OTB to HRZ Converter

Easily convert OTB to HRZ image format in your browser

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Cross-Platform Access

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

Effortless Process

Converting OTB to HRZ takes just a few clicks — no technical knowledge required. Upload, choose your format, and download the result.

Cloud Conversion

All OTB to HRZ processing runs on Convertio servers — your device stays fast and free while the conversion happens in the cloud.

How to convert OTB to HRZ

1

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

2

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

3

Let the file convert and you can download your hrz 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
HRZ is a simple raster image format associated with slow-scan television (SSTV), a method of transmitting still images over radio frequencies used by amateur radio operators since the late 1950s when Copthorne Macdonald pioneered the technology. HRZ files store images at a fixed resolution of 256x240 pixels in raw RGB format, with each pixel represented as three bytes (red, green, blue) at 8 bits per channel, producing uncompressed files of exactly 184,320 bytes. The format has no header, no metadata, and no compression — the file is simply a sequential dump of raw pixel data in row-major order. This extreme simplicity reflects the format's origins in the amateur radio community, where SSTV images are transmitted as audio tones encoding luminance and chrominance values over narrow-bandwidth HF (shortwave) radio channels. The fixed 256x240 resolution corresponds to common SSTV transmission modes, and HRZ files serve as the digital capture or storage medium for received SSTV transmissions. One advantage is the format's zero-overhead structure: with no parsing, decompression, or metadata processing required, HRZ files can be read by any program capable of reading raw pixel data with known dimensions — a single function call in virtually any programming language. The format's connection to amateur radio SSTV culture is another notable aspect: HRZ files document a unique form of image communication where operators transmit photographs over thousands of miles using nothing but radio waves and audio encoding, a practice that continues today alongside digital modes. HRZ files can be opened by ImageMagick, GIMP, and specialized SSTV software.
Developer: SSTV Community
Initial release: 1985

Frequently Asked Questions

Why would I convert OTB to HRZ?

Few modern tools handle OTB natively. HRZ provides slow-scan television image format from amateur radio, making it widely recognized across operating systems and applications.

What programs open HRZ files?

Open HRZ using ImageMagick, specialized SSTV software. Cross-platform support means you can access these files on virtually any system.

What exactly is the OTB format?

OTB (Over-The-Air bitmap format for early Nokia phones) originated in Nokia mobile phones. It has very limited modern application support but can be converted to modern formats on Convertio.

How long does OTB to HRZ conversion take?

Conversion is nearly instant for most OTB files. Since these are small images, the entire process — upload to download — takes only moments.

Can I convert multiple OTB files to HRZ at once?

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