Digital Type

In typography, type generated by a computer, as opposed to metal or photographic type. Digital type gets its name from digital computers, which are based on the binary principle of on/off. A digital image is created with dots, and the individual dot is either there or not there—on or off. The individual dot is also called a pel or pixel (both terms are shorthand for picture element), and a group of overlapping dots forming a straight or curved line is called a raster.

Typesetters that use line segments—or vectors—to outline a character still use dots as the basic building blocks. All digital typesetters use the very basic principle of turning some light source on or off to create an image. That light source can be a cathode ray tube (CRT) or a laser, or it may not be a light source at all, as newer technologies apply electro-erosion, magnetography, and light-emitting diodes.

The placement of the dots for an individual character is stored in memory. Rather than turn the imaging source on and off for each dot, many devices employ a principle called run-length of coding, which allows the beam to sweep continuously over a series of on dots, rather than turning on and off for each one.

Because every character is made up of dots, diagonals and curves may not be as smooth and sharp in their edge resolution as straight lines. At 1,000 dots per inch (dpi), acceptable quality is produced. At 5,000 lines per inch (lpi), there is no visible difference between digital type andf other photographic type.

The best place to check the quality level is the dot on a lowercase i'—the location of the greatest curvature—or the entire typeface Optima, as it has almost no straight lines.

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