The Contract Proof - 2000
There are two types of ink jet—continuous flow and drop-on-demand. Continuous flow ink-jet systems deliver superb quality, virtually continuous-tone images. Rapid bursts of "micro-drops" form each single droplet, whose densities are varied by varying the number of micro-drops from which each is made. Only a small number of density levels are possible, so the system is not truly "continuous tone." But by screening with these variable-density droplets, ultra-smooth prints are possible at relatively coarse device resolutions.
Because continuous-flow printers are drum-based, they are expensive to build, and because a continuous flow of ink is required even when printing white areas (the unused ink is deflected into a drain), ink is a major cost.
Drop-on-demand ink-jet technology produces ink droplets only when needed, so no ink is wasted, and it is by far the faster of the two methods. Instead of varying drop size, dithering (variable droplet spacing) is used to achieve tonal variations.