Protocols and standards
TIFF-F
Acronym: TIFF-F
TIFF-F is the TIFF profile used to store a fax: a bitonal, compressed image, one page per sub-image within a single file.
It is the format in which a received page is archived before being printed or converted. Bitonal means strictly black or white, with no grey levels — the constraint that explains why grey text or a pale stamp vanishes on arrival. A PDF being sent goes through an equivalent conversion before it reaches the line.