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Luma matte problem

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Mirza Kadic
Luma matte problem
on Feb 10, 2020 at 2:11:46 pm

Hi everyone!

I'm trying to solve a problem for few days now, and I have quite some experience with After Effects, C4D, Redshift etc.. But this I just cannot figure out, and it's kinda basic stuff

So, I'm selling video renders for a marketplace and for that reason I need 2 files in zip package, one beauty pass and another black & white luma matte (for users to combine the two to get alpha channel).

For example...
Beauty (with post fx applied - bloom,glare etc.):

Luma matte (combined post fx and with alpha channel to get this luma matte):

But, when I use beauty and set track matte in ae with luma matte (example above), it does make an alpha, but a lot of information kinda dissapears, notice the glow/bloom is almost not present (image does have an alpha channel, but showed it with black BG to show what I mean):

Of course, I tried to brighten luma matte, but then I get this:

I'm getting grey hair as we speak, so any insight would be really appreciated!

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Cassius Marques
Re: Luma matte problem
on Feb 10, 2020 at 5:03:04 pm

You should get only the basic color correction from you 3d engine, leave the bloom and the rest of the post for AE. If you're leaving the luma so your clients can change the BG in the template, you won't ever get it right on the half visible pixels. light that composites fine over black wont do the same in a lighter color.

If you're not sure what is happening now, its simple. Your current workflow (since there is no alpha before you apply the luma) gets as much black as it gets the "light" from the grey luma pixels in the matte. Since the pixels there in the beauty are a combination of "light" and black bg. When you extract, lets say, 50% of that, and reapply over black you essentially took 50% of your light off, thus the dimming.

You should either do it in post or save with an imbued alpha.

Cassius Marques

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