indirect illumination for skin shading

In this post, I will talk about applying indirect illumination to the skin shader  using ambient light and AO

Mental ray's  misss_fast_maya_skin shader is a  one of the better skin solutions.

Like its name implies, it's fast and quite easy to accomplish a quick skin look.

But if you look for more realistic results, you need to provide with indirect illumination to the skin.

First of all, you need to approach the skin shader from two different directions. direct and indirect illumination.

Most of the skin tutorials generally deal with direct illumination part only.

Sometimes direct illumination only can create a satisfactory result, especially for cartoonish look characters.

But a realistic human skin cannot go without considering the indirect illumination.

So, I'd like to show a method of doing this, not using expensive final gathering but ambient light and AO combo.

Here's a scene with a head model. A skin shader is alreay assigned to it.

I have set up two light sources. One from the front for epidermal and subdermal scatering and the other from the back for back scattering.

Area 1: This is where the direct illumination hits the sufrace.

Area 2: This is where you can see scattering.

Area 3: This is where no illumination or scattering is found.

miLabel attribute to control ambient occlusion

Mental ray's ambient occlusion material doesn't respect transparency and this can create undesired occlusion for transparent materials like windows.

You can easily turn on and off AO for a certain object using miLabel attribute.

Let's look at the simple scene here.

  

 

All three objects in this scene are assigned with the same ambient occlusion material.

What if object#2 is a transparent object like window. If the window is transparent enough,  it should not cast that much occlusion on the floor.

How to use Mia material with Maya's ambient light

Mental ray's mia_material is a versatile, physically correct shader which is the right choice for Final Gathering. However, final gathering is not a cheap and easy solution for animation. In many cases,

a traditional "Ambient light" approach for simulating indirect illumination is still a popular solution.

The problem is the mia material doesn't respect Maya's ambient light. They don't interact at all by default.

So, I'm going to show how to make a mia material respect Maya's ambient light.

Here's a simple scene, a plane and the dragon.

A Lamber shader si assign to the floor and a mia material is assign to the dragon.

The only light source in the scene is just a single ambient light.

The below is the render result.