Glossary of Terms

Database

A store of structured information, normally held on a computer storage system. This can be selectively searched, and information added or retrieved to order.

Degassing

Methods for removing dissolved air and other gasses from inks within a printer that might otherwise form bubbles and disrupt or completely stop the flow. Methods include passing the ink across a permeable membrane that has a reduced air pressure on the other side, before the ink reaches the printhead: the pressure differential induces air to come out of solution and form bubbles that can be safely removed before they reach the printhead and ink chamber.

DFE

Stands for Digital Front End. In graphic arts, the control software (and sometimes hardware) for a digital printer. It is often used as a alternate term to a RIP or Rip-Workflow.

Digital

All current commercial computers are digital, that is they base their operations on the rapid shuffling around of whole numbers, or digits, usually 0 and 1, representing off and on in an electrical switch. Digital is normally used as the opposite of analogue, where values are continually variable.

Dithering

One of the halftone patterning techniques commonly used by inkjet and other digital printers. It allows an extended range of tones and colours to be achieved in photographs and blends, by applying small dots with varying spacing. A variation called stochastic screening is used in offset printing and some other processes. See Halftone

DoD Inkjet

Stands for Drop on Demand. This describes a class of printheads that are precisely controlled to produce ink drops only when required. The term was coined to distinguish this type of head from Continuous Inkjet. All current large format and office/desktop inkjets use DoD printheads, whether they are based on thermal or piezo technologies. See Piezo, Thermal, Continuous Inkjet

Dot gain

A printed effect where ink droplets or halftone dots are larger than desired for a given tonal effect. Nearly all print processes are subject to dot gain of some degree, though the causes may differ.

DPD

The number, or maximum number, of sub drops in a printed drop. This is mostly of interest to inkjet scientists and developers, though it is important in understanding how greyscale heads work. See Greyscale Heads

DPI (aka Addressability)

Drops per Inch. A measure of the number of ink drops that appear on the final printed image from an inkjet printer. This can be different in the head pass and the media transport directions, so typically you'll see 720 x 360 dpi. Printed DPI is usually greater than the NPI (nozzles per inch) because of techniques like multiple passes and multiple heads.

Drop Interleaving

Also called Drop Interlacing or Interleave Printing. These are terms used for print patterning techniques that mitigate the problem of blocked nozzles, or reduce visual banding on low resolutions or low numbers of head passes. Typically the swathe of ink drops are controlled to create a scalloped (way) line at top and bottom edges. The scallop positions are varied for subsequent passes, breaking up the edges to reduce the visual impact.

Droplet size

Inkjet drop sizes are measured in picolitres. One picolitre is a millionth of a litre. Depending on the printhead configuration, the drop sizes normally range from 3 or 4 picolitres to more than 100 picolitres. Photo-quality printers such as Epson Stylus Pros generally produce the smallest drop sizes, and many of these use greyscale heads that vary the size of drop too. Printers used for signage and similar applications that are viewed from a distance can use larger drops, which cover a given area more quickly to allow greater print speeds. See Binary and Greyscale.