Protocols and standards
JBIG
Acronym: JBIG
JBIG is a lossless compression standard for black-and-white images, more efficient than MMR, which some fax machines use to transmit faster.
Its name comes from the expert group that designed it. Rather than coding runs of dots, it predicts each dot from its neighbours and codes only the difference from the prediction, using arithmetic coding. The gain is especially clear on halftone images and photos converted to black and white.
Why it matters for fax
In fax, JBIG is a negotiated option: both machines must support it and error correction must be on. It shortens pages heavy with images, but remains uncommon outside high-end office machines and fax servers.