I was browsing the interwebs and I found this research that was done to depixel pixel art
here is the links
http://research.microsoft.com/en-us/um/people/kopf/pixelart/
http://research.microsoft.com/en-us/um/people/kopf/pixelart/supplementary/multi_comparison.html
full PDF
http://research.microsoft.com/en-us/um/people/kopf/pixelart/paper/pixel.pdf
I found it very interesting, I'm pretty sure its open source too, though it appears it doesn't work well with anti-aliased inputs, so the more pixelated(jaged) it is the better it will work