FWIW, we did consider a histogram heuristic, and I believe GreaterWrong still uses one rather than InvertOrNot.com. But I regularly saw images on GW where the heuristic got it wrong but ION got it right, so the accuracy gap was meaningful; and that's why we went for ION rather than port over the histogram heuristic.

Really appreciate this AbanoubRodolf, thank you. The brightness analysis code and the image bounds are both already in the project, I just never connected the two. The distance between where I am and where you're suggesting I go is really short. Feedback like this is exactly why I posted here. Thanks again