Posted by automatoney 5 hours ago
I found that picking out plausible but diverse skin tones for my digital art and game development projects was kind of difficult, and I got curious about if there was a way to define a color space that made it easy.
I've built a color picker and procedural generation algorithm based on the space as well as a bunch of other fun js features and demos throughout the page that use the equations. If you find it interesting, I have lots of explanations of how I built it and what properties the space has.
The methodology might be a bit shaky, but hopefully the result is as helpful for others as I have found it! There's lots of room for improvements (see the Future Work section), but I'm really happy with how it turned out.
It seems like some work was done to research existing approaches, but I don't see any reference to Pantone Skin Tones [0]. Without intending to, I've worked on 3 different projects which involved measuring skin tones for makeup applications. The Pantone range is not 100% perfect, but it's pretty well done and easy to understand. There are two axes: a light/dark one, and red-yellow one [1].
[0] https://www.pantone.com/na/en-us/skintone
[1] https://cosmeticsbusiness.com/pantone-skintone-guide-80945
Pete Shirley (author of Ray Tracing In One Weekend) is also a part time color scientist, and he clued me into the fact that if you crank the saturation to 100% of pictures of people of any race, the skin color comes out orange. I think I heard that some face detectors may work on this principle, but I don’t remember where I heard that.
Then, I thought this would stop at using the U-space vectors (the ones that form the basis of the PCA image) and their corresponding ellipse to form our color space, but no, the function fitting is a very slick idea, even if it was executed by hand.
Lastly, I love the presentation of sampling from different r values. Whether you sample from a fixed r value or a range of r values, I bet this has great applications in game design or animation.
I still don't quite get the manual data labeling process at the beginning? It seems like it would encode some bias, but the consistency of the first point cloud and the results certainly speak for themselves.
Once upon a time, I encountered a sort of interactive museum book called "Earthsearch". One of its "exhibits" was a color wheel, made of two spinnable pieces of tinted acetate, that purported to be able to generate any skin tone. I suppose this is three degrees of freedom, since for any position of the two wheels you could access a range of colors around the edge - but the printed page underneath was simply a grayscale gradient, so one degree of freedom was simply luminance.
The book was released in 1994, and was very confident. It even went as far as to encourage the reader to see a doctor, should their skin tone not be achievable! What color model were they using?
But I can’t vouch for the accuracy of the book, but I suspect it was an approximation.
The haemoglobin and melanin are roughly in separate layers of the skin. There is an approximation known as Beer-Lambert that models the skin as two semi-transparent layers. This ignores subsurface scattering, but is roughly correct.
So, in theory two acetate sheets might replicate this. That’s my intuitive opinion. It has been many years since I did this work.
There is a separate effect of increased bilirubin content, that would appear if someone was ill.
It's fascinating to learn that melanin and haemoglobin are the two primary factors (and cover the vast majority of cases), but I'm curious how many other illnesses / disorders can produce compounds with visible effects.
Thank you for your posts on this thread -- I appreciate you knowledge-sharing on this!
People only turn yellow if they have kidney or liver damage. However, some distinctive features like Lucy Liu's natural freckles are tough to draw right.
We looked around a lot for a procedural texture/shader to help make the project characters look less sickly, and please also consider supporting the persons work if you are able:
https://kuhantilope.gumroad.com/l/ultimate-skin
Best of luck =3
The "The Ultimate Blender 3D Sculpting Course" covers several sculpting techniques, and while this course has a number of challenges it does cover several basics. Probably wise to wait for a sale event if interested.
https://www.udemy.com/course/blender-3d-sculpting-course/
Best of luck =3
This is not true. Roughly 5% of people have Gilbert's Syndrome which is genetic, metabolic abnormality where the bilirubin from dead blood cells are conjugated slower than the baseline patient leading to yellowing of the skin. It is not due to liver damage or disease and is a benign condition. Not to mention there is carotenemia from eating too many carrots or squash -- again not kidney/liver damage related.
This thread discusses physiology in an art context. Maybe get outside for a walk, and consider if LLMs are making people silly. =3
I was looking at this a little while ago, and used some of The Pudding's data on makeup/foundation shades (https://pudding.cool/2018/06/makeup-shades/) and plotted it into the Oklab colorspace (https://observablehq.com/@55th/foundation-shades). The shades form themselves into that same crescent as seen in the article.
"Only realistic colors" would be a different problem. And I'm not sure if there's a way to solve that problem without excluding some real colors too.
(Maybe if the colour selector was a different shape? I don't know much about color spaces.)
"not sure if there's a way to solve that problem without excluding some real colors too" - 100% right on that too. A big part of this work was to define a way to tweak/improve the equations in order to approach a solution to these issues - part of my hope in sharing is to get more eyes and brains thinking about this and proposing improvements!
This is a really nice project. Great work and a great write-up. Thanks for sharing.
You'd be surprised: https://en.wikipedia.org/wiki/Argyria
Wish I had this on hand like this three or four years ago when I was working on VR avatar software - we had hard-coded skin tone options at the time - would have been a cool addition!
But absolutely the hope is that this is a tool that stays accessible to people for whatever they're building and everyone can slow down on reinventing the wheel here for every character creator/digital art application.
When you’re actually painting, skin can really be any color. Blue is a perfectly valid (and fairly common) skin color - just look at someone in the moonlight. It takes two to tango, and the other dancer is the light source.
The 2.0 “outliers” cover those skin tones.
Masai and some Somali skin tones, similarly, look better represented by the outliers.
The full range of possible human skin tones is perhaps a bit of a challenge for technical colour representation, partly because diffuse reflectance seems to vary so much and that is hard to approximate on screen (e.g. as any website designer could attest, the difference between representing silver and grey is the use of highlights), though the representation of skin tones is a lot better than the early colour film era.
The issue I ran into was what happens when the space moves beyond RGB, but I think the fix is to just add clamps to the end R, G, B values.