Master MODO portraits: Perfect the Skin Material and the Shader Tree

In this third tutorial, we will take a look at the Skin Material and Shader Tree

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

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

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

These are appropriate settings for the old fisherman's skin

When you click Add Layer, this is where the Skin Material is located

When you click Add Layer, this is where the Skin Material is located

Make sure you set the Indirect SSS to Both

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

A first level of skin detail is provided by the Normal Map

The second layer of detail comes from the Bump 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

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

The Epidermis SSS Color map is applied

Step 6: Skin Material - Lower Dermis Subsurface Color

The lower dermal area contains more blood vessels and is typically the layer that contributes the most red because of this. Choose Add Layer > Image Map > Load image. Select the Lower Dermis SSS Color map. Set its Effect to Custom Material Channels > Skin Material Channels > Lower Dermis Subsurface Color.

Next in line is the Lower Dermis SSS Color map

Next in line is the Lower Dermis SSS Color map

Step 7: Skin Material - Upper Dermis SSS Color

The upper dermal layer contains tissue for cushioning the epidermis, and also houses the nerve endings, hair follicles, sweat glands and blood vessels. Because of these constructs, the light scattered from here will be differently colored than the epidermal layer. Choose Add Layer > Image Map > Load image. Select the Upper Dermis SSS Color map. Set its Effect to Custom Material Channels > Skin Material Channels > Upper Dermis Subsurface Color.

With 3 SSS Color maps, MODO has some serious scattering to do!

With 3 SSS Color maps, MODO has some serious scattering to do!

Step 8: Skin Material - spec amount

The uppermost layer of skin excretes an oil that produces a shiny, specular reflection on its surface. Depending on the amount on the skin, it becomes less or more shiny. To simulate this, let's load in the grayscale map that we painted in MARI. Choose Add Layer > Image Map > Load image. Select the Specular Amount map. Set its Effect to Custom Material Channels > Skin Material Channels > Oil Specular Amount.

As we don't want to overdo this effect and want just a very subtle amount, lower the opacity of this layer to 4%. I like to use this map also for Oil Reflection Amount and Oil Reflection Fresnel, both at a very low opacity of 5%.

He's in sunlight and a bit sweaty, but we don't want to overdo the shininess of the skin

He's in sunlight and a bit sweaty, but we don't want to overdo the shininess of the skin

Told you we'd get there!

Told you we'd get there!

Step 9: Skin Material - Roughness

The Roughness setting determines the size of the spread for both Specular and Blurry Reflections. Choose Add Layer > Image Map > Load image. Select the Specular Roughness Map. Set its Effect to Custom Material Channels > Skin Material Channels > Oil Roughness. I also lowered the opacity a bit, to about 70%.

The Roughness Map applied at 70%

The Roughness Map applied at 70%

Step 10: Now for the eyes, shirt and hat

The eyes get a material that is 100% transparent, 0% Diffuse, with a Reflection Amount of just 0.5%. The human cornea has a Refractive Index of 1.376, so we dial that in as well.

The shirt is a basic material setup with Diffuse Color, Bump and Diffuse Amount layers. The stains we painted in MARI are on a separate layer, set to Multiply at 80%.

The hat fabric has a Diffuse Color and Bump layer with a Gradient Incidence layer set to Multiply, which is a common setting with fabric materials. For the metal pieces I choose the Matte Silver material preset out of the fantastic and extensive library of material presets inside MODO.

MODO has a great set of material presets

MODO has a great set of material presets

And this concludes the materials and textures part of our tutorial. In the next lesson, we'll take a look at lighting and rendering in MODO, as well as post work in Photoshop. Stay tuned! And if you've missed out any of the previous parts of this tutorial, be sure to check out Part 1 and Part 2 to get the full picture.

Top tip: The Normal Map is a special case

Make sure the Colorspace of the Normal Map is set to None. If it is set to Default (as all other images) you will get strange shading results (see screenshot).

Bad shading

Bad shading

Good shading

Good shading

Top tip: Bump Amplitude vs Camera Distance

2mm may seem high. For close-ups I would probably lower this Bump Amplitude amount, depending on the scene and lighting. But for a medium-distance shot, this seems to work as a good value!

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
Download a free trial of MODO
Discover more free tutorials for MODO from The Foundry
Find out more about the AMD FirePro™ W9000

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