Gamma

1. Measurement of the relation between input density and output density of an image. 2. Command in a scanner interface for adjusting gamma levels. A rating of 0.1 to 2.0 affects the shadow areas, a 2.1 to 6.0 affects midtones and 6.1 to 7.9 affects the highlights. 3. Term used to describe the contrast in a monitor.

Gamma Correction

Correction or creating new tonal ranges in an image by adjusting the tonal curve.

Gears, Pulleys and Capstans

In a scanner mechanism, one or more of these basic elements is used to move the carriage the length of the scanner bed. Gears are notched wheels that turn another wheel when two notches meet. Pulleys are wheels with a grooved side to accommodate the metal cable between the motor and carriage. They redirect the force of the pull. Capstans are also grooved wheels that either redirect the cable, or contain slack cable that unwinds during movement. In the latter case, they are spring-loaded to provide tension.

GIF

Acronym for Graphics Interchange Format. A graphic file format commonly used for images on web pages. Originally developed by CompuServe, GIFs use only 256 colors and can be compressed to save disk space. Files saved in this format have ".gif" as their file extension.

Gigabyte

Amount of stored data roughly equal to one billion bytes. There are 1,024 megabytes in a gigabyte and 1,048,576 kilobytes. Also written as G or GB. See byte, kilobyte and megabyte.

Grayscale

1. Video display setting consisting of 256 shades of gray. 2. Scanner interface setting for scanning images in shades of gray such as black and white pictures.

GUI

Acronym for Graphical User Interface. Pronounced "goo-ee," a GUI is a computer program that interfaces by means of menu bars and dialog boxes contained within a constant shell. All applications in a GUI use the same shell, which reduces confusion in searching for common tasks from one application to the next. The Windows and Macintosh operating systems are examples of GUIs.