Artifacts

[Alan_WP]

Hello everyone,

I’m encountering some unexpected artifacts I can’t resolve.

The model is a single object with ~2.2 million polys. One element shows artifacts (see attached image), but they disappear when I detach it from the main object. The same multi-sub material is applied in both cases.

Mesh Cleaner and STL Checker report no issues. I’ve also applied weighted normals, and the UVs show no distortion.

Any ideas what might be causing this?

Thanks in advance!

[MartinBeh]

Hard to tell from just the images - Could be an issue with the mesh data or format, which gets "fixed" when you detach. 

Would it be possible to share a trimmed-down version of your object, e.g. by deleting all the geometry as long as the artifact still shows?

[Alan_WP]

Hi MartinBeh,

thanks for responding, I started detaching objects, whilst doing so, the artifact disappeared. Now I will slowly detach Elements until I find the culprit and investigate further. 

If I get stuck again or find a solution I will post again - thanks.

[MartinBeh]

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@Alan_WP wrote:

thanks for responding, I started detaching objects, whilst doing so, the artifact disappeared. Now I will slowly detach Elements until I find the culprit and investigate further. 

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That sounds like a geometry issue; some parts of the mesh are being recalculated while detaching, which makes the artifact disappear...

Does this also happen when you attach a new object to the mesh? And what happens if you add a Turn to Mesh / Turn to Poly modifier on top?

[Alan_WP]

@MartinBeh I have found the culprit, and I have tried your recommendations above with no change. I have tried Turn to Mesh / Turn to Poly on the main object as well as the problem Object before re-attaching, nothing. Attaching a new object made no difference positive or negative.

In the scene attached, I have removed all other objects and materials. Upon attaching the 'Problem' object to the 'Main Object' you can see the artifacts on t'Main Object' upon rendering, I would appreciate any assistance you can provide.

Thanks 

[MartinBeh]

So far, I am not able to reproduce the issue.

Here is what I do

1. I run "for o in objects do o.material = undefined" to get rid of all the missing maps etc.

2. Next, I delete the existing Arnold light as that one also uses a missing map.

(without steps 1 and 2, I only get a black image)

3. I render the Perspective view you set up in the scene -- maybe you want to place a camera to clearly focus on the artifact?

Result: No artifact visible

4. I select "Main Object" epoly and attach "Problem" and render again

Result. No artifact, same image as step #3

So maybe this is related to the light/materials you set up? Or I am simply looking at the wrong part of your mesh?

[Alan_WP]

Hi @MartinBeh,

thanks for your testing. Normally there are no missing maps—I removed them before sending you the file, including the cameras.

Based on your feedback, I did some further testing and got the following results:

• I tested other sub-objects (using Arnold Subsurface and Arnold Image maps), and the artifact persists regardless of which sub-object is used.
• When using a subsurface material without any maps, the artifact disappears.
• After reapplying the original Multi/Sub-Object material in slot #15 and removing the OSL UVW Transform (along with all Arnold Image maps), the artifact disappears.
• Using a Physical Material (no Multi/Sub-Object) with Arnold Image maps causes the artifact to appear.
• Removing the normal map makes the artifact disappear.
• Disabling the Tangent Space option in the normal map node also removes the artifact.

It seems that the issue is related to tangent space. However, I’m a bit confused: in a previous project where I used this Multi/Sub-Object material, disabling tangent space caused issues as well. At the time, I ensured that tangent space was not computed per fragment upon project creation in Substance Painter, as recommended by multiple  online sources for use with 3ds Max and Arnold renderer.

So I’m not entirely sure what the correct setup should be here or where my mistake is.

I am open to any clarification/corrections thanks.

[MartinBeh]

Sounds like you made some good progress in identifying the root cause.

AFAIK tangent space for normal maps can be a bit finicky, so that is definitely a good candidate for such artifacts.

- How were your normal maps generated?

- Do you really need those normal maps? The geometry I saw in the .max file seemed fine without - but maybe I am just not checking carefully enough.

If normal maps are the cause I am not surprised I cannot reproduce this issue - so far, you have only shared a .max file but none of the assets used.

[Alan_WP]

@MartinBeh That is true, without the texture maps, you will find it difficult to re-produce. 

I could do without the Normal maps on a few materials, it would not be missed and are quite subtle, I often think, that when even the smallest details are missing, it can add to the realism of the whole picture...the brain un-subconciously feels something is missing. Maybe I am being to perfect, when the materials themselves are not ultra realistic. 

Still I have many other assets, that need the normal texture - and these could cause issues...