What is the Lightroom Classic catalog? – An explainer

Ever wonder what the Lightroom Classic catalog actually is and does? Well you’ve found the right article to answer your questions. I’ve been researching this topic for long enough. Today we’ll be taking a deep dive into the technical aspects of the Lightroom Classic catalog.

The Lightroom Classic database?

In computing terms, the catalog is a plain old database. Nothing more, nothing less. To be more precise it is an SQLite database, which is a relational database management system. SQLite is just shy of 20 years old and is used in a wide variety of desktop applications. In fact, Lightroom Classic is unlikely to be the only application you have installed which uses SQLite. You’ll find it in Skype, Evernote, and Apple Photos to name just a few.

Why Adobe opted to name it the catalog and not just the database I do not know. I guess it’s part of their attempt to appeal to photographers.

What the Lightroom Classic catalog does

The catalog tracks three key pieces of information about each photo you add to it:

  • Where the photo is stored on your system. That could be your internal drive, an external SSD or a network drive.
  • Instructions for how you want to process the photo. That is everything you do in the Develop Module.
  • Metadata such as ratings, keywords and copyright information.

Each time you import a Photo from an SD card Lightroom Classic is doing more than just copying the file onto another drive. It is creating a link between the photo itself and the record of that photo in the catalog. Picture your catalog as a spreadsheet. Each new photo will be another row in that spreadsheet.

Any work you do in Lightroom Classic is stored in the catalog and does not change the actual image file. That includes all of your development settings such as exposure, contrast, curves and even local adjustments.


Once you’ve edited your photo and want to export it Lightroom Classic will apply all of your changes, which are stored in the catalog, and apply them to a copy of the photo.

Let’s break these three points down one by one. I’m going to assume that most of you, because you are using Lightroom Classic, shoot raw. But if you do just use the jpegs, the same goes for them everytime I’m talking about raw files.

The reference system

Lightroom Classic isn’t a traditional file browser, such as Windows Explorer or Finder on a Mac. If you’re using an external drive to store images a file browser will only be able to show you those image files if the drive itself is connected.


Lightroom Classic uses a catalog to keep track of photos, no matter where they are stored, they’re all referenced in the same, central catalog. And using previews it can also display your photos whenever that drive might be disconnected.

Photo processing instructions

Lightroom Classic does not touch the raw file you import into it’s catalog. Everything you do in the develop module is stored as an instruction. If we continue the spreadsheet analogy from earlier, each edit would be an added column containing information on your edits.

That includes global edits such as contrast and exposure but also local edits such as the local hue adjustments that were just recently added in an update.


Ever wondered why Lightroom Classic first displays your unedited raw file and takes a second or two to overlay the adjustments when switching to the develop module? That’s because it will first load a preview of your raw file and then fetch the instructions on how you want the file edited from the catalog.


Metadata is a set of standardized information about a photo. Most cameras will already add some of the metadata to the raw file such as the exact dimensions in pixels, the file format, and the date and time.

Lightroom Classic will automatically write any adjustments and settings metadata to the catalog. You can also instruct Lightroom to write that metadata into a so-called XMP sidecar file.


Let’s say for example you forgot to change the timezone on your camera and you came back from a trip with photos with the incorrect time. You can adjust this in Lightroom Classic and it’ll then show the actual date and time because that is what is stored in the catalog. Mind you, that will not be reflected in the original file so there you have another reason to enable the writing to XMP sidecar files.

Just as Lightroom Classic enables you to have presets in the Develop Module you can also save metadata presets. If you haven’t done this yet do it right now. You can add details such as your name and email to your files and have those added automatically during the import. The metadata will then also be applied to a file during export.

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