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Image sequence with two alphas?

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Steven BarbourImage sequence with two alphas?
by on Aug 26, 2009 at 2:48:02 pm


I have rendered out a sequence with 2 alpha channels (called alpha 1 and aplha 2). One contains the traditional alpha and the other z-depth information from maya.

Problem is AE seems to see neither (no transparency) and I have tried using various effects to extract them but can't find a solution.

I am thinking I may have to render out again with only one, and that after effects will only recognise 1 alpha channel, called just "alpha"?



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Larry S. Evans IIRe: Image sequence with two alphas?
by on Aug 26, 2009 at 6:24:58 pm

After Effects only recognizes the primary alpha channel, and I don't think it's a matter of what it's named as much as if there is an additional channel.

However, there are ways of applying data from two alpha channels provided you render them separately.

You can bring in your clip with the basic alpha channel for transparency. And then you can import the z-depth alpha render and use it as an alpha matte to the imported video. This will then enable you to apply effects like fog, blur, color correction, etc. to the video track using the z-depth information.

I frequently use this approach as I have the capacity to output z-depth as a greyscale sequence from applications like Vue Infinite, so that I have just the "alpha" information to use with the rendered video plates. Of course in that instance, I would use luma matte instead of the alpha matte because I'm using the greyscale values of the z-depth render itself, and not the z-depth information that is embedded in an alpha channel of a second video clip. If Maya will render the z-depth out as a greyscale sequence (I would think it should), you can do the same thing, and have less file overhead for the same effect.

Hope that helps.

Larry S. Evans II

Executive Producer

Digital I Productions

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Steven BarbourRe: Image sequence with two alphas?
by on Sep 4, 2009 at 12:51:25 pm


thanks for your response.

I have re-rendered with a single alpha channel for transparency, and another seperate pass with z-depth as you suggested and this has worked fine.

thanks again,


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