Thread

1. vermarish · 1785859472 · focus · HN ↗

   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.

   1. dr_scully · 1785860437 · focus · HN ↗

      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.

      <a href="https:&#x2F;&#x2F;discovery.ucl.ac.uk&#x2F;id&#x2F;eprint&#x2F;10093345&#x2F;" rel="nofollow">https:&#x2F;&#x2F;discovery.ucl.ac.uk&#x2F;id&#x2F;eprint&#x2F;10093345&#x2F;

      1. dTal · 1785861922 · focus · HN ↗

         Oh goody, an expert in a question I&#x27;ve always wanted to ask.

         Once upon a time, I encountered a sort of interactive museum book called &quot;Earthsearch&quot;. One of its &quot;exhibits&quot; 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?

         1. dr_scully · 1785864315 · focus · HN ↗

            That’s sounds very interesting. I’m not sure. In the thesis, I generated spectral curves and transformed them using the light and camera sensitivity curves. So, in theory it could be used in any color space.

            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.

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