[digiKam-users] Metadata in PNG files

Gilles Caulier caulier.gilles at gmail.com
Wed Apr 24 22:25:52 BST 2019


You are right, PNG has 2 place to store metadata :

One older way, very powerfull and implemented first in ImageMagick, using
special PNG chunck to store Exif/Itc/Xmp data bytearray.

digiKam and Exiv2 use this way (i implemented myself this code in Exiv2).

 Adobe few year ago has finally accepted to support PNG and as standardized
the XMP only storage in PNG in another chunck. I supose that Exiftool
support this Adobe and ImageMagick.

I'm sure that Exiv2 do not support yet the Adobe solution, as i don't touch
Exiv2 PNG code since a while.

This is why you see a difference between Exiv2 and ExifTool.


Gilles Caulier

Le mer. 24 avr. 2019 à 21:11, woenx <marcpalaus at hotmail.com> a écrit :

> I have noticed that there is something funny with metadata in PNG files.
> I sometimes use the exiftool command to edit metadata (mainly add or
> correct
> dates to pictures). I can write and read the metadata from PNG files using
> that command, and the metadata seems to be saved correctly.
> However... digikam does not see that metadata. It's like there is nothing
> in
> it. BUT, it can write its own metadata to the same PNG file.
> So, both digikam and exiftool can write and read metadata from PNG files,
> but that metadata must be stored in two different places, because a picture
> can contain both entries, one for the exiftool metadata, and another for
> digikam metadata, and can only be read by each program respectively. And I
> am not talking about Exif, XMP or IPTC. Both of them are Exif.
> So, what's going on? Is this normal?
> --
> Sent from:
> http://digikam.1695700.n4.nabble.com/digikam-users-f1735189.html
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