Sub-surface scattering (SSS)

In the introduction to this series I explained how Physically Based Render engines work – simulated light bouncing around interacting with surfaces.

SSS is the process that defines –

• How light passes through a translucent object,
• How it interacts with the properties of that object, and
• How it exits the object (at a different point – hence scattered).

In practical terms, particularly with skin, it is the effect where you see light pass through extremities like the ear, producing a reddening glow.

Showing Sub-surface scattering (SSS) effects as it passes through the ear, producing a reddening glow.

That is about as far as I can take the science, so let’s look at how SSS is controlled within Octane.  SSS is applied to a material node using a scattering node, which can be applied to both diffuse and specular materials (but not glossy ones).  If you look at the skin shader material in our previous skin tutorial, you will see there is a scattering node attached to all four material nodes (3 scattering nodes, as one is shared between two specular nodes).

Node-graph diagram of our skin shader showing the a scattering node attached to a material node.

The diagram below shows the three scattering nodes controlling (from left to right) the skin’s deep/mid layer, the mid-layer and the surface layer.

Settings for three scattering nodes controlling (from left to right) the skin’s deep/mid layer, the mid-layer and the surface layer.

Octane Scattering Node Settings

1. Density

Density controls how fast light travels through an object, the higher the value the faster it travels (a value of 0 would result in no scattering).  My interpretation of this is that the higher the value, the deeper light can penetrate a surface.  When using other materials, particularly those from the online database, I have found this setting to be very low.  It is very dependent on the size of the model, and therefore the scale used within Daz.  Normally these materials have been developed for use within other 3d applications with a different scaling system, which is why they tend to be set lower.

2. Absorption

The scattered light will be the opposite of the absorption colour.

This setting defines which light is absorbed faster, in the case of the 3^rd node it’s a green/blue.  It took me a while to get my head round this, but essentially the effect is the scattered light will be the opposite of this colour (from a wavelength perspective).  The image shown here is from the colour picker within octane – a colour set to absorb blue will scatter as red.

3. Scattering

Scattering is similar to absorption, but defines the speed at which light will be scattered when it passes through an object.

4. Phase/direction

This controls the direction the light is scattered:

• 0 – light scattered the same amount in any direction
• 1.0 – more light continues to travel in the direction it was originally traveling
• -1.0 – light backscatters in the direction it came from

5. Adjusting the scattering nodes

Sadly there is no one definitive setting that will work across all objects. It very much depends on scale, lighting, position, kernel settings and so on.  It is very much a case of trial and error, and an area I still need to work on.

Practically, you may not need to worry about this setting too much, for example if the object is distant or if the ears are covered.  But if you do need to, it’s a juggling act between getting the right amount of scattering across all skin materials. 

Light wouldn’t scatter like that through a hand.

Note – any changes you make to one material (e.g. ears) will have to be adjusted in other skin materials (e.g. arms), otherwise the change will be visible in the UV seams.  Consider the girl with the red ear above – she was one of my first attempts at SSS.  Now look at her hand …

Light wouldn’t scatter like that through a hand.  As a result I tend to pose a model with the hand next to the ear, and then adjust the density (starting with the deep scatter node).  Density (from left to right) 1, 250, 500.

I tend to pose a model with the hand next to the ear, and then adjust the density. Density (from left to right) 1, 250, 500.

Glossiness

The last area I would like to cover regarding the skin material is gloss/reflection.  This is for subtle gloss effect, so you wouldn’t use this for a wet skin look, but more for areas like the lips, nails, lacrimals, or eye socket. 

Gloss is controlled in Octane using the Roughness setting in both specular and glossy nodes, but is not available in diffuse nodes.  The scale between 0 and 1 determines the level – the lower the roughness, the more glossy/reflective the surface.

The lower the roughness, the more glossy/reflective the surface.

Let’s consider a practical example using the lips.  The lips are currently sharing a material with the face and the ears, which is no good as we don’t want a shiny face! 

• Return to the Material tab and select the Lips surface.
• Select the material assigned to the lips and copy as a new material.
• Now apply this new copied material to the lips. It now has its own material that we can edit.

Select the material assigned to the lips and copy as a new material.

You can get away with this with the lips as they have a clearly defined line between the surrounding face surface, so the seam is less obvious.

