Dear Robert,
Am 18.02.19 um 17:54 schrieb Robert Krawitz:
the comment holds some validity in this particular case since darktable
can't losslessly crop a JPEG file, but other tools can. If the original
poster ended up just cropping (and not rotating) most files, something
like cropgui[1] would actually yield better image quality.
Well, that's interesting to know. Unfortunately, cropgui isn't quite
right either; it doesn't do rotation.
Yeah, lossless rotation is only possible in 90 degree steps with JPEGs.
jpegtran (the tool working in the background of cropgui) exploits a
special property of the JPEG compression scheme. This property makes it
possible to discard parts of the image data without having to re-encode
the rest. There are certain limitations to this trick (you can't cut at
every pixel coordinate, but only at the bounds of slightly larger blocks).
But if all you have is a JPEG, you only want to cut it, and image
quality is a concern, then jpegtran/cropgui would be a better option
than most generic image editing tools.
cheers,
Simon
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