Yeah, much more natural with shine! Thought I wonder if it fits the toned blue environment…
Now time to test with different light scheme if it does behave well under different light (maybe boat scene again or some very contrasty non tonemapped hdr?). How well does the skin respond to purely diffuse lighting (flat white environment) and very strong single light without fills.
I’m wondering mostly about the IOR if it will be the correct one that I won’t let too much of light through the character. I took liberty to draw on your render to mark some areas. I really like the look of the ears. I think it’s the correct behaviour to get reddish when the light shines through. Also the area marked in violet looks translucent, but I’m wondering if it’s caused by the correct light. I’d turn off key light for a small test to try if that area is caused by the rim light or it’s the effect of leaking light through the neck. If it was gone then I think that for such closeup Vicki would need some skeleton made from reflective sphere and cylinder placed inside the mesh (that will make the light return to the upper layer of the skin). The other solution might be playing with the IOR to change the direction of the rays. As for the nose and lips - I think that lips look enough reddish but it’s not caused by light going through but rather reflection, but for the (inside of the) nose I think the effect is very subtle. I’d make Vicki even more transparent or add some skeleton so that light will return to the surface and light the thinner parts like lips, ears and nostrils.
The problem I am having, beside the most obvious, is that I don’t have a good “absorber” to put inside the model. Ideally I would like a volumetric cloud that followed the geometry of the model and soaked up the rays that got diffused into the core. Instead I’ve used a shrunken version of her own head. But due to the geometry of the model, it is difficult to get the absorber close enough to the skin while at the same time not intersecting the mesh and becoming visible. I tried using Wings3D to produce a “shrunken” version of herself, but the mesh was unmanageable with my limited skills at Wings.
The IOR is a bit of a problem because only at refraction 0 is it possible to avoid showing the “seams” up in the mesh model. There is also a conflict between the specular halo setting I want to drive the specular effect and the setting needed for blurring transmissions and reflections. Three different controls would help at this point since the changes needed, while subtle, seem to have a significant impact on the plausibility of the skin.
Here I’ve tried to apply the skin for the whole body, setting back a duplicate model away from the camera to act as an absorber and prevent rays travelling right through the figure. The problem being, because the duplicate model is not smaller but just further away, the depth of skin that can be entered by the rays varies and this creates lines where the absorber gets close to the surface. Like in the inside of the arm where a hard shadow has occurred.
A skeleton is a good idea, but I think it would let too much light through the model. What’s needed I reckon is a “fat” skeleton.
Sorry for late answer, meh… I can’t catch up behind literately anything recently.
I see so you’re already using some kind of blocker inside. Speaking about skeleton I meant in fact a ‘skeleton’ build out of primitives or simplified mesh as you’ve suggested rather than real skeleton which as you noted would allow too much light to pass through. Building simplified mesh would be the most helpful atm, but it’s taking additional time. As for volumetric medium - it’s quite close to reality, but inability to set edge softness is not helping in this situation. There’s possibility to paint density map so that the volume would be thicker in different parts of body. The dedicated depth control would be easier to control though. To build skin that’s good enough (also realistic water) there’s at least the need for combining standard material with volumetric, or at least working absorption.
The main reason why currently rendering is that slow is that often dedicated skin shaders are only an approximation of a single scatter (incoming ray going into medium in random direction, travelling for defined depth, going in ‘given’ direction phase and leaving the surface or not) , so 3 bounces might be enough for full simulation. Currently the combined shaders are cause of performing lot more redundant calculations with no real impact on the quality. Now, can explain what I meant by ‘given’ direction: direction of ray going out of the surface is the result of direction of incoming ray, IOR, diffusion strength (we try to simulate this with specular halo), phase controlling backward-forward scattering ratio (random direction with probability to go forward or return in incoming direction, we try to control this with introducing the dark, blocking medium inside - forward scatter, or bright or reflective back scatter). Making these controls joined tightly with the current shader model causes loss of control of the other basic features while trying to simulate the other material behaviour. Your suggestion to create a separate specular halo for reflection and refraction is a very reasonable feature request considering this case + would be useful in some others.
The seam that you’re getting with IOR different from 0 might be caused by reflection being joined with refraction combined with insufficient blurring for refraction after setting the correctly looking specular halo. I believe that IOR for skin is something like 1.33 as the skin is composed out of water.
Coming back to your skin shader. I drawn the areas that have visible sss (green), areas where I’d more expect them to be (orange) and bonus double-fingers-area (blue). As for the head render (with key light + hdr ibl) I see that the light is not leaking through, but I’m still more more strength of sss (for nostrils and lips).
Maybe one of the solutions is to render in passes?
Oh…. and the nice thread about making realistic skin: http://forums.cgsociety.org/showthread.php?f=176&t=664371&page=14&pp=15
on that page there’s an example on which you can see the ‘skeleton’ I meant
Warning - thread with lots of skin and nudity