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How to use the overlapping area of 2 layers as a matte?

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Aivaras Seduika
How to use the overlapping area of 2 layers as a matte?
on Apr 4, 2011 at 6:18:50 pm

Hi guys,
This is wrecking my brain, please help!
The brief is to have 3d layers floating around, and images reveal as 2 pre-determined layers overlap. The image is within the overlapping area of the 2 layers.
Kind of like a boolean operation in 3ds max if someone's familiar with this, where you can set the result to be the intersecting area.

Is there any way to achieve this with what's built in to AE?
I've tried playing with channel operands but not really getting anywhere.

I've been trying to use overlay modes to combine RGB channels of 2 layers and use the combined value as a luma matte, but not getting anywhere.

Anyone point me in the right direction?
Thanks loads.


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Brian Charles
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 4, 2011 at 6:32:49 pm

Is it possible to Precomp the 2 intersecting layers and use them as a track matte?



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Aivaras Seduika
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 4, 2011 at 6:36:41 pm

Thanks for your reply Brian,
Yes this works, but the track matte becomes the combined alpha area of the 2 layers, not the intersecting (or overlapping) area.
Just the overlapping bit is the bit I need to be the matte.
Cheers


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Dave LaRonde
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 4, 2011 at 6:55:25 pm

Are you animating a 3D camera in the final comp?

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


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Aivaras Seduika
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 4, 2011 at 7:10:46 pm

Hi Dave,
Yes I will be, but only in the master 'top' comp containing these layer-overlapping pre-comps, so the camera inside the actual pre-comp will be static.


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Dave LaRonde
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 4, 2011 at 7:22:23 pm

That's too bad. I could have offered a way to do it if the camera didn't change, but I can't figure a way to deal with perspective changes of an animated camera.

You may have to create this in your 3D application.

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


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Aivaras Seduika
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 4, 2011 at 7:28:54 pm

Thanks dave,
How would you have done it if it was a static camera?
Thanks


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Dave LaRonde
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 4, 2011 at 7:47:59 pm

I would have used the upper layer in the timeline as a track matte for the lower layer -- either a luma matte or a luma inverted matte -- and prerendered the result as an alpha channeled movie. I could then use the prerender as an alpha matte.

It assumes that all 3D layer movement has been established, in the same way a movie edit is locked before color correction. If you make a change to the layer movements, you have to do another prerender.

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


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Walter Soyka
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 4, 2011 at 8:40:39 pm

[Aivaras Seduika] "The brief is to have 3d layers floating around, and images reveal as 2 pre-determined layers overlap. The image is within the overlapping area of the 2 layers."

Copy those two layers into a new comp. Color the top layer white, and color the bottom layer black. Add a blank adjustment layer in between the layers (to break 3D intersection). Toggle the Preserve Transparency switch [link] of the top layer.

The top white layer will only show when it intersects the bottom black layer. You can use this comp as a luma matte.

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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Aivaras Seduika
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 4, 2011 at 9:27:20 pm

Thanks very much guys for taking your time to reply! I'll give these ideas a go tomorrow, will update then.
Cheers


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Aivaras Seduika
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 7, 2011 at 3:45:18 pm

Walter, thanks very much for your advice - it worked! It's still not very flexible as a device due to the need for duplicate pre-comps (one to use as a luma matte, the other sitting over the top as a diffuse layer), but it works well enough for what I need.
Thanks again!


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Walter Soyka
Re: How to use the overlapping area of 2 layers as a matte?
on Apr 7, 2011 at 3:48:28 pm

[Aivaras Seduika] "Walter, thanks very much for your advice - it worked!"

Glad to hear it, and happy to help!


[Aivaras Seduika] "It's still not very flexible as a device due to the need for duplicate pre-comps (one to use as a luma matte, the other sitting over the top as a diffuse layer), but it works well enough for what I need."

Totally true. This is the sort of thing that's a lot more straightforward with a nodal compositor than a layer-based compositor. Good luck with the rest of your project!

Walter Soyka
Principal & Designer at Keen Live
Motion Graphics, Widescreen Events, Presentation Design, and Consulting
RenderBreak Blog - What I'm thinking when my workstation's thinking
Creative Cow Forum Host: Live & Stage Events


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