Apple Final Cut Pro 7 - Manual (Page 1208)

Travel Matte - Alpha
When you apply the Travel Matte - Alpha composite mode to a selected clip, the alpha
channel from the clip below is applied to the selected clip. Only two clips are required
to use this composite mode, but in most situations, you will use three layers:
• Foreground (top layer): This layer appears on top of the background layer, as seen
through the alpha channel. Apply the Travel Matte - Alpha composite mode to this
layer.
• Alpha channel (middle layer): This layer provides the alpha channel (transparency
information) for the foreground layer.
• Background (bottom layer): This optional layer appears beneath the foreground image
wherever the foreground image is masked by the alpha channel. The background can
be a single layer, or multiple layers blended with transparency or composite modes. If
no background layer exists, the Canvas displays the default Final Cut Pro background
color (checkerboard, black, white, and so on), and black appears during output and
export.
Foreground clip End result Alpha channel
Travel Matte - Luma
The Travel Matte - Luma composite mode does the same thing as the Travel Matte - Alpha
composite mode, but the transparency is derived from the luma information (instead of
the alpha channel) of the clip below. The luma information may be derived from a
grayscale equivalent of the RGB channels, or directly from the luma (Y
′
) channel in the
case of Y
′
C
B
C
R
video. White is equal to 100 percent transparency and black is equal to
100 percent opacity (solid).
Using Travel Mattes to Hide or Reveal Parts of a Clip
Travel mattes are useful when you want to use one clip to selectively hide or reveal part
of another. For example:
• To show parts of a video layer selectively revealed by a round spotlight shape
• To partially reveal video images playing through a title or logo graphic
• To use an imported graphic to obscure, or mask, part of a layer you don’t want to show
1208 Chapter 71 Compositing and Layering