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No keywords in PNG files?

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Lightroom Classic version: 11.3.1 [ 202204181225-f90ebff5
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  1. Windows 11
Am I missing something?
If I export an image as a JPG then all the keywords and a plethora of other metadata is saved with that image :). However, if I save the same image as PNG then all this data is missing.:mad:
 

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Assuming you have included all metadata when you export as PNG, it may be an issue with Windows in relation to the PNG format. If I export as PNG on my Win10 system, and choose the add to catalog option, I can see that LrC will continue to show all metadata (including keywords) in the right-hand panel in the Library (in other words, the keywords and other metadata is in the file and is read by LrC). But the same exported image does not show any EXIF or other user-added metadata when looking at the file properties in the File Explorer. However, if I copy the same PNG to my Mac system, all the keywords and metadata does show up using the Finder>Get Info command.

So the apparent conclusion is that File Explorer in Win10 (and presumably in Win11) is not reading the XMP contents of PNG files.
 
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To build on Jim's reply with more than you want to know:

LR writes metadata to the industry-standard XMP section of an exported PNG but not to the EXIF or IPTC sections. While Mac Finder reads the XMP of PNGs, Windows File Explorer does not (though it does read XMP from JPEGs). The XMP section can store everything that the EXIF and IPTC sections can plus more, so no information is lost when LR writes just to XMP but not EXIF or IPTC.

De jure and de facto support for PNG metadata has changed over the last 15 years, more than for JPEGs. Both Windows and Mac have reasonable, extendable, internal architectures for accessing metadata from arbitrary file formats (though I think Windows is stronger). Neither Windows nor Mac have invested much in this over the past 5-10 years, and both platforms have many issues with metadata. In particular, Windows hasn't kept up to date with the changing PNG standards. This thread appears to be reasonably accurate about PNG metadata:
https://stackoverflow.com/questions/9542359/does-png-contain-exif-data-like-jpg

Note that LR isn't up-to-date either. EXIF was added to PNGs in 2017, but LR doesn't write the EXIF section. But as mentioned above, this is of smaller consequence, since LR duplicates the EXIF information in the XMP section.
 
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Thanks guys, a little too technical for me, so struggling to see where that leaves me.
My problem is if I export it as JPG and then upload to somewhere like Picfair or ClickaSnap all the keywords and captions are carried over. However, the same is not the case with PNG. There are no keywords or comments that are read by either program.
 
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When I upload a PNG there are no keywords, but they are there in an identical JPG
Almost certainly Picafair and Clickasnap aren't implementing the newer metadata standards for PNGs (standards that are at least ten years old).

LR is writing the keywords into the XMP metadata section of the PNGs, which is the only way specified by industry standards for adding keywords to a PNG. But Picafair and Clickasnap apparently don't follow the XMP standard for PNGs and thus can't read the keywords.

You could contact them and ask whether they support keywords for PNGs, and if they do, which metadata fields they expect to read the keywords from. If they're reading the keywords from a non-standard metadata location, I can probably suggest how to use an export plugin to copy the keywords into that location.
 
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