You'll have to ask Maxim about the possibility of saving in a different format, since it will no doubt involve additional coding that he might/might not be willing to do.
As for the PNG format, you don't have to worry as it is lossless as well. Personally, it's my favourite format because it's widely used and close to the best file size you can theoritically get for a lossless format (though you might have to fiddle with programs like PNGGauntlet to achieve the best result since there are no optimal settings that will achieve the smallest size for all PNGs; it's pretty much a case of trial-and-error).
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"With the first link, the chain is forged. The first speech censored, the first thought forbidden, the first freedom denied, chains us all irrevocably." [...] The first time any man's freedom is trodden on, we're all damaged. - Captain Jean-Luc Picard
Current projects: Mega Man V (GB), Mega Man Zero (GBA), Battletoads (NES), Sonic CD (Sega CD)