Does V-Ray have this problem? (Bump mapping causing strange fresnel effect)

[stevejjd]

Hi all,
hope you are all well.

After so many years I finally saw this problem illustrated in the help documentation of Arnold https://support.solidangle.com/displ...Specular+Layer

please scroll down to the bottom of the page where they discuss an issue with bump maps causing a stage effect on the fresnel.

I swear I have ran into that issue so many times in the past using V-Ray and I have no idea what it is. I am trying to make an example in 3ds max and V-Ray. While I try and mimic the result to find out what the problem is I wanted to ask if anyone knows if this is a noted issue with V-Ray?

Thanks for your time.

Steve ~

[Svetlozar Draganov]

There are some very old reports on the subject discussed here:
https://forums.chaosgroup.com/forum/...on-sss-renders

At this specific thread the issue is not considered as a bug however, if you think it is it would be helpful if you could send us a scene for investigation.

[vlado]

Recent versions of V-Ray should avoid this particular problem, at least for the VRayMtl material.

You might still get it with the alSurface material though - I didn't fix it there.

Best regards,
Vlado

[stevejjd]

Hi Vlado,

Will this problem happen in the case of using a VRayBlendMaterial with a VrayMaterial plugged into layer 1 (to contribute the its reflection) and then blended with a Fresnel falloff map?

I think I am seeing some odd characteristics happen in my case.

I'm just a bit confused and stuck. I want to use the VrayMaterial as a reflection coat because it avoids this issue raised in this thread and seen above. VrayMaterial has really nice controls and features. I like the Glossy reflections, the GTR tail falloff and the rough Fresnel.

But all of this seems to fall apart when using VRayMaterial as a coat of reflection due to the need to use a Falloff map

Does using the falloff map cause the above mentioned issue?

Thank you

Steve ~

[stevejjd]

Here is the image taken from the Arnold site that shows again what this issue is

[Svetlozar Draganov]

Can we see those odd characteristics like screenshots or scenes so could provide a more reliable answer?

[stevejjd]

Can we see those odd characteristics like screenshots or scenes so could provide a more reliable answer?

Hi Svetlozar,

Thank you for your question.

I am trying to understand how to layer reflection coats correctly and one of my questions is "Does using the falloff blend map produce this artefact?" - I am trouble shooting this at the moment and I am not able to reproduce the artefact. I wanted to ask you guys if it did. So I don't have a scene to give you that can show the falloff blend method producing this artefact.

I'm not convinced using any falloff map is the "correct" way of creating reflective coat materials in VRay as it does not represent the reflections found on a VRayMtl.

One of the reasons I want to use VRayMtl's reflective algorithm is because Vlado said he fixed the above mentioned issue.Also, Vlado mentioned that he did not adress the fix for ALSurface and so I wish to turn off the Roughness reflection in ALsurface and layer a reflective coat from a VRayMtl.

VRayMtl has really nice Reflection controls. I like using Glossiness as a opposed to roughness, I love the GGX and GTR tail falloff parameter, I love that Vlado fixed the above mentioned problem --- so all of that means I want to use VrayMtl for these properties. I wanted to test if all these parameters I like in VRayMtl get blown away when using a falloff curve.

I do not wish to use a falloff curve because it looks terrible and I don't know if its going to produced the above mentioned artefact. Its playing on my mind and troubling me because I don't know if that artefact will be produced when using a falloff curve.

I would urge chaos group to prioritise some kind of reflective coat workflow so that we can layer many coats of VRayMtlReflection. Reflections will appear as the should and there will be no question about weather or not they suffer from the above mentioned artefact. That way, there would be no need for additive mode as well.

For now I am using the Shellac or Additive mode to blend reflective coats as the reflections look 95-99% the same, all the nice things about VRayMtl are preserved. Instead of me worrying about the above mentioned render artefact, I only have to deal with making sure my material is energy conserving - a single problem I would rather wrestle.

Thanks for taking the time to read all my feedback in my posts.

I hope you can understand where I'm coming from and forgive my ignorance.
Steve ~