Maya RANDOMLY inverting Normal maps

SPQMan

While using Arnold in Maya, I faced an unusual problem:

There are 32 teeth models in the project (16 upper and 16 lower). I use 4 UDIM maps; one for each eight teeth. For some reason, Maya visually inverts the Normal maps along the Y axis ONLY for the lower teeth, while the upper teeth remain as they should (in the final render also). I could click "invert Y", but then everything becomes the opposite - the upper teeth are wrong inverted and the lower teeth are correct.

All this happens considering that:

1) I baked each Normal map in OpenGL format.

2) In other programs (Blender, Marmoset Toolbag 4) Normal maps work correctly (none are inverted). (In Blender I also used UDIMs, while in Marmoset they are not supported, I used each texture separately).

(This problem is NOT due to the fact that I forgot to set color space RAW or UV Tiling mode UDIM(Mari))

(Normal maps - 8 bit RGB)

I tried many solutions to the problem:

1) I used "aiBump2d" instead of "aiNormalMap" - the result is the same.

2) Freeze Transformation - the result is the same.

3) Combine all 32 objects into 1 - the result is the same.

4) Connect textures separately (not using UDIMs) - the result is the same.

5) Tried different versions of Maya and Arnold - the result is the same.

6) Tried to use Normal maps baked in DirectX format - the result is the same (just inverted Y axis as expected).

7) Tried to use Normal Maps baked in different programs (Zbrush, Substance Painter) - the result is the same.

8) TX textures - do not affect the result.

9) This is not the influence of the scene light on the render (no matter how I rotate the model, the camera, the light - the result is the same. Even using "Isolate selected" in Arnold, clicking on the "aiNormalMap" node, I clearly see the difference which model has the Y axis inverted (model like this has visible seams).

10) I tried to test it in a completely new file - the same result.

I might have missed something (I have been messing with this for a week now).

From what I have already done, I can conclude that this is not related to the quality of Normal maps, the work of UDIMs and models. The problem is Maya.

Most likely I'm missing some setting that I haven't heard of, due to my inexperience working with Maya. I scoured the internet and couldn't find anything like it (only dozens of "forgot to set color space RAW"). I hope someone here can tell me what I'm doing wrong. For now, the only solution I see is to simply create a second, separate shader for the lower teeth and invert the Y axis there. Although it seems a bit messy to me. But I'm very interested to know why Maya does it like this.

Neox

try checking the tangentspace handedness in your mesh

the funky part is, even if those settings are the same between maya and marmoset toolbag, the resul isnt the same. slightly infuriating

SPQMan

It seems like nothing happens.
I forgot that I already tried changing these settings previously...

Neox

How? I would invert the green channel and therefore something must change?

SPQMan

Of course, when I invert the Y or the green channel it changes but as I said earlier, one mesh will still remain incorrect:
I invert the Y in the common "aiNormalMap" node to correct the mesh on the left, then it becomes correct while the mesh on the right becomes incorrect.

And when I change tangent space handedness nothing happens:

Alex_J

if you change a parameter in material and the mesh doesn't update that would indicate it does not have that material applied to it

SPQMan

What do you mean? When I change a parameter in material, it works like it should, as you can see in this image. But Maya inverts the textures that shouldn’t be inverted.

"And when I change tangent space handedness nothing happens" - it's not a material parameter, or I'm wrong? It's like a "Shape". And when I change displacement parameters (Arnold>Displacement Attributes) or subdivision, it works fine.

Alex_J

looks like you are right, i didn't look close enough. handedness is part of shape node, not the material

poopipe

given that this is maya it's probably a shit transform somewhere on one of the objects

SPQMan

I don't know, I mean, I tried to combine objects into one mesh even using different software and importing to Maya, but it's always the same.

poopipe

are UVs flipped on the problem object ?  it shouldn't be a problem in this day and age but you never know .. 

SPQMan

No, of course not. Everything works fine in the other software like Blender and Marmoset with exactly the same meshes, like I said.

poopipe

it working in other applications is no guarantee that the UVs aren't flipped - marmoset certainly handles it correctly.

I don't personally know if arnold/maya does

SPQMan

You were right, poopipe, UVs are flipped.

At first it just seemed strange to me that they could be flipped while only normal maps were working incorrectly. And even if they were flipped, I wouldn’t even think that it may be a problem for Maya. But after you wrote that you weren't sure how Maya works with flipped UVs, I decided to double check.

Thank you for your time. I'll be more careful next time.

poopipe

glad it's sorted

it usually pays to check the silly things early on in my experience - specially when you're dealing with Maya