I have a .png file I would like to display on Google Maps as a semi-transparent overlay. In order to do this, I would like to make approximately every other pixel in the .png file transparent. (The .png file already has a transparent "color".)
Is there a (1) free, or (2) commercial application with which this can be done without too much trouble? If so, can you point me in the right direction on how to do it?