TurboTips: V-Ray FastSSS2 Material, Part 2

Calvin Bryson 3D Modeling, Artists, TurboTips, V-Ray FastSSS2

The following is an in-depth guide to the regular V-Ray Blend Material. In this series, we will cover the theory behind many of the features of the material.  We’ll also show specific examples of settings and give you some tricks to use. While the images used are from 3ds Max, the same concepts and settings can be used for V-Ray for Maya. Currently, the SSS materials in V-Ray for C4D behave differently, so this tutorial will not be as valuable for C4D users.

Diffuse and SSS Layers

This is the most important (and, generally, the most confusing) part of the FastSSS2 material. The problem is, there are many different colors to set up and they all seem to affect one another in some way, so it can be a bit difficult to work non-destructively.

In this tutorial, we’ll attempt to de-mystify these settings so they’re a bit easier to work with.

Diffuse Color, Diffuse Amount, & Sub Surface Color

Let’s start with the Diffuse and SubSurface colors: essentially, they set up the inner and outer color of the object and allow you to set exactly how much each one affects the final material. To demonstrate how this works, we’ve set up the Diffuse to be a pure blue, while SubSurface  is set to a pure red. Look how everything changes as we adjust the Diffuse Amount value:

At 0, only the SSS layer is visible, while at 1, only the Diffuse is visible, with no light scattering inside of the object. Everything in-between is a mix of the two.

Overall Color

Now, we’ll bring the Overall Color into the equation. This acts as a filter for both the Diffuse and Subsurface and it affects how much of the set color is to be seen in the actual material. Pure white [255;255;255] lets through 100%, while medium grey [128;128;128] lets through 50%.

This sounds simple, but it also works the same way with colors: pure red Overall color [255;0;0] only shows the red channel of both Diffuse and SubSurface colors. In this case, it is pure black, since neither of the colors have any red channel value. Basically, the RGB value of Overall color determines exactly what percentage of each channel is visible in the other two colors.

We recommend sticking to grayscale values or grayscale textures in this slot. Otherwise, it is very hard to predict the resulting look. It’s not ‘intuitive,” but mathematical.  However, a simple B&W map can be good way to make everything a bit more interesting, without getting unexpected colors.

Scatter Color

Finally, there’s one other color to adjust: Scatter Color. This defines the color of the scattered light rays once they enter the surface of the object. That means it also affects the intensity of the scattered light, so if you set it to black, the light turns black and no scattering is going on.

Again, this one is a bit tricky to use if you use colors instead of grayscale values, since it interacts with the SubSurface color in a mathematical way. We’re not 100% sure of the exact formula behind it, so your best bet is trial and error- try first to adjust the lightness of this color and then tweak the hue until you get the exact look you want. Usually, the Subsurface hue and Scatter color hue should be pretty close.

Scatter Radius

Scatter Radius allows you to set an exact depth to which the light rays can penetrate the surface. If you need to be sure the result is accurate, take care to keep the Scale at 1 and make sure the object’s XForm is reset.

Phase Function

We’re almost done!  The last parameter to adjust here is the Scatter Phase. It can be set from -1 to +1 and it controls the way light rays travel within the object’s surface. Zero (0) scatters the rays in all directions equally; positive values focus the light mostly forward; and negative values make most of the rays go backwards. As a general rule, water-based materials (skin, juice, milk) tend to scatter the rays forward, while hard materials (marble, glass) tend to scatter them backwards.

 

Next week, we will continue this series with a talk about the Specular Layer and some more miscellaneous settings in the Fast SSS2 Material.  If you have any questions about this week’s tutorial, please feel free to discuss it with us in the comments below.

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This series of tutorials was made with our friends at Viscorbel.

If there are any topics you’d like to see in a future edition of  TurboTips, let us know in the comments below, or Tweet your question to @TurboSquid with hashtag #TurboTips.