Animal fur with VRayHairNextMtl?

[dgruwier]

Is there any philosophy on dealing with animal fur colors in the new hair material, or was that never part of the consideration? I tried using the dye color with a texture map for the colors, but I couldn't get anything that looked even remotely right out of that, and I can't find a way to reliably translate RGB values into melanin and pheomelanin values, especially grey colors.
I suppose animal fur is too fundamentally different from human hair?

[dgruwier]

I found the blog post about the new hair material, and I read the paper it’s based on. I understand a lot more now, but I have some questions that it doesn’t seem like the blog post or the documentation covers. I think this requires help from someone who is familiar with the inner workings of the shader, maybe vlado ?


A) Where should I plug in a fur color texture to accurately have it affect the hair color similar to how the melanin would? After further reading, I expect the dye color should not be used, but instead I should use the tinting parameters. If so, should I use the transmission AND secondary tint, or only transmission?
Also, if using the tint is indeed correct here, it would be extremely helpful to have random hue, saturation and value parameters for tint.

B) In the paper they talk about “color reparameterization”, automatically adjusting the texture color to compensate for the effects of multiple scattering. In particular they seem to make dark colors significantly brigther and more saturated to match artist expectations. Is anything like that implemented in your version? If not, is there a reliable way to achieve a similar result? My method has been using a gamma curve to brigthen my texture and adding saturation, which kinda works, but I’m not super confident in the accuracy.

C) In the paper they mention “Azimuthal” and “longitudinial” roughness. I assume this is lumped together in the glossiness paramter in VRayHairNextMtl?
They also mention a “primary reflection roughness” parameter that is linked to the longitudinal roughness, used to help emulate cuticle and medulla on animal fur. Is this the same parameter called “primary glossiness boost” in VRay? If so, how is this value mapped to the glossiness parameter? Should I set it to 0, 0.5 or 1 for it to have no effect?