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Steve5D7C
Inspiring
April 23, 2025
Answered

Interpret with alpha, then remove alpha?

  • April 23, 2025
  • 3 replies
  • 937 views

Is there any freaking way in AE to bring in footage (multichannel EXRs) with alpha, then IGNORE the alpha for compositing purposes? I've been looking for this solution for years.

 

I want to be able to bring in my footage ONCE, then composite WITHOUT ALPHA, but still have the alpha available for final stenciling. This just does not seem possible in AE.

 

When extracting channels from the EXRs with the Extractor effect there is an "unmult" checkbox, but it does not remove the alpha. Presumably it unmults the edge pixels with the import color that's set in the interpret footage menu. But, even with this unchecked, comps STILL result in unwanted alpha stacking on edge pixels.

 

So, the ONLY solution I've come up with is to import all my sequences twice, once with alpha ignored (for comping) and once with it premultiplied. The second one is only used as an alpha stencil where appropriate in my comp flow.

 

This is incredibly hacky and inconvenient, especially when dealing with endless versions of a shot. There's got to be a better way that I don't know about, right?

 

RIGHT?

Correct answer JohnColombo17100380

Hi @Steve5D7C,

I'd expect you would be able to include the alpha as a channel that EXtratoR could see, so that you wouldn't need to have each EXR imported twice, but @fnordware would be the best person to answer questions related to EXR channel handling. Perhaps the Unmult option of EXtrator is doing something incorrectly or differently than what you would expect.

 

- John, After Effects Engineering Team 

3 replies

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fnordware
Inspiring
May 5, 2025

If the EXR is imported with alpha set to premultiplied, you just comp that footage over a black solid and you'll have the same result as ignore alpha. If you're using EXtractoR, you can comp your extracted footage over black or use Shift Channels to set the alpha to Full On before EXtractoR is applied.

F
fnordware
Inspiring
May 5, 2025

It's true that the ProEXR Comp Creator doesn't really set up the AE comp they way you need to to comp multiple passes, mostly because it doesn't know how you intend to use each pass. In general you want to:

  1.  Use Shift Channels to set the alpha to Full On for each layer, revealing the jaggy unpremultiplied pixels.
  2.  Comp all the passes in jaggy-land.
  3. Add a layer to the top that has the alpha intact and set it to Stencil Alpha mode.

Of course, that comp should be a pre-comp. You don't want that Stencil Alpha affecting your background or whatever.

JohnColombo17100380
Community Manager
JohnColombo17100380Community ManagerCorrect answer
Community Manager
May 5, 2025

Hi @Steve5D7C,

I'd expect you would be able to include the alpha as a channel that EXtratoR could see, so that you wouldn't need to have each EXR imported twice, but @fnordware would be the best person to answer questions related to EXR channel handling. Perhaps the Unmult option of EXtrator is doing something incorrectly or differently than what you would expect.

 

- John, After Effects Engineering Team 

    S
    Steve5D7CAuthor
    Inspiring
    May 5, 2025

    Thank you! TBH it's never occurred to me before that the Extractor plugin could extract the alpha in the same way that it does any other channel (partially because I always rely on the Create ProEXR Layer Comps script to auto shuffle my channels out, and this ignore the alpha channel). Bringing in footage with alpha ignored and then shuffling the alpha with Extractor is exactly how Nuke works, and a quick test shows it seems to do the job just fine. Thanks for the answer!

    Kevin-Monahan
    Community Manager
    Kevin-MonahanCommunity Manager
    Community Manager
    April 23, 2025

    Hey @Steve5D7C,

    Thanks for the question. I'm Kevin from Adobe Support. I'm a moderator here. I'll ask the developers if there is a better workflow given your needs. I hope we can assist you in getting an answer back for you and for the benefit of the community as soon as possible. Sorry for the hassle. Thx, ^KM

    Kevin Monahan - Sr. Community and Engagement Strategist – Adobe Pro Video and Audio
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