Bad shadow on SSS2 material

[G0M0]

Please take a look:

As you can see, the problem is that the shadow is different if I use sss2 material.
I don't know if it is related to that the sss2 is one sided material, is so such bug should not appear inside of the nose.
Somehow the bug is related to scatter radius.
Or am I doing something wrong?

[vlado]

Can you get me a scene for this to vlado@chaosgroup.com ?

Best regards,
Vlado

[G0M0]

Scene send.
Thanks for quick reply.

[Morbid Angel]

i think the one sided is the cause. How is your sss2 material one sided?

[G0M0]

It seems to always be one-sided.

[Morbid Angel]

weird, i just open max, load vray sss2, assign it to box and i can see the inside (I deleted one face). Are you sure?

[G0M0]

I've just checked - there is indeed some bug in this particular material - it is one sided, other (default) is indeed 2sided but lighting appears only on front side (that is probably my conviction of it working only one-sided).
Also I am probably using sss2 derivated from this bad working one in many scenes.
So thanks for pointing that out - I'll make further investigation.

[G0M0]

Ok, after some more test there are some conclusions:
The SSS2 is one sided in refractive mode
The problem with shadow was caused by sun light - It has set up shadow bias to 0,7 - after changing to 0,0 - everything looked fine.
I have found another bug which appears in reflective mode and phase function set to 0,0 - some sort of reflections visible through skin:

And that is not always visible.
Right now I hope the refractive mode will work without any new problems.

[Morbid Angel]

really, you don't need to use refractive or reflective modes, if you wish to have true raytracing in the sss, use regular vray material.

[G0M0]

Well, the point is to have most accurate and quite fast sss skin.
I have some prototypes with simple vray material with translucency, but until getting some good textures it is still just a research.

[vlado]

The problem was indeed the shadow bias for the sun light.

For the refractive mode - have you tried using the "raytraced (solid)" mode instead (it should be quite accurate too).

Other than that, I'm working on a brute force model for the sss effect, which is super-precise (although for the moment quite slow too).

Best regards,
Vlado

[G0M0]

Yes I tried raytraced mode - it produced that artifact (look at the nose):

But as the refractive mode works fine with corrected bias of sun's shadow, I can move on with project.