glow banding at the edge of alpha

Hi, apologies for the noob question. I think I'm doing something fundamentally wrong.

I have a fire effect rendered in maya/vray using phoenix fd. The image is premultiplied.

originalFire.png (980.63 KiB) Viewed 3152 times

I've added a glow in fusion. Which looks fine in fusion, either against a black background or composited over another image.

glowInFusion.png (776.5 KiB) Viewed 3152 times

But when render the image (originalFire + Glow) and bring it into Resolve and composite over the footage, it has a nasty band at the edge of the glow.

glowAlphaBand.png (600.29 KiB) Viewed 3152 times

Does anyone know where I'm going wrong in the pipeline? This seems to happen if I render pngs or exrs.

Any help would be very gratefully appreciated.

What settings in Resolve?

premultiplied alpha and normal composite mode

It looks to me like the glow isn't premultiplied but the fire footage is premultiplied. So when I set the clip attributes to premultiplied alpha, it is compatible with the fire but not the glow.

The only solution I've found is to have two copies of the fire footage (with the glow) in Resolve layered on top of each other. Make the composite mode for the bottom layer "multiply" and the top layer either screen or add. Screen looks closest to the effect I'm going for, but it seems to go wrong when the background layers pixels are very bright.

Kind of works, but feels like a fudge...

(PLEASE IGNORE MISREAD THE POST)

Try using the Soft Glow tool, it has a threshold for glow which I find is more useful for fire effects otherwise it will add glow to even the dark parts of the clip. Also setting the viewer to HiQ will give you a better idea as to how the final render will look. Something else to try may be to add the glow after the merge to see what happens, this could indicate if it is a prob with the merge and premult.

[Steve Roberts]

In the glow tool, try using Multibox instead of Gaussian Filter and see if that makes a difference.

You can also try to add a "Alpha Multiply" node before the Saver.

Thanks all, I'm an idiot. I re-rendered all the source files as exr and that fixed it.
So you know when I said "This seems to happen if I render pngs or exrs." Yeah you can ignore that...