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If I load a JPG file (2-4 MB in size) into Gimp for photo manipulation and try to export it, Gimp reports the file size will be in the region of 1.3 GB!

I have to export it as PNG, which results in a file size of 10-20 MB, then open it in Paint and save it as a JPG to get a file of roughly the same size as the original (2-4 MB).

What am I doing wrong?

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What is your target format? – Marco May 12 '12 at 10:41
Have you actually tried to save a JPEG with Gimp, to see what the actual filesize is? The estimate simply might be way off. Especially since you say that you get 10-20 MB filesizes when exporting to PNG, which is less efficient for photos than JPEG. – Indrek May 12 '12 at 12:30
I've seen that same predicted size in the export dialog; plus you also get a predicted file size at the bottom of the preview window that is pretty big. But once the file is saved it's never much more than 2 to 3 times the original jpg size and I normally save at max quality. – BJ292 May 12 '12 at 14:45
I've observed the same behaviour and one more connected with it: default settings (e.g. saving or not EXIF data) ar not saved. – psur May 20 '12 at 12:57

Yeah, it's the prediction that is wrong. But if you are targeting a certain filesize JPEG, saving as PNG and opening elsewhere to convert to JPEG is the best choice. I'm having the same problem with GIMP 2.8,so it's not just you or anything you are doing wrong. I'd suggest trying another build, like maybe the 32-bit version, or the unofficial builds at

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Just roll back to 2.6.12 until they fix 2.8.

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