Mastodawn

@riot I was trying to create a Python script for personal use to get an idea of the pixelation of images as I had a very large number of them to sieve.

I found a function I'd apparently created or copied months ago whilst trying to do the same thing that generates some number from the image. I decided to try this, and it turns out it is indeed a very good proxy for what I want.

I still don't know what the number is, or what the code in the function means, but it works with lower numbers indicating its likely to be 'bad' . . .