On the “test bowls,” I left most of the UberSurface settings at their defaults—- in the attached composited screencap, a bunch of the subheadings have been collapsed. Those values are as the base UberSurface load initialized them. Proceeding from the top,,,
The Diffuse color is a jpeg, medium beige, with a little multi-color Gaussian noise added, and multiplied by a peachy [255,238,221] off-white. It’s a nice utility skintone for when I want to isolate the effects of settings—- the painted-in details in a good skin texture make those harder to pick out. Why 95% strength? Because in early experiments, highlights were getting “blown out” (i.e., kinda over-exposed looking) when I added in Ambient and SSS. Depending on the skintone/lighting/glossiness you’re using, that dialing back may not be necessary.
There’s just a smidgen of texture in the Bump channel: a little Gaussian noise again.
Went a little bit shiny with the Specular, for a slight ceramic effect on the bowls. On skin, the UberSurface defaults are pretty plausible, but this is something you’d adjust according to the needs of the image.
This is a fairly bright & saturated Ambient color, but it’s dialed way down to 4.2%. It’s also applied only in the areas designated by my SSS map. Again, you have a lot of creative leeway here, depending on the skintone and desired effect.
Velvet is used here to emulate looking through a semi-transparent ceramic glaze layer near the edges of the object, where the surfaces are almost turned away from the viewer. So you’d be looking through it at a shallower and shallower angle as you approach the edge, and therefore a thicker and thicker amount of the glaze. It’s a similar idea with the fine hairs on human skin. Lots of leeway for experimentation here.
And finally, the main event: Subsurface Scattering.
For its color, I used that medium beige jpeg again, this time multiplied by a traditional pink—- that “subcutaneous blood” tinge that skin SSS is meant to emulate. Went pretty high with the Strength here, racking it up to 75%. And it’s applied where my SSS map specifies, naturally.
Searching around, I found refractive index numbers for skin (and water, responsible for a large part of skin’s optical properties) quoted ranging from 1.3 to 1.5, depending on bunch of factors—- notably, the wavelength of light involved. I chose a kinda middle of the road value; for skin, the 1.3 to 1.5 range of settings doesn’t seem to cause wild changes in the final effect.
The Scale setting, however, was a surprise. I’ve read various descriptions of it as determining how far the light penetrates the object—- which is true enough, I suppose. But I find it more useful to think of it as affecting how much blur is in the final SSS effect, as seen in the actual render. For a larger object, such as a giant creature or humanoid, you’d use a larger Scale value to soften the edges, to be “in scale” (nyuk nyuk) with that larger being. And you’d go smaller for smaller figures, naturally. The ratio is nicely linear, fortunately.
(When I first started my SSS experiments, I had the Scale value way too high, which caused the SSS effect to blur into imperceptibility. Sheesh!)
Group? I have no idea yet what this is actually used for. I set it to a plausible integer and then ignore it. 8^j*
[Update!] There’s a thread explaining this very slider. Short version: you put surfaces in a group to have them calculated together as a unit, AND to avoid them getting interference from a different group. For example, group all the skin zones as one group, and group all the mouth surfaces in a different group—- and maybe, just maybe, avoid what Rawn calls “Lava Mouth.” More experimentation on this to follow.
Shading Rate is a quality setting. Unlike the Uber lights, higher values mean lower quality, less computation load, and faster renders. On this relatively simple image, the delta between rendering at 128 and rendering at 16 was only about a 2% increase in render time. Pushing to 4 took 11.5% longer than the render at 128. Visually, the higher quality translates to a smaller blur and more intensity in the SSS effect. The default of 32 is probably a good tradeoff point; I couldn’t see a significant difference between the the renders at 16 and 4.
Click thumbnail to see full-size image