Apple Final Cut Express HD - Manual (Page 801)

Chapter 54 Compositing and Layering 801
IX
Changing Canvas and Viewer Background Colors
When working with clips that have an alpha channel, you can choose different
backgrounds that make it easier to see which areas of your picture are transparent.
Translucent clips or generated text may be easier to see if you choose a background
that emphasizes them, such as Checkerboard 1 or 2. If you’re compositing colored
images, a contrasting color would work better.
When a clip is rendered for export to tape, the background is always set to black. If it is
rendered for export as a QuickTime movie, the background will still appear to be black,
even if the alpha channel is exported along with it.
Exchanging Media With Alpha Channels
Alpha channels are simply grayscale images or frames, where levels of white and
black determine varying degrees of transparency. If you look at a clip with an alpha
channel in the Viewer with the alpha option in the View pop-up menu checked, you’ll
see that the solid areas of the image are represented by 100 percent white, and that
transparent areas of the image are represented by 100 percent black. Lighter to
darker shades of gray indicate lesser to greater areas of transparency.
Other editing applications may use white and black differently than Final Cut Express HD.
If you’re exchanging media with other editors and broadcast graphics designers, let
them know how you need clips with alpha channels to be set up for use in
Final Cut Express HD.
Dark areas are
transparent.
White areas are solid.