Apple Final Cut Pro 7 - Manual (Page 1215)

The Item Properties window appears.
2 Control-click the Alpha row in the Clip column, then choose the alpha channel type from
the shortcut menu.
• None/Ignore: If a clip has no alpha channel, or if you want to turn off the alpha channel
of a clip so that it’s no longer used, you can use the None/Ignore setting.
• Straight: Typically generated by a 3D animation or compositing program, straight alpha
channels contain only the pixels rendered for an image with no background (although
the background appears black). Because of this, movies with translucent effects, such
as volumetric lighting or lens flares, appear distorted unless they’re composited with
something in the background. Movies or images with a straight alpha channel are easy
to composite and always have very clean edges when composited in a multilayer
sequence.
• Black: Also known as premultiplied with black. Most other alpha channels, especially
channels that are hand drawn in Photoshop, are premultiplied. This means that, unlike
a movie with a straight alpha channel that contains only the pixels of the foreground
image, movies with alpha channels premultiplied against black always look right, even
if they have translucent lighting effects. This is because the entire image is
precomposited against black.
• White: Also known as premultiplied with white. Works the same as the black alpha
channel, except that the clip is precomposited against white.
Tip: If necessary, you can also Control-click the Reverse Alpha row in the Clip column
and choose No or Yes from the shortcut menu.
Control-click in the Alpha
row, then choose an
alpha channel option
from the shortcut menu.
To change the alpha channel type of a clip using the Alpha Type menu item
1 Select a clip in the Timeline or open a clip in the Viewer.
1215 Chapter 71 Compositing and Layering