Double the size of a sprite without quality loss.

[RoleOfGSHC]

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

I would like to mention that this is not a factor of 200%, but rather 400%. As you are doubling the size both length and width-wise, you're essentially doubling it twice, so that each pixel becomes four pixels in size.