[Digikam-devel] [digikam] [Bug 347737] Tagged RAW files do not show tags after round trip to RawTherapee

[Gilles Caulier]

https://bugs.kde.org/show_bug.cgi?id=347737

--- Comment #8 from Gilles Caulier <caulier.gilles at gmail.com> ---
The XMP in which file ? JPEG generated by RawTherapee ?

If yes, the Exif spec permit to do it but it's not recommended with JPEG (and
in general), as JPEG Exif chunk is limited to 64Kb. JPEG IPTC and XMP chunk are
also limited in size to 64Kb, but as separated than Exif. To resume :

Exif = 64Kb
IPTC = 64Kb
XMP = 64Kb

If you host IPTC and XMP to Exif chunk as well, there is a risk to overload
this chunk quickly and to break JPEG structure. This is why, if i remember
well, Exiv2 drop this Exif entries.

Note : i know that Adode has proposed a way to extend each JPEG chunk to use
more than one 64Kb blocks, but i'm not sure if this is already standardized.

In all case, RawTherapee must store IPTC and XMP in dedicated chunks.

Gillesq

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