Iray, Uber shader and SSS

Jovanni

Hi everyone. I've been studying 3D for some time now, and recently, I've been delving into implementing various algorithms for subsurface scattering (SSS) calculations. Apart from full volumetric subsurface scattering in Iray, I've experimented with approximate methods such as Random Walk and Christensen-Burley. I must note that while full volumetric scattering provides the most reliable results, it tends to work slower.

I'm particularly intrigued by how the Uber Shader is structured under the hood. Imagine a sphere—it has an outer surface and an inner one. When you adjust properties like glossiness and diffuse, these characteristics apply to both sides of the surface. However, when there's translucency and an volume, should diffuse or glossiness be present on the inner side? That's what I'd like to discuss. Also, typically, light transmission weight falls within the range of 0.8-0.9. This implies that the diffuse weight is approximately 0.1-0.2. Is there any explanation for why these values are typical for surfaces with SSS? Besides skin, humans have mucous membranes (e.g., oral cavity), and even teeth exhibit SSS. What weight of diffuse should be used for them? Mostly, I adjust these parameters based on my own intuition, but I feel like I'm missing some fundamental knowledge in this regard