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Premultiply - matted with color

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Graham Macfarlane
Premultiply - matted with color
on Sep 2, 2011 at 5:25:35 pm

I have a layer with transparency which needs premultiplying with black but I would rather not render it out in order to apply the standard interpret footage method as it will create a massive intermediate render.
Is there a way to achieve this same premultiplying effect on a single layer (using AE CS5)?

Many thanks
Graham

Graham Macfarlane
3D animator and VFX specialist
London UK


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Tudor "Ted" Jelescu
Re: Premultiply - matted with color
on Sep 2, 2011 at 7:13:00 pm

This tutorial may give you the answer you are looking for:
http://library.creativecow.net/rollason_ben/lens-flare/1

Tudor "Ted" Jelescu
Senior VFX Artist


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Darby Edelen
Re: Premultiply - matted with color
on Sep 2, 2011 at 7:14:49 pm

Could you explain a little more about what it is you have and what you're doing with it? I'm having a hard time figuring out why you'd need to premultiply footage for a workflow within AE.

Are we talking about removing premultiplication?

Darby Edelen


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Walter Soyka
Re: Premultiply - matted with color
on Sep 2, 2011 at 7:31:12 pm

Channel Combiner has a straight-to-premultiplied option.

Solid Composite will let you stick a black matte behind your transparent layer.

But, like Darby, I'm curious as to why you want pre-multiplication in AE.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Graham Macfarlane
Re: Premultiply - matted with color
on Sep 5, 2011 at 1:29:12 pm

Tudor, thanks for the link. Very useful info there!

Darby and Walter,
I have an asset containing coloured blurry graphics against black (no alpha channel) which I wanted to be against white. When Track Matting the asset in AE to make an alpha and using this over a white background one sees dark fringing in the blurry edges of the graphics.

I could have rendered out the asset with this alpha and then loaded it back in and interpreted the footage using, Premultiplied – Matted with colour (black) but I wanted to avoid the extra file space usage of an intermediate asset.

The Channel combiner effect does exactly what I need!
Many thanks for your help guys!

Graham Macfarlane
3D animator and VFX specialist
London UK


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Walter Soyka
Re: Premultiply - matted with color
on Sep 5, 2011 at 1:37:35 pm

You can also use Red Giant Software's free UnMult [link] next time you need to remove a black background from a semitransparent object.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Graham Macfarlane
Re: Premultiply - matted with color
on Sep 5, 2011 at 1:41:43 pm

Downloading now!!!
Cheers!

Graham Macfarlane
3D animator and VFX specialist
London UK


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Walter Soyka
Re: Premultiply - matted with color
on Sep 5, 2011 at 1:48:18 pm

Happy to help!

I was a little thrown by your original question, because AE doesn't really expose premultiplication to the user like many other compositors do, but it all makes sense now.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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