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Prob with Glow on Layers with Alpha

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Christian Sturm
Prob with Glow on Layers with Alpha
on Jul 18, 2012 at 2:22:45 pm

Hi,

When applying a glow effect to my layer and increase the radius, the result is an ugly black feather.
The black feather appears at areas where the glow crosses the outline of the object on the layer.
It looks like it is because the black areas that are hidden by the alpha channel affect the glow.

When apply the glow effect on an adjustment layer on top, the glow looks better. No black feather. However now I have the blackground glowing, which it is not supposed to.

How can I get rid of the black feather caused by the glow?
I want to glow the layer with the alpha channel only. The background should be unaffected.

Thanks in advance, Chris


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John Cuevas
Re: Prob with Glow on Layers with Alpha
on Jul 18, 2012 at 2:33:22 pm

I've had problems with glows/alphas too, particularly when using a straight alpha. What I've done in the past is to change my background color(Cntl + K) to a color similiar to my glow, ie...if I have a blue glow I'll change my bkg color to a similiar blue. Finally when rendering I'll change my alpha to pre-multiplied.

Perhaps others here will have a better recipe for glows/alphas, but this has worked pretty well for me to get a glow in the alpha channel into an Avid.

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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Christian Sturm
Re: Prob with Glow on Layers with Alpha
on Jul 18, 2012 at 3:50:14 pm

Thanks! Unfortunally my background is an image too. The composition background does not take an effect..

I would just use an adjustment layer, but unfortunally this background image should not be blurred.

I tried to find a work around using a subcomp for my layer to be blurred, but still the black feather appears.. So I am looking for another solution..


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Dan Fredley
Re: Prob with Glow on Layers with Alpha
on Jul 18, 2012 at 3:52:34 pm

One trick is to have the glow by itself on a second layer above the original layer.

Duplicate the layer.
Add a simple choker on the top layer.
Then put your glow effect underneath the simple choker.
Set the Composite Original to None.
Set the Glow Operation to None.
Adjust the choke as needed to get rid of the black edge.
Set your Blending Mode on the top layer to Add or whatever you prefer.


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Christian Sturm
Re: Prob with Glow on Layers with Alpha
on Jul 18, 2012 at 4:20:12 pm

that's it.. Thanks Dan.. working perfect!


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