OTB to MOBI Converter

Online OTB to MOBI — from image to e-book instantly

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Cross-Platform Access

Whether you are on a desktop, tablet, or phone — convert OTB to MOBI from any device with a modern web browser.

Secure Processing

Uploaded OTB images are erased right after conversion, and the resulting MOBI files are purged within 24 hours — your data stays private.

Batch Processing

Upload multiple OTB files at once and convert them all to MOBI in a single session — ideal when you have many legacy images to migrate.

How to convert OTB to MOBI

1

Select files from Computer, Google Drive, Dropbox, URL or by dragging it on the page.

2

Choose mobi or any other format you need as a result (more than 200 formats supported)

3

Let the file convert and you can download your mobi file right afterwards

About formats

OTB (Over-the-Air Bitmap) is a monochrome image format developed by Nokia as part of their Smart Messaging specification in 1997, designed for transmitting small graphics — operator logos, group graphics, and picture messages — to Nokia mobile phones via SMS. OTB files contain 1-bit (black and white) images at small fixed resolutions, typically 72x14 pixels for operator logos and 72x28 pixels for group graphics, encoded in a compact binary format suitable for embedding within the payload of SMS text messages. The format uses a simple structure: a header byte indicating whether the image is an operator logo or group graphic, width and height values, and the raw bitmap data where each bit represents one pixel packed eight per byte. The extremely tight format — designed to fit within a single SMS message (140 bytes maximum payload, shared with addressing overhead) — reflects the severe constraints of mobile communication in the late 1990s. Nokia's Smart Messaging system was one of the first commercial implementations of rich content delivery to mobile phones, and OTB images represented the entire visual content capability of Nokia handsets before MMS and mobile data browsing arrived. One advantage is the format's historical role as a pioneer of mobile visual messaging: OTB images were among the first graphics that ordinary consumers could send to each other's phones, predating MMS, camera phones, and smartphones by nearly a decade. The format's minimal footprint is another characteristic — entire images fit in a few dozen bytes, reflecting an era of extreme bandwidth constraints. OTB files are supported by ImageMagick, various Nokia phone management tools, and specialty mobile format utilities.
Developer: Nokia
Initial release: 1997
MOBI is an ebook format originally developed by Mobipocket SA, a French company founded in 2000 that was later acquired by Amazon in 2005. The format builds on the PalmDOC/PDB container structure, adding support for HTML-based content markup, embedded images, a DRM layer, and a JavaScript subset for limited interactivity. MOBI files use a record-based database architecture inherited from Palm OS, with a header structure containing metadata like title, author, publisher, and language followed by compressed HTML content records. The format became the foundation of Amazon's early Kindle ecosystem — the original AZW format used on first-generation Kindles was essentially MOBI with Amazon's own DRM wrapper. MOBI supports reflowable text with basic formatting including bold, italic, headings, lists, and tables, as well as internal hyperlinks and a built-in table of contents. One advantage is broad device compatibility: MOBI files are recognized by Kindle devices and apps spanning over a decade of hardware, as well as numerous third-party readers on desktop and mobile platforms. The format's lightweight structure is another strength — even long novels produce compact files that load quickly on modest hardware. While Amazon has since moved to the more capable AZW3/KF8 format for new publishing, MOBI remains widely circulated in existing ebook libraries and continues to be produced by conversion tools like Calibre for maximum Kindle compatibility.
Developer: Mobipocket SA
Initial release: 2000

Frequently Asked Questions

What is the reason to convert OTB to MOBI?

Converting OTB to MOBI packages your images for e-readers. MOBI is a widely supported e-reader format, making it suitable for portable reading devices.

Which software can view MOBI files?

MOBI files can be opened with Amazon Kindle, Calibre, FBReader, Moon+ Reader. Most of these are available across Windows, macOS, and Linux.

Does converting OTB to MOBI affect quality?

The conversion preserves the visual content of your OTB image. MOBI will reproduce the same pixel data within the limits of its format capabilities.

Can I convert multiple OTB files to MOBI at once?

Yes — upload several OTB files in one session and Convertio processes them all into MOBI simultaneously, saving you time.

Is OTB to MOBI conversion free?

You can convert OTB to MOBI for free on Convertio. Premium plans are available if you need higher throughput or larger file allowances.

Are my uploaded files kept private?

Yes — your OTB files are deleted immediately after processing. The resulting MOBI files are also removed from servers within 24 hours.