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Automatically fill holes in Alpha?

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Sam Pipes
Automatically fill holes in Alpha?
on Feb 24, 2010 at 3:08:31 pm

I have a sketchy animation that exists as a PNG sequence, black lines on a transparent background. For the sake of clarity, I'm trying to find a way to automatically generate a white background behind the animation, mirroring the shape of the drawings.

I've already had limited success by applying a hard-edged white glow to a duplicate of the animation on a lower level. This leaves a lot of empty space inside, so I increase the glow width until it's all filled in, then use a choke to shrink it down on the outside. While this almost works, the resulting shape is really blobby and doesn't conform to the original drawing enough to look good.

What I'd prefer to do is leave it at the glow phase, making it just wide enough to form an outline. What I'm looking for is something that can identify a pocket of transparency surrounded by solid shapes, and automatically fill it. Is this a pipe dream?


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Dave Johnson
Re: Automatically fill holes in Alpha?
on Feb 24, 2010 at 3:37:05 pm

I'm not at all sure that I understand what you're trying to accomplish (perhaps a screenshot would help?), but it sounds like you basically want a drop shadow that's white and doesn't have any blur. If that is the result you want, but you don't want to do it that way for whatever reason, perhaps just duplicate your animation, map the black lines to white, then offset it a few pixels?


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Sam Pipes
Re: Automatically fill holes in Alpha?
on Feb 24, 2010 at 4:19:39 pm

Sorry for the confusion. Here's a more descriptive image.



The top example was made by making the glow radiu so wide that it filled the monster's insides, then using a choker to bring it back down to a reasonable scale. I'm looking for a better, more precise way to dynamically get the effect, since I'll be working with hundreds of images at a time.


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Dave LaRonde
Re: Automatically fill holes in Alpha?
on Feb 24, 2010 at 4:26:31 pm

Was this PNG sequence created in Photoshop?

If so, just fill the areas in question in Photoshop. There really isn't any automated way to do what you want in AE.

There's a reason why it takes so long to do cel animation.

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


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Sam Pipes
Got it!
on Feb 24, 2010 at 4:42:51 pm

Eureka!

Turns out the Paint Bucket effect can do this splendidly, provided you manage to get the areas you want to fill nice and closed off. Set the Fill Point way off the canvas, so it fills everything outside the shape, then simply toggle "Invert Fill." Look great!


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Dave LaRonde
Re: Got it!
on Feb 24, 2010 at 4:46:54 pm

Glad you got it, and sorry I misunderstood you -- I thought you only wanted certain selected areas of the line art filled. I had no idea you wanted the entire figure filled.

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


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Sam Pipes
Re: Got it!
on Feb 24, 2010 at 4:54:21 pm

No problem, and thanks for the help! It never would have occurred to me if I hadn't made that image :P


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Dave Johnson
Re: Got it!
on Feb 24, 2010 at 5:58:13 pm

Ok, then so I was way off the mark ... was wondering why you'd want a white mirror of black line drawings, but figured why ask why and tried to just answer the question. Thanks, Dave, for stepping in and providing a more useful suggestion ... I'll try to read more carefully before replying next time. ;~)


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