# What is the accepted method of converting shininess to roughness, and vice versa?

Most modern renderers use physically-based materials and their models are often parameterized over roughness. Since this wasn't always the case with renderers, conventional assets often don't have a notion of roughness. Instead, we see "shininess" or "specular power" as a common material parameter.

I understand that there is no exact conversion between the two, but is there a rule-of-thumb / approximate way to get roughness for a material whose specular power or shininess is known?

• How about rendering a series of comparison swatches and try to fit a conversion curve? – joojaa Sep 18 '15 at 6:36

• Brian Karis uses a squared roughness values in this Microfacet BRDF overview. This illustrates also nicely how differently roughness is used in different Normal Distribution Functions. Blinn-Phong power is here defined as 2/roughness^4 - 2.