I use darktable since 2019 and it is amazing, however I have a problem since the last version, I can’t export Exif data in png format, I haven’t any problem in TIFF but in PNG simply don’t export. I have removed all local data and reinstall three or four times, for have a default settigns, but no, I have supervised export metadata preferences and all is similar than TIFF environment. I don’t know what do. TIFF files are very heavy, and JPG is not a option. Thank you very much for your attention, Can anyone help mi, please? Regards.
PNG did not use to support exif data. I think the specs were revised to add them but I’m not sure if darktable supports it.
Why is JPG not an option?
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Thank you very much. I don’t want use JPG because I use these images for photogrammetry, I can use it, but is not the better option.
The data are exported, but (unfortunately) in the “Raw profile exif” text key that was prevalent before the aforementioned standardisation. Although it is widely used for years, perhaps not all software supports it.
You can pass the PNG through exiftool and it will relocate the data to the new standard location.
P.S. This is an exiv2 issue, not much darktable can do about it at the moment…
P.P.S. You could also use TIFF as its compression is lossless as well.
Thank you very much for this information, TIFF is most heavy for thousands of photos 
Up to you, but compressed TIFF w/ horizontal predictor (and e.g. level 9) is only slightly worse than PNG compression… (Both use the deflate/zlib algorithm.)
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Correct, but as mentioned, not all 3rd party SW knows about this legacy “Raw profile type exif” storage scheme used for decades… OTOH, not all 3rd party SW probably caught up to the PNG spec update either (only added as an extension in July 2017, yet to become officially published as part of the 3rd PNG spec edition)…
In any case, there is now an exiv2 PR to switch writing to the location given by the spec.
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