With the newly assigned lip material selected, open the node viewport.  I have found, surprisingly, that the best place to adjust the roughness for the lips is in the uppermost scattering node (the one for the deep scatter), which to me, sounds counter-intuitive.  The image below shows the lips with roughness set to 500,250 & 0 (top to bottom).

Lips with roughness set to 500,250 & 0 (top to bottom).

Finishing up in Daz

Octane comes with a free online material database containing 100s of organic and non-organic materials.  I used the auto-material function in Octane for the eye-lashes. This feature takes the surface settings from within Daz and tries to convert them into Octane. The results vary, and it struggles with iRay materials (though it is getting better). Within the Material tab, right-click the item and select Create new material > Auto Material.

I used the auto-material function in Octane for the eye-lashes.

The other materials I used in the Mei portrait are:

1. Cornea and Eye Reflection – Clear cornea shader  (Octane database)
2. Eyelashes – Auto-material
3. Iris – RedSpec
4. Pupils – RedSpec
5. Sclera – TonySculptor Sclera (Octane database)
6. Hair (Actual Hair 2) – RedSpec Hair Shader

The RedSpec materials are part of a set purchased from a 3^rd Party.

I used the iRay OOT Hair Shaders for colour and transparency maps.  I sometimes increase the smoothing value within Daz for hair as well.

Mei portrait

I have always had a real dislike of the Tear object around the eye, which is now part of the eye moisture object in Genesis 3 characters.  I remove it in Daz by using the geometry tool.

• Click anywhere on the tear.
• Right-click and do Geometry selection > Select connected.
• With the tear now selected (see image below), you can right click Geometry assignment > Create surface from selected.
• Name it, and then repeat with the other eye.
• I then apply a null-shader (diffuse node with no settings, and opacity set to 0) to the tears, and there you have it, no more tears!

Selecting the tear area on our figure’s eyes.

Summary

So that’s it for Daz Studio, Octane, and skin.  I still have some work to do, in particular on skin reflection, index of refraction, Fresnel effect, falloff textures and more.  I also want to break down the material a bit more and make it more processor efficient.

Having spent so much time on the skin, I also need to work on bringing the standard of my other materials up to scratch. You will notice many of my models don’t smile, simply because I am yet to develop a material I am happy with. Same goes for clothes.

Thank you for visiting my Daz Studio Octane tutorials. Hope you enjoyed them.

This article and all of the images within were created by the very talented Brian Sains. Copyright © Brian Sains. Check out his gallery here.

We will need a working version of the Daz Octane plugin installed (full or demo).  This can be downloaded at www.otoy.com.  Please note – if you are using the demo version then image size is restricted and will be watermarked, and you will not be able to access the material database. If you are not familiar with Daz Studio Octane, this introduction article will give you an overview.

In this tutorial, I will use the Mei portrait image below as an example.

Daz Studio Octane Skin Shader Tutorial

1. Start by downloading this .duf file.
2. Open Daz Studio.  If the plugin is installed correctly, you should have the following icons in your toolbar
3. Make sure the icon on the right is set to ‘Duf’ (click on it to cycle through the options) – this setting will make sure that all Octane settings and materials from the Duf file are loaded (Manual loads no Octane settings, Auto will try and build materials based on the settings within Daz).
    
   The left icon is for the Main Octane Settings, the middle opens the render viewport.
4. Unzip and open the SkinShader.duf file you just downloaded.  You should find a simple scene with a Sphere primitive.  If you open the render viewport the sphere will be rendered, but will be quite dark and not look very much like skin at the moment.
5. Now import a model – I have used Genesis 3 model (Mei Lin 7) in this example but you can use any model you have. Note that the available surfaces will be different for earlier generation models, but the same principles will apply – e.g. Torso in Gen 3 is Head, neck, hips etc. in Gen2.  For best results try and use a model that has a diffuse map that is photo-referenced, and not hand painted – Mei Lin 7, Olympia 7, Michael 7 and Michael 6 are good examples.
6. With your chosen model loaded, open the Octane Settings window, and select the materials tab.

The Materials Tab of the Octane Settings window.

The left part lists all available/used materials, the middle part lists current scene models with their available surfaces. When you select a surface a yellow dot will show you which material is attached.

