American Standard Code for Information Interchange – an internationally applied US standard code to describe alphanumerical characters in the computer for purposes of information exchange between different computer platforms.

Abbreviation of "binary digit" – the smallest digital data unit which can be processed in a computer. It can only accept the values 1 or 0.

Also called a bit pattern image. A file of pixels arranged in a matrix which indicate specific halftone or colour values so that text, graphics or images can be created. Acts as a set of on/off instructions for a laser beam, print head, computer screen, etc.

The smallest addressable data unit, comprising 8 bits.

Abbreviation signifying the process colours: cyan, magenta, yellow and key (black).

The propensity for scanners, monitors, proof printers and printing presses to misrepresent the scanned-in chromatic values of an image original. All these devices deviate from each other in their colour capacity.

Computer-to-Plate – the process of writing a digital image directly onto the printing plate without the use of film.

A proof created directly from a data file for various purposes e.g. for determining or monitoring colour reproductive, print or layout accuracy.

Dots per inch – frequently used measurement for indicating the resolution of input and output devices. Computer screens generally have a resolution of 72 dpi, laser printers between 300 and 1800 dpi, image setters between 600 and 12000 dpi and scanners up to 11000 dpi. The higher the resolution, the larger the volume of data required.

Encapsulated PostScript – a graphics and image-data format developed by Adobe, with pixel and/or vector data. Good for inserting line graphics or images into bigger PostScript documents. It consists of a header, which contains information relevant for output on PostScript image setters or printers and a PostScript file with the actual image data. In addition to this image description, EPS contains a low-resolution image for displaying on the screen.

Integrated Services Digital Network – public communications network embracing the services provided by national telecoms companies to allow the simultaneous transmission of data, text, language and images.

Joint Photographic Expert Group – an interdisciplinary group of experts on photographic and electronic image recoding and data transmission. Created the data-exchange format JFIF, an ISO standard for the compression and decompression of continuous-tone data. The storage and transfer of high-resolution photo realistic images previously demanded an uneconomically high hardware performance which storage media and public data-transmission lines were unable to accommodate.

Line per inch – the unit of measurement for screen width. In the metric system it is expressed as lines per cm, e.g. a 60 lcm screen equals 152 lpi (1 inch=2.54 cm).

Portable Document Format – part of the Adobe Acrobat programme which allows a cross-platform, programme-independent document exchange, i.e. the original typography and image layout are mimicked on the transferred pages, which can be processed elsewhere by exporting text and image data.

Adobe System’s programming language for describing document pages with text, image, graphic and layout data in a uniform pixel format (bitmap) which is suitable for output via RIP on printers, image setters and digital printing systems. Version 3 of Extreme (an RIP technology formerly called Supra) combines PostScript with Acrobat’s PDF, offering printers and digital printing systems almost unlimited document portability.

Reproductive accuracy of an image or output, usually expressed in pixels, lines or dots per cm or inch.

Typical device colour space e.g. in scanners, digital/video cameras, monitors, data projectors and image databases. Based on the additive colour synthesis red + green + blue = white. Unsuitable for print.

Raster Image Processor – hard and/or software capable of converting the various vector or pixel formats into a uniform pixel graphics form known as a bitmap.

Tagged Image File Format – cross-platform pixel-data format for digitised picture contents (also several images in one file). TIFF images, unlike EPS images, can be processed, compressed, and to a limited extent, enlarged. In addition to the actual image information a TIFF file consists of a header, tags and an image file directory (IFD) which provides the image processing and reconstruction data.

Also called spread and choke, or bite – a minimal overlap between two adjacent colours in order to avoid flashes and substrate showing through due to slight mis-register. The lighter colour should overlap the darker one. Modern layout and graphics applications have functions which automatically spread adjoining areas of different colours.