Apple Final Cut Express HD - Manual (Page 792)

792 Part IX Effects
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 transparent and black is equal
to 100 percent opaque (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
Because travel mattes use information in one layer to affect another, if the alpha
channel, black, or white elements of that layer move, then the resulting matte also
moves. This movement can be a result of:
 Using a video or animation clip as your matte layer
 Moving that layer around with keyframed motion parameters
For more information, see “ Creating Keyframed Motion Paths in the Canvas ” on page 735.