How to bake roughness (or glossiness) textures for PBR shaders

[jonhuhn]

I use render to texture to bake textures for Unity pbr shaders. I can't get Vray to output the roughness map correctly. I'm assuming that's what VRayMtlReflectGlossinessBake is for, however the values it outputs is way off. It doesn't make a different if I toggle the material's BRDF setting to Use Glossiness or Use Roughness, either way the output does not match the material's glossiness (or roughness) value. It seems like it might be a gamma thing, but I just can't find the solution.

[hermit.crab]

Yes, using VRayMtlReflectGlossinessBake with Use Roughness is correct. Presuming I understood correctly, you would need to invert the map when plugging it back to the Roughness map slot. If not, send some screenshots, illustrating the issue, optimally a simple scene here, or to support@chaosgroup.com so we can take a look. Mention this thread in the e-mail along with your V-Ray and host platform versions.

EDIT: I've logged an improvement request (internal bug-tracker id: VMAX-9895) about the map inversion when "Use Roughness" is active so that Roughness maps be read accordingly when a VRayMtl is adjusted for the PBR workflow.