artifacts again [SOLVED]

[karla]

My render of a relatively high resolution human head mesh (approx 10k vertices) consistently gives shadow-like artifacts (see numbers 7 in attached image). I'm aware that, say changing sampler type to Metropolis and surface integrator to bi-directional or increasing mesh resolution may fix this, but they don't seem to correct the defect. The artifacts occur with both glossy and glossy translucent materials. I've exported and re-imported .obj models to clean the mesh, checked and flipped normals and recalculated normals on the outside several times also. Shining the light onto another area of the face hasn't helped either. Has anyone a suggestion for me to try out or is there still an occasional problem with artifacts in LuxRender?

[jensverwiebe]

Hi

1. Check over the normals by letting show you the normal directions

2. Often repeating the recalculating of normals outside give more and more muddled result in complex objects i found. ( dunno exactly how blender interpolates this atm. )

3. Imported .obj data is often scaled and has redundant vertices. Check for duplicates and remove doubles then with the smallest margin to set ( < 0.00010 ) in edit mode.

Jens

[pablo]

You are using glossy translucent with homogeneous volume, aren't you?
Then the #7 should be artifacts from the volume, as it doesn't consider the smoothness of the object.
With glossy material it shouldn't happen though.

pablo

Edit: It could be also due to a too high bump value.

[karla]

Thanks Jens, I've already tried these methods several times on several versions of the model over the past few weeks.

Thanks too, pablo. I'm already using your skin material. Bump value 0.0020 (yours = 0.0010).

I've just carried out a quick test and render which showed that the artifact appears to be caused by too coarse a mesh. Subdividing the head mesh from ~10,000 vertices to ~160,000 vertices eliminates almost all of the jagged artifacts. I'll now have to consider whether to proceed with this type of model configuration.

[pablo]

What looks strange to me is the strenght of the issue, the lights could be liable, toghether with the volume.
Which type of lights are you using? It looks Sun & Sky, they are problematic in such situations, try light planes and a Hemi for diffuse lighting, instead.

pablo

[Meelis]

When u open the obj model in MeshLab and go:
filters - selection - select self intersecting faces.
Are there any of self intersecting faces?
Or any non manifold edges?

[karla]

@pablo
It seems that the sun-sky lighting is causing the problem. I checked back on my earlier images and files and saw no artifacts when I used area lights. When looking at the archives the artifact problem doesn't arise immediately after change from area to sun so I didn't pursue that particular factor. At the time I changed to sun-sky after advice from "MH" Manuel to create shadows. BTW your Test2-1.blend has sun-sky with no problems - which you obviously know.

@Meelis
Thanks for the suggestion. The original mesh was created by MakeHuman, exported to Blender, head cut off, head cut in half, modelled to character, duplicated, mirrored, welded together as a complete head, duplicate vertices eliminated. To try and overcome the artifacts problem the normals were checked and fixed, the mesh exported as .obj then re-imported as .obj to try and clean it up. The areas with artifacts were checked very closely and no mesh defects found. I think - apart from my initial poor re-assembly on the vertical seam halfway round the rear of the head - that the mesh integrity was perfect.

I didn't understand what MeshLab was 'till I checked just now. I haven't got it and I use Ubuntu 11.04 64 bit and there are indications that it may not run anyway. Thanks again.

I'm marking the problem as solved and will watch the lighting setup in future.

[karla]

Hemi light with HDRI is now being used. Many other changes have also been made. I'm posting details on Blender Artists as I progress. http://blenderartists.org/forum/showthr ... ight=karla