[cqz]

Very cool. I tried using PNG compression, it does actually do better, slightly:

    PNG : ~15.1 seconds, 83% accuracy

I also tried dropping in zstandard compression:

    Zstd (level=3) : ~3.5 seconds, 88% accuracy

Much faster than gzip, at least. And iff I use (x1-x2)*2 instead of x1+x2 to calculate Cx1x2 that pushes zstd up to 93% accuracy.

I'm somewhat interested in the fact that if I stack the two arrays on top of each other instead of adding them together, I get absolutely garbage performance (<20%), however as far as I can tell that actually works well when classifying strings.

[w-m]

Re garbage performance on stacking: I had tried interleaving the values (creating a 56x28 img), it dropped one percentage point of accuracy when using gzip.