Principled - Reflectance of the base layer depending on IOR of the coat layer

[Paulfx]

Hi,

I noticed when using a principled material with following parameters : CoatIOR = 1.5, BaseIOR=1.5, and CoatStrength=1 that the base layer still has specular reflection. However, as the coat and the base has the same refractive index, the reflectance at the interface between the coat and the base should be 0, so in theory there shouldn't be any specular reflection under the coat layer.

Can you please explain how you calculate reflectance at this interface ?

Thanks

[atafra]

Hi,

It is common practice in principled materials to control the reflectance of the layers independently, ignoring the IOR of the layer below/above. This makes the material parameters more artist friendly. E.g. see the Autodesk Standard Surface: https://github.com/Autodesk/standard-surface

The OSPRay Principled material follows this convention for better compatibility with other popular material models.