Gamut

The range of colors that can be captured or represented by a device. When a color is outside a device's gamut, the device represents that color as some other color. The RGB gamut contains a possible 16 777 216 colours and the CMYK gamut contains only 1 000 000 colours (not including shades that use black ink).

GIF

Graphic Interchange Format. An image format type generated specifically for computer use. Its resolution is usually very low (72 dpi) making it largely unusable for printing purposes.

Graphics Tablet

A device that allows the user to draw on a tablet using a pen or stylus which is then digitised and translated into the graphics application of the user. A more naturally intuitive pointing device than a mouse. Can be used to simulate illustration and airbrush techniques.

Gravure

A rotary printing process where the image is etched into a metal plate attached to a cylinder. The cylinder is then rotated through a trough of ink, after which the etched surface is wiped clean by a blade leaving the non-image area clean. The paper is then passed between two rollers and pressed against the etched cylinder drawing the ink out by absorption.

Greyscale

A bitmap image format that containing shades of grey values as opposed to only pure black and pure white. This format is used for single colour usually black photographs and images. There are 256 possible values of grey from white to pure black.

Halftone

A photographic print is referred to as being "continuous tone" as the shades of grey are areas of flat or continuous tone. Printing presses can only print one colour ink at any given time so the photo has to be converted into a different format. The halftone format converts the discreet shades of grey  into an array of round dots. Dark areas have few dots, light areas have many dots. In full colour printing these halftone dots are further separated into which colours belong on the cyan, magenta, yellow and black plates.

Histogram

A graphic representation of the distribution of tones within an image. The horizontal axis represents each pixel value possible from black to white. The vertical values indicate the number of pixels in the image that occur at each value level.

HSB

Hue Saturation Brightness. A colour model that utilises Hue, Saturation and Brightness as the three coordinates. Hue is the dominant colour, Saturation is the purity of the colour, and Brightness is a neutral scale of how light or dark a colour is.

Imagesetter

An imagesetter is a high resolution photo-imaging device that prints digital computer files to film (like the negatives used in traditional camera). This film is then used to make printing plates.

Imposition

The arrangement of pages on a printed sheet, which when the sheet is finally printed on both sides, folded and trimmed, will place the pages in their correct order.