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One of the holy grails of rendering and shading is skin. Peaches, watermelon, grapes, anything that has a semi translucent material surface, and then some kind of meat inside of it and that meat takes some of the color and then reradiates that color back out through the skin to the camera. That's called Subsurface Scattering or SSS. We'll call it SSS. That should be easy enough for me to say couple, dozen times. So, any objects, like specially organic objects have this skin and in order to simulate that effect, Blender recently got an upgrade to its material system, which we'll link to over here, and I'll make it a little bigger.
In the SSS panel, under Links and Materials, we have all the normal material settings and then we have this SSS panel. So we have the normal base color of the surface and the specular color. We used to have to use Ramps to get this effect, but now SSS is very accurate. First of all, you want to enable Subsurface Scattering here for this material. Next, you're going to want to make sure that you've enabled Subsurface Scattering as a render pass here in the Render panel, so that the pass is taken on.
It does take quite a bit of compute power. So if you're doing temporary renders, you might want to turn that off for all of the objects in the scene, just that one place and then turn it back on again, when you're ready to do your file renders. Now, SSS takes this base material color and then adds in a couple of presets, one is for chicken, chicken has a yellow fat underneath the skin, to make it kind of yellowish looking. Cream, if you look at cream in your coffee, it's got like a white scattering underneath the surface. Ketchup is obviously red.
Marble has a stone color, depending on the color of the stone underneath a clear, like a quartz surface as well. Potatoes, skim milk, I'm getting kind of hungry here, but skin, we have two settings for skin, Skin 1 and Skin 2. I've used Skin 1 here as a setting and whenever you click these, all it does is it loads up a couple of different presets for you. So the main thing is this color effect and this is kind of a brown kind of a murky color, so like somebody who has a really great tan.
Then the control here sets the amount or the degree of influence that this color from underneath affects the overall skin tone that you see. So if I crank this up to 1 and do a render, you can see that Blender makes two passes. One pass is that white shade, which says okay, based on the angle of the skin, relative to the camera and the thickness of the object at that particular point, how much Subsurface Scattering would occur and then blends in the amount of color on to that surface.
So for just a very slight effect, as if the person had, let's say, thick skin, there's not too much of an effect, but still enough to give you those highlights that you get from skin as well as then when you look at it from the side or more of an angle, you get more of a darkening kind of a color. Now, there is a couple of different effects that go on with Subsurface Scattering. One is called Front side scattering, and the other is called Back side. So if you hold your hand up to a very bright light, where the light is in back of your hand, you'll see some red color coming through, because it's passing through the blood.
That light is picking up the color from that red blood and then it's coming out through the front of your skin and that's called Back Scattering. So these two controls allow you to vary the amount of front scattering and back scattering that you want to occur. Also, skin and as like with all semitransparent materials has an Index of Refraction as well. Then the relative size of the object in Blender units is indicated here for both transmitting the red, green and blue. Different surfaces absorb, those different wavelengths to different degrees.
So in this case with skin, the red and the blue travel pretty far, because that's purple, the color of blood, and whereas the green doesn't travel very far at all. So that's Subsurface Scattering, how to use it, how to enable it and what it does for you in trying to make a photorealistic render of something that is an organic surface.
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