When you convert the standard 2x3 photo ratio to decimal value, the ratio is 0.6666666 repeating. Your 19x28 ratio is 0.6785714, which is actually almost indistinguishable from the standard. Sadly, there is no analog equivalent to the 2x3 you want, so my suggestion would be to simply take the 2x3 standard and let your editing program show you the crop. I suspect it will be hardly noticeable, and you should be able to use the 2x3 value. FYI, the closest equivalent to your measurement would be 18x27, only one unit away in length and width. Good luck with the conversion.