7. Now apply the skin material to the model – click and drag SkinShader from the left and drop it on the Face surface.  Apply the same material to the Lips and Ears.  You can now delete the sphere from within Daz Studio.  It should now look like this:

After applying the SkinShader material from the left to the Face, Lips, and Ears surfaces.

Now you have the material applied open the render viewport.  It will still look a little dark and not skin like yet.  We need to add a few more  things to the material using the Nodegraph Editor (highlighted with a red rectangle in the image above).

Exploring Our Octane Skin Material

When rendering an object using a PBR (physically based renderer) like Octane, the material needs to replicate its real world equivalent.  With skin this involves creating layers for the deep scatter (blood vessels), hypodermis & dermis (fatty tissue), and epidermis (the outermost layer).  At the very least I feel you need the first and last if you want that lovely red translucency (scattering) in the ears. 

One way is to generate independent layers on the model (each with its own material), but this is cumbersome and from my experience does not add anything.  I prefer to generate all the layers within one material.

I do this by combining different nodes.  Octane has four primary nodes – Diffuse (solid matt surface), Glossy (solid shiny surface) and Specular (clear or transparent surface).  The fourth is a Mix Node where you can combine two or more of these surface nodes.

Node structure of the skin material I used in the Mei portrait.

The above is the node structure of the skin material I used in the Mei portrait.   Nodes 2 & 3 are adapted from the amazing skin material developed by TonySculptor (freely available in the Octane library) . I have added the other nodes around it, and they loosely represent the layers of skin as follows:

1. Specular Material (blood vessels, or deep scatter)
2. Specular Material (skin mid-layer)
3. Specular Material (skin mid-layer)
4. Diffuse Material (skin surface)
5. Displacement map (add texture and definition to the surface)

In isolation, each of the five nodes will look like the following (Figure 6 is all combined):


The five skin layers I am using in my Mei portrait skin. Figure 6 shows all of the layers combined.

The additional nodes in the skin material are:

6. Output node – the item/s that the material is applied to
7. Mix material node – used to combine two material nodes
8. Image node – used to place an image within a marterial
9. Colour node – used to set an RGB/Greyscale setting to a node
10. Scattering node – used to set the scattering parameters for specular or diffuse nodes

Note however, that our current skin material does not contain any texture maps. We will need to put in appropriate texture maps according to the nodes described above.

In particular, there is a Diffuse map in the 4^th picture – let’s go ahead and put that into the skin material.  Select the RGB Image node connected to the Diffuse node. The following settings should appear on the right of the editor:

Settings for the RGB Image node.

It’s all set to receive the diffuse map – simply select the drop down list and either Browse to the diffuse map location, or (if loaded) from the map list that is generated (in this example, the maps available for Mei are offered).  I want the MeiLin7FaceD_1001.jpg image.

Browse to the diffuse map location, or (if loaded) from the map list that is generated .

Now let’s return to the Material tab and generate two more skin materials – one for the torso, and one for the arms.  Right click on the SkinShader material and Copy as new material.

Generate two more skin materials – one for the torso, and one for the arms.

A copy will be created in the unused section (blue – not assigned).  Now drag this material over to the torso surface to assign it.  With the torso selected, open the Nodegraph editor and change the diffuse map we set before to the appropriate Torso diffuse map image.  The RGB node should now look something like this.

RGB image node after applying the appropriate Torso diffuse map image.

Repeat this again for the arms. We can ignore the legs and nails as they will not be visible. Your completed skin material list should look like this:

Completed skin material list.

You can right click each material and rename it if you wish, always useful when scenes get more complicated.  You can also save them as pre-sets so they are available in other projects.

We Are Done!

Congratulations! You have just created a Daz Studio Octane skin material. Open the render viewport again, and the image should start to look more like skin now.

How our Octane skin material looks in the render viewport.

To transform this image to a finished portrait, we will need to work on setting up displacement, lighting the scene and then setting up the camera. We will discuss how to do this in our next Octane tutorial.

Our finished Mei portrait with appropriate camera, scene lighting, and post-work.

This article and all of the images within were created by the very talented Brian Sains. Copyright © Brian Sains. Check out his gallery here.