Group 4 compression
Group 4 compression, usually abbreviated as G4, is a method of image compression used in Group 4 fax machines, and document scanners defined in the ITU-T T.6 fax standard. It is only used for monochrome (black and white) images. G4 compresses files at a rate of 20:1. An example is an 8.5"x11" page is scanned at 200DPI. It is 456.54KB (uncompressed) in size. Once G4 compresses it, it is reduced to 22.82KB (456.54KB\20 = 22.82KB). It is also available in the TIFF image file format, as well as in the PDF document format.
- "Group 4 Compression". GraphicsAcademy.com. Retrieved March 4, 2010.