Hi Greig,
You basically want to replace some EXIF information present in the raw file.
A number of people (including me) would strongly avoid ever modifying a
raw file. These are full of dragons. First I would make a backup of the
raw files for fear or any change triggering some wrong checksum
somewhere and making other software (or the camera itself) refuse to do
anything with it, claiming corruption. If any software claims to be able
to perform changes, I would open a binary comparison of before/after to
check what is the actual change. And keep the original raw files in a
backup, indefinitely.
The situation is somehow similar to a more common one : camera clock was
off and you need right times in EXIF after the facts. The typical case
being: at some events (wedding, etc) several cameras were used, clock
mismatch as always by minutes hours or days, making a mess of timeline
order. Fortunately the case of adjusting time is somehow covered by
darktable, which copies EXIF DateTimeOriginal to the XMP sidecar, as XML
attribute of rdf:Description XML element like this :
exif:DateTimeOriginal="2020:11:11 09:54:44" . Changing this line in the
XMP while darktable is not running was enough for me to get correct
datetime in Darktable and exported EXIF data, yay!
I checked the source code (current git master), and alas this is
specific to DateTimeOriginal, darktable current code does not consider
overriding EXIF metadata from the XMP file, other than DateTimeOriginal.
Would your need happen to me, I would either just ignore the problem and
live with it, or modify darktable source code to save that data to XMP
and read it back, then offer a Pull Request to the darktable team.
It may be possible to manually edit EXIF values in the database, but I'm
not sure this can even work, and furthermore the current design of the
database is fragile with respect to the locations of raw files. More
concretely, whenever the raw file is moved, or happen to be stored on an
external drive that is mounted at a different place, you would probably
lose your customization. With the XMP sidecar, darktable would load it
again in those cases.
Addendum: to handle comfortably the "several cameras with random time
offsets take pictures of same events over a time range" case, I wrote a
year ago a script to automatically adjust batches of pictures. It saved
the day several times for me and I am considering publishing it as
open-source. Anyone who reads this (even years after) please consider
telling me if you're interested.
-- Stéphane
Le 15/11/2020 à 02.55, Andrew Greig a écrit :
Hi All,
I shot and developed a roll of B+W film, and I will scan it using my
Canon EOS 5D iv with the EF 100mm f2.8 Macro lens. As I was shooting
the roll of film I maintained a notebook where I wrote down the
settings, what is the best way to substitute the info in the resulting
.CR2 files with the info from my notes? I am really looking forward to
loading these into Darktable/Negadoctor.
Thanks
Andrew Greig
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Stéphane Gourichon
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