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Clean up green edges when using a key as alpha matte?

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Josh Pigford
Clean up green edges when using a key as alpha matte?
on Jun 5, 2012 at 9:29:39 pm

I'm keying some footage and I've got the same footage duplicated. The top layer is keyed and is set as an alpha matte for the bottom footage.

This creates a quick and pretty clean key for the footage that isn't all that great, but now I can't seem to quite get rid of the green around the edges (click to see full size):



The black in the very middle there will have video footage, but I took that out so you could see the green edges better.

I don't want to to just clip the edges as technically those green edges should act as shadows.


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Dave LaRonde
Re: Clean up green edges when using a key as alpha matte?
on Jun 5, 2012 at 9:52:49 pm

I see you pulled your key after all. Congratulations! Now just use multiple instances of AE's own Spill Suppressor on the upper layer, and you should be okay.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Josh Pigford
Re: Clean up green edges when using a key as alpha matte?
on Jun 5, 2012 at 10:20:45 pm

Yeah, another trick you posted back in 2007 about using multiple layers and alpha mattes ultimately did the trick.

Will try the spill suppressors.

What color would I be settings the suppressor to? The green?


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Spencer Tweed
Re: Clean up green edges when using a key as alpha matte?
on Jun 6, 2012 at 4:30:53 am

I can't see your photo, but from what you say here I'd use Keylight. The spill suppressor on that is... extreme - but if you know what you're doing it'll do the best job you'll get without 3rd party tools.

To make it not change your alpha channel set the "clip white" to 1 and up the "screen shrink/grow" to something like 10 or so. Then for most projects you'll want to change the "Replace Method" to "Hard Colour." Lastly change your "Replace Colour" to something that fits your image.

- Spencer


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Josh Pigford
Re: Clean up green edges when using a key as alpha matte?
on Jun 6, 2012 at 4:31:43 am

Can you see this image? https://img.skitch.com/20120605-ccgbw6y6j8ru88y1k2q68p4a54.png


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Spencer Tweed
Re: Clean up green edges when using a key as alpha matte?
on Jun 6, 2012 at 4:34:57 am

Yup, there we go. This should be totally fixable with Keylight. Good luck!

- Spencer


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Josh Pigford
Re: Clean up green edges when using a key as alpha matte?
on Jun 6, 2012 at 4:37:21 am

Yeah, I'm already using Keylight. Like I mentioned in the main post, it's not a straight forward key. I'm using two layers of the same footage, with the top layer acting as an alpha matte.

Those green edges are effectively the shadows from the surrounding footage and I need them to be something more...shadow colored? :)


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Spencer Tweed
Re: Clean up green edges when using a key as alpha matte?
on Jun 6, 2012 at 4:59:21 am

Yes, you use a second instance of Keylight. On the footage that is doing the matting (but not being the matte) you apply keylight and use the settings that I mentioned to not effect it's alpha channel. To make it more shadow colored choose black as the "Replace Colour" (or whatever color your shadows should be).

- Spencer


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Spencer Tweed
Re: Clean up green edges when using a key as alpha matte?
on Jun 6, 2012 at 5:01:05 am

That's pretty much how I always key ;) it allows me to build a matte with a bit more detail out of several keys, which I then pre-compose and use as a luma matte for my spill-suppressed layer.

This is how Keylight works in Nuke - but The Foundry have not updated Keylight for After Effects in a while...

- Spencer


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Roland R. Kahlenberg
Re: Clean up green edges when using a key as alpha matte?
on Jun 6, 2012 at 9:40:54 am

Here are Keylight Tutorials from The Foundry - http://www.thefoundry.co.uk/articles/2009/12/02/65/nuke-basic-workflows-key....

As you will see, procedural keying is an important part of the process. Not all the parameters sync with AE's rendition of Keylight but the workflow and procedural requirements are.

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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