Iray skin surface question

marble

I have noticed something odd about IRay skin and using Cutout Opacity. I have a kind of mask that I use to make parts of the skin transparent (for medical or horror images). The trouble is that the rest of that skin surface (Torso, legs, etc.) now looks like it is glowing. I think it is something to do with SSS but I can't find out which parameter makes a difference. This can be easily replicated without any mask. Load Edie 8, for example, and just move the Cutout Opacity for the Torso a tiny amount back from 1 (say, 0.98): the first thing youu see if you are using OpenGL in the viewport is that the whole torso looks weird. Then, if you render with IRay you will see what I mean. 

With the mask, you can leave the Cutout Opacity fully on (value=1) but the presence of the cutout mask will affect the whole Torso.

Note that some characters are affected more than others. It is hardly noticeable on the standard G8 female skin, for example. I could also have used G3 characters with similar results.

Richard Haseltine

If you make parts of the model semi or wholly transparent you are letting light shine in and bounce around, the model is only a single skin of zero thickness. For the same reason the SSS algorithm, which treats the enclosed volume as a solid I believe, is also going to be confused in itself, additional light aside, by an opening.

marble

Richard Haseltine said:

If you make parts of the model semi or wholly transparent you are letting light shine in and bounce around, the model is only a single skin of zero thickness. For the same reason the SSS algorithm, which treats the enclosed volume as a solid I believe, is also going to be confused in itself, additional light aside, by an opening.

Even at 0.98? That is hardly semi-transparent - it is almost opaque. Here's the Edie example attached.

Richard Haseltine

marble said:

Richard Haseltine said:

If you make parts of the model semi or wholly transparent you are letting light shine in and bounce around, the model is only a single skin of zero thickness. For the same reason the SSS algorithm, which treats the enclosed volume as a solid I believe, is also going to be confused in itself, additional light aside, by an opening.

Even at 0.98? That is hardly semi-transparent - it is almost opaque. Here's the Edie example attached.

I suspect that's the second part - you are chnaging the way the thing looks when Iray tries to handle for the SS calculations (in 3delight there's a pause when the render first hits an item with SSS as it calculates the scattering, I'm guessing that Iray does something similar).

JonnyRay

In this thread ... Iray Uber Shader - Subsurface scattering with cutout opacity map? ... we discussed that when Iray sees a surface with anything less than 100% opacity (either by tweaking the opacity value or by applying a map), it treats the surface as if "Thin Walled" were set to On. This would mean that effects like subsurface scattering won't work. That seems to track with your results.

You might take a look at Oso's latest shader ( Product: Oso Blendy Two Layer Shader for Iray : Support Thread: support thread here ) and see if that might help you accomplish your goal?

marble

JonnyRay said:

In this thread ... Iray Uber Shader - Subsurface scattering with cutout opacity map? ... we discussed that when Iray sees a surface with anything less than 100% opacity (either by tweaking the opacity value or by applying a map), it treats the surface as if "Thin Walled" were set to On. This would mean that effects like subsurface scattering won't work. That seems to track with your results.

You might take a look at Oso's latest shader ( Product: Oso Blendy Two Layer Shader for Iray : Support Thread: support thread here ) and see if that might help you accomplish your goal?

I'll take a look at that, thank you,