blurry alpha channel edges

# 1 08-05-2005 , 12:04 AM

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Hello,

I am trying to render some foreground stuff in a separate pass so I can later composite it into the background, but the edges in the alpha channel aren't sharp enough, resulting in a blurry halo around the foreground objects. Does anyone know how to make the edges of the matte sharper?

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# 2 09-05-2005 , 12:21 AM

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its not blury I belive, if you will look close, its that the background color got mixed in with the color along the AA'ed edges. 2 ideas for it a more nutral background color with the things you are compositing with. 2nd is do a negitive a inverted background, with a inverted mask. < should suck out the offending color.

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# 3 09-05-2005 , 10:11 AM

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is motion blur turned on? post a pic so we can see.

Alan

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Currently working on: Your Highness

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# 4 09-05-2005 , 11:27 AM

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Originally posted by Pony
2nd is do a negitive a inverted background, with a inverted mask. < should suck out the offending color.

Originally Posted by

Man my head is spinning :o Can you explain this further Pony

Regards
Paul

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# 5 09-05-2005 , 08:38 PM

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pure, some pic's for you. If this is what there talking about. Its not motion blur.

tga image saved out with alpha. Alpha is acruat. Note the black background.
btw 2x size on the image to show things more clearly, used nerest naber on the resize.

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# 6 09-05-2005 , 08:41 PM

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ok using the alpha map corectly you will still see that some of the black of the background was mixed in to the semi-tranparnet AA'ed pixels on the edge.. This creats the ring efect. Not a bad alpha.

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# 7 09-05-2005 , 08:42 PM

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I'll wait to see what pure thinks, BMS. Might not need to do that if he knows something.

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# 8 09-05-2005 , 09:10 PM

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Hello,

Thanks for the tips! The image i'm trying to get is of an island with some vegetation on it. I did the vegetation with Paint FX and I was just simply unable to get a good alpha of just the paint FX and their shadows, so what I did was I rendered a pass with both the island and the paint FX (top pic):

https://animation.filmtv.ucla.edu/stu...na/alpha2.html

The problem I am having now is getting a good ocean pass. The biggest problem is getting rid of the Sky portion of the Water/Sky envFog Material. Even if I set it to just Water, there still seems to be some Sky fog showing up. The pic you see here of the alpha channel had the levels adjusted in photoshop to more clearly show the lingering fog. The last pic I tried rendering against a white background, but that didn't work either. I have no idea where to go from here, any help would be greatly appreciated. Thanks!

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# 9 09-05-2005 , 09:54 PM

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got some cool pfx on that. try chaning the envimrnet color on the camara for the render of the water. to your sky color. Should help some.

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# 10 10-05-2005 , 08:21 AM

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Pony my first guess is that it's a premultiplication problem. That can create halo effects and stuff around objects in comp. I'm not 100% on that but its definatley where i'd start.

user added image

Alan

Technical Director - Framestore

Currently working on: Your Highness

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blurry alpha channel edges

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