palette picker does not handle narrow color-range images well

[DTrejo]

possible fix:

• iterate over image once to find the min-Y and max-Y, then divide that space into buckets.
• hack: re-run the algorithm with more and more buckets until you've got as many colors as you want. binary search lol

example:

[brycebaril]

It also doesn't seem to handle wide ranges well. E.g. I put a photo of someone wearing a bright yellow shirt with a tree behind them, and I get black and five shades of green from the tree. No yellow, no skin tones, no hair color, etc.