Sub-surface Scattering Tutorial

3dsmax + Vray
Welcome to our 3dsmax + Vray human skin sub-surface scattering simulation tutorial. In this article, we will be explaining a bit about what SSS (Sub-surface Scattering) actually is, and what it does in your renderings.

What is Sub-surface Scattering ?

Subsurface scattering (or SSS) is a mechanism of light transport in which light penetrates the surface of a translucent object, is scattered by interacting with the material, and exits the surface at a different point. The light will generally penetrate the surface and be reflected a number of times at irregular angles inside the material, before passing back out of the material at an angle other than the angle it would have if it had been reflected directly off the surface. Subsurface scattering is important in 3D computer graphics, being necessary for the realistic rendering of materials such as marble, skin, and milk.

In more common terms, let’s take a look a these images to understand SSS :

Now we can see that SSS simulates light going into a non-solid object, such as skin. Now let’s take a look at how we can integrate SSS into our 3dsmax scenes using Vray.

VrayFastSSS Material

Open up 3dsmax, select Vray as your renderer, open Material Editor, and create a new Material of type “VrayFastSSS”

You will get these initial settings in the material properties. Now let’s tweak these a bit.

Notice the two main parameters, shallow radius & deep radius, highlighted in orange for you in the picture. These control how much light scatters through the material. In general, when applying SSS to a human model, and working in Meters, it’s a good idea to set these to a default of 0.01m for the Shallow Radius, and 0.03m for the Deep Radius.

Now, change the skin shallow and deep colors to shades similar to the human skin, as shown in the following image :

Notice how i’ve changed the shallow and deep radius to 0.01m and 0.03m, try these settings yourself, you’ll see that these work well for human-sized characters. Lastly also notice the shallow texmap and deep texmap, which are textures that can be used as skinmaps, which is exactly what i’ve done here.

Since i’m using a Poser model (Jessi) for my mesh inside 3dsmax, the mesh already has UV texturing coordinates for the Jessi_Body.jpg skin texture map, and therefore, the model needs no UV work. If you wish, and you have the files from Poser, go ahead and create Bitmap maps for the shallow and deep texmaps.

Now, light your scene with GI (dont know how?  read our other tutorials on architectural photorealistic rendering..) , and do a test render…

Not bad for first try. Notice how light is scattering mostly inside her legs, in this lighting situation since lighting is coming from below.

Now let’s try to render her inside a daylight scene.

Using the same parameters, render her inside one of our previous tutorial’s daylight scenes using XRef Object instancing.

We can see that the results are consistent once we have set up VrayFastSSS material correctly. When working in a real scale (meters), using the correct Shallow and Deep parameters works incredibly well in Vray. We only have to tweak the material once and voila, instant, picture-perfect SSS every time, in almost any lighting situation.

Thanks for reading our SSS tutorial.

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