iphoto doubles picture size

why does iphoto double my picture size when i use the export function rather than dragging the picture from iphoto to the desktop...if the answer is because it saves the original and modified into one file, why when i import it into another iphoto library it doesn't recognize it's a modified picture and treats it as on original that's never been touched. also i've tried exporting a picture that's never been modified and it still doubles the size. i've tried even unchecking the export titles and locations boxes

exporting - depends on how you are exporting - changing the file format, etc.

importing - it is a new master file in the new iPhoto library as it's never been there before

i just export as a j-peg with maximum quality, but wouldn't maximum quality be the same as the original (iphoto obviously can't increase quality)

Exporting maximum size should be the same size as the original photo. When you drag a photo to the desktop, you are dragging the thumbnail size, I believe - thus it is smaller.

that's the thing, i've compared the original (before importing) to the pic after dragging it out of iphoto onto my desktop and they are identical. but exporting at maximum size doubles the size