I think you counted the zeroes right, because my BMP export was 300MB. I think most of the time saving to BMP format is spent writing the huge file to disk. The PNG export was just 4.9 MB. JPG was around 3 MB, but it took so much longer it's not worth the savings. Probably faster for a user to open the exported PNG in MS Paint (or whatever) and "save as" a JPG.