Importing PNG files with metadata doesn't parse keywords correctly

Question

I am trying to import PNG files that already have intact metadata fields. I have been using the ExifTool (a standard tool for reading, writing, and editing EXIF metadata) to inject all the metadata I need into the PNG files, and most fields import correctly into Lightroom such as Title, Caption, and Copyright. The only field I'm struggling with is the keyword tags.

If I have keywords such as "tag1, tag2, tag3" in the PNG metadata (located in the Subject, Keywords, or Weighted Flat Subject fields), when this is imported into Lightroom it gets assigned as a single keyword called "tag1, tag2, tag3" instead of separating them as individual keywords "tag1," "tag2," "tag3," (even though commas in keyword names are supposedly disallowed in Lightroom, since they are used to delimit keyword lists). Here is how it looks in the keyword list after import:

The same happens if I delimit the keywords with semicolons in the PNG metadata, they are imported as a single keyword "tag1; tag2; tag3". If I edit the keywords in the keywording panel, such as adding a keyword, it will then split out all the keywords into individual keywords, leaving behind an unassigned "tag1, tag2, tag3" keyword in the keyword list.

If I wanted to edit the keywords for every photo I import, this could work, but would leave behind a lot of unassigned keywords that I would also have to purge. It's a lot of unnecessary work. I want Lightroom to recognize the keywords individually when importing the PNG file. Anyone know how to format the keywords in the PNG metadata so they are imported individually in Lightroom, or is this a bug in Lightroom import that should be separating keywords when imported and is not doing it correctly?

Thank you.

Lightroom Classic: v13.3.1

Windows 11 Pro 23H2

Hesadanza3 · Accepted Answer

I think I figured it out. The issue was with ExifTool, not with Lightroom.

As explained here, if you just inject the keywords as a comma-separated list, it will be treated as a single keyword.

For example, this is wrong:

exiftool -keywords="one, two, three" test.jpg

If you want the values of list-type tags split into separate items, you have to use the -sep option to indicate the delimiter.

exiftool -sep ", " -keywords="one, two, three" test.jpg

Once I injected the keywords with the -sep option, then when I imported the file in Lightroom, the keywords were recognized as individual separate keywords!

umlautnord · Answer

The only thing I've run into with exiftool, pngs, and metadata is that Adobe doesn't like some of the metadata in IPTC (and maybe EXIF). Rather, it needs to go into the XMP tag group. You may have already tried this, and I admittedly have somewhat limited understanding... but, it's what I've run into. In general, I think Adobe doesn't read IPTC for PNG, but that may be too broad a statement. I think there are some threads with more detail on IPTC and EXIF for PNG specifically.

So, for a jpg, for example, keywords work for me comma separated in "-IPTC:Keywords=" . For a png, it only works for me if they are comma-separated in the "-XMP:Subject=" field.

I'm not sure what you're getting the metadata from to inject into the image files, but whenever I'm injecting metadata from an XMP file into a PNG, I just use something brute force like

exiftool -tagsfromfile %d%f.xmp "-all>xmp:all" -ext png ./

to get everything into the XMP metadata space in the PNG rather than IPTC or EXIF. Conversely, for jpgs, I'll use the xmp2iptc and xmp2exif args files that exiftool provides. They just don't work for PNGs, though. Something to do with the history of the file format not originally defining some/all of these metadata spaces.

Anyway, I hope that's helpful/not just repeating things you already know!

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