VRay 6.2 - VRayAlSurfaceMtl - Rendering Artefacts ACES

[jordan_dubosc]

Hey guys, we are facing strange result with the VRayAlSurfaceMtl in ACES workflow:

Tested on :

- 3dsMax2023 with VRay 6 Update 1.2 (6.10.09 Build 32197)
- 3dsMax2024 with VRay 6 Update 2.1 (6.20.06 Build 00000)

Both with ACES Workflow.

We spotted the problem while rendering character in lookdev:




We managed to reproduce it on a basic scene with just a sphere and a VRayColor (attached)
To reproduce it we need a basic VRayAlSurface by default with SSS mix at 1

It looks like the problem is visible only when we use sRGB primaries in the VRayColor.


RGB primaries = None

RGB primaries = ACES primaries


Since we work in ACES Workflow we must work in sRGB primaries, it feels like the artefact is stronger with reddish colors (Aces related I guess), we also spotted that if we up drastically the min shading rate (6 by default) it softens the artefact (weirdly we found out that a value of 3 or 4 also reduce it).

As I said we have some ways to bypass this issue either changing rgb mode (for this specific character) or up the min shading rate on every character renderlayers but all of those feels a bit messy for a production what's your take on this?

I've attached our ACES config and 3dsMax2023 scene.

Thanks!

Jordan

[hermit.crab]

Thanks for the provided scene. This seems unrelated to color management in general, it only enhances the effect. I managed to reproduce the weird edge with the legacy Gamma Workflow and only with the VRayAlSurface itself (no textures, VRayColors). Not exactly sure what's happening, since rendering with IPR yields expected results.

What seems to mitigate the effect is lowering the Diffuse strength to ~0.8. Otherwise, I'll continue troubleshooting.

EDIT: FYI, I've logged it in our system (internal bug-tracker id: VMAX-14740).

[jordan_dubosc]

Hey thanks for the quick answer, I couldn't manage too reproduce it only with de VRayAlSurface itself but didn't try in the old Gamma Workflow, I don't think we will be able to lower Diffuse strength value since we will be using maps from Painter we got to stick with 1 (at least for now).

Not exactly sure what's happening, since rendering with IPR yields expected results.

Exactly, our lookdev didn't spot it at first since there are in IPR while working, though I managed to get rid of the weird edge by upping the min shading rate to 100 ( I feel like this is somewhat similar to what IPR does since its dynamic).To be honest, though, I have no idea what this value would mean on a production scale.

Feel free to ask me if you need anything I could provide to help