In this third tutorial, we will take a look at the Skin Material and Shader Tree
3D Artist Bert Heynderickx - aka Alberto Ezzy - takes a look at the Skin Material and the various Layers and their Effect settings in the Shader Tree to achieve good-looking human skin
See Part 1 of this tutorial series: Perfect the geometry of a male head
See Part 2 of this tutorial series: Learn to paint convincing image maps
In Part 1 of this tutorial series we looked at the creation of a male head portrait in MODO, revealing how to use the Sculpt Tools in MODO to clean up the geometry of scanned head data, as well as adding and modifying a hat model to perfectly fit the character. And in Part 2, we moved on to use MARI and Photoshop to create the different image maps needed to feed the Skin Shader in MODO.
Now in Part 3, we will import the previously made image maps into the Shader Tree in MODO and take a look at the different Effect settings for each layer in order to properly feed MODO's Skin Shader.
In this tutorial we take a look at the Skin material in MODO
Step 1: Camera setup
Okay, so let's start by setting up the scene so I can easily and clearly evaluate my materials and any adjustments I'll make along the way. I want 2 cameras: one with the final point-of-view and one that will move around freely, for testing purposes and to zoom in on details.
I find having 2 Preview Renderers open at the same time is a great workflow that I couldn't live without anymore! But I also find that I need a high-performance graphics card to be able to do this without slowing down my system. I am using the AMD FirePro™ W9000
for this workflow. It is very responsive and a joy to work with.
For the main camera, I choose a Focal Length of 88mm, which is appropriate for portraits, and once I'm happy with the position and rotation, I right-click on the Camera in the Item list, and choose Lock, so that I can't mess anything up by accident. The second camera gets a Focal Length of 35mm to get a wider viewing angle for checking out the skin.
This 2-camera setup offers twice the effect of MODO's superb Preview Renderer
Step 2: Add Skin Material
First I select the head model in the Item List, press the M shortcut key to give it a material, and call it "Male skin”. I delete the automatically generated Material and choose Add Layer > Custom Materials > Skin Material.
This skin material is designed to completely replace the shading calculations of the standard Material item. It also depends heavily on SubSurface Scattering (SSS). When using Global Illumination - as we do here - we have to tell MODO how the indirect lighting in the scene will affect the surfaces with SSS. So let's go to the Shader Tree > Render > Properties > Global Illumination and set the Indirect SSS to Both.
This setting is the most render-intensive, but will give the best results when we apply all our previously made image maps as SSS color maps. Check out the settings in the screenshot. After quite a bit of trial and error, I found these settings to work the best for the skin of our old fisherman.
These are appropriate settings for the old fisherman's skin
When you click Add Layer, this is where the Skin Material is located
Make sure you set the Indirect SSS to Both
Step 3: Skin Material - Normal and Bump
Let's give the surface some detail with our previously created Bump map and Normal map. In the Shader Tree, choose Add Layer > Image Map > Load image. Select the Normal Map that was exported from ZBrush and flipped on the Y axis. Set its Effect to Surface Shading > Normal.
Now a very important tip: Make sure the Colorspace of this image is set to None. If it is set to Default (as all other images) you will get strange shading results (please refer to my Pro Tips at end of this tutorial).
Next, load in the Bump Map and set its Effect to Surface Shading > Bump. We don't want to overdo this effect so lower the Opacity of this layer to 15%. The Bump Amplitude in the Skin Material is set to 2mm (please refer to my Pro Tips at end of this tutorial).
A first level of skin detail is provided by the Normal Map
The second layer of detail comes from the Bump Map
Step 4: Skin Material - Epidermis Diffuse Color
The epidermis is the outer layer of effectively dead skin cells, and is quite thin. Let's give the skin its first layer of subtle color. Choose Add Layer > Image Map > Load image. Select the image map that is provided with the scanned model, the one that is the base from which we derived all the other maps in the previous tutorial. Set its Effect to Custom Material Channels > Skin Material Channels > Epidermis Diffuse Color. As with all the other maps for the skin, the Projection Type is the UV Map from the head model.
The first of 4 layers to give the skin its color
Step 5: Skin Material - Epidermis SSS Color
This layer determines the Color of the light that is absorbed, scattered, and then reflected back out at the epidermis level. Choose Add Layer > Image Map > Load image. Select the Epidermis SSS Color map. Set its Effect to Custom Material Channels > Skin Material Channels > Epidermis Subsurface Color. Now the eyes start to get some color and definition, too.
The Epidermis SSS Color map is applied