How can I convert sprite images to retina display?

I mention "retina devices" with respect to not honoring unit sizes, but this is just as much a mobile browser problem as merely "retina." The reason "retina" images and the file@2x name scheme is required is because the OS and browser on devices with these displays connected are purposely altering the numbers: they are attempting to fix the physical viewing size which is a very hairy problem given the variety of screen sizes and cabilities.