loosing quality while saving a GIF file.

I'm just opening a GIF image and then saving the exact same thing, without modifying it. For some reason I loose image quality:

Dim img as image = image.fromFile("C:\pic.gif")
img.save ("C:\savedPic.gif", img.rawFormat)



:confused:

I've tried this on a couple of gif-files, but I can't see any difference in quality....