how to get rid of the reflection in metallic/rough

[HapZungLam]

I originally made this rusty metal substance in spec/gloss.  However I notice that substance painter doesn't handle spec/gloss substance.  So I rewire it for duel output.  However no matter how high my roughness goes, it still appears to have about 20% reflection.  Is it how metallic/rough works?  It'll always have 20% reflections?

[Cyrille Damez]

Non-metals always have a bit of specular reflection (usually in the 3-4% range). Most PBR shaders using the metallic workflow uses that fact and set the specular reflection for non metals to a constant value (usually 4%). Some use an additional greyscale texture to modulate that value (Designer's Metal/Rough shader call it the SpecularLevel channel).

In any case, you should not have 0% specular reflection if you want to be physically realist. The spec/gloss workflow allows it but it is not physically accurate.

The specular texture you get after conversion with the "metal->spec/gloss" is a uniform 20% grey because it is in sRGB (20% sRGB corresponds to 4% linear).

[HapZungLam]

I see.  It makes sense that everything should have 4% of specular.  However I have 2 more questions:

1.  When I port the spec map into render engine after export them as PBR spec/gloss.  Do I treat the spec map as linear or sRGB

2. I've tried creating an extra output and set it as specularLevel under metallic/rough shader in Designer.  And give a uniform colour of black for the specularLevel output.  It doesn't have any impact in Designer's render.  Did I do something wrong with the output or is ignoring.