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. GolDDranks · 1785860788 · focus · HN ↗

         I&#x27;ve heard that the so-called &quot;yellowish&quot; skin color that non-tanned East Asians tend to have, is due to relative abundance of subcutaneous fat. If that&#x27;s true, is that captured by the haemoglobin dimension or is it a yet another degree of freedom?

         1. dr_scully · 1785863546 · focus · HN ↗

            We used the approximation that the hypodermis was a perfectly white reflector; so the thickness wouldn’t matter. The collagen fibrills scatter light in such a way to create a yellower tint. So a person’s skin might appear this way in the absence of melanin and haemoglobin. I’m not an expert on population statistics, and so cannot give an opinion on specific skin types. Everything was based on ranges.

            There is a separate effect of increased bilirubin content, that would appear if someone was ill.

            1. HanClinto · 1785866293 · focus · HN ↗

               This brings up an interesting topic of atypical compounds that can visibly affect skin coloring -- whether temporary or more long-lived (such as elevated methemoglobin levels in the Blue Fugates of Kentucky).

               It&#x27;s fascinating to learn that melanin and haemoglobin are the two primary factors (and cover the vast majority of cases), but I&#x27;m curious how many other illnesses &#x2F; disorders can produce compounds with visible effects.

               Thank you for your posts on this thread -- I appreciate you knowledge-sharing on this!

               1. dr_scully · 1785867346 · focus · HN ↗

                  In theory, you can construct a skin model of any condition you want. It would be a case of knowing the concentration, scattering profiles and reflectance spectra of any chromophores. For the thesis, I wrote a Monte Carlo skin simulator using OpenCL, when it has just come out. You could plug anything in there.

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