Creating Realistic Skin in Substance Painter 2: Diffuse

Tutorial / 20 May 2022

Over the past year I've focused on my Sculpting skills, this lead to me ignoring some of the other necessary skills necessary for good Character Art. To rectify this I did a deep-dive into creating realistic skin using ZBrush and Substance Painter, for rendering in Unreal Engine 4. Through this little series I'll be detailing how I made the Height, Diffuse, Roughness and Subsurface maps.

So, we've got our model in Substance Painter. It's got good height detail, everything's baked and ready to go. Going forward all new layers will have only colour data. No roughness. No metallic. No Scattering. Only Colour. It's a good practice and helps keep everything clean and organised on a natural model like this.

So, how do we start working on the Diffuse? Here comes the most difficult part for me. Creating the Skin Base layerI have found no tricks for this other than trial and error. Caucasian skin fits in the desaturated orange region so I usually start there and adjust until I'm happy. For this character I chose something like this: 


Hard part: Over. It only gets easier and more fun from here. 

Step 2: Ambient Occlusion. Take that skin layer, duplicated it, make it redder, more saturated and darker. Something like this:

Then all we have to do is mask it out using our AO map. I add a bitmap mask using our baked AO map and add a levels. I simply invert the levels, and boom! We've got some decent AO and idle SSS. I use a levels instead of an Invert Filter because we have more control over the AO with a levels. We can clamp and bring in values as we need them. Remember this, we'll be using it a lot later. 

After the AO I tackle the Subdermal Colour Zones. There's plenty of reference out there for those colour zones around the face but not much for the rest of the body, so I made a Human Subdermal Colour Zones model that outlines where all the Red, Blues and Yellows are through the whole body. For some reference that isn't mine, have a look at RBX imaging, which is a type of imaging meant to detect sun damage through the skin. It clearly shows where the reds and yellows are through the face. In darker skin tones these Subdermal Colour Zones are a lot more subtle

I like to tackle the RED first because it's the most obvious. The red areas of the face and body are where the skin is thin and/or there are a lot of muscles, and therefore blood vessels. To make these subdermal colours look good, natural and believable the name of the game is:

BREAKUP BREAKUP BREAKUP

To start I break up the painting of these areas into 3 paint layers. The Base, which are the lightest areas. The Mid, which is where these areas start getting obvious. The Deep, which I put around the nose and cheeks. To save another layer stack I put another paint layer on for the lips. I use a Dirt 1 brush with a low flow and stroke opacity, it's a very natural brush that creates some good layering and a very natural breakup.

Just these 4 layers by themselves still create a very painted on feel instead of the natural layered feeling we're after so on top of all this I put a

FILL LAYER DIRT 4

set on multiply. Up the scale, adjust the balance and decrease the opacity and this creates a semi-random and natural break up of the values.

Next we do the same thing for the yellows and blues. Breaking the paint up into 3 layers varying in intensity and adding a 

FILL LAYER DIRT 4

set on multiply over the top.

The blues on our body are due a large collection of veins carrying de-oxygenated blood.  This is most obvious on the face and jaw because of how thin the skin is. The yellows areas on our body are due to the lack of muscle and blood vessels, it's kind of like a neutral zone. The forehead, elbows parts of the forearm are pretty noticeable yellow spots. The overlapping the yellows of our body are similar browns for the same reason, for our brown layer all we have to do is duplicated our yellow layer and adjust the FILL LAYER DIRT 4. There isn't much special or different about the methodology, just the placement so I'll just show the buildup of blue, yellow and brown at the same time.



This is still a bit homogenous, even with the different colours. The yellow and brown's a bit overpowering, so now it's time for even more 

BREAKUP BREAKUP BREAKUP

Human skin has a wide variety of colours. We can go more intense with some of the veins, add some burst capillaries manually, add some more intense brown spots, bring in some more fake SSS based on our Thickness Map and add more pinks based on our Curvature Map. So let's do that now. This is probably the last we can do through generators and Mesh Maps. 

Our fake SSS is going to be faked in two ways, by adding a peachy colour based off the Thickness map and a Deep Red based off the Curvature map. We can adjust these through the use of Levels, like we did all the way at the beginning with the Ambient Occlusion. Despite the hand painting and using our mesh maps, sometimes a grunge smart mask is just what you need. I find the Dust Dirty smart mask to be great with a FILL LAYER DIRT 4 set to multiply on top. Let's do that now. 


Now all we have to do is manually paint out the areas we don't want. Easy peasy. 

The visibility of actual veins differs from person to person. Unlike the general dark blue areas, we'll be looking at the thin lines that can sometimes be visible. If you've got really pale skin you can see these on the underside of your wrist. Only one of these lines are visible on the Human Face, you can find a good reference here.

 At the same time we'll be adding some burst Capillaries using the Cracks brush, turn down the opacity and stamp away. Currently we've got a bit of a Perfect Face, this isn't very realistic so we've got to add some asymmetry with some Brown Spots and Moles. The only fancy trick here is to use the Spots brush and change the Alpha, other than that we've just got to paint them on by hand.


And that's it! That's our Diffuse map! Definitely the most complicated out of our maps, create a folder and chuck EVERYTHING inside. 

Thanks for reading along! Up next is Roughness and Scattering