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I had some difficulty finding information about the usage of the Subsurface Scattering parameters in the Principled BSDF node for a skin material, so here are some questions I have that are still unanswered despite my efforts regarding the parameters:

  • Is the Subsurface parameter value always at 1.0 for a skin material? If not, does it need to be mapped with a texture?
  • Would the Subsurface Radius parameter be constant across the face of a real person? If not, how can I map this value with a texture given it accepts a Vector input?
  • Is the Subsurface Color intended to have a subdermal map as its input?
  • Is there a document that lists parts of the skin and common SSS values for them?

I'm working with a cartoonized character and I think introducing more realism to its skin can give me better results, but accuracy isn't a priority.

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  • Is the Subsurface parameter value always at 1.0 for a skin material? If not, does it need to be mapped with a texture?

Some parts of the skin have more SSS than others, therefore a texture helps... and rarely a skin gets 100% SSS. So a value of 1 is unrealistic.

  • Would the Subsurface Radius parameter be constant across the face of a real person? If not, how can I map this value with a texture given it accepts a Vector input?

Also another non-constant value. Depending on the density and depth of the skin, if there's bone or flesh under it, etc; this value can change. Here you can play in conjunction with the SSS color, as this parameter is only there to help SSS color to get higher radius. Note that Cycles simply multiplies both Radius and Color. If your SSS has a maximal radius less than 1, you can just use the SSS color. Vector texturing is possible in formats like EXR or HDR (and since in this case, the radius is allways positive, you can use also PNGs or any +16bpp format)

  • Is the Subsurface Color intended to have a subdermal map as its input?

Same thing as the above.

  • Is there a document that lists parts of the skin and common SSS values for them?

There are plenty of artists who shared their common values... But this is not rocket science, and there's always plenty of room for artistic interpretation.

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Okay,I can tell that you're a little confused and I was too when I first used the Principled BSDF shader. I'll clear up the controversy so you can better understand it.

  1. The answer is no. Nothing in this world is completely translucent. Human skin typically has a susbsurface value between 0.1 and 0.2.

  2. If you're asking if the color is consistently red,then yes. If you're asking if its brightness is consitent,then no. The Subsurface Radius is lighter or darker depending on how thick or thin the tissue is. The most noticeable examples of thin tissue include the lips,the ears and the inside of the nostrils.

  3. The Subsurface Color socket is actually the color for SSS shading. It can be used any way you want it,but if you want to create realistic skin,I would definitely recommend using a subdermal map just to be safe.

  4. As of right now,there isn't one. As Rey said,it's open to interpretation.

I hope this helps you. :)

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