How does Lightroom store data about photos?

Question

I've seen numerous mentions of Lightroom's database, or catalog, and having to back it up. Being used to Bridge and Camera Raw, I'm accustomed to seeing sidecar .xmp files alongside my RAW files. These can easily be backed up with my RAW files since they are actual files.

Does Lightroom use sidecar files, same as Bridge, or does it use its own database for storage of image tags, metadata, etc? Or is it some combination?

NickM · Accepted Answer

Lightroom (on a Mac at least) has its own database, which it calls a catalog, which is stored and backed up separately from your image files. It's called 'Lightroom Catalog.lrcat'. There is an option in 'Catalog Settings' to 'Automatically write changes into XMP'.

The following page tells you more about how Lightoom handles metadata and adjustments:

http://help.adobe.com/en_US/Lightroom/3.0/Using/WS638E3AC9-A04C-4445-A0D3-F7D8BA5CDE37.html

ex-ms · Answer

If you choose to write data to file (as Nick's answer explains), then all the adjustments are also written out.  For example, here's some data extracted from one of my files1 showing crop, dust spotting and an exposure adjustment:

Crop Angle              : 0
Crop Bottom             : 0.989721
Crop Left               : 0.043881
Crop Right              : 0.972479
Crop Top                : 0.007033
Exposure                : +0.35
Retouch Info  : centerX = 0.086913, centerY = 0.126265, radius = 0.010000, 
                sourceState = sourceAutoComputed, sourceX = 0.061588, 
                sourceY = 0.134257, spotType = heal,...

1 which are mostly TIFF film scans; the data's extracted using the rather excellent exiftool.

sebastien.b · Answer

As Nick pointed out, there is an option in 'Catalog Settings' to 'Automatically write changes into XMP'. I personally turn it off because I do not want to update my files that often (for performance and backup synchronization reasons). However, you can manually write metadata, keywords, rating, labels and develop settings by selecting one or more files and using 'Metadata > Save Metadata to File(s)' (Ctrl+S or Command+S). You can also click on the 'Metadata File Needs To Be Updated' icon (a down arrow) in a thumbnail in the Grid view, then click Save.

The extent of this update depends on the file type. For a DNG file, this will pretty much copy everything currently in the catalog and pertaining to that file back to the file. For a RAW/CR2 file this will update the sidecar. For a JPG, TIFF and PSD file this will update the tags, some EXIF info and potentially a sidecar if the "Write develop settings to XMP for JPG, TIFF, and PSD" option is On.

This is explained in more details with a few useful tables here: http://www.adobepress.com/articles/article.asp?p=1211707

Andrew · Answer

This is more of a question than an answer about how lightroom stores metadata?
If Key Tags are exported to a saved jpg file from light room, for example: Adam; Jim; John; Sam;
Then they show up under Details as Property {Description {Tags in the windows file Properties viewer/ editor.
But they do not show up as vector data and as an item with the Name: 40094 in Visual Basic
If in the Windows editor you modify the Details {Property {Description {Tags from example: Adam; Jim; John; Sam; to-> Adam; Jim; John; Sam; test  Then they do show up as vector data and as an item with the Name: 40094 in Visual Basic.
How do I access Lightrooms save Jpg file Details {Property {Description {Tags in Visual Basic??

How does Lightroom store data about photos?

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