[jedberg]

Here is the code:

https://github.com/reddit-archive/reddit/blob/753b17407e9a9d...

But in short, it's a histogram of the values of the pixels.

[andbberger]

Which is not really image entropy at all, as it totally neglects spatial structure. You could sort an image and get the same entropy using the histogram approach.

[bavell]

"Entropy" in this context also left me wondering. Perhaps "variance" or "deviation from the mean"?

Thanks for the insights!

[MauranKilom]

Entropy usually boils down to "sum p * log(p) for all p (and possibly normalize)", assuming you have discrete probabilities p. It is not related to variance or mean.