Do I remember rightly in that it previously has been mentioned that it is possible to use darktable’s export function in a way that will compress the image along one axis?
My wife has an image in 4:3 format that she needs to put into a 60 x 40 cm frame for an exhibition. Cropping is not an option, and to add some padding is not a preferred method. The image may, however, possibly stand a compression from 45 to 40.
But how can that be made?
I am unsure how this could be achieved in DT but it certainly could be achieved in GIMP. DT allows an xcf export that is very suited for further editing in GIMP or you could just use the Tiff or PNG file formats if you prefer.
Thanks a lot, Kofa.
I’ve overlooked that module – perhaps because the documentation in the manual is not updated. (“darktable detects images that need correction using their Exif data and automatically activates this module where required. For other images the module always remains disabled. The module has no controls.”)
I never knew that module could be used for that purpose. Again I learn something new from the forum, but I am not sure when I would need to use this in a real world situation.
There are also utilities or apps which allow the x and y exif printing resolution (0x011a and 0x011b) to be changed independently.
Maybe to restore the original aspect ratio of images taken with an anamorphic lens?
I sometimes use it to align lines, corners, or edges that stand out to me, usually within a square frame. I can be quite particular about that! 
That said, as soon as circular elements are involved - like the sun, the moon, or occasionally people - it becomes noticeable, and I tend to leave it as is or reframe the image entirely. In the end, it just needs to work compositionally.
