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3d Room lit from outside leaks light

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Chip Maynard
3d Room lit from outside leaks light
on Feb 20, 2010 at 1:19:00 pm

Has anyone got a solution to this problem?

I've built a 3D room in After Effects using solids and a jpg for the floor.
I've cut windows in one of the walls using masks and placed a spotlight outside the room to create the effect of sunlight shining through the windows and casting light on the floor. It works perfectly with one minor exception.

All the seams between the walls and ceiling leak light!

I was careful to line them up exactly and built all the walls to nice easy to line up dimensions
Walls are 600Wx300H, floor & ceiling are 600x600. The comp is 600x600.

I've tried scaling up the walls 1 or 2%, and even shifting them a little, but nothing seems to fill in the gaps.

I'm thinking there must be some simple solution I'm overlooking...

Anyone?



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Bruce Wainer
Re: 3d Room lit from outside leaks light
on Feb 20, 2010 at 2:02:26 pm

did you try alpha add blending mode? it should add the anti-aliased edges together to make a solid corner (the edges of solids are anti-aliased in all but draft mode, i think, which cause the edges to not match up 100%. alpha add should fix it)


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Chip Maynard
Re: 3d Room lit from outside leaks light
on Feb 20, 2010 at 4:16:03 pm

That helped! Thanks Bruce.

Here's before:



Here's after Alpha Add. Now I've just got to fix the floor a bit:


What exactly does the Alpha add do?



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Chip Maynard
Re: 3d Room lit from outside leaks light
on Feb 20, 2010 at 4:24:44 pm

Also, props to the Grayscale Gorilla for the video explanation
http://greyscalegorilla.com/blog/2009/08/how-to-align-3d-layers-perfectly-i...



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Todd Kopriva
Re: 3d Room lit from outside leaks light
on Feb 20, 2010 at 5:15:29 pm

> What exactly does the Alpha add do?


from "Blending mode reference", found by searching for 'alpha add':

"Alpha Add
Composites layers normally, but adds complementary alpha channels to create a seamless area of transparency. Useful for removing visible edges from two alpha channels that are inverted relative to each other or from the alpha channel edges of two touching layers that are being animated.

Note: Sometimes, when layers are aligned edge-to-edge, seams can appear between the layers. This is especially an issue with 3D layers that are joined to one another at the edges to build a 3D object. When the edges of a layer are anti-aliased, there's some partial transparency at the edges. When two areas of 50% transparency overlap, the result is not 100% opacity but 75% opacity, because the default operation is multiplication. (50% of the light gets through one layer, and then 50% of the remainder gets through the next layer, so 25% gets through the system.) This is like partial transparency in the real world. But, in some cases, you don't want this default blending. You want the two 50% opacity areas to combine to make a seamless, opaque join. You want the alpha values to be added. In these cases, use the Alpha Add blending mode.
"

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Todd Kopriva, Adobe Systems Incorporated
putting the 'T' back in 'RTFM' : After Effects Help on the Web
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Bruce Wainer
Re: 3d Room lit from outside leaks light
on Feb 20, 2010 at 7:12:12 pm

wow... I never knew all that. thanks Todd!


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