[EDITED to correct an error]
When Lightroom imports a file, the metadata in that file are rewritten — into the JPEG itself, or into the sidecar file for raw files (I don't use DNG files—I suspect that they have their own set of rules). I have found a number of inconsistencies in this process, and it is making my life more difficult. Are there known rules for this process of rewriting the metadata?
Here is what I have found:
1) Some fields are copied from a raw file to its sidecar file, presumably for convenience, and some are left only in the raw file. It is not clear to me which fields are copied or why.
2) When these fields are copied from a raw file to its sidecar file, a new value can be synthesized and written into the sidecar file. (Lens is an example).
3) In order to be consistent (I guess) Lightroom shows the same value for Lens, regardless of its value in the image file, so that the value shown in Lightroom is not the value in the file.
4) Certain fields are "synthesized" according to other fields and written into both JPEGs and sidecar files.
Here are examples of these issues. All the following photos were taken on a Canon 5D Mk III with a 65 mm macro lens. The photos were transferred to my computer (a Mac) and imported into Lightroom. Then a field (copyright) was added into each file and the metadata saved. (The file "1K8A7447orig.JPG" is locked, so Lightroom can't write into that file.)



And what is interesting is that the string "Zeiss Makro-Planar T* 2/100 ZE" doesn't even occur in the JPEG file:
Thanks
When Lightroom imports a file, the metadata in that file are rewritten — into the JPEG itself, or into the sidecar file for raw files (I don't use DNG files—I suspect that they have their own set of rules). I have found a number of inconsistencies in this process, and it is making my life more difficult. Are there known rules for this process of rewriting the metadata?
Here is what I have found:
1) Some fields are copied from a raw file to its sidecar file, presumably for convenience, and some are left only in the raw file. It is not clear to me which fields are copied or why.
2) When these fields are copied from a raw file to its sidecar file, a new value can be synthesized and written into the sidecar file. (Lens is an example).
3) In order to be consistent (I guess) Lightroom shows the same value for Lens, regardless of its value in the image file, so that the value shown in Lightroom is not the value in the file.
4) Certain fields are "synthesized" according to other fields and written into both JPEGs and sidecar files.
Here are examples of these issues. All the following photos were taken on a Canon 5D Mk III with a 65 mm macro lens. The photos were transferred to my computer (a Mac) and imported into Lightroom. Then a field (copyright) was added into each file and the metadata saved. (The file "1K8A7447orig.JPG" is locked, so Lightroom can't write into that file.)
$ exiftool -G -lens -lensid -focusdistanceupper -focusdistancelower -approximatefocusdistance 1K8A7447.JPG 1K8A7447orig.JPG 1K8A7458.CR2 1K8A7458.xmpWhat we see is
======== 1K8A7447.JPG [Composite] Lens : 65.0 mm [Composite] Lens ID : Canon MP-E 65mm f/2.8 1-5x Macro Photo [MakerNotes] Focus Distance Upper : 0.24 m [MakerNotes] Focus Distance Lower : 0.23 m [XMP] Approximate Focus Distance : 0.23 ======== 1K8A7447orig.JPG [Composite] Lens : 65.0 mm [Composite] Lens ID : Canon MP-E 65mm f/2.8 1-5x Macro Photo [MakerNotes] Focus Distance Upper : 0.24 m [MakerNotes] Focus Distance Lower : 0.23 m ======== 1K8A7458.CR2 [Composite] Lens : 65.0 mm [Composite] Lens ID : Canon MP-E 65mm f/2.8 1-5x Macro Photo [MakerNotes] Focus Distance Upper : 0.24 m [MakerNotes] Focus Distance Lower : 0.24 m ======== 1K8A7458.xmp [XMP] Lens : MP-E65mm f/2.8 1-5x Macro Photo [Composite] Lens ID : Canon MP-E 65mm f/2.8 1-5x Macro Photo [XMP] Approximate Focus Distance : 0.24 5 image files read
- "Approximate Focus Distance" is synthesized and written both JPEGs and sidecar files.
- The value of "Lens" is rewritten as "MP-E65mm f/2.8 1-5x Macro Photo" for xmp files, so it is different between the raw file and its sidecar file.
- If we look in Lightroom, all these files are shown having a "Lens" of "MP-E65mm f/2.8 1-5x Macro Photo" regardless of the value of "Lens" in the file. So the value shown for JPEG files in Lightroom is not the value actually in the metadata in the JPEG file.
$ exiftool -G -lens -lensID 1K8A7456.JPG 1K8A7457.CR2 1K8A7457.xmp ======== 1K8A7456.JPG [Composite] Lens : 100.0 mm [Composite] Lens ID : Carl Zeiss Makro-Planar T* 100mm f/2 ZE ======== 1K8A7457.CR2 [Composite] Lens : 100.0 mm [Composite] Lens ID : Carl Zeiss Makro-Planar T* 100mm f/2 ZE ======== 1K8A7457.xmp [XMP] Lens : Zeiss Makro-Planar T* 2/100 ZE [Composite] Lens ID : Carl Zeiss Makro-Planar T* 100mm f/2 ZE 3 image files readHere we see again that a new value for "Lens" has been synthesized and added to the xmp file, but not to the JPEG file. And in Lightroom both these images show a value of "Zeiss Makro-Planar T* 2/100 ZE", regardless of the value in the files.



And what is interesting is that the string "Zeiss Makro-Planar T* 2/100 ZE" doesn't even occur in the JPEG file:
$ exiftool 1K8A7456.JPG | grep '2/100' $If there is any documentation of any of this anywhere, I'd love to know about it.
Thanks