SSS and Displacement bug

[Squirtle]

I'm having a problem using a specular material with displacement - looks like a bug to me.

The problem is in both Octane Standalone 2.25 and 3.0 alpha 4. As soon as a I add displacement to my specular material the scattering goes completely out of whack and looks very wrong. Adjusting the Scattering color and scale don't help, and neither did adjusting the displacement values. I'm using a 16 bit TIFF displacement map exported from zbrush. I also tried a couple of other image formats in the displacement texture input as a test but get similar major problems no matter what.

I tried looking around online for a fix with no luck. I saw an older post that mentioned a possible fix of plugging the skin material into both inputs of a mix material and using displacement on the mix material, but this didn't help or change anything.

Here are some screencaps showing the problem, showing what the material looks like in Octane 2.25 and 3.0 alpha before displacement and after displacement.

Anybody have any insight into this?

[bepeg4d]

Hi Squirtle,
the Displacement node is slightly changed in the latest version, the Shift parameter has been replaced by a more logical Mid level.
Because of this, if you open a file with displacement from an older version, there should be some issues:

just create a new displacement node and replace the old one or change some parameters to restore the situation:

By the way, take care of the scale of geometry with Octane (all the measures are in meters), 14 cm of displacement are way too high for a face
here is how looks like at a half of your value:

crazy effect

Here is a more detailed explanation from abstrax:

Displacement
The UV map in the displacement texture is now taken into account. The "shift" parameter in the displacement node has been replaced by a new option "mid-level". The old parameter defined the shift of the displacement in meters, while the new parameter defines it in texture value range. So if you for example have a Zbrush export that has 0-displacement defined at 0.5, you set the "mid-level" to 0.5 and can then scale the displacement height independently. Should be more convenient than the old system.

ciao beppe

[Squirtle]

Thanks! I adjusted the scale of the model and got better results, but still with artifacts. Looking at the render you posted where the displacement settings are correct, I think you might actually be experiencing the same problem that I'm having.

This is only happening on Specular materials - Even with the model at the proper scale and the displacement height set extremely low, adding a displacement map to the node noticeably darkens the color of the whole object and creates odd artifacts at the edges of geometry. I can see these artifacts even in your render with fixed settings - in your render there are thin glowing lines around the extreme edges of all geometry. If you remove the displacement node from that scene, do those weird glowing lines go away? If so, then I think you're experiencing the same problem that I am.

My memory of dealing with a similar issue in Octane about a year ago is coming back, and sadly I never found a solution then... if you can double check your own scene and see if those glowing lines disappear when you remove the displacement node, that would make me think it probably is a bug caused by displacement. Should I file a bug report with Octane if that is the case?

I switched to using a normal map instead, which looks quite nice though. For now I'll just reserve displacement mapping for objects that don't use specular materials, and try to dig into this again another time - maybe when we've got procedural displacement to play with

Thanks again for your help, and going to the trouble of posting those screencaps!

[Robbert]

I'm having the exact same problem. Has this issue been addressed yet?
The material turns way darker, not the same as inverted normals, but as if the density has changed.
I also tried the older method with mixing the same material twice and using the displacement channel from the mix material, but to no avail yet...

Any fixes?

[bepeg4d]

Hi,
this is an old discussion, which version are you using exactly?
Could you share some screenshots of the effect youbare having and of the material in the node editor?
ciao Beppe

[Robbert]

Hi Beppe, thanks for replying.
See attached the nodes and the differences.
I'm using V3.08 by the way.

Left the displaced SSS, right without.

[bepeg4d]

Hi,
please, set the Kernel to InfoChannel and share a screenshot of the geometry normals, and UV coordinate pass.
ciao Beppe