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I use Photo Mechanic and Adobe Camera Raw. I convert my RAW files to (locked) DNGs. I then cull these DNGs in Photo Mechanic, and then I edit them in ACR, which creates a sidecar XMP file. If I later star, or color label my DNGs in PM, ACR loses the DNG←→XMP association. All my edits are lost unless I either manually load the XMP again, or if I click in ACR on "Previous Conversion".

If I instead use Adobe Bridge to reset previous settings, Bridge errors out with "The Camera Raw settings could not be applied because there were no Camera Raw files selected or selected files were read-only.". I believe Bridge, unlike ACR, is trying to apply those settings to the DNG directly, which fails because the DNGs are read only, instead of just restoring the association with the XMP file.

All this starring and labelling works fine if I use fastRawViewer instead of Photo Mechanic. If I label in FRW, I can see the rating/color in Adobe Bridge (but NOT in Photo Mechanic), and the file opens up correctly, with edits applied, in ACR.

Also, things seem to work fine with normal, unlocked DNG files, though in that case the DNG file itself is modified (even though I set ACR to always generate XMP file). I am using locked DNG files, because my backup/version control system doesn't bode well with constantly changing DNG files. And I am using DNG files because I am using a 3rd party RAW convertor for my RAF (Fuji X system) files.

Photo Mechanic is configured with Adobe compatibility, as instructed here.

What's going on?

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  • \$\begingroup\$ Have you tried contacting Photo Mechanic tech support? \$\endgroup\$
    – xiota
    Aug 21, 2018 at 16:50
  • \$\begingroup\$ @MichaelClark both DNG and XMP are open formats and can be parsed by anyone. While the interpretation of some XMP fields is application-specific (especially Adobe specific), nothing should break if some application decides to add an unknown XMP tag (though, in this case, it adds a known and well defined tag for rating (stars)). It is unclear if PM does something bad with the XMP, or if ACR is simply confused by locked DNG files (see my edit). Btw, since FRW+ACR can do this, I see no reason why PM+ACR should not. \$\endgroup\$
    – Aram Hăvărneanu
    Aug 21, 2018 at 18:29
  • \$\begingroup\$ @xiota yes, waiting for their response. I asked here though as this seems a pretty common thing to do and I was wondering if "I am doing it wrong". \$\endgroup\$
    – Aram Hăvărneanu
    Aug 21, 2018 at 18:30
  • \$\begingroup\$ @AramHăvărneanu Yes, but Adobe designed DNG around what their products use and don't use. If one uses the Adobe convertor to convert raw files to DNG, then most of the info Adobe does not consider vital, including much of the maker notes section of the EXIF, is stripped from the file. I don't know why my original comment was deleted. \$\endgroup\$
    – Michael C
    Aug 22, 2018 at 3:29

1 Answer 1

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Ok, problem solved. It appears Photo Mechanic does not support external XMP sidecar files for DNGs, even though if DNGs are locked (read-only).

Here's what's happening, these are the "original" files, after I have processed them in ACR:

horizon:2$ ls -lO 
total 117568
-rw-r--r--  1 aram  staff  uchg 59453466 Aug 11 18:43 image.dng
-rw-r--r--@ 1 aram  staff  -        8813 Aug 16 17:50 image.xmp
horizon:2$ 
horizon:2$ 
horizon:2$ sha1sum image.dng 
feba47d8cdd3c94971ffd8bd605de87c86218a61    image.dng

Notice how the XMP file is newer than the DNG file, and how the DNG file is locked (uchg flag).

I make a copy of the XMP file for further investigation:

horizon:2$ cp image.xmp old.xmp

Then I star the file in Photo Mechanic, and check the XMP file again:

horizon:2$ diff -u old.xmp image.xmp 
horizon:2$

No change! But wait:

horizon:2$ ls -lO image.dng 
-rw-r--r--  1 aram  staff  uchg 59453466 Aug 22 14:49 image.dng
horizon:2$ sha1sum image.dng 
2b5597257a4b3693154331fc9a44efac3a926b6f    image.dng

The DNG file is changed! I find this very surprising since the file was supposed to be read-only!

After seeing this, the observed behavior makes sense, Photo Mechanic overwrites the DNG file, making it newer than the XMP, so ACR is ignoring it. However, I still think it should perform differently.

At the very least Photo Mechanic should not overwrite read-only files without warning. Also, I think adding an external XMP sidecar option for DNG files would be very useful as explained here in this feature request thread: http://forums.camerabits.com/index.php?topic=11515.0

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