How can I change the dpi value recorded in a JPEG file without actually touching anything else, nor recompressing the image?
Linux compatible solutions are welcome.
This 2011 link says we may not have had a tool to do it back then...
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1 Answer
You could use exiftool to manipulate EXIF data on different file formats. It's a perl-library accompanied by a command line utility:
$ exiftool test.jpg | grep -i resolution X Resolution : 72 Y Resolution : 72 Resolution Unit : inches Focal Plane X Resolution : 3959.322034 Focal Plane Y Resolution : 3959.322034 Focal Plane Resolution Unit : inches In this example, EXIF data tells that test.jpg has a resolution of 72×72 dpi. To update this values to e.g. 100×100, exiftool would have to be called like the following:
$ exiftool -XResolution=100 -YResolution=100 test.jpg 1 image files updated And voilà:
$ exiftool test.jpg | grep -i resolution X Resolution : 100 Y Resolution : 100 Resolution Unit : inches Focal Plane X Resolution : 3959.322034 Focal Plane Y Resolution : 3959.322034 Focal Plane Resolution Unit : inches 
- 2I also had to add
-ResolutionUnit=inchesbecause JPEGs produced by Simple Scan didn't even have that.Norrius– Norrius2019-07-13 17:11:17 +00:00Commented Jul 13, 2019 at 17:11