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I'd like to open a PNG image in GIMP, change its DPI, and save it (overwrite the original file). I only want to change the DPI and nothing else. I mean size, colors, transparency, compression etc. must not change. What should I do exactly?

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    Why do you think you need to change the DPI? DPI has no meaning until an image is printed, or in some cases dropped into pagination software, which will use it as a size guide. Until that point all it has is dimensions in pixels. – Tetsujin Jun 19 at 8:28
  • I'd like to keep the original pixels as they are. I only want to change the displayed/printed size of the image, which is determined by the DPI. In this particular case I exported an image from Inkscape, and since DPI cannot be set in Inkscape (if you change it, it will change the exported size in pixels, which is stupid), I have to fix the DPI after the export. I tried to do this with Irfanview and NConvert, but these programs sadly also change other properties of the image. I hope Gimp can be configured to change only the DPI. – kol Jun 19 at 8:33
  • I have found the perfect solution: exiftool. See superuser.com/a/1143321/174684 – kol Jun 19 at 8:58
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You can use Image > Print Size, to change the PPI without resampling the image, i.e. while maintaining the same size in pixels.

In the Print Size dialog, you can either set the PPI you want and GIMP will work out the print size, or change the physical print size, and GIMP will calculate the PPI.

enter image description here

  • Thanks. I found this, but how do I save the image with the modified resolution as PNG, without changing things like transparency and compression properties? – kol Jun 19 at 8:41
  • I have found the perfect solution: exiftool. See superuser.com/a/1143321/174684 – kol Jun 19 at 8:58
  • @kol Changing the print size does not change transparency or compression. Just use File > Export to save as a PNG again. – Billy Kerr Jun 19 at 9:19
  • @kol note that PNGs don't really have a resolution, other than the image size in pixels. PNG isn't a print format - it's an image format for the web. Use something else like TIF instead. – Billy Kerr Jun 19 at 10:04
  • @kol Be warned, PNG has a standard way of setting pixel pitch in mm and 2 often used nonstandard ones. Be sure you understan what application understands which way. So for example adobe does not support 2 of the 3 methods. Test your pipeline – joojaa Jun 19 at 13:34

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