In case you didn't under stand what i did in previous post I'll explain better.\
using
http://pixlr.com/editor/start with circle image
make new transparent image that has a height 2x the original.
select original image, select filter/polar coordinates/polar to rect
copy the result of step 3, and paste into step 2, Rotate canvas 180 degrees, using top right tool move layer to desired location, do a second paste, and again adjust position of layer (it maybe needed to switch back and forth between layers),To prevent a hole be sure to position Image to the top of the canvas. save image close image
Open image just saved, set image size 256x256
Go back to select filter/polar coordinates/rect to polar, save and done