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When working with 3D scenes involving transparent-background fire or other glow effects, what is the standard format to render & save them in that will be compatible with VFX software, and allow overlaying the image/sequence over other footage?

This has been a problem I've run into a occasionally as a 3D artist who also creates renders and animations, and although it's not critical for my work I really want to know the answer!

As an example, take this basic scene in Blender involving an emissive square with bloom effects, and a volume with emission and 0 density. In Blender, they appear as you'd expect; but after rendering and saving as a PNG, all the glow effects are gone.

enter image description here

Now this is a pretty common problem I see online, and everyone says to just use EXR instead of a PNG - but when I import an EXR from Blender into Davinci Resolve, the color space ends up wrong - and correcting that issue requires downloading a custom LUT, which seems to once again remove the glowing areas, bring me right back to where I started.

And sure, I'm not a VFX artist so I may be doing something wrong, but I feel like there's no way it has to be this complicated - when I download transparent fire effects from online, they just come as a PNG sequence and work perfectly fine.

So, back to my question; In terms of image formats and alpha channels, what is the standard way to take a transparent-background fire simulation, glow effect, etc. from 3D software to VFX software? And why does everyone say that using EXR will solve the problem when clearly it's possible to have effects like this in PNG format too?

Apologies if this question is confusing or overly long - it seems like there are so many different aspects to the issue that it's hard to narrow it down to a single concise question!

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  • This is a good question. I sometimes export PNG passes for lights etc with an alpha that can then be composited using Add or Lighten, and additional conventional passes with alpha than can be comped using the normal compositing. There's a great (and funny) video here about how alpha passes work: youtube.com/…
    – tomh
    Jun 15, 2023 at 10:28

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