PBR Metalness Implementation: specColor at Value 1?

Question

I am doing a BRDF supporting the metalness/roughness workflow. I know that in cases of Metalness = 1.0 the reflectance value is taken from the albedo map - so is the specular color to tint the highlights.

My question is if the specular color is taken at the same value that it is in the albedo or is it set to 1.0 first and then used ?

Example:

A Pixel in my Albedo Map has a Hue/Sat/Value of 0.5/0.5/0.5

With metalness = 1 the reflectance is 0.5.

Is specColor

a) 0.5/0.5/0.5 b) 0.5/0.5/1.0 (to not dim the specular) ?

Thanks, Jens

Answer 1

Short version: a) 0.5/0.5/0.5

In the metals workflow, the specular colour will be exactly as sampled in the Albedo map. It's possible with PBR to have some metals shinier than others (while of course still obeying conservation of energy), which can only be achieved by allowing dimmer colours in the Albedo Map to result in dimmer specular values.

Answer 2

It's not quite as simple as simply tinting the specular color with albedo for metals. For metals the albedo is used to define specular reflectance at normal incidence, but this color goes to white at grazing angles due to Fresnel effect. You can use Schlick's approximation for this computation.