05 May 2003 | |
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VFX supervisor
portfolio
Jonas Ussing
Freelance VFX supervisor
Jussing VFX
Copenhagen,
DK
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![]() Hi all!
Given that it should be mathematically easy to make a premultiplied clip UN-premultiplied, based on its alpha and the background color, I'm sure there has to be a way to do this in most professional compositing packages, right? So..... how? ![]() I'm using After Effects (but posted here, hoping the package-independent forum would increase chances of a solution). Any advice would be greatly appreciated! Cheers, - Jonas |
05 May 2003 | |
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New Member
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Re: UN-premultiplying footage w/alpha? How?
AFX as you know have tool for unpremultiply (in interpret footage ...), same as many other compositing apps. If there is no such tool, you can simulate operation by dividing color chanels by matte, where:
red = red/matte green = green/matte blue = blue/matte In this case "semi-transparent" areas wont be completly corrupted (unpremultiply is not perfect proces) during for example - CC. Result then should be remultiplied by original matte chanel after CC or whatever (in Discreet FFI this is done automaticaly). For same purposes, you can use Knoll "unmult" plug-in, Sapphire MathOps etc. Regards Goran |
05 May 2003 | |
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Vfx Viking
Arvid Björn
Sr. 3D artist
Sthlm Post Production (Stopp)
Stockholm,
Sweden
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Afx only lets you set if you're using premultiplied footage or not.. I cant find any way to unpremult footage..
![]() ![]() Last edited by opacity : 05 May 2003 at 07:40 PM. |
05 May 2003 | |
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New Member
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You can use Knoll "unmult" plugin, or "Remove Color Matting" to remove color fringes from layers that are premultiplied with a color. Well, I am not AFX expressions expert but AFX 5.5 has 4D vector containing (r,g,b,a) and DIVIDE math-op., so I believe it can be done true expressions too, maybe ...
Goran |
05 May 2003 | |
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VFX supervisor
portfolio
Jonas Ussing
Freelance VFX supervisor
Jussing VFX
Copenhagen,
DK
|
Thanks for your replies, guys!
![]() I think I'll have a go at that expression thing, then... Cheers, - jonas |
05 May 2003 | |
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New Member
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Maybe you should try
http://www.walkereffects.com/products/ it seams they have premultiply/unpremultiply plugin. And there is free demo too. If you achieve something, let us know. Goran |
01 January 2006 | |
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Expert
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