How MH, MR, and MMR each compress a scanned fax page, and why cloud faxing doesn't require choosing between them.
- Fax compression methods, MH, MR, and MMR, are the specific coding schemes Group 3 fax devices use to shrink a scanned page's data before sending it.
- Modified Huffman (MH) compresses each line independently; Modified READ (MR) and Modified Modified READ (MMR) also reference the line before it, compressing further.
- MMR generally compresses a typical text page more tightly than MH or MR, but needs more processing power to do it.
- Fax.Plus handles compression automatically when sending a fax; there's no setting for a sender to choose between these methods.
What Are Fax Compression Methods?
Fax compression methods are the specific coding schemes a Group 3 fax device or service applies to shrink a scanned page's data before transmitting it. They're the concrete implementations of the broader coding method concept, and every standard Group 3 fax supports at least the first of the three below.
MH, MR, and MMR
- Modified Huffman (MH): compresses each scanned line on its own, replacing common patterns of black and white pixels with shorter codes. It's the baseline method every Group 3 fax device supports.
- Modified READ (MR): compresses a line by referencing the line immediately above it, encoding only the differences between the two, which shrinks a typical text page further than MH alone.
- Modified Modified READ (MMR): extends the same line-referencing approach with fewer fallback cases, generally achieving the tightest compression of the three, at the cost of needing more processing power to encode and decode.
Compression, TIFF, and Fax.Plus
A fax page compressed with one of these methods was historically often stored or exchanged as a TIFF file, the container format, not the compression itself. These schemes are formally defined within the ITU-T T.4 recommendation, part of the wider ITU-T fax standards. A newer standard, JBIG compression, improves on all three for certain image types, though it saw far less real-world adoption. Fax.Plus applies compression automatically on every transmission; there's no method for a sender to select or configure.
Why Compression Matters for Send Time
How well a page compresses directly affects how long it takes to send: a mostly blank page with a few lines of text compresses down to very little data, while a densely packed page, a photo, or a page full of fine detail compresses far less efficiently and takes proportionally longer to transmit at the same connection speed. The actual savings from any of these methods depend entirely on what's on the page, so there's no fixed percentage that applies to every document.
A Common Case: Comparing Two Fax Machines' Transmission Speed
A small office notices one of its two fax machines finishes sending the same multi-page document noticeably faster than the other, a difference traced back to the newer machine supporting MMR compression while the older one only supported the baseline Modified Huffman method.
FAQs
Which fax compression method is the most efficient?
MMR typically compresses a standard text page the most, followed by MR, with Modified Huffman (MH) compressing the least but needing the least processing power.
Can a sender choose which fax compression method is used?
No. Fax.Plus applies compression automatically on every transmission, so there is nothing for a sender to select or configure. The device or service handles the choice behind the scenes.
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