XMP Sidecar files

When can we expect RawTherapee to convert to XMP sidecar files?

Jim L

what is the advantage? i know very little?

I am a user of Lightroom and because of Adobe’s move to the creative cloud, I envision a time when they will make lightroom unavailable as a perpetual license and only available in the CC cloud. They already limit updates if you are not subscribed to the CC cloud, like I am. That will mean I will be stuck with a copy of Lightroom that can still be used, but will never again be upgraded unless you are a CC subscriber, hence an old frozen version. I will NEVER go CC. I resent any software company making me rent their software for an annual fee and I will reject their software out of hand no matter how good it is.

I have thousands of photos processed in Lightroom using XMP sidecar files. If I revolt from Lightroom and go to Rawtherapee (a fantastic raw developer, by the way), all my raw files as developed in Lightroom will not carry over to RT since they use a different sidecar format (the photos will show up in RT, but the develop changes will not} , hence my question. I know that the RT development team does plan to change over to XML at some time. I am just curious if there is a timeline when this might happen.

Jim L

The bigger question is if they will attempt to port over import of functionality from LR to RT when they do, as opposed to simply using XMP sidecars for RT data storage. There are many areas where I’m sure there isn’t a 1:1 mapping between an LR function and something in RT (which would break an import workflow). It’s a good question, though. @heckflosse or @Morgan_Hardwood would be able to answer more definitively… :slight_smile:

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You hit the nail on the head!

OPPS!!! That “little” problem didn’t occur to me and could potentially cause a solution not to work as I invisioned.

Jim L

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You could use this as an opportunity to move away from Adobe and only use free software moving forward… :wink:

From darktable I know that it uses XMP sidecars, however the actual processing information is not compatible with Lightroom (*), so you can keep your ratings, color labels (to some degree), keywords and similar stuff, but not the actual edits. With RT it would be the same I guess.

(*) actually darktable has some rudimentary Lightroom support for taking over processing information, but it only covers basic things like exposure, …

Actually I’d be happy with just support for the ratings and color labels. Every other tool I’m using supports these ratings in some form and it would be nice to be able to better integrate RT into my workflow.

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Is there a published XMP schema that Adobe is using for these LR functions? Or would we need to derive them from actual sidecar files?

I found mention of the crs and crss schemas that Adobe appears to be using for this. I could add those to exiv2.

XMP namespaces are:


But I have not found a published schema for all the properties yet. The individual properties could be derived from XMP files left lying around on the Internet, but better would be the official schema or at least sample XMP files that are licensed for Free Software use.

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Of course, I should have realized that these XMP properties are already supported by exiftool …

In Phil Harvey’s words: Photoshop Camera Raw namespace tags. It is a shame that Adobe pollutes the metadata space with these incredibly bulky image editing parameters.

Just being able to read the numbers from the XML file isn’t enough though, you (or rather the program) also has to make sense of the values, which is next to impossible in the general case.

Ok. That looks like https://github.com/darktable-org/darktable/blob/master/src/develop/lightroom.c

So some of the development settings have been decoded. With enough eyes on the issue, perhaps the rest could be too.

Nope. The ones darktable supports are easy and straight forward (exposure, tonecurve, cropping, …) but most settings would require to implement the very same algorithm as Adobe uses, structure the processing pipeline the same way and THEN figure out the meaning of the values in the XMP. No way that would be feasible.

Regarding the LR processing tags, those are now in exiv2: http://dev.exiv2.org/issues/1190

Getting back to the original question, we bumped up against RT’s unusual way of handling XMP data a year ago. This is issue #2307 in RT: https://github.com/Beep6581/RawTherapee/issues/2307

We are looking at workarounds in exiv2 so that other applications (digikam, shotwell, gimp, etc) can use the XMP data that RT writes in a non-standard and non-spec way. Comments and/or patches are most welcome! http://dev.exiv2.org/issues/1154

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I can’t wait until either RT or exiv2 have this fixed. I know RT is in the wrong here, but since so many make use of exiv2, if the workaround there would be implemented…it’d simplify things so much for me. Right now I have an extra step of re-adding the data after raw processing.

23 posts were split to a new topic: darktable and LR/Fast Raw Viewer XMP Files