Just a couple of pints on image formats;
png might be great for display and webs images etc, but none of the programs I use support it and I use;
ImagesPlus 2.5
MaximDl 4.11
Certainly if you are serious about processing your images (stacking etc) you will only be using fits, which is the international standard for astronomy software (not totally compatible I will give you) and you would normally only go to png or jpg as a publication step.
Personally I keep all of my images from capture to final in fits, and I know most serious astophotgraphers do too.
As Dave Grennan notes using jpg for anything other than final low res output is a waste of time. Even if you select level 10 the dynamic range gets compressed and lost forever, not somthing you ever want to do in image processing.
Later,
Jed.
  