XnView Software

In Setting→General→Formats→Write I have all 4 metadata checkmarks ticked/enabled (as far as I understand, this is a common section for all formats, so should also work for PNG)

• Keep EXIF
• Keep IPTC
• Keep XMP
• Keep ICC profile

However, when I resave a scanned PNG file (via export or cropping and saving or saving as), the EXIF section of the file is gone

XnView: MP 1.3.1 64 bit
OS: macOS 10.15.7 64bit (though same thing happens on Windows 10)

EXIF is not supported by PNG

Well, it is supported by the PNG:

• it's part of the original file created by the standard macOS scanner app
• from this SO answer https://stackoverflow.com/questions/954 ... a-like-jpg it's part of the PNG spec since 2017 (Version 1.5.0 (July 2017) of the Extensions to the PNG 1.2 Specification)

yes right, i didn't know that a special chunk was added. Could you send me a PNG file with EXIF data?

Sure thing, the attached file is a tiny screenshot of a white screen area, it does show IFD0 and Exif IFD fields

See issue for current status and some details.

This problem is supposed to be fixed in XnView MP 1.4.3. Please check and confirm the bug fix here.

Upd: I've learned that the Apple chunk is supposed to disappear per PNG spec, but that still doesn't explain the warning

Just converted a screenshot in the new version and noticed that there is a warning from exiftool, though not sure what it is
before after

could you send me the file?

Sure
xn1.png is the original screenshot
xn2_edit.png is the same file cropped in XnViewMP with the warning

it's only a warning, LIBPNG writes at the end the EXIF chunk...