vrayFur with vrayFastSSS2 combo?

[MartinB]

Has anyone tried this combination?

I'm getting some nice still renders of a fleecy woolen material by using the fast SSS shader with a load of vray Fur thrown on top.

The only problem is when this surface moves the SSS element flickers pretty badly. If I turn off the fur and just render the surface thats below then the subsurface is pretty solid, maybe with just a hint of flickering, but the hair seems to be picking this up an amplifying it.

cheers for any help or pointers
Martin

[Morbid Angel]

whats your prepass set to?
It may be that the fur is so fine that the lightmap is just not enough to make an accurate enough estimation between the thin lines of hair. You may be better off using physical sss in this case.

[MartinB]

Hmmm.... that makes sense, I've got the prepass set to 1 but it does look like a noisey mess, which would explain the noise being calculated in the fur....

Not really used vray SS much.

I'll give the raytraced option a go but from testing it earlier it just didn't look half as nice as the simple method and took ages to render.

[Morbid Angel]

that is the case...to get physical sss to work in vrayMtl you need to set your refraction color to full white, glossiness to 0.1 and set your fog color to some sort of darker red (if its skin) and enable translucency. After that the adjustment of the sss quality is basically the refraction glossy subdivisions and translucent subdivisions.
Alternatively you can render the model in two passes, with hair hidden (only shadow on the fast sss model) and then the opposite and comp them together.

[MartinB]

Thanks for the explanation and pointers Dmitry. I gave the vrayMtl physical SSS route a go but couldn't achieve the same effect as the vrayFastSS simple scatter way. But it is nice to finally understand how its meant to work on other surfaces!

I think I've kind of got it working as I want now. I ended up still using the Simple Scatter method with a prePass value of 2 and a prePass Blur value of 8 which seems to make the noise subtle and fine enough that it will blend in with general film noise, where as before it was these writhing big spotches.

Thanks again!