What are Asset Catalogs?

Asset catalogs have been introduced in Xcode 5, making it easier to manage images, especially when dealing with multiple resolutions. However, they may become obsolete with future macOS or iOS releases. At the time of publishing this article, we will reflect the state of asset catalogs in macOS Mojave and iOS 12.

When reverse engineering, there is no guarantee that the data is fully accurate. But these tools simply use some private APIs from Apple and don't directly parse files. There are several tools, including my own (which I plan to open-source at some point), that can dump the content of a CAR file. You shouldn't have to directly deal with CAR files as done here.

Note that the documentation in this article and the CARParser tool are purely meant for educational purposes. The complete source code of this tool is available for download at the end of this article.

The Structure of an Asset Catalog

In this article, I attempt to remedy the lack of information on the CAR file format by describing its global structure and different elements. The CAR file format is not documented by Apple, and surprisingly, I couldn't find much information online.

A CAR file is generated when the application is built with Xcode. It is less known that an asset catalog is compiled to a CAR file. As mentioned in the WWDC 2018 session 'Optimizing App Assets,' Xcode 10 added support for High Efficiency Image, Apple Deep Pixel Image Compression, and Dark Mode for macOS Mojave.

What Can You Do with an Asset Catalog?

Xcode 9 added support for Color Assets and improved support for vector assets (PDF). An asset catalog lets you organize and manage the different assets used by an app, such as images, sprites, textures, ARKit resources, colors, and data. Apple is also extending the asset catalog features each year.

An Asset Catalog is an important piece of any iOS, tvOS, watchOS, and macOS application. It provides incremental search for strings and numbers, printing, and other features that make it a quite powerful tool.

Synalyze It! - A Hex Editor

Synalyze It! features enhanced support for many character encodings and enables you to interactively define 'grammars' for various file formats to speed up analysis and reduce manual decoding of files. Synalyze It! Pro is a simple-to-use hex editor that will allow you to easily edit and analyze binary files of any size.

By synalyze it find structure, an Asset Catalog can be a powerful tool in managing your app's assets.

Synalyze it find structure