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How to use alpha channel (instead of plain old transparency) ??

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BRussell
How to use alpha channel (instead of plain old transparency) ??
on Feb 23, 2006 at 8:16:58 am

I exported a Photoshop image from After Effects. However, instead of giving me a transparency, it gave me a fourth channel, an alpha channel. How do I use this alpha channel to create a transparency? (For instance, I want to export the image -- a feathered title w/ glow -- as a png w/ transparency, etc.) Thank you!

"THE LOST SKELETON OF CADAVRA" -

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Marky A
Re: How to use alpha channel (instead of plain old transparency) ??
on Feb 24, 2006 at 5:24:07 am

Use the alpha channel as a selection and cut out the background of the other layers with it. Is this what you are asking? I think Ctrl clicking on the alpha channel will turn the ants on.



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BRussell
Re: How to use alpha channel (instead of plain old transparency) ??
on Feb 25, 2006 at 12:21:04 am

Hi, thank you. Actually, that's not quite doing it. The feathered parts of the image have the background mixed in when I cut-and-paste with the selection made by CTRL-clicking the alpha channel. Not the true transparency I need back. When I import this image into Avid (alpha inverted) the result is correct there. So I know the transparency can be extracted, I just don't know how....


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Richard Harrington
Re: How to use alpha channel (instead of plain old transparency) ??
on Feb 25, 2006 at 6:14:06 pm

Your alpha is being premultiplied with a color...

Suggest going back to program and exporting another file type *such as PNG or layerd PSD

Under comp menu is AE you can choose to save a layered PSD (this and more in PSNLE book too)

Richard M. Harrington, PMP

Author: Photoshop CS for Nonlinear Editors
Co-Author Final Cut Pro on the Spot, After Effects on the Spot, Broadcast Graphics on the Spot, and After Effects @ Work
Check out the new DVD: Photoshop CS: Essentials for Digital Video from http://www.photoshopforvideo.com

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BRussell
I've got the answer
on Feb 25, 2006 at 8:31:34 pm

Thanks for your reply! And thanks for the layered PSD info, that's good to know.

So well, actually, what you said is normally what I would do... go back and export a PNG. But I don't have access anymore to the original AE file. I knew there would be an answer, because I can import the PSD in Avid (like I always do) and the resulting transparency in the system is not mixed with the background color. HOWEVER, I have found the solution, and it is simple. Goes like this (for posterity): After using the selection from alpha to isolate the title, I then choose Layer | Matting | Remove Black Matte. Magic, it's perfect, just like the original.

I have no idea how that works -- there is some of the same value black inside the logo, and even streaked across the feather and glow, and that is not removed or changed at all. Pure magic. Anyway, I'm happy.

Thank you and cheers!

"THE LOST SKELETON OF CADAVRA" -

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