You should not open a RAW format using darktable-plugin for gimp directly.
You had better not edit a PNG in GIMP.
here is what happen if i do so.
GIMP version: 2.10.32
Darktable version: 4.0.1
OS version: Windows 11 64bit
I always use GIMP as a part of my photograph process workflow (amateur). Since last week I need my export from gimp more professional and I found the Exif-metadata in the export file was lost. In particular the RAW format is first processed by the Darktable-plugin then to the GIMP. The issue cause by Darktable. It’s output XCF file when running in plugin mode and will not contain the original Exif-metadata, So I manual export PNG file use Darktable then open it in GIMP. The Exif-metadata is saved but GIMP work too slow when I do any move. Then I give a lot of try to avoid these issues. Finally I found first export TIFF format use Darktable then open it in GIMP, although 32 bit the GIMP can work fine.
(forgive my poor English expression I’m not living in the English country.)
I never observed this but I just tested and you are right. You are wrong in the output which is EXR and not XCF but exif info does not show up in GIMP post-import by the dt plugin and prior to exporting from GIMP.
I’ve gone over all of the settings in both DT as well as GIMP and cannot find a way to set this straight. I’m running a fully updated Manjaro with a fresh DT4.2 and GIMP2.10.32
Let’s see if others can duplicate the issue before reporting as a bug - it may all be due to some setting or preference after all, it often ends up being so. In the meantime I’ll try the other way around with the lua script which fires up GIMP from DT and see what happens there.
From the dt 4.2 release notes:
For formats JXL, AVIF and EXR, darktable will not include the metadata fields unless the user selects all of the checkboxes in the export preference options.
Checked that, but no joy, does not help. All checkboxes selected but still no exif in the EXR transmitted to GIMP.
Metadata (especially EXIF metadata) and EXR is a known issue with the format itself.
TIFF would be ideal for this use case.
I am not really addressing your original post, but I personally open all my RAW files directly in DT and 99% of the time do not need to use GIMP anymore. However, if I do need to use GIMP I export my DT image as a 16 bit Adobe RGB file and do what I need to do in GIMP before exporting to required file format. Times I might use GIMP or Lightroom is when I want to do exposure merging using layers in GIMP or the automatic photo merge options in Lightroom. I also use GIMP for photo restoration. BTW, I am not sure that PNG has an advantage over Tiff, but I defer to more experienced people to answer this. Good luck.
FYI, an EXR file exported w/ all the metadata boxes checked should look something like this in the hex editor:
Btw, this is a non-standard way to carry Exif metadata in EXRs, as there is no standard… Somehow this convention emerged between dt and GIMP (and similar for XMP).
But yeah, I’d agree it best to use TIFF (there are 16b, 16b float and 32b float options) for interchange as it is well supported container with rich (and standardized) metadata capabilities.