Claudia Herbst-Tait
Professor
Pratt Institute
Department of Digital Arts


Surfaces & Sub-Surface Scattering

Many "opaque" objects absorb light into the surface to some degree; the 3D term for this is sub-surface scattering.
Light penetrates the surfaces and, depending on the material, bounces around. In the words of the Maya folks:

"Subsurface scattering refers to light penetrating an outer surface and then being scattered diffusely beneath.
This creates the look of a soft surface, often with a very subtle glow. An example of subsurface scattering is
human skin, where the soft, porous quality and semi-translucent glow are essential to achieving a realistic look.
Other surfaces that require scattering are leaves, wax and gel."

Here are a couple of examples (figure 1, 2, 3, 4).



Figure 1




Figure 2 and 3




Figure 4



In Maya, the following materials feature a "Scatter" attribute in the Mental Ray section: Anisotropic, Blinn, Lambert,
OceanShader, Phong and PhongE surface. Tuning this "Scatter" attribute is one way to create the look of subsurface
scattering. Note that the "Scatter" attribute interacts with the Ray Depth Limit attribute of your scene's light; try a value
of 2 or higher and compare the results.



Experiment:

Open the file grapes_blinn.ma located on DDA transfer. The grapes are illuminated by an Area light.
I assigned a Blinn material and added a color map, translucency map, and a specular map. Take a look at the different maps:
it's the same map in each instance but I rotated it to create some offset and changed the Color Gain attribute and contrast,
depending on type of map. For example, the specular map is less bright because grapes are usually somewhat matte.



1) Test render, keep the image. In the Blinn material's Mental Ray section, find the Scatter attribute.
Set it to a value of 1 or higher and test render again (keep the image, compare...). Experiment with the
Scatter Color and also the Translucency settings.


Create your own shader network using your own maps and account for light penetrating an object's surface and for
the texture beneath the surface -- different types of fruit (real or imagined) are great for this. Feel free to use the grape
model but if you do, make them green (or any other color, just not red...) Alternatively, you may use an object from the
assignment you are currently working on.