Back to Beauty - Compositing Problem

[vfx_film_televsion]

Hey Chaos-Group-Team and forum-members,

we are currently struggling getting the exact same result in nuke with multi layer compositing. We are using the Raw-Workflow to have more freedom over certain aspects of the rendered image. However we are noticing some slight difference in light exposure and color mapping between the rendered beauty and the comped image.
We are rendering with Exponential Color Mapping, "Apply Color Mapping" is checked within all RAW-Passes. I attached 2 images of "buddha" showing the difference.

Another issue we are facing is that after combing(with a plus merge) all light select passes as RAW-Type and using them as replacement for the Raw-Light pass, we are getting white edges around objects and lights are starting to disappear on objects. I attached 2 more images showing the error.

Is anyone else experiencing slight differences in their comps?

Let me know if I should upload the maya and nuke scene to wetransfer and where to email it.

Thank you in advance
Pirmin

[joconnell]

I thiiiiink you'll only get proper recombines if you're rendering linear rather than exponential - the maths of all the passes in nuke only work on standard linear data. Most people will deal with overbrights by doing the comp fully in linear and then adding a tone curve or grade at the very end.

[vfx_film_televsion]

Thank you very much joconnell! We were able to get the exact same beauty in comp by using the Reinhard Color Mapping Type. But we still struggle with the Raw - Light Select Passes.

We are using the "Advanced Back to Beauty" - Workflow which we found in the documentation(https://docs.chaosgroup.com/display/...Beauty-b2bComp)

However we are still having a problem with white edges around objects. Instead of using the RAW-Light Pass we rendered all the lights in RAW-Mode with LightSelects Elements and plused them back together in Nuke.

I attached two images with and without the white edges in the comped beauty and 2 images comparing the RawLight-Pass with the Plused Raw-Lightselect pass and it seems the aliasing is looking different....

Any help would be much appreciated

Kind Regards Pirmin

[joconnell]

Ah yes - I think there's an issue with multiply overall so people find it safer to do something like render the light selects in diffuse mode, divide them by the diffuse filter pass to make your own raw and then mult back together after you've done your light CC. Alternatively if you don't want to deal with per light spec / reflect / gi then you could maybe try the light select full mode? It's less fine in terms of control but for more naturalistic results it's the equivalent of putting gels and ND filters over the lights in your render and affecting all it's contribution at once...

[vlado]

Yes, making your own “raw” elements by dividing a regular diffuse lighting element by the diffuse filter is generally more robust. We do that internally in V-Ray for some render elements, but maybe not for the light selects - I have to check.

Best regards,
Vlado

[vfx_film_televsion]

By dividing the Diffuse Lighting from the Lightselect-Pass we were able to recreate the beauty! Thank You very much joconnell and vlado!