Apple Final Cut Pro 5 - Manual (Page 1161)

374 Part II Project Interchange
Importing Clips With Alpha Channels
Some clips and images you import may have alpha channels. Ordinary video clips have
three channels of information for the red, green, and blue channels respectively. An alpha
channel contains additional information that defines areas of transparency in the movie.
When you import a QuickTime movie or an image file, its alpha channel is immediately
recognized by Final Cut Pro. After you edit this clip into a sequence, Final Cut Pro uses
the alpha channel for compositing against background layers. You can turn off alpha
channels if you decide not to use them.
Important: When you import a clip with an alpha channel that contains no data, the
clip appears white. To display the clip properly, change the alpha channel for the clip to
None (see “
Changing a Clip’s Alpha Channel Type ,” next).
Changing a Clip’s Alpha Channel Type
There are several reasons why you might want to change a clip’s recognized type of
alpha channel in Final Cut Pro:
 Sometimes Final Cut Pro misinterprets the alpha channel when it imports a clip,
which can result in “fringing” around the edges of solid objects. For example, if a clip
with a black alpha channel is incorrectly identified as having a straight alpha channel,
a black fringe appears around the edges of the imported image.
 Some editing and compositing applications output alpha channels that are the
reverse of what Final Cut Pro uses. When this happens, what’s supposed to be
transparent is solid, and what’s supposed to be solid is transparent.
In all these cases, you can change or reverse the alpha channel setting.
Foreground
graphic
Alpha
channel
Background
graphic
Final
composite