Then I amped up the IOR all the way to 20. So with this test I set diffuse to black, and set the otherwise white spec value to our nice rubber ball red. That means that any diffuse values get transferred to the specular map for metals. Getting ahead a bit to render SP maps in mental ray, you will need to output them as diffuse/specular maps, as intended for the specular workflow. Left side SP with 0% metallic, right side some mental ray renders.ġ.2 was too dim, 1.5 too glossy 1.4 seemed just about right to me. Anyway, first step is to get that non-metallic look to be the same. The substance folks have some really nice documentation on PBR, including some information on what to do with IOR. But thats ok there is a fresnel IOR slider. There is no Metallic slider on the mila_material. Personally, I like the rimlight a white spec creates on rough surfaces in MR, so I hooked this inverse roughness up through a very high gamma so only the very high values (say, 0.9 and over) start to eat away at that rim-light effect (mainly to prevent that weird velvet fresnel you see happening with the 100% roughness in image 2). Not exactly the same results, but it looks pretty good to me. I went with a gut feeling and hooked up the inverse of the roughness through the same gamma correction and connected that the the specular tint. Whatever the case, a gamma correction of somewhere between 2.2 and 2.4 gives a good result (I prefer 2.4 myself, I want that roughness to really show)Īlso, noticed how the higher roughness values leave the renders in MR much more shiny? It seems that in SP the specular values are toned down as roughness goes up.
also, a gloss map seems to be the inverse of roughness in sRGB space, while inversing it in linear space should give a totally different outcome.
Now I'm not entirely sure how SP was intended to work (and I am no expert on all this gamma stuff), but I've also noticed that in Marmoset, the gloss map needs to be flagged as 'sRGB space' to have the correct effect. So I played a bit with the values there, and ended up settling with a gamma value of 2.2.Haha.įor anyone who ever did anything with gamma correction, this value should sound familiar. Let's ditch the value remap, and try a gamma correction node instead. What I got after some fiddling around is something that looked like this:Īnd I thought to myself, that looks a lot like a gamma curve.
I figured I make a custom attribute on my sphere in maya, and patch it through a value remap node into the roughness on the mila_material, and see just remap the input values somewhat to have that custom value correspond properly with the SP roughness value. So, at first glance, the 40% roughness in SP seems to correspond with about 75% roughness in mental ray.