The Contract Proof - 2000
Drop-on-demand ink-jet technology comes in two flavors—thermal and piezo-electric. Thermal ink jet actually heats the ink to push it from the nozzle. Piezo-electric technology applies pressure to squeeze the ink out of the nozzle.
While thermal is faster, the speed comes at a price. Heating the ink causes some colors to shift and creates a larger, less consistent droplet. Piezo ink flows better, with smaller droplets that make sharper prints. Piezo ink colors are also purer, and piezo printheads do not need to be replaced at regular intervals, the way thermal printheads do, which translates into greater stability.
And now—true halftoning.
One Halftone Analysis
The main argument against ink-jet proofing was always the lack of halftone dots, but this limitation is passing. As ink-jet resolutions approach those of an imagesetter, halftone-accurate ink-jet proofs up to 175 lines per inch are now feasible.
The main reason for halftone proofing is to predict moiré. At 720x1,440, the current AgfaJet Sherpa 43 can already generate 70- to 100-lpi screen-angle rosettes and, with future enhancements, the Sherpa will simulate 150- or 175-lpi screens. If the same RIP is used, the halftone dots will be the same shape, ruling and angle as those on the press sheet—not just an approximation.
Ironically, Agfa's initial research showed that a large majority of potential digital proofing users couldn't care less about halftone dots, so long as they got accurate color and consistency. But if we can give them dots and color accuracy and speed and economy and consistency, we figure no one's going to complain.
Why six colors? The most important advancement in drop-on-demand ink jet has been the addition of continuous-tone capabilities through more than four inks, i.e., multiple densities of the basic four colors. For example, the AgfaJet Sherpa 43 adds a light magenta and a light cyan to the CMYK process. This multi-density approach solves the problem of graininess.