OTB to G4 Converter

Migrate OTB bitmaps to G4 format online and for free

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Any Device Works

Convert OTB to G4 from Windows, macOS, Linux, or mobile — the browser-based tool adapts to any screen size and operating system.

Browser-Based Tool

No software to download — convert OTB to G4 entirely in your web browser. Works on any device with an internet connection.

Lightning Fast

OTB files are small and convert to G4 in seconds. The cloud-based engine handles the transformation quickly so you can download right away.

How to convert OTB to G4

1

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

2

Choose g4 or any other format you need as a result (more than 200 formats supported)

3

Let the file convert and you can download your g4 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
G4 is a monochrome image format based on the ITU-T Group 4 facsimile coding standard (Recommendation T.6), ratified by the CCITT in 1984 as an improvement over Group 3 for use on error-free digital networks like ISDN rather than analog telephone lines. G4 files contain 1-bit image data compressed using exclusively two-dimensional Modified Modified READ (MMR) coding, where each scanline is encoded as a set of differences (changing elements) relative to the line above it. By eliminating the one-dimensional coding fallback and the end-of-line synchronization markers required by Group 3, G4 achieves 20-50% better compression ratios on typical document pages while producing a simpler, more regular bitstream. The format is most commonly encountered as a compression method within TIFF files (TIFF compression tag 4), where it became the standard archival format for scanned documents in enterprise document management, government records, and legal imaging systems. G4 compression is specified at 200, 300, or 400 dpi depending on the scanning application, with 300 dpi being the most common for archival-quality document imaging. One advantage is exceptional compression efficiency for document content: G4's two-dimensional prediction exploits the strong vertical correlation in text and line art pages, typically compressing a 300 dpi letter-size page to 30-50 KB — roughly half the size of equivalent Group 3 encoding. The format's entrenchment in document management infrastructure is another strength — G4 TIFF is the mandated format for many government digital records systems, court filing systems, and corporate archives, supported by every enterprise imaging platform.
Developer: ITU-T (CCITT)
Initial release: 1984

Frequently Asked Questions

What is the reason to convert OTB to G4?

OTB is tied to Nokia mobile phones. Switching to G4 gives you high-speed fax compression encoding and broad support across platforms, browsers, and devices.

How do I open a G4 file?

Software that handles G4 includes ImageMagick, IrfanView, fax software, GIMP — giving you options on every major operating system.

Can I convert multiple OTB files to G4 at once?

Convertio supports batch mode — drag in multiple OTB files and they all convert to G4 together, which is much faster than one-by-one.

What exactly is the OTB format?

OTB is an Over-The-Air bitmap format for early Nokia phones. Originally from Nokia mobile phones, it has become a legacy format — conversion is the most practical way to use these images today.

Is OTB to G4 conversion free?

You can convert OTB to G4 for free on Convertio. Premium plans are available if you need higher throughput or larger file allowances.

Is my OTB file safe when converting online?

Convertio takes privacy seriously — your OTB uploads are deleted after conversion and the G4 results are cleared within 24 hours.