This is a format created in the Acorn Draw program, intended for image visualization by using vector lines. It’s used for storing information in the publishing business (brochures, logotypes, etc.). The main advantage is it’s high quality source images when printing. It’s been in use since 1980.
The G3 format is used to compress image files in TIFF format when sending faxes. The compression algorithm allows for the use of a standard 10-times compression, which can be increased. It is used to remove excess image data, which makes it possible to reduce the size of the image and speed up delivery.