Problem with Bumps and VRayLights at flat angles

[instinct]

Hey there,

i ran across this problem quite a few times already and finally managed to do a generic recreation to nail it down.

I get severly visible Edges with Lights coming from flat angles on a surface with bump.

In the example it's a simple Polyshape with a default VRayMaterial that has a Specklemap added as bump.
The Cylinder has a basic gray VRayMaterial with some glossy reflection.

My first thought was to tweak the light bias. But even tho that helps (edges are still visible even tho a lot less) it introduces HEAVY banding artifacts. (See image 2)

Any ideas ??

Regards,
Thorsten

[vlado]

This is somewhat normal; bump mapping is not continuous across triangles.

The only way to reduce these artifacts is to refine the geometry, or to reduce the bump.

Note that this is not specific to V-Ray; you will get the same results with other renderers in 3ds Max also. You can notice this effect very well if you apply a Gradient map as a bump map on a sphere, for example.

Best regards,
Vlado

[instinct]

I gotta admit that i dont really get it. I tried my very very best to reproduce it with both mr and scanliner to no avail.

In addition it DOES go away if i turn on "Force Backface Culling" wich is sadly not really an option for us.

Regards,
Thorsten

[vlado]

Ah, then it may be a different issue. If you wish you can get me that portion of the scene to vlado@chaosgroup.com and I'll take a look.

Best regards,
Vlado

[instinct]

the zip attached in the first post ist the scene in the screenshots

Thanks for taking a look. It has gotta a rather common issue (with car interior headlinings mainly )

Kind Regards,
Thorsten

[vlado]

It will work much better if you add some thickness to the surface and set the Shadow bias of the V-Ray light to a small positive value like 0.01.

Best regards,
Vlado

[vlado]

First is the original image; for the second one I've added a Shell modifier and set the light Shadow bias to 0.01.

Best regards,
Vlado

[instinct]

I noticed that too. Sorry forgot to mention in the first post. The Problem is that with the original meshes we usually cannot shell them. They originate from CAD data and contain Vertex-Normals that are destroyed/get lost when the mesh is edited


Kind Regards,
Thorsten

[vlado]

It is enough to have another surface between the problem surface and the light; you can keep the original surface intact.

Best regards,
Vlado

[instinct]

Damn. Didnt even think of that. Works like a charm. Thanks a lot Vlado!

Regards,
Thorsten