar to a Luma key. A View
pop-up menu allows you to look at the source of the clip (with no
key applied), the matte created by the filter, the final matted image,
or a special composite of the source, matte, and final image for
reference. Use the Threshold, Tolerance, and Softness sliders to
adjust the matte. The Copy Result pop-up menu allows you to copy
the luminance result to the RGB or alpha channel of your clip, and
the Invert checkbox allows you to invert the result.
Four-Point Garbage Matte Similar to the Eight-Point Garbage matte, but it creates a four-point
polygonal matte.
Image Mask Takes the alpha channel or luminance from another clip and uses it
to create a matte for the current clip. The Mask clip control allows
you to select the clip from which to take the alpha channel or
luminance values. The Channel pop-up menu lets you choose
whether to use the clip’s alpha channel or luminance level. The
Invert checkbox allows you to invert the resulting matte.
This filter is especially useful for taking custom edge masks that
you can create with any image editor and applying them to clips in
your sequence that you want to matte the edges out of. Unlike the
Travel Matte composite mode, the Image Mask filter attaches a
matte to the selected clip. You can use motion effects to move the
affected clip around, and the matte follows.
Mask Feather Blurs the alpha channel of the clip by the amount you specify with
the Soft slider.
Mask Shape Generates a mask shape to use to matte out the clip. You can
choose a diamond, oval, rectangle, or round rectangle from the
Shape pop-up menu. Use the Horizontal Scale and Vertical Scale
sliders to adjust the size and aspect ratio of your mask shape. The
Center point control allows you to specify the center of the mask,
and an Invert checkbox lets you reverse what’s transparent and
what’s solid.