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Compositing an Alpha Channel Video
I’ve been struggling to get what I thought would be a very simple task to occur. I created a set of rendered frames with the alpha channels rendering as separate frames (because there’s no way to combine them in Maxwell Render). All that I want to do is bring the video of the alpha renders into the alpha channel of the main video (or rather, somehow, create a video with the transparency I need). I’ve tried a bunch of things in Premiere, After Effects, and even Photoshop all to no avail.
Thanks in advance!
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4 Replies
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In After Effects, import both your animation and the alpha channel frame sequences. place the animation on a timeline with the alpha render above it. Every layer in After Effects has a pair of drop-downs, “Mode” and “Track Matte.” On your animation layer, set the track matte to “Alpha Matte *YOUR ALPHA LAYER*”
Brendan Coots
Splitvision Digital
http://www.splitvisiondigital.com -
Thanks so much Brendan! I got it to work, but for some reason not by setting the Alpha Video to an Alpha Matte. For some reason that made everything black. What did work (and I don’t really understand why) was setting the Alpha Video to a Luma Matte. Thanks again!
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And for anyone else who runs into this, I also now know the same thing can be done with the Track Matte effect in Premiere, then references the Video Track that the Alpha Video is on. Hooray.
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Ah sorry, Luma Matte is indeed what I meant to say. Alpha Matte “borrows” the alpha channel from the layer above, Luma Matte uses the luminance.
Glad it worked out!
Brendan Coots
Splitvision Digital
http://www.splitvisiondigital.com
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