subdivision rendering artifact

[eliz]

Hi,

I'm trying to render a pretty low resolution obj format model in houdini with mantra's micropolygon renderer. I would like to smooth the model for the render. I have tried both selecting "polygons as subdivision (mantra)" on the geometry SOP as well as applying a subdivision node to the file node within the geometry SOP. Both cases result in black spots showing up on the model.

Also, the only light in the scene is a light template with a VEX global illumination light shader applied for ambient occlusion.

The black spots lessen when I move the camera in on the objects. Increasing the pixel samples doesn't seem to have any effect.

I have attached 2 pictures--the first shows all the black artifacts. The second shows the camera moved in toward the model and how the artifacts lessen when the model takes up more image space. You can still see black spots on the model farther from the camera, though.

I'm new to using Mantra. Does anyone have a suggestion for me to try?

Thank you!

[edward]

Could it be bad geometry? Append a Divide SOP: turn OFF convex, turn ON remove shared edges. Your model should have no geometry left. If you have shards left, then it means that you had holes in the topology of your geometry.

[Matt_K]

Hi Eliz,

It may be that your normals are messed up so try adding a facet SOP with "Post-Compute Normals" selected at the end of your network.

Hope that helps!

Matt.

[hopbin9]

Add a Facet SOP to the network and turn on "Orient Polygons". This often fixes issues like that for me.