What is the ITHMB file format?

What is the ithmb file extension? How is it created? What devices use .ithmb? Why are .ithmb files so large in size? We’ve prepared this article to answer these common questions about ithmb files .

First, the basics:

File extension: iTHMB
Stands for: iThumbnail
Type: Media file
Company/creator: Proprietary file of Apple Computer Inc.
Compliance: Specific to iOS devices (Apple’s mobile operating system for: iPod, iPhone, iPad)

In other words, files with an .ithmb extension are created by Apple for use on iPods that display images.  These files are a collection of thumbnail files and are used for browsing images on iPods or iPhones and for organizing images in photo management programs specific to these devices. Thumbnail images are smaller versions of larger images that are used as a link to the original larger image located on the device where the thumbnail is stored.

How are they created?

Each time a photo is saved to an iPod an iTHMB file is automatically created for convenient viewing.  Small thumbnails are stored together in one file.  On a PC, an iTHMB file is created when syncing an iOS device with iTunes.  The file is saved to the original device and to your PC.

Other information about iTHMB

The photo application for iPod can display up to 25 thumbnails at a time.  iTHMB files can contain multiple thumbnail images in one file.  Basically, an iTHMB file is made up of four different images with different resolutions.  These images are optimized specifically for the iOS device display mode and screen size.  The intention of these files is to make navigation faster which provides the added advantage of saving battery power.  As they are a specific format to the iPod device, they can be challenging to open when using other operating systems.

Along with iTHMB files, iTunes also creates an index file that contains information (metadata) such as filename, date, and size.  Together these two items, iTHMB and index files, form what can be considered an image database.  The location of these files varies depending on the iOS device and the iOS version itself.  Previous versions stored the index file (“PhotoDatabase”) in the mobile/Media/Photos/ directory and iTHMB files in the Thumbs subfolder.  More recently versions store the index file (“Photos.sqlite”) in the mobile/Media/PhotoData/ directory and iTHMB files in the “Thumbnails” subfolder.

Why are they so large in size?

iTHMB files contain 16-bit uncompressed raw pictures and uncompressed graphic data.  The file size can be considerably larger than the total size of the originals.  When an iTHMB file reaches its maximum size a new file is created and the succession is captured in the filename.  One postulated theory to the uncompressed nature of the data is that the processing power of iPod is insufficient to decompress archived files and would result in too much of a draw on battery life.

Challenges with iTHMB file on other OS’es:

iTHMB files are specifically for iOS devices (iPod and iPhones in this case).  Opening these on other operating systems, such as on your PC, can be challenging.  These files can be transferred easily, like any other file, but your PC does not have a default program that can open these thumbnail images for viewing unless you use an iTHMB converter to change these images into another format (for example, a TIFF image).  Correct iTHMB viewer software is required to view and to convert the iTHMB file.