Pareidolia, but underwater: What is under the green paint?

[oshfdk]

The report I just posted shows the results of that basic analysis.  What do you think of them?  

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I'm not sure I understand how it works exactly, I generally fail to understand Bayesian approach (I know the formula and can work the math, but I often struggle with the why part).

where Pr(p∈S) is the prior probabiliy of pixel p belonging to province S -- that is, the probability we assign to that fact before we are given its color C

Where do we get this prior probability, is it just by estimating the proportion of the pixels representing paint, ink or vellum? I think these may vary wildly depending on which part of the book or the folio we are dealing with.

To make the images more intuitive, the image for parch is shown as computed (probability 1 = white) while the others are inverted (probability 1 = black).

Made it counterintuitive for me, to be honest