Nice job! Works pretty great. It beats out Pro Motion 6.5, 9 times out of 10. An option to be able to set what the max number of colors per tile, would be great. Instead of using all 16, sometimes sorting algorithms get better results when max tile color of 14 and 13. And usually no perceivable detail is lost.
Btw: I took the image output of this app and ran it back through my own sorting app (though mine is lossless, so it doesn't reduce anything color wise):
http://www.pcedev.net/j2pce/pic1.pnghttp://www.pcedev.net/j2pce/pic2.png Pic1 is mine, pic2 is the new app (the source image is from both though, so the new app did the reduction). I was able to squeeze the subpalettes from 16 down to 13.
I usually do this anyway (with Pro motion, quither, etc); two stage process. One app does the reduction and then I re-run through my app to see if I can get the subpalettes crunched smaller.
Edit: My sorting algo is pretty simple, if you guys want to implement it. Though it can be processing intensive at times.