When and how to use diffuse roughness (oren-nayar)
polycounter lvl 7
Most of the major render engine has a roughness attribute on diffuse/albedo
(image from arnold support)
I normally never touch diffuse roughness. I'll just leave it as is (usually 0.0) But as I dig in more. Especially in Renderman it has its unique name for diffuse roughness which is called oren-nayar. I googled oren-nayar and it blew my mind. Highly rough surface will create this effects due to the diffusion light being scattered. That is reason why the moon looks flat from earth.
Then it raises more questions on my head:
(image from arnold support)
I normally never touch diffuse roughness. I'll just leave it as is (usually 0.0) But as I dig in more. Especially in Renderman it has its unique name for diffuse roughness which is called oren-nayar. I googled oren-nayar and it blew my mind. Highly rough surface will create this effects due to the diffusion light being scattered. That is reason why the moon looks flat from earth.
Then it raises more questions on my head:
- What value should I put in there under what kind of situation?
- Do I put a map like we usually do for specular roughness?
- Do we put the same specular roughness in there? Or a separate diffuse roughness map?
- How rough a surface need be to give 1.0 diffuse roughness?
- Highly rough microfacet surface like chock, sand, concrete, fabric are all very oren-nayar looking. What value should they be at?