Specular label on Diffuse or Diffuse SSS Bottle Incorrect Shading
Posted: Thu Jun 19, 2025 6:21 am
I'm doing a clear label with printing on a plastic bottle with subsurface scattering and find that mixing any diffuse into the bottle material creates incorrect colouring under the label. It gets more saturated. The diffuse problem is not just adding a percentage of diffuse but includes using 100% sss with the diffuse transmission option found in the standard surface, diffuse material layer plus coat layer, and the universal material. I get OK results if the bottle is specular transmission only, but I usually prefer to use some diffuse in this situation to increase the brightness of the material and speed up rendering. The label and bottle are set up correctly with overlap and nested dialectrics, ray epsilon is appropriate as is ray depths. The diffuse example here is only diffuse which shows the strongest effect.
I've made a simple example scene. It appears to be a combination of fake shadows and IOR on the Specular label material with diffuse on the bottle. I can make the label IOR 1 or thin wall and the problem goes away. But this changes the shadowing of the opaque label parts on the bottle surface.
I've made a simple example scene. It appears to be a combination of fake shadows and IOR on the Specular label material with diffuse on the bottle. I can make the label IOR 1 or thin wall and the problem goes away. But this changes the shadowing of the opaque label parts on the bottle surface.