Vray bump map - dark edges on polygons

[james_malloch]

MAYA_test-scene_question4.zip When rendering a polygon surface with a bump map, dark lines appear on the edges of the polygons. The dark edges only appear on the glancing edges, but this makes the bump unuseable. Does anyone know how what the problem is please?

The VRayMtl has a texture channelled into it's bump slot (see attached screengrab to shop the bump settings)

I can mostly fix it by adding a subdivison node, but the surface has already 5 million polygons, so I can't afford to further subdivide it due to the increase in render time.



Vray V-Ray 6 for Maya (v6.00.02 from Aug 30 2022).
Maya 2023.2
Windows 10
128Gb Ram

[intercard]

Hello this only my opinion but maybe your mesh need more subdivision or try to use VRay displacement map for making new surface with more subdivisions and use the bump just for details no?

regards

[hermit.crab]

Seems odd to me. Does the issue occur on a fresh scene and a similarly deformed surface? Could you send the scene and texture so we can take a look?

[james_malloch]

Hi hermit.crab,
Thanks for your interest in this problem - yes the problem occurs in a fresh scene where I have made a new VRayMtl and attached a new texture into the bump slot. The issue happens at glancing angles only, where the surface on the angles facing towards the right-angle of the camera view darkens.

I have attached a simplified version of this Maya scene, alongside the screengrabs in my initial post.

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Also, thanks intercard for looking at this. Yes it is very low rez in these screengrabs, but I still don't understand why the bump is acting like this. Surely the bump should flow over the polygonal surface, even if it is angular?

[hermit.crab]

Not entirely sure what's going on, so I logged the issue (internal bug-tracker id: VMAYA-11605) so the devs can take a look. Although not optimal, I suggest you use the Subdivision solution.

[james_malloch]

Please if anyone has thoughts on this issue, please tell me!

I haven't been able to find a workaround and I'm getting so many black spot/artifacts, despite trying many alternative methods. I'm on the verge of having to forget using bump maps in my projects due to this. Displacement mapping is a killer for render times, making my animation projects almost unviable.

[SonyBoy]

Your bump map looks super low rez. I'm also wondering whether you've tried playing with the bump value. If you have it turned up much too high I would imagine it might cause artifacting like this.

[james_malloch]

Thanks SonyBoy for your thoughts.

It can't be the low rez bump map - it happens with different texture maps and even procedural textures. The bump value is within a reasonable range and the problem happens at low values too - it is interesting because any non-zero bump value makes the black artifacts appear.

I have had to stop using bump maps in our latest animation because of this, so any thoughts would be appreciated!

[james_malloch]

Please if anyone knows what is causing these black glancing edges, I would be very happy. This has been plaguing me for months.

I have been working professionally in 3D for over 20 years and never had these kind of problems with bump mapping with other renderers (3DS, Lightwave, Renderman, Mentalray).

[Morbid Angel]

Hi James,

I checked your scene, the issue is also happening with arnold, I think its a shading limitation of a renderer/bump map approach. The low res geometry is unable to produce the necessary shading at glancing angle. I've comeup with a quick solution for you though, if you take a sampler info and plug it's facing ration into a ramp, then multiply the ramp's black value of the glancing angle over the bump map *(essentially removing the bump map at glancing angle it should produce a nearly identical result without the black edges, see attached images and maya scene. Hope this helps.

[james_malloch]

Hi Dimitry ( Morbid Angel)

Fantastic, this is an excellent solution
Thanks for taking the time to help me on this problem - also this will be crucial for many different projects into the future!!

Hopefully this will help many other guys too, it's really interesting that this is also a problem on Arnold!