Apple Final Cut Express 4 - Manual (Page 828)

828 Part IX Effects and Color Correction
Using Video and Graphics Clips with Alpha Channels
Ordinary video clips have three channels of information for red, green, and blue. An
alpha channel is an additional channel that defines areas of transparency in the clip or
image. If you import a QuickTime movie or a still image from another application, or a
file that’s been created by a 3D animation program, it may have an alpha channel in
addition to its color channels. An alpha channel is a grayscale channel where levels of
white and black determine varying degrees of transparency applied to the color
channels during compositing.
When you import a QuickTime movie or an image file, its alpha channel is recognized
immediately. When you edit the movie or image file into a sequence, Final Cut Express
uses the alpha channel to composite the movie or image file against any clips
appearing in video tracks below it.
Note: Alpha channels work the same in video and still-image media files
Don’t Add or Delete Layers from an Imported Photoshop File
Final Cut Express keeps track of each imported Photoshop layer according to its
position relative to the bottom layer. While editing a layered Photoshop file that’s
already been imported into Final Cut Express, it’s not a good idea, under any
circumstances, to:
 Add additional layers: If you add a layer, any layer pushed above the topmost layer
that was imported into your Final Cut Express project is ignored when you go back
to Final Cut Express.
 Delete layers: Deleting previously imported layers can have even more unexpected
results. If you must add or remove a layer from a previously imported Photoshop
file, do this in Photoshop and then reimport the file into Final Cut Express. For
additional information about importing layered Photoshop files, see Chapter 15,
“
Importing Media Files into Your Project ,” on page 205.
Foreground
graphic
Alpha
channel
Background
graphic
Final
composite