Roughness vs specular

swaterik

Hi

I never understood the relationship of roughness and specular. I'm creating textures in Substance Designer with a roughness/metallic workflow.
In unreal Engine however I still have the specular plug-in. Would I use this to further add to reflectivity effect or would I just keep it at 0,5 overall? I mean, isn't the roughness map sufficient enough?

thx for answers

JordanN

Epic always claimed specular in Unreal Engine 4 was a legacy feature. Not related to specular you see in other engines/renderers.

Of course, it doesn't stop people from using it. I remember it being useful when I wanted to render grass. 

Obscura

Roughness map and specular map serves to different purposes. Yes, sperular in Unreal is different from what it would be used for in another renderers. Its default value is 0.5, that is going to give you the non metal reflectivity (~4%). However, you can use it enhance/reduce reflectivity, but its not required in the most of cases. You should just focus on a good roughness map that tells how blurry the reflections are, because of the microsurface unevennesses.

hildner

I believe that the specular input looses all its influence on metallic materials as the specular gets set to 1 in that case.
But I also never really touch the specular value anyway, just let it stay on the default 0.5 I guess.

Kyetja

As mentioned above it's best left at 0.5, if you're interested in employing it google micro shadowing, it's a method where the curvature/AO maps are used to reduce reflections in crevices etc. it's quite neat, but definitely a novelty.

radiancef0rge

Specular input in UE4 is really meant for micro occlusion. A cavity map would be good here. 

swaterik

Kyetja said:

As mentioned above it's best left at 0.5, if you're interested in employing it google micro shadowing, it's a method where the curvature/AO maps are used to reduce reflections in crevices etc. it's quite neat, but definitely a novelty.

Oh that makes sense. Thx for your answer

poopipe

If they've implemented it properly you want to plug in what amounts to a cavity map (or the bottom 10% ish. Of an AO map)  multiplied over the specular value of whatever material you're trying to emulate (dielectrics only) . 

I've not used it in ue4 yet but thats what we do at work.