That last one is talked about in the article -- it sucks!
I think if you were going to "downsample" for the purpose of creating a color set you could just scan through the picture and randomly select 10% (or whatever) of the pixels and apply k-means to that and not do any averaging which costs resources and makes your colors muddy.
I think if you were going to "downsample" for the purpose of creating a color set you could just scan through the picture and randomly select 10% (or whatever) of the pixels and apply k-means to that and not do any averaging which costs resources and makes your colors muddy.