http://livedocs.adobe.com/ Macromedia LiveDocs - online documentation with user feedback. Copyright 2009, Macromedia, Inc. 2009-11-25T21:42:46 en-us http://livedocs.adobe.com/en_US/AfterEffects/8.0/WSbaf9cd7d26a2eabf53ab041041081290f-7ff7.html#78445 Aharon Rabinowitz's video "What is an Alpha Channel?" is a good introduction to alpha channels in general:<br /><br />http://cowcast.creativecow.net/multimedia_101/index.html Todd_Kopriva 0 0 2007-12-13T14:10:40 http://livedocs.adobe.com/en_US/AfterEffects/8.0/WSbaf9cd7d26a2eabf53ab041041081290f-7ff7.html#74684 If you're exporting a movie with an alpha channel so that you can composite it with other elements, consider cropping around the opaque portion of the image so that you are exporting the smallest rectangle that contains all of pixels that aren't completely transparent. Transparent pixels still take up memory and storage, so cropping out the transparent pixels around the outside of the image can make the output file smaller. Todd_Kopriva 0 0 2007-10-08T18:53:14 http://livedocs.adobe.com/en_US/AfterEffects/8.0/WSbaf9cd7d26a2eabf53ab041041081290f-7ff7.html#68933 The Knoll Unmult plug-in can be used to create an alpha channel from the dark areas of a layer. This works well for a layer with a light effect (such as a lens flare) that you want to composite on top of another layer.<br /><br />http://www.redgiantsoftware.com/unmult.html Todd_Kopriva 0 0 2007-06-24T16:19:23