Show HN: Simple algorithm and color space to generate diverse skin tones

Show HN: Simple algorithm and color space to generate diverse skin tones(toneyalexander.github.io)

229 points by automatoney 2 hours ago | 59 comments

Hello HN!

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.

s1mon 33 minutes ago |

It's always entertaining to try to understand these things from first principles. Color and skin color in particular are very complex things to measure and model. It's not just a physical quantity, it's also a matter of human perception based on lighting and a host of factors.

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

ptmkenny 13 minutes ago | |

There's also the Monk Skin Tone Scale by Dr. Monk and Google (available under a CC attribution 4.0 international license). It was developed for machine learning, so it's not exactly the same use case, but it provides 10 colors in a variety of formats, including hexadecimal. https://skintone.google/get-started

zild3d 13 minutes ago | |

well its not a free as in beer color space

vermarish 2 hours ago |

This is beautiful work! First, I thought this would involve using PCA to go from 3D to 2D, which would result in an easier selector to use, but at the expense of representing every person.

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.

dr_scully 1 hour ago | |

If you look at my doctoral thesis, in fact skin colour can be parametrised using melanin and haemoglobin concentration; which it means it is indeed (roughly) two dimensional. This allows you to invert the colour of a pixel and identify someone’s chromophore concentration. This is based on previous work of others cited in the thesis.

https://discovery.ucl.ac.uk/id/eprint/10093345/

dTal 1 hour ago | | |

Oh goody, an expert in a question I've always wanted to ask.

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?

GolDDranks 1 hour ago | | |

I've heard that the so-called "yellowish" skin color that non-tanned East Asians tend to have, is due to relative abundance of subcutaneous fat. If that's true, is that captured by the haemoglobin dimension or is it a yet another degree of freedom?

automatoney 2 hours ago | |

Thank you! I call out the manual labeling bias and also that a future work improvement would be to be scientific about that labeling process (multiple labelers, expert labelers), and then to feed that into the equation generation steps. Part of where the "good enough" naming comes from - I was hoping that using my art brain and keeping a bunch of reference images in mind (shout out to the Humanae project) would maybe offset the bias a bit. But 100% right on the bias being there.

ecesena 12 minutes ago |

Nice. This is relatively old work (2020) but Pinterest had/has skin tone features, for example if you're searching for cosmetic products. Worth a check if anything might be useful for your work. https://medium.com/pinterest-engineering/powering-inclusive-...

zetanor 7 minutes ago |

Setting R² to various large values like 50, 500 and 5000 then moving the slider around seems to give a decent and simple visual representation of what's happening.

mbo 1 hour ago |

Love it!

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.

automatoney 1 hour ago | |

Woah I LOVE both of these! When I get a chance these are 100% getting linked from the writeup.

andai 2 hours ago |

Nice. Most of these colors look right to me, but I'm also seeing green, blue and purple? If you're curating colors from the space manually then it's not a problem.

"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.)

automatoney 2 hours ago | |

Yes absolutely right on - I mention much deeper in the page that in a picker UI you can use a bigger range, but that in a generation context you might want to be a bit more selective. I go into it a bit more when I explain what R^2 is.

"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!

compass_copium 1 hour ago | | |

I would have "show sphere" on by default--this kind of threw me at first, too.

This is a really nice project. Great work and a great write-up. Thanks for sharing.

richiebful1 1 hour ago | |

Reducing the R^2 value to ~1.5 excludes skin colors that are extremely blue, green and purple. That seems to be a happy medium between including real outliers and excluding colors like green.

wongarsu 2 hours ago | |

If you drag the bottom slider all the way to the right you only have plausible skin tones. Drag it all the way to the right and you can match skin tones for orcs, Na'vi and djinn

stephantul 2 hours ago |

Love it. I especially thought the introspective “aside” section on related resources was great, and I wish more people would show this kind of reflection.

automatoney 1 hour ago | |

Thanks! I hope to send lots of love those ways, they're basically all things that I found outside of this work that I liked enough to remember (I think Humanae was the one that I found while doing this).

E-Reverance 38 minutes ago | | |

I definitely don't speak for all non-white people when I say this, but personally I find people obsessing over it disturbing/offensive independent of whether their intentions are racist or anti-racist. I did find modeling/data-driven perspective cool though

manoDev 1 hour ago |

Skin tones are particularly difficult to pin down, besides the pigmentation there are two effects at play: 1) sub surface scattering (light goes thru and bounces under the skin a bit) and 2) some infra-red emission (the responsible for making some people appear magenta on digital photography)

So even when you get the palette right, to paint it like a believable material in a convincing way is still super hard!

xp84 1 hour ago |

This part ( https://toneyalexander.github.io/inclusive-color-space/#pick... ) is especially cool.

Would love to see this 3-D picker ability in the many character designers out there, instead of the lame 8 swatches or whatever.

barbecue_sauce 20 minutes ago | |

I think the ideal would be to use this picker to select a few tones, and then gradient map those across different parts of the body according to a grayscale map. Then you could fine-tune things like palm color, cheeks, facial tone, etc. individually.

dofm 1 hour ago |

Interesting though that the 1.5 setting (at least on my older iPhone) doesn’t really ever seem to cover the range of skin tones of indigenous Australians (“aboriginal” and Torres Strait Islanders), who apparently get their skin tones from a somewhat different expression of genes than other peoples with darker skin.

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.

automatoney 1 hour ago | |

Yes, 2.0 is the value I tuned the equations around - but I think there's definitely room for improvement in terms of squashing the space along the fair/deep axis in order to get better results at lower R^2.

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.

PullJosh 1 hour ago |

I love this! Such a beautiful use of some real nerdy math to benefit humans in a way non-nerds would appreciate.

m_w_ 2 hours ago |

This is super cool! I have always loved projects that try to categorize color space. Usually my work has gone in the other direction - isGray, isCloseToWhite, isPastel - but it's the same insofar as it's defining shapes like your matplot visual.

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!

automatoney 2 hours ago | |

In sharing this around I've found more people than I thought who've done things to semantically chop up the color space - definitely a more interesting area than I first thought of when working on my narrow use case. Feels like it'd be fun to play with something that has a whole bunch of different regions of color space labeled - like "here's where IsPastel overlaps with IsGreen".

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.

rrradical 1 hour ago |

Very neat project. Could I use this code to generate skin tones in my own project? Or more meant to just be educational/inspirational? I guess I'm wondering if you've considered adding a license.

automatoney 1 hour ago | |

Good catch, added MIT license - feel free to use it! On top of that, my understanding is that math/equations are not subject to copyright, so the core part of this work (the equations/ideas) I think legally has 0 limitations - even if there were a restrictive license. But IANAL so might have some misconceptions.

Joel_Mckay 1 hour ago | |

Procedural generators are often free if you look around for a bit.

https://kuhantilope.gumroad.com/l/ultimate-skin

https://extensions.blender.org/add-ons/mpfb/

https://github.com/alessandro-zomparelli/tissue

ymmv, as some paid plugins actually speed up the funky blender workflow (the auto-Bake plugin by the same author is important for procedural generated textures.)

https://sanctus.gumroad.com/l/SLibrary?layout=profile

Have a great day =3

ptsneves 1 hour ago |

On the movie Dolemite by Eddy Murphy, they go over the fact that black people absorb light and white people reflect, and how that changes the motion picture shooting process totally. Also how one size does not fit all. Cool project! I am not much into the humanities part of the project. For me this is as natural as having a localization framework, just in this case for skin tones.

RIMR 2 hours ago |

For anyone confused, turn off your dark mode extension. :)

automatoney 1 hour ago | |

Oh wow, didn't even think of how that sort of thing might affect the page.

efitz 1 hour ago |

Never seen anyone #E6FFF8 (bottom right corner).

An albino that consumed too much colloidal silver for years?

hluska 1 hour ago |

This is excellent work! You’ve got a 49 year old and a 10 year old equally into it. That’s impressive - nice work.

aaroninsf 1 hour ago |

Not my domain though I followed the data science enough to nod as if I really followed it,

but this is just lovely and inspirational work. A unique marriage of hacking in the celebratory sense, thoughtfulness, and meaningful contribution. Outstanding.

automatoney 51 minutes ago | |

Wow what a touching compliment, thank you so much!!

Abh1Works 2 hours ago |

Cool work!

ralusek 1 hour ago |

If you're ##CCFFFF please go to the hospital

bellowsgulch 1 hour ago |

Skin is so interesting as a surface to think about how light passes through and bounces off of.

There is at least one article published by a technical artist at Pixar who describes modeling a skull within a human scan so that subsurface lighting is more accurately rendered.

I suspect you could combine this with dr_scully’s comment and GolDDranks’ to reach the nuance involved in long tail realism details.

automatoney 1 hour ago | |

There's a lot of really good research papers that touch on this area from what I saw - would definitely be cool to see if that extra nuance could be added without dramatically increasing the math complexity; in its current state, the code could be used in any programming language without a library.

uhdozo 21 minutes ago |

Very interesting, I'll need to read it again lol

moralestapia 2 hours ago |

Interesting.

It might be a bit biased though, as there's much more variation on fairer skin tones than on dark ones (there's only one that looks like the colloquial "black").

This contradicts all research and social media from the past decade.

Tossrock 2 hours ago | |

...Did you read the article, or use the picker? It's a continuous (up to the limits of RGB quantization) space which includes thousands upon thousands of shades of black. The selected tones at the top of the article are random and change continuously.

383toast 2 hours ago |

Seems to underrepresent pale skin tone variety

LocalH 1 hour ago | |

Turn off your dark mode reader extension

hneqy2wqls 1 hour ago |

This hits different after a long week