WORKFLOW: Color Science, Not Science Fiction

Moore's Law, the 1965 prediction made by Intel co-founder Gordon Moore, contends that the number of transistors on a microchip would continue to double every two years. I'd like to add Hal's Law: the number of colors in inkjet printers will increase 75% every five years.

In 1997, HP's Deskjet 694C battled with Canon's BJC-5500 for the desktop marketplace, while a little upstart named Epson introduced the Stylus Color 600 (capable of a blazing fast six ppm). These 4-color devices were quickly eclipsed by 6-color printers, then by the 7-color Stylus Pro 7600 and 9600 in 2002. Add five years, multiply 7 by 1.75, and you've got Canon's new 12-color imagePROGRAF high-resolution inkjet printers. (O.K., so it multiplies to 12.25; don't be so picky!) Canon's polymer-encapsulated 12-color LUCIA ink set provides improved “lay down” of ink on the printed substrate for reduced bronzing and surface artifacts.

Over the past two months, I've enjoyed the chance to work hands-on with the 24´´ imagePROGRAF, the iPF6100. As an avid photographer, I was curious to see how the 12-color system would reproduce some flower images I had last printed back in 1999, on a 4-color Scitex IRIS Realist inkjet. The addition of red, green, blue and two different gray inks (in addition to photo cyan, photo magenta and matte black) were supposed to provide a noticeably expanded color gamut.

The results were incredibly sharp, with stunning detail. Tiny 4-picoliter droplets from an astounding 30,720 nozzles brought out new textures and patterns. Color transitions were silky smooth and ultra-realistic, without a hint of banding or stepping. But was the gamut increased by all these added colors? Based on my visual evaluation, I would have to say no—exactly as I expected, based on the principles of color science.

Whether inkjet or litho, print is a subtractive medium. The visual