im not sure if there are ways to select HOW the file is compressed, but that is what happens when u save to a lesser format.... things get sac'd
BUT, if you find ways to eliminate size on the original, like taking out colors and rendering it softer instead of defined i think there will be alot less of an impact,
in short make the original as small as you can be before compressing,
i.e use blend, and take out colors after you've made something you like (control size & appearance, then the compression wont do it for you)
any 1 feel free to correct me if im wrong