specular roughness

rouncer 103 Jan 24, 2011 at 17:51

If you get specular roughness right on a surface, like an orange or a face, it looks strangely photorealistic.

Im thinking about a skin shader, even if you just pre baked the sss with ambient occlusion that would pretty much be fine, as it doesnt depend on view direction, but what about the specular? even with the finest sss you can get, you still have this unrealistic specular on top that makes your character look like he just took a dip and came out wet. Blender has this problem!

Skin has a rough specular, and im not quite sure what this means, its just ive seen skin renderers with parameters for roughness of specular. Mental ray and keyshot to name two, mental ray looks a lot “drier” than blender and looks really good when the specular is ringing down the side of the head, for the classic blue rimmed skin effect.
When you do a skin render in blender you might as well have the specular just turned off cause it doesnt work at all.

So, is this possible in realtime? and how would it actually be implemented at all?
I dont understand it much, its just im aware of its existance, and perhaps if you got the specular roughness, it would look alot like real skin even without subsurface scattering at all!

this is what I mean by correct specular…

Thats mental ray, and its impossible to get that look in blender. (although blender can look good, just different)

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rouncer 103 Jan 24, 2011 at 18:12

I heard from wikipedia that it “blurs” the specular highlight… does this mean if i pass a nice fat blurring kernel on the specular based on surface orientation, thats what I need to do to get this effect? so it becomes fatter and more translucent.

Reedbeta 167 Jan 24, 2011 at 18:17

I don’t know about blurring the specular highlight. A skin shader typically blurs the diffuse (that’s what SSS is, more or less), but the specular comes from the thin layer of oils at the very top layer of the skin, so it shouldn’t get blurred.

Anyway, Fresnel is very important for skin, so maybe that’s what’s missing. It is a distinct effect from specular reflection. See: http://filmicgames.com/archives/557 (although nothing about skin on that page).

We are using Fresnel, UV-diffusion SSS, and ordinary Blinn-Phong specular on our skin, and it seems to work quite nicely.

rouncer 103 Jan 24, 2011 at 19:48

Thats very important, what you just told me, thanks for sharing.
But I mean how do you make the specular look “dry” rather than “hot and wet” the best approximation I can get of this is by lowering the falloff of the specular, but it doesnt look like mental ray or keyshot.

When you add roughness in keyshot the specular highlight disappears and spreads… but your right, I tried blurring the specular and all it did was just seem to glow a little. :(