What does roughness actually do?

[fael097]

so recently I started working with substance painter, unreal engine, etc. and PBR materials have a setting called roughness, wich basically another name for Rglossiness.

vray materials also have a roughness slot, and it should be really important since it's the second thing you see, after diffuse color, however I've never seen anyone using it for anything, also vray documentation says it's used to simulate rough surfaces, wich appears to me to be just wrong.

the material editor thumbnail preview doesn't really know how to behave and gives you inacurate feedback when you input roughness, and if I render the same material with different roughness values, I don't even know what I'm looking at. it appears that the light spreads more into shadowed areas, but it doesn't look phisically accurate to anything I've observed, and it doesn't seem to imitate a rough material at all.

is roguhness in vray materials just a vestigial parameter, left over from the past, that should eventually be removed, or does it have any practical application? if so, does anyone know a good example of a real life material that is reproduced more accurately using roughness?

thanks

[joconnell]

Normal roughness (as compared to pbr roughness which as you say is glossiness in vray) is indeed for non smooth surfaces so for things like concrete, clay, chalk, fabrics where the surface isn't totally polished and even - anything dusty can be simulated with this setting too. As you say it's all about the falloff from light to shadow so it's a setting affecting the diffuse lighting only.

[vlado]

Actually many materials like the Physical Material in Advanced mode have also two roughness values - one for the diffuse component, and one for the reflection component. They are different. Like mentioned above, the diffuse roughness is used for materials like chalk, dusty surfaces etc.

Best regards,
Vlado

[DanSHP]

Sorry to bring up a old thread.

The question I have is, why would one use 'Roughness' over 'RGlossiness' if they are both the same? Is there some particular benefit for using one or the other, for say a concrete material, as mentioned above?

[vlado]

They are just two different ways to specify the same thing. If you get a model set up with roughness texture maps, it is convenient to just plug it in without adding inversion nodes or anything.

The underlying implementation in the code for reflections is exactly the same.

Best regards,
Vlado

[bernhard]

do you recommend to switch the GGX to roughness then, instead of using glossiness?
I also noticed, that the roughness map slot is not really available.. I mean, you can't just drag and drop into that slot any texture map.
Seems to be locked.. the slot, right underneath of the Difuse channel.. confused now...

thanks for clarification!
cheers