[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 #30 from Gilles Caulier <caulier.gilles at gmail.com> ---
Alan,

Exactly. As i said previously, digiKam as to Exiv2 to store XMP data to CR2.
Exiv2 choose the right place to do it.

For CR2, as it's TIFF/EP file based, the way to store XMP in tiff is to use
XMLPacket from Exif. There is no separated section/chunk in tiff. After all,
tiff structure is a tree of tags.

This way is the same for DNG.

So this is normal until now.

When you convert RAW tiff based with XMLPacket to JPG,  the fast way is to move
XMLPacket to dedicated section. RawTherapee must do it, but it let XMP to Exif
tags. Later when Exiv2 will read JPG file, it found XMP in XMLPacket instead
XMP section. This is ignored because XMLPacket is deprecated than XMP section
for JPEG. Why ? because for JPEG, as Exif section is limited to 64Kb, XMP must
go to XMP section instead to bloat Exif section to prevent to break JPEG
structure. A section more than 64Kb give a corrupted file, excepted if more
than one section are chained to host Exif data (The Adobe way). But i'm not
sure that Exiv2 support it well, as all other metadata framework (excepted
Adobe tools of course).

I don't know how RawTherapee work, but for me the metadata workflow is wrong.

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