Bruce's point about XMP and DNG is an important trick; I've got some additional observations along these lines. If you're like me, you love XMP sidecars and the simple integration it offers with Adobe Camera RAW (ACR) - I use custom scripts to apply common settings based on lens and camera body by editing XMP sidecars directly. Having XMP contained within DNG makes for an easily portable file, but makes scripting ACR controls via XMP much more difficult. I've been experimenting with both. Here's what I've noticed:
- Adobe DNG Converter merges the XMP sidecar (if present) with your RAW or DNG file when it's processed, like Bruce says; I recommend doing this to "freeze" metadata into your DNGs.
- Adobe Photoshop's File Browser creates new XMP sidecars for DNG files if you edit any metadata or ACR settings that would normally be stored in XMP; you may easily end up with redundant and inconsistent XMP in both the DNG and the sidecar files when you work with DNG.
- XMP sidecars take precedent over embedded XMP when working with DNG; redundant elements in the sidecars trump those same elements in the DNG.
Now, when I'm working with DNG, I can easily create a new XMP sidecar (if none exists) with just the elements I want to change. For instance, I use a script to apply Chromatic Aberration correction based on the camera body and lens; I can create a very simple XMP sidecar via a script, with just the CA parameters I want. Next time I open in ACR, the new parameters are used to override whatever is set (or not) in the DNG itself.
This leads the way to a nice multi-level XMP solution I'm exploring now -
- Store common, basic metadata within the DNG - keywords, IPTC
- Store processing settings externally (in a database, or loose files>
When you need to pull up a particular rendition of a RAW/DNG, swap in the appropriate external sidecar just before opening in ACR. I've got a solution working here with multiple sidecars per DNG - my demo shows multiple "derivatives" from a single RAW. Tres cool!
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