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I have a bunch of photos in JPEGs (not in RAW or any other lossless format). I turned on the option "Include Develop settings in metadata inside JPEG" in Lightroom. If I understand it correctly, it takes the information about my actions in the Develop module and saves it into the original file in the XMP format. When I edit JPEGs, I don't want to use Lightroom's Export, because it always generates a new JPEG, and the additional compression may lead to a quality loss.

Is there any program that I can invoke as an external editor, that can read the original file and the information about the changes, and apply these changes, if possible, without recompressing the JPEG file, or at least recompressing only the parts of the image that have been modified?

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I turned on the option "Include Develop settings in metadata inside JPEG" in Lightroom.

What this option basically does is saving the recipe to reproduce all the Adjustments you made within the JPG File in an XML-Format, instead of creating a so-called sidecar file.

Is there any program that I can invoke as an external editor, that can read the original file and the information about the changes, and apply these changes, if possible, without recompressing the JPEG file, or at least recompressing only the parts of the image that have been modified?

No. Because the XMP-Information is only a set of instructions that need to applied to the JPG file to get a desired effect, this would only be possible if the Program in Question uses exactly the same engine which also Lightroom does.

Your only chance to avoid the JPG re-compression is to use a different, lossless format (like TIFF) when exporting for an external editor. What at this time happens is that Lightroom decompresses the original JPG image, then it applies all changes like specified in XMP. The resulting pixels are then saved to a new file, and the external editor is invoked with this file as path - which is where the lossy compression would happen if JPG is selected as "intermediate" format.

  • +1. Note that if you use very high quality JPEG levels for your original, and also export to high quality, the artifacts from recompression one time should be minimal, and in fact completely unnoticeable under most circumstances. – mattdm Sep 10 '15 at 17:40
  • Yep, but if you then export is as JPG again (e. g. you did some further adjustments on the result of the external retouching), you have already 3 times JPG Compression - so I would never recommend using a lossy format for such "intermediate" files... – Vertigo Sep 10 '15 at 17:47
  • Right, if you make further edits, you would want to go back to the original in Lightroom, not the modified version. No way around that. – mattdm Sep 10 '15 at 19:00
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When I edit JPEGs, I don't want to use Lightroom's Export, because it always generates a new JPEG, and the additional compression may lead to a quality loss.

Preventing quality loss due to re-compression is exactly the reason why you want to create new .jpeg files. LR always creates the exported images from the raw files and applies all changes. LR basically only edits the XML file, which is a recipe on what transformations should be applied when generating a jpeg file from the raw image.

If you work from the raw files LR never touches an exported jpeg again.

If you want to apply further changes to an existing jpeg file in a lossless way, you have to save the result to some lossless format (not jpeg). Saving to jpeg is when the compression is applied.

Is there any program that I can invoke as an external editor, that can read the original file and the information about the changes, and apply these changes, if possible, without recompressing the JPEG file, or at least recompressing only the parts of the image that have been modified?

That is exactly what LR is doing, btw.

  • I know how to edit RAWs. My question is about modifying JPEGs. – michau Aug 11 '15 at 14:59
  • @michau I edited my answer, you have to save to some other lossless format. Your question appears to be entirely unrelated to XMP files. Please clarify why you mentioned them. – null Aug 11 '15 at 15:06
  • I clarified the question. I don't have RAWs, only JPEGs, and would like to modify them without recompression. I know that there would be no problem if I had RAWs, but that doesn't answer my question. – michau Aug 11 '15 at 15:32
  • XMP contains a list of changes to be applied to an image file. I'm looking for software that can apply such changes to a JPEG without recompressing it, if possible. – michau Aug 11 '15 at 15:34
  • @michau I'm afraid that's not possible. – null Aug 11 '15 at 15:45

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