ARNOLD SUB-SURFACE SCATTER
11.21.2017 Hi guys, not even 2 years and my Mental Ray SSS Tutorial went out of style. I'll have an Arnold SSS tutorial but its way easier and much better then Mental Ray. I will have updates.
MENTAL RAY SUB-SURFACE SCATTER SHADER
Sub-surface scattering describes how light bounces inside objects that are translucent. There are many different rendering systems out there but for the purposes of this tutorial we're going to use Mental Ray. I know with Maya 2015, there is a new SSS shader that is supposed to be easier. I didn't find that much easier. In my opinion Maya and Mental Ray needs an entire UI/UX overhaul.
Mental Ray is a bit dated and the scientists who created it have no idea how artists think. They will make control modules that instead of scale from 0-10 or 0-100, they will scale from -255 -255 or something like that. I will complain more about 3D UI because at this point of my life, I consider myself a UI designer over a 3D artist.
We're going to get started by going to the hypershade and going down to Mental Ray to find the misss_fast_skin_maya shader and one of my 3D models I called "The Brute."
From a UI standpoint this tab should be at the top of the miss_fast_skin_maya shader properties. This control module is what controls the amount of sub-surface scattering in an object based on its size. If you dial it up, the level of scatter will not penetrate as easily and the shader will look like solid and glossy. By dialing it down, it will create too much scatter and look translucent like candle wax.
Lets set up a scene. I will put a point light behind the ears of one of my models. This is used to see if I can create the warm glow behind the ears. I will use a directional or spot light to create the main shadows. Lets turn on Mental Ray, final gather and global illumination. I do want to start with a low res render window to make my renders fast. When you apply the the shader to the model it will show up as this red color.
What we do is pick a scale conversion less than 1 and then jump up to say 200. Depending on the size of your model, less then 1 will over scatter creating that glowing washed out look. It will seem like light is emitting from the skin. Go ahead and try it. Then try say 200 and watch it turn solid like stone. Start to pick values in between until you get the right balance for human skin. In this case I settled on 35.
You may have noticed I increased the weight of the subdermal scatter to .6 and made the color a bit hotter and reddish. This will produce a warm rosy color on your human beings and prevent that cool pale and dead wax looking skin.
Pushing too scale too far will give the shader the wet clay look.
Its still a bit waxy looking but for not having any diffuse color, vain maps, and other light maps, I think it looks pretty good. Also depending on the art style, one could tone down the SSS for more realism or slightly make it more translucent for that Pixar look. The important thing is to put some glow in the ears and pink in the cheeks and nose for blood flow. I like this shader, its almost as good as Z-brush shaders. Hope this helps. Feel free to send me a comment.
My character is a bit stylized, Here is more realistic render of head I pulled form the student resource directory. The important part is to get the glow behind the ears. Don't let the model start to emit light enough to get rid of the shadows or get speckled dots. Here I bounced between 20-15 in the scale conversion.