This is irrelevant to your main point, but if you’re going to make the picture look more realistic with a filter, the HQX scaling filter (http://en.wikipedia.org/wiki/Hqx) works a lot better on pixel art. Here’s the original picture scaled down and then scaled up again with HQ2x: http://i.imgur.com/w9RIK1p.png. I think that looks a lot better than your median-filtered version, though I’m not sure whether I like it more than the original.