I've been playing around with SSS shaders in the new cycles engine, attempting to understand the logic behind it. I think I grasp the concept and I am on my way to build a decent skin shader. But I've come across a strange artifact and I am skeptical that I've arrived at the correct answer of the source.

On this character, the SSS creates a red ring around the eyes. (My SSS is, of course, red. The eyes are missing in this image, as I was trying to debug the issue. The red appears when the eyes are present also.) I can decrease the SSS scale, but that defeats the purpose. The scale is supposed to represent the depth the light ray penetrates and is diffused. I've set it at .003 here, which I guess would be equivalent to 7cm converting from poser units. Since there is no light inside the head, there should not be this effect.

Here is a shot of the back of his head. I've adjusted the SSS scale so that the light passes through the ears just enough to give a realistic impression. The scale is uniform across the entire body.

So my first theory was that they may be reflections from the eyes, such as the eye surface. So I made those invisible and the problem continued. So I put a camera inside the head to see what it looked like. This was interesting, because there is a skin flap here for the eye to rest against and it showed up bright red, like the ears.

So, my new theory is that these skin flaps create a radiation of red color that reflects back out the front of the face. One possible solution would be to create a morph and eliminate the skin flap so that it does not react to the light and create an ambient red to reflect out the front of the face. This seems difficult and may not even work. Another possible solution, without eliminating the SSS entirely across the entire face, is to create an alpha mask and just turn off SSS around the eyes.

Any other bright ideas?

FYI - lighting is an HDR of an abandoned warehouse, using an EZDome saved from P11. No other lights. This is an G2 character imported from DAZ. The cycles shaders are my own using the techniques from this tutorial. Lance Pham: Skin Material in Blender 2.8

I have similar problem with Dawn around her eyes. Does not happen to V4. I suspect it has something to do with normals like the issue they were having with mesh lights messing with spot lights in that other thread.

I am seeing it with V4 using the PrincipleBSDF. I'm suspecting the SSS around the eyelashes but I need to try a few things before making my conclusions.

Okay, eyelash is not the culprit. When using Subsurface on the PrincipleBSDF for the skin face texture, that value should be around 0.01, probably lower. That mesh must be very thin to radiate that so much scatter. I ran Subsurface at a 0.015 value for the rest of the body. I would imagine that you would need to set the scale much lower to overcome that artifact. I will try to post something preliminary tomorrow but I'm glad to find a solution.

This is what I get and my settings. One thing to note: I use a natural face texture for the red filter and a makeup texture for the SSS. This separates the makeup and tattoos from the SSS calculation.

That's an interesting arrangement. Are you using nodes generated from EZSkin 3?

hborre posted at 8:43AM Thu, 12 November 2020 - #4404290

Okay, eyelash is not the culprit. When using Subsurface on the PrincipleBSDF for the skin face texture, that value should be around 0.01, probably lower. That mesh must be very thin to radiate that so much scatter. I ran Subsurface at a 0.015 value for the rest of the body. I would imagine that you would need to set the scale much lower to overcome that artifact. I will try to post something preliminary tomorrow but I'm glad to find a solution.

I am using a 3 layer SSS to represent the three layers of the skin, then mixing them together. While the Deep Red SSS is .03 scale, it is only mixed at 40%. The top two layers are mixed 50%/50%, then specular and oil layers are added on top of that. I added a mask on the Deep Red SSS to remove the effect around the thin eyelids, but it is a P.I.T.A. It feels like this is an error somewhere. Either my shader setup, or the software itself.

yes, I use an EZSkin3 Cycles setup by a guy that was a regular on the SM forum.

https://www.sharecg.com/v/85846/browse/9/Plug-in/Cycle-based-plug-in-for-EZskin3-poser11-only

I knew I recognized the nodes. I have that plug-in already so I have other options to play with. Thanks for bringing that to my attention.

Silly question. If EZSkin3 does not work in P12, how are you using the plugin, or the normal setup? Are you manually copying it, or setting it up in P11 and saving it there to play with in 12? Curious about workflow until the script works again in P12.

You can set everything up in P11 if you have it installed and either save the character with the modifications or save a material collection to apply to a new model. There might be some tweaking when imported into P12 but there are no changes to the nodes themselves.

Okay, just completed renders using the PrincipleBSDF in Superfly and these are the results I got. This is the node arrangement I settled on ATM, something simple yet effective.

I attempted to use a higher Subsurface value (0.015) for rendering and got this with super bright SSS strength around the eyes. Forgive the roughness on the face, bump values are off.

After tweaking the Subsurface value to 0.01 and correcting the bump values, I re-rendered and got this:

Ears are very close to perfect although it might need a lower Subsurface value to control the slight glow. I am pleased with the appearance. V4 model and studio lighting arrangement.

Edit: I just noticed that Sheen is active and it shouldn't be. My bad.

Got it, thank you.

Some tweaking, envsphere for primary lighting.

One light plus dome.

It would be interesting trying to tone the SSS chip in combination with a base map. I might play around with darker skin which can cause render problems.

Sorry this is off topic for this thread: Just an example of using two different maps for skin that has tattoos and makeup. When you use the natural skin map for the redfilter and the tattoo map for the texture/color/SSS you preserve the reflection and SSS of the skin. The normal way people SSS is just plug the tattoo map into both and the result is that the tattoo/makeup part of the skin does not get the same reflection/SSS treatment that the rest of the skin gets. The normal way makes a tattoo look like paint ON TOP of the skin as apposed to ink that is under the skin. Have a look.

Node modifications, and new render.

I don't think it's off-topic at all. It helps to understand the how's and why's. Thank you for your clarification on your set up. I would like to explore that further.

That's nice

Thanks for the comments. i've learned quite a bit working through the SSS shaders.

I reproduced the red effect around the eyes in Poser 11. So very unlikely that its a Poser issue. I created a graduated mask in Photoshop to deal with the effect around the eyes, to try and stay consistent. I'm quite happy with the results overall. @ghostship2 thanks for your shaders on sharing - they've been very helpful. Each year I make minor improvements that keep adding up. I'd like to figure out hair next...

:)