Author Topic: SSS and Material IDs  (Read 1710 times)

2017-12-22, 00:05:02

xcube

  • Users
  • *
  • Posts: 2
    • View Profile
When I reneder character, there is a nasty seam. This seam appears at the boundaries of different Material IDs. The seam only appears if you use SSS materials.

Is there a way to avoid it?
Thank you!

2017-12-22, 16:05:23
Reply #1

cecofuli

  • Active Users
  • **
  • Posts: 1492
    • View Profile
I have your same "result" if I zoom a lot.
Maybe you have a 3ds max file unit



2017-12-22, 21:05:28
Reply #2

xcube

  • Users
  • *
  • Posts: 2
    • View Profile
The size of the seam depends on the depth of dispersion. And if both Material IDs will be assigned to the SSS the size of the seam work twice as thick.
While the best solution for me is to use the standard CoronaMtl without SSS. In addition, the result is easier to adjust and eventually looks more volume.

2017-12-27, 04:55:32
Reply #3

jgalloway@pakglobal.com

  • Active Users
  • **
  • Posts: 10
    • View Profile
Your may need to paint a flesh colored strip around your texture. It is probably sampling the black pixels from the map.

2018-01-03, 13:20:50
Reply #4

maru

  • Corona Team
  • Active Users
  • ****
  • Posts: 9269
  • Marcin
    • View Profile
I was not able to reproduce it using one material and one object with different mat ids.
If this is happening with multi-sub object material and few materials assigned, where at least one of them is SSS, then I would say it's expected. It's pretty much like having the geometry divided into a few parts, and some of them have SSS enabled.

2018-01-27, 04:54:40
Reply #5

jgalloway@pakglobal.com

  • Active Users
  • **
  • Posts: 10
    • View Profile
What is all of the sub mats are SSS? Seeing the same results here.

2018-01-28, 22:04:40
Reply #6

Fluss

  • Active Users
  • **
  • Posts: 437
    • View Profile
hmmm looks like a fresnel calculation issue as described here :

Quote
VRay Skin Mtl: This uses a two lobe specular model with a sharp and broad reflection. It also uses Phong as the reflective BRDF. This model proved to work well in many situations, but at glancing angles, based on the way that it would cut out the SSS, could cause darkening. This is because the Fresnel effect is computed as a function of the angle between the viewing direction and the surface normal, ignoring the directions from which lights illuminate the surfaces.

alSurface: This model also uses a two lobe specular model. However, instead of using a smooth BRDF like Phong or Blinn, it uses a microfacet one. The Fresnel effect is computed as part of the BRDF calculations (a.k.a. “glossy Fresnel”) and takes into account the viewing direction, the surface normal, and the light directions. The user has a choice between GGX and Beckmann BRDF models. Based on the nature of the micro faceting, it can avoid the darkening effect at the glancing angles through retro-reflection. Additionally it does not cover the SSS at the same glancing angles.

source : https://www.chaosgroup.com/blog/v-rays-implementation-of-the-anders-langlands-alsurface-shader

That would be strange tho, as corona is using GGX BRDF.

2018-02-04, 02:17:33
Reply #7

jgalloway@pakglobal.com

  • Active Users
  • **
  • Posts: 10
    • View Profile
I've seen this problem before in Vray - many years ago.
In Arnold the problem is solved by "tagging multiple objects as belonging to the same SSS 'set' so that illumination will blur across object boundaries"
See here:
https://support.solidangle.com/display/AFMUG/SSS+Set+Name
And see the last pict on the left "Without 'shareSSS'".

We need this shareSSS feature in Corona!!!