Issue with exporting Volume grid images and compositing.

[KushKush]

Hello, I'm trying to export smoke/dust from volume grid separately from the image so I can composite it later on. I ran into issue, adding smoke image(isolated smoke) to beauty image resulting in smoke looking much darker. I've tried using blending modes, exporting both in PNG and EXR and in both scenarios I could not overcome the issue. Volume grid is in Volumetric mode, I've also tried Volumetric geometry(Vray popped a massage before rendering to maximize transparency levels to 565).
Beauty+smoke/dust, rendered together not composed (on top of the tank)
Beauty
smoke isolated.
Example of the issue( smoke being applied to beauty image, rendered separately) Composite issue I'm talking about. Beauty+smoke together without the blending modes.

[Zdravko.Keremidchiev]

On my side, it doesn't compose similar to yours. Which blending operation are you using, Add? How was the smoke lit when rendered?

[KushKush]

On my side, it doesn't compose similar to yours. Which blending operation are you using, Add? How was the smoke lit when rendered?

Hi thanks for answer, I want to clarify that the first image is not a composite(Its render of image as it is, both smoke and rest of the scene) its the desired result which I'm trying to get. I tried all of the blending modes. How smoke the smoke lit? I simply isolated the smoke which had Vray sky as background. My second attept was to add floor but make it invisible to camera, so the floor could be applied as background for smoke.

[Zdravko.Keremidchiev]

Do you have an Atmospheric render element from the original image where the smoke is part of the RGB? If so, you can compare it to the new one to see the difference.
Rendering the smoke alone might cause such an issue as it will not be lit according to the scene GI, but instead, it will appear a bit blueish because of the sun. If you want to composite the dust, you need to tweak it in the compositing software to match the color and intensity. Or you have to re-render the smoke in the scene environment where the GI is affected by the desert. Try using invisible to the camera floor.

[KushKush]

Dust layer on top of background layer, no blending mode.
Dust layer and atmospheric layer, yellowish colour(indented result)
Dust layer with atmosphere dust layer on top of background blended. Looks like there is loss of details in addition to wrong colour.

[KushKush]

Do you have an Atmospheric render element from the original image where the smoke is part of the RGB? If so, you can compare it to the new one to see the difference.
Rendering the smoke alone might cause such an issue as it will not be lit according to the scene GI, but instead, it will appear a bit blueish because of the sun. If you want to composite the dust, you need to tweak it in the compositing software to match the color and intensity. Or you have to re-render the smoke in the scene environment where the GI is affected by the desert. Try using invisible to the camera floor.

I did not solve the issue yet, should we continue looking for solution here or should I address support?

[Joelaff]

If it's not the GI affecting things as suggested above then are you using at tone mapping or other adjustment in the VFB itself (Filmic ToneMap, color correction, etc.)

We have found that these do not properly unmultiply the alpha before being applied, and thus ruin anything transparent and any edges. (They only work correctly if you image has a solid alpha).

[KushKush]

If it's not the GI affecting things as suggested above then are you using at tone mapping or other adjustment in the VFB itself (Filmic ToneMap, color correction, etc.)

We have found that these do not properly unmultiply the alpha before being applied, and thus ruin anything transparent and any edges. (They only work correctly if you image has a solid alpha).

Interesting, so you suggesting not appliying any tone mapping in vfb but rather in Post software, I understood correctly?

[Joelaff]

At least to try it, yes. It may be unrelated