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Alpha Channel Retarded
Hello I know that this must be something simple that I’m overlooking…
I have a client that wants me to give them QuickTime Files of a host that I’m going to key out from a green screen with the Alpha key in it so that they can import the files and right away read that alpha channel and put objects behind the subject.
While I have no problem keying in various programs such as After Effects, Motion, Final Cut etc. When I make a graphic in programs such as Live Type & Zaxwerk’s Pro Animator the QuickTime file that I bring in is automatically recognized and transparent around the text without me doing anything.
How can I create such a QuickTime file that is instantly recognized and makes everything transparent around my subject or such as this object?
When I attempt to create such a file and test it I can tell that it has an Alpha Channel but I cannot get programs such as After Effects & Final Cut Pro to automatically recognize it like if I made a quicktime file in Live Type.
Thanks to any and all who spend time answering this question!
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2 Replies
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Most importantly, make sure your output module settings in AE are correct. Next to channels it should say RGB + ALPHA . Next to colors it should say Millions of Colors + . This plus sign means to include an alpha channel. Next you will need to choose if the alpha channel should be premultiplied or straight.
I don’t have enough information to tell you whether you want premultiplied or straight. What editing or compositing app will the client be using this quicktime in? Some programs (including Final Cut)prefer straight alpha channels, while others prefer premultiplied alpha channels. After Effects can render out either one. If your client is using After Effects, either straight or premultiplied should work because AE can almost always tell what type of alpha the clip has when you use the “guess” option.
~Colin -
Also make sure that you are exporting in a codec that supports an Alpha channel Quicktime Animation is usually a favorite. You’ll most likely have better results with a straight alpha than a pre-multiplied, but make sure that whatever app they are using supports it.
Erik
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