Can multiple editors store separate non-destructive edits in the same DNG file?
Asked 2/19/2014
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2 answers
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If several RAW editors support writing metadata directly into a DNG instead of using separate sidecar files, can each program keep its own non-destructive edit instructions inside that same DNG? Or do they generally write to the same XMP metadata area and risk overwriting each other’s settings? For example, Lightroom warns when a DNG has been edited elsewhere.
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
12y ago
2 Answers
2
Short Answer
No, I don't think that it is supported. I'm not sure though if it is generally possbile.
Long Answer
To find out the truth, we need to look at different Specifications.
(Hint: All Page numbers in the following text are the page numbers a PDF reader reports, not the one on the bottom of the page.)
This documentation states, that Lightroom uses XMP for Storing development settings. It also states that Lr can write those Settings either in an XMP Sidecar file or directly into a supported file format and DNG is a supported type of file.
To find out what exactly is happening, we need to look at the DNG Specification.
Here ist the specification for DNG 1.4 as PDF.
XMP is only Mentioned on Page 14:
Additional metadata may be embedded in DNG in the following ways:
- Using TIFF-EP or EXIF metadata tags
- Using the IPTC metadata tag (33723)
- Using the XMP metadata tag (700)
This gives us an hint, that only one XMP-"Thingy" can be saved within an DNG File. So next we need to look at the XMP Specification itself.
That one can be found here. Here is also a direct link to the core specification, which is essentially the ISO Standard 16684-1.
On page 12, in Chapter 6 "Data Model" it gets interesting. This chapter explains the concept of an XMP-"Packet", which within the context of my answer boils down to a sidecar-file.
A little bit later we read the following statement:
All properties in a single XMP packet shall describe a single resource. Separate XMP packets may describe the same resource. Conflict resolution for separate packets that describe the same resource is beyond the scope of this document.
This essentially tells us, that neither DNG nor XMP Specifications say anything specific about handling of multiple Sidecar-Files embedded in one DNG, so it seems to be totally unsupported.
Originally by user26144. Source · Licensed CC BY-SA 4.0
user26144
12y ago
0
Generated from our catalog & community — verify before relying on it.
Generally, no. In practice, most non-destructive RAW edits written into a DNG are stored as XMP metadata inside the file, and different applications usually read and write that same metadata area rather than maintaining separate, independent edit histories.
That means:
- If two programs use the same XMP fields, one program can overwrite the other’s settings.
- If a program uses private or app-specific metadata, another editor may ignore it, strip it, or replace it when saving.
- Lightroom’s warning that a DNG was edited elsewhere is consistent with this behavior.
So while DNG can embed metadata, it is not a reliable way to keep simultaneous, separate edit instructions from multiple editors in one file.
If you want safer multi-application workflows, sidecar files or separate derivative files are the better choice, because they reduce the chance that one application will overwrite another application’s adjustments.
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AI12y ago
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