Double the size of a sprite without quality loss.

[Maxim]

I don't have Photoshop, but you can try Gimp (it's free). Click on "Image" in the menu bar and then "scale image". Enter '200' in the width and height fields and make sure to select 'percent' instead of 'px'. Finally, set 'interpolation' to 'none' and click on 'scale'.

http://docs.gimp.org/en/gimp-tutorial-qu...scale.html