Alpha Channel from Black

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Alpha Channel from Black
by Ronn Kilby on Jan 20, 2012 at 12:23:16 am

Simple problem - hopefully a simple solution. :)

I have an AE project from someone else that I need to output with an alpha channel. Currently when I do that, the alpha is the whole screen. This is some animated text with lens flares. It's over black in the comp, and keys nicely if I put video in the comp under it - retaining gradations etc. How do I add an alpha channel that will then allow me to key it over video elsewhere (Avid MC)? The originator uses FCP and uses a transfer mode to key it therein.

I have AE 5.5 and Avid MC6.0 - any help much appreciated.

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Re: Alpha Channel from Black
by John Cuevas on Jan 20, 2012 at 1:00:39 am

If I'm reading what you are saying right, the comp doesn't have a background, you just need to know how to render out a file for Avid with an alpha channel? If that's the case then it's pretty straight forward, just select your comp and add it to the render queue(shift + cntl + /). Choose the correct render settings("DV" for an avid stardard def project, "Best" for HD). Probably easiest would be to use Quicktime Animation and under channels choose "RGB + Alpa" and change the color to "Straight"

Personally, I use the Avid Codecs for Quicktime. You have to change a couple of settings in the Output Module > Format Options, but when it gets to the Avid it doesn't have to transcode the footage so it's pratically an instaneous import.

Johnny Cuevas, Editor
Thinkck.com

"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.

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Re: Alpha Channel from Black
by Ronn Kilby on Jan 20, 2012 at 1:26:48 am

Thanks for the response John. I know how to output with alpha (including using DNxHD) - the problem is how to tell it to create an alpha from the background (or lack thereof) so the animation will key. Currently the alpha it outputs is the full screen.

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Re: Alpha Channel from Black
by John Cuevas on Jan 20, 2012 at 1:37:08 am

Gotcha, wasn't sure from the original question. Without seeing the project, I would guess that you have a solid with a lens flare effect on it. Try using Unmult from Red Giant. It's a free plugin that will knocks black out of layer.

Sometimes after using unmult you might want to add a levels effect, change the pulldown to Alpha and add change the imput whites and blacks to strengthen the alpha.
Johnny Cuevas, Editor
Thinkck.com

"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.

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Re: Alpha Channel from Black
by Ronn Kilby on Jan 20, 2012 at 5:06:41 am

Thanks John - I'll give unmult a try and report back.

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Re: Alpha Channel from Black
by Ronn Kilby on Jan 20, 2012 at 4:50:08 pm

Thanks John - unmult did the trick.

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Re: Alpha Channel from Black
by John Cuevas on Jan 20, 2012 at 6:46:50 pm

Glad I could eventually help.

Johnny Cuevas, Editor
Thinkck.com

"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.

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