Apple Final Cut Pro 7 - Manual (Page 1216)

2 Choose Modify > Alpha Type, then choose a new alpha channel type from the submenu.
To change the alpha channel type of a clip in the Browser
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Control-click in the Alpha column in the Browser, then choose a new alpha channel type
from the shortcut menu.
To reverse a clip’s alpha channel
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Do one of the following:
• Select a clip in the Timeline or open a clip in the Viewer, then choose Modify > Reverse
Alpha.
• In the Browser, Control-click in the Reverse Alpha column next to the clip you want to
modify, then choose Yes from the shortcut menu.
If there is a checkmark by the Reverse Alpha menu item, the clip’s alpha channel is
being reversed. If there is no checkmark, the alpha channel is left alone.
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 selected in the View pop-up menu, 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 Pro. If you’re
exchanging media with other editors and broadcast graphic designers, let them know
how you need clips with alpha channels to be set up for use in Final Cut Pro.
Dark areas are
transparent.
White areas are solid.
Viewing RGB and Alpha Channels in the Viewer
When you’re working in the Viewer, it can sometimes be helpful to have a quick look at
the alpha channel of your clip. The alpha channel defines areas of transparency and can
change if various filters are applied. For example, if a blue-screen clip is added to the
Viewer, and a blue-screen filter is applied to the clip, you can check to see what the alpha
channel looks like by itself by choosing View > Channels > Alpha.
1216 Chapter 71 Compositing and Layering