UberSurface, subsurface scattering, and translucency

sriesch

I was playing around with the UberSurface shader to see what effects I could get on the wax for a lit candle. Unfortunately I don't see descriptions for most of the parameters used in this shader relating to subsurface scattering and translucency, so I've been mostly guessing and/or randomly flipping sliders around to see what happens. (hopefully there's no "history eraser" slider. A shiny, candy-like history eraser slider!)
Does anybody have any good explanations for these parameters that I could write down for future reference, or if I'm looking at old documentation, can anybody point me at the latest and greatest version? Thanks!
And of course if you have any information, suggestions, or previous threads aimed at lit candles, I'd be interested to hear about that as well.

SickleYield

Docs: http://www.omnifreaker.com/index.php?title=UberSurface#User_Guide

I made this mistake at first because of the name, and also because the docs don't mention it that I've found yet, but translucency is not what you'd think it is. It's used to change the color and/or shading of backfacing normals compared to the frontfacing ones (for e.g., the lining of a cape when it's a single sheet of polys). There is no reason to use it on a candle, skin, or any manifold (fully closed) object.

SSS is well explained by the link.

In practice, PWSurface2 does SSS better than UberSurface does. (You probably have them both, I think they both came free with DS4.5). I've seen no difference in their velvet effects. If you use either at less than 30% it's barely going to do anything. (Do some test renders of the same object in the same light at different values and you'll see what I mean.)

I haven't done a lot with candle wax, but I would play with SSS and velvet that are a little MORE saturated than your main color, since it's wax rather than flesh and candles do show a brighter halo at their edges when lit.

Does that make sense?

Herald of Fire

One important thing to note is that as far as I'm aware there are no TRUE translucent surfaces available. Both pwSurface and UberSurface do not allow light to pass through, and the translucence only affects the appearance of the surface itself. This happens whether you're using area lights or raytraced spotlights. An example is below (top image). The same effect is present whether it's pwSurface2 or UberSurface2.

One way around this is to create a 'geometry shell' and apply an area light to the surface, giving it the 'Fantom' tag so the surface itself is invisible. See below (bottom image). It's not ideal, since the light path will now be parallel to the emitting surface rather than refracted from the source, but it's enough to work as a decent trick in many instances.

Szark

and pwSurface 2 doesn't come free. :)

Slosh

Mess with Ambient a little bit, too. I discovered this by mistake while trying to create a skin shader. I found that by applying a slightly pale color similar to your diffuse to the Ambient setting and keeping the strength between 25% and 65% that I got a nice waxy look. Just be careful, too strong and it will wash out your diffuse color. If you do this, then lower the opacity by about 10-15%, light should shine through it AND you get waxy look. Please share a render if this suggestion works for you. I would love to see it.

sriesch

@SickleYield:
I can't find much information on subsurface scattering at the provided link. I followed that link through to the HumanSurface link mentioned on that page to get to http://www.omnifreaker.com/index.php?title=HumanSurface . It does describe and shows examples of the Subsurface Refraction and Subsurface Scale. However I don't see any explanation of Subsurface Group, Subsurface Strength, Subsurface Shading Rate, or Subsurface Color (although I'm assuming I can guess correctly the last two based on their names.)
I haven't had a chance to try the velvet suggestion yet, however yes, that does make sense, and I do plan to try it and see what happens.

@HeraldOfFire, thanks for the clarification on translucency, I was indeed misunderstanding that.

@Slosh, I've been experimenting with some of your suggestions. I've been trying to finish up a render that has a candle off in the distance, and was concentrating on getting that looking ok prior to trying any candle closeups. Here's an experiment; kind of small because it's just a tiny piece of the render zoomed in:

SickleYield

I still don't understand what those settings mean myself, actually (other than color and shading rate). Mostly what I notice is that if you turn SSS up past 50% and you have a saturated color, your entire object is that color. Some more recent projects I've seen actually use a desaturated texture map for SSS on an object like a body, but it's probably not necessary on a candle.

I'd say from that render you're on the right track.

Richard Haseltine

SS Group is a way of separating materials that should interact, such as teeth or eyes and the skin. If surfaces belong to the same group then light falling on one can come out of the other.

SS Strength just controls the amount of the effect - lower it to reduce the visisble impact while keeping all other settings the same.

SickleYield

Richard Haseltine said:

SS Group is a way of separating materials that should interact, such as teeth or eyes and the skin. If surfaces belong to the same group then light falling on one can come out of the other.

SS Strength just controls the amount of the effect - lower it to reduce the visisble impact while keeping all other settings the same.

Richard to the rescue!

Thanks, that's good to know, I'm sure not just to me and the OP. ;)

sriesch

@Richard, thanks for the info! I have added it to my notes.

Here's another experiment for a different candle in the scene. I don't think it turned out quite as well, and I couldn't get the specular part on both the front of the candle and the reflection of the candle in the mirror without having it either too bright at one angle or too dark at another, so I fudged it and jammed a primitive with lower specularity into the top corner of the candle to solve the reflection problem. Still needs work.

AlexBarclay

After trying to figure out how to use SSS with Human Surface to add that "extra" level of realism, I finally made some progress.

Notice the Spotlight behind Victoria illuminating her ear in my attached render. But SSS really adds a great level of depth to the skin overall. I'm happy I finally made some progress in figuring this one out.