Apple Final Cut Pro 5 - Manual (Page 1166)

Chapter 18 Compositing and Layering 379
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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 it, you can check to see what the alpha
channel looks like by itself by choosing View > Channels > Alpha.
There are several channel viewing options in the View menu:
 RGB: This is the default color option; it shows the three color channels that make up
the actual video image, so the image appears as it would when output to tape.
 Alpha: This option represents the alpha channel as black against white, where absolute
black represents 100 percent transparency, levels of gray represent varying degrees of
transparency, and absolute white represents nontransparent areas of the picture.