The Lightroom Catalog: the Basics

Many people who are using Adobe Lightroom are confused about the concept of a catalog and have many questions about it.

I keep getting questions myself, so I thought I’d write a series of articles to hopefully provide some answers and demystify some of its most obscure features and confusing aspects.

Lightroom vs. Lightroom Classic

What follows is relevant to the product that is officially called Adobe Photoshop Lightroom Classic, or more concisely as Lightroom Classic. This is how its “About” dialog looks like.

Adobe Photoshop Lightroom Classic about dialog

Some time ago, Adobe, in their infinite wisdom, decided to put out a cloud-based version of Lightroom and call it just Lightroom, while renaming the existing Lightroom to Lightroom Classic. This caused and still causes a lot of confusion. Just keep in mind that Lightroom Classic is the evolution of the old Lightroom that was first released in 2007 and has always been a desktop product. Its current release, as of March 2020, is 9.2.

What is Lightroom Classic?

Lightroom Classic is a desktop application for managing the whole life cycle of photos, from the moment you download them from your camera to their final output as prints, digital files, web sites, slide shows, and books.

It provides an impressive set of features to let you manage your image files and process them, without in most cases having to resort to other applications. It is truly a comprehensive and professional photo management application and the go-to solution for many professionals and amateurs alike.

At the heart of Lightroom Classic sit two fundamental building blocks:

The catalog
The processing engine, based on Adobe Camera Raw

You can find many articles about processing images with Lightroom on this website and also at Visual Wilderness, a site with which I collaborate. In this series of articles, I am going to explain everything I know about the catalog.

What is the Lightroom Catalog?

In a nutshell, Lightroom’s catalog is a database. It contains a list of all the images you have added to it, their properties and all the processing steps you have applied to them.

Let’s look at those elements in detail.

The Catalog is a Database of Images

When you import images into Lightroom, the program creates a list to keep track of where they are located on your hard disks.

Note that the catalog does not contain the images themselves, only a pointer to each image’s position on your disk, that is its path.

This is a very important thing to remember, for a couple reasons:

When you backup the catalog, you are not backing up the image files.
If you move the files around, outside of Lightroom, the link between the catalog entry and the file on disk is broken.

In a future article I will present my strategies for doing backups and for making sure the catalog and the files are always aligned, but for now just keep in mind this very important point.

The Catalog Keeps Track of Image Properties

All digital files have properties. All properties of digital files are collectively called metadata.

Those properties include, amongst the others:

Everything that is written to the file by the camera, most notably what are usually called EXIF data, like aperture, shutter speed, ISO, capture time, and many more.
Everything that Lightroom adds when you import files, like time of acquisition and any other properties you can add via its metadata profiles, like copyright information.
Every other property you set later, like flags, ratings, colors, keywords, titles, descriptions, comments, geographic coordinates, and more.

The Catalog Remembers All Your Processing Instructions

Lightroom is a non-destructive image editor. What this means is that it never modifies the original file. Every processing step you carry out on an image in the Develop module is recorded as part of a processing history that can be replayed, rewound, and modified as much as you want.

Where are all those processing instructions recorded? If you guessed in the catalog, congratulations!

The most important consequence of this fact is that, in the unfortunate case you should lose your catalog, all of your images would still be safe, but you would lose all of their processing history and you would be forced to redo it from scratch, if you wanted.