The best way to archive is to keep them in RAW , and an XML file that you have all your corrections on (assuming that you use either Aperture or Lightroom). If you're looking to save the file as it was after you edited it, you really should be saving it as a 16-bit tiff. Compressing down to 256 colors simply crunches your histogram, and you lose much of your dynamic range. While saving a 12- or 14- bit image as a 16-bit one may seem like a waste of space, the reason why you're forced to choose is that many editing softwares like PS can do an 8-bit or a 16-bit image (well more like 15+1, but I digress) but not anything in between.