Something that always bugged me about palette generators I've used is how they end up not picking any colors intense enough for the deepest highlights/shadows, because they use colors close to the average of various sets of pixels.
The result is that the most eye-catching parts of an image end up washed out, reducing the appeal.
My hack to address this has always been making a larger image with big white/black bars around the original image to push the palette generator to include a few really bright or dark colors.
From the look of your examples, your project addresses this too, right?
Btw, I opened an issue about the graphs in your readme because, as a programmer, they don't tell me if your program is fast or not. From a user's perspective that thinks in terms of the side length of an image, the numbers presented are very useful, but they might be even more useful in table format.