Cannot write to Portable Pixel/Bit/Gray Map images (PPM / PBM / PGM)

[Huayi]

When trying to write to PPM, PBM or PGM, exiftool does not throw an error but outputs this message:

exiftool -XMP:Author=Huayi sample_1280×853.ppm

Code Select Expand

    0 image files updated
    1 image files unchanged

I tested with several tags from XMP and EXIF (writable ones).
This happens with exiftool versions 11.59 and 12.05, I haven't tested others.
You can find ppms to test here : https://filesamples.com/formats/ppm
pbm here : http://netghost.narod.ru/gff/sample/images/pbm/index.htm
pgm here : https://filesamples.com/formats/pgm

Thank you very much for your support on this great tool.

[StarGeek]

If you check on the main page under Supported File Types, you'll see that exiftool doesn't support either reading or writing of EXIF, IPTC, or XMP data to PPM, PBM, PGM files.  The fact that exiftool does not even support reading such metadata suggests to me that the format simply doesn't support such metadata, though Phil would have to verify this.

[Phil Harvey]

the format simply doesn't support such metadata

I think this is correct.

- Phil