[Gimp-user] image information disappearing

[Per Funke <per funke gmail com>]

in the attached image there are two property windows, both from Gimp.
The left showing an image before doing a crop in Gwenview, the right after
doing a crop WITHOUT removing anything from it. The difference in size is
7.2MB! There is no quality deterioration as far as I can see, both images
seem to be exactly the same

1) What has been removed? (Nothing that the eye can detect anyway)

2) When adjusting an image in Gimp (Colors => Curves) and exporting, it
grows bigger than the original.

What has been added?

Since I store some 30000 images at home I'd prefer that Gimp exported
images as small as the cropped ones from Gwenview, if possible...

Anybody having any thoughts on this?

Best,
Per Funke
(using ubuntu)