G3 to HRZ Converter

Digitize G3 files to HRZ — free online converter

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Secure Processing

Source G3 files are deleted instantly after conversion. HRZ output files are auto-removed within 24 hours.

Multiple Files

Process several G3 files in a single session. Each produces a separate HRZ file for individual download.

Fax Preservation

Preserve fax content by converting G3 to widely supported HRZ — future-proof your document archive.

How to convert G3 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

G3 is a monochrome image format based on the ITU-T Group 3 facsimile coding standard (Recommendation T.4), ratified by the CCITT in 1980 as the universal compression method for fax transmission over telephone networks. G3 files contain 1-bit (black and white) image data encoded using Modified Huffman (MH) one-dimensional coding, where each scanline is independently compressed by replacing runs of consecutive white or black pixels with variable-length codewords from a predefined Huffman table optimized for typical document content. The standard also defines an optional two-dimensional coding mode (Modified READ) that encodes each line as differences from the previous line, achieving better compression for pages with vertical redundancy. Standard G3 resolution is 204 pixels per inch horizontally and either 98 (standard) or 196 (fine) pixels per inch vertically, producing the characteristic slightly-stretched appearance of received fax documents. The encoding was carefully optimized for the real-time transmission constraints of 1980s modems operating at 2400 to 14400 bps, where encoding and decoding speed had to match the communication channel rate. One advantage is universal telecommunications compatibility: Group 3 encoding remains the mandatory baseline codec for every fax machine manufactured, ensuring that G3 image data can be transmitted to or received from any fax device worldwide. The format's efficiency for document content is another strength — the Huffman tables were statistically tuned to the run-length distributions found in business documents, and typical pages compress to under 30 KB. G3 files are supported by LibreOffice, ImageMagick, and fax server software.
Developer: ITU-T (CCITT)
Initial release: 1980
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 convert G3 to HRZ?

HRZ is widely supported by image viewers and browsers — converting from G3 eliminates the need for fax tools.

Which viewers support HRZ?

Open HRZ files using specialized image tools or HRZ-compatible ham radio software.

Will the HRZ result match G3 quality?

G3 to HRZ conversion is lossless for document content. Lines, text, and graphics all remain intact.

Does converting G3 to HRZ cost money?

No — standard conversions cost nothing. Premium plans offer higher limits for power users.

Does the converter accept multiple uploads?

Yes — the converter handles multiple files per session. Each G3 upload converts to HRZ on its own.

What platforms support this converter?

The converter works in any modern web browser — Windows, macOS, Linux, Android, iOS. No installation required.