Following the Base tints working out about how I was hoping.  I have moved on to processing an additional scan, this time of an African person.  My intention is to process the base color passes of the scan to remove any lighting present and then process the lower values of the scan to extract a Melanin mask that can be used in conjunction with the base pass we already have.   The Goals of this process were:

1. Get a Natural feeling gradient tint map for Melanin that can be ramped up or down to provide different intensities.
2. Ensure that we can achieve Plausible and beautiful dark skin tones that do not feel like a base multiply or something that would crush the depth of color we have in the base pass.
3. I wanted to be able to ensure that the Melanin Tint remained separate from the base tint but worked will in conjunction with it, so we did not end up with the two tint values fighting with each other or creating undesirably dark or bright values.
4. Especially wanted to focus on the lips, hands, and nail beds to make sure that as the tint was ramping up we were retaining some of those good flesh tones in the areas where melanin would naturally be less present.

Here is the Melanin Map at first pass.  There are a few minor things id like to adjust still, but this is sufficient for a Proof of concept

In the new skin Master material I wanted to make sure, as stated above, that the base tint pas and the Melanin tint never ended up oversaturating or breaking the values of the characters skin.  Because of this I decided to use the Melanin map, further dialed in through a threshold with range node, as a Lerp alpha between the Base Color Tint and the color tint for the melanin.  I am doing this prior to overlaying the colors on the base pass just for ease of setup, and to minimize failure points.

Disclaimer:  The gif below the color range is pretty greatly limited due to file size on Artstation and Gif compression. Please check out the actual screenshots below to see how the values hold up.

Here you can see the gradual ramp working with better color compression. these are at 20% steps in the melanin value control.

Here is a closeup shot of the hand to display how the Melanin map reacts at 0, .5, .75, and 1 values.  I think it needs some additional painting and possibly cavity masking to be prefect, but I'm pretty happy with this initial result. If this asset was for like an FPS I would probably put alot more scrutiny on the quality of the melanin maps correspondence with the initial scans landmarks.

Below are a few shots of some of the variety you can achieve between the base and melanin maps.

Bp Control setup( sorry about the compression again gifs in 10mb if you wantt o be able to read them the colors get crunched):

After the initial scan transfer and cleanup, I decided to do some poking around in the metahuman materials.  I knew I wanted a few functions in there that would require some additional processing of the scan textures.  At this point I kinda hit a minor roadblock as I had become very familiar with the Metahuman Skin materials prior to 5.6.  However, the new material in 5.6 is significantly different from the previous version. Honestly, that is a very good thing.  The new material is extremely well presented and organized, however, some of the texture inputs and how they work has changed, so I needed to take a few days to familiarize myself with the new material setup and start working on my own version.  I decided to adjust how the textures are packed so that I could free up a few channels for Melanin and Ao, more on that later.  

Following the high level concepts from the GDC talk about the Heads of Horizon Forbidden West, and how they got such incredible tones for both light skinned and dark skinned background characters,  I determined I wanted to approach things similarly.  To be able to get very convincing darker skin tones that still maintained depth of color and tinted in a more compelling way than many older games that just do a general overlay or multiply of different tone swatches over the base tone, I needed to follow the step of neutralizing the mid tones of my base scan so that those tones could be added back in the material in Unreal engine as an overlay.  

Additionally, I would need to pull down a second scan of an African or African American person to be able to study and attempt to extract some plausible melanin patterns to add to that mask when the time comes.

Raw Transfer

Here is the updated version with neutralized mid tones, and some lighting cleanup. Hopefully, this pass will be sufficient to provide some strong color variation through the base color overlay tints ill be adding to the metahuman material.

Below are a few shots from the Metahuman Lighting levels of the Neutralized mid tone.  In these shots the other textures required have already been authored, but I will get into al the packed textures and what they do in the next post.

Here is an example of the flat version of this texture.

• T_(Texture Set Name)_D  (Diffuse)
• T_(Texture Set Name)_N  (Normal)
• T_(Texture Set Name)_ScMelFn  (Scatter, Melanin, FingerNail Mask)
• T_(Texture Set Name)_SRAo  (Specular, Roughness, Ambient Occlusion)

Here are some examples of base skin tone swatches overlayed on the Neutralized mid tone to display the base skin tint quality and depth of color.  Threw a few more out there colors into the mix at the end there just to show the stability of the setup even with blues and greens.

Notes:  By request from JB  this is the most green green i am allowing in the shader