A set of standards for facsimile (fax) machines published by the ITU-T in 1980 as T.4. Group III devices convert a document to digital form and employ a run-length encoding algorithm, as described below, that compresses the document prior to transmission. Group III machines are backwardcompatible with Group I and Group II devices. See also backward-compatible, compression, facsimile, Group I, Group II, ITU-T, run-length encoding, T.30, and T.4.