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I'd like to use an image texture to fully control my SSS radius in a Principled BSDF. However, given that the SSS radius input seems to want a vector output, I'm not entirely sure how to go about this.

Advice on solving this mystery would be welcome.

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It's a vector because you can control the amount of scattering for R, G, and B separately if you wish. It's a bit weird because there is also a "Subsurface Color", but if you set Subsurface color to white, you can see the effect of changing the Subsurface Radius vector:

enter image description here

if you don't want different behavior per RGB color, just pass the color of your image in for that vector. Assuming it's a grayscale image the RGB values will be the same.

Note that it's not really a radius per se; you can't set it to ".5 inches" for example. It's more of a relative amount of scattering per color, and multiplied by the Subsurface value.

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  • $\begingroup$ "Assuming it's grayscale the RGB values will be the same" I tried this, and it appeared to create a substantially different result to just typing the numbers individually. $\endgroup$
    – Legoman
    Nov 24 '18 at 20:13
  • $\begingroup$ Additionally, as I stated in the question that I would like "full" control over the radius using the texture, if you could edit your answer to address that as well (whether or not it's possible) I might be able to accept the answer. ;-) $\endgroup$
    – Legoman
    Nov 24 '18 at 21:11
  • $\begingroup$ I'm sorry, I don't understand your comments. I just tried creating an image with a medium gray (128, 128, 128) and it gives pretty identical results to setting the Subsurface Radius to (0.5, 0.5, 0.5). I then tried extracting just the Red channel and it works the same. See this image; the one on the left is using only the Red channel, and the one on the right is using Subsurface Radius of (0.5, 0.0, 0.0). imgur.com/a/qyiDml8 Also not sure what you mean by "full" control? $\endgroup$ Nov 25 '18 at 0:35
  • $\begingroup$ Ah, I think I misunderstood. The RGB value does not directly match the XYZ value, it seems. Apologies—thanks for your answer! $\endgroup$
    – Legoman
    Nov 25 '18 at 0:53
  • $\begingroup$ oh sorry, I thought you knew that Blender puts stuff in the 0-1 range instead of 0-255. Another point in case you don't notice it in that imgur image link: if you're using a grayscale map for the SSS radius, be sure to set the image texture to "Non-Color Data" because otherwise Blender will gamma-correct the image and your values could be different than you might expect. $\endgroup$ Nov 25 '18 at 1:02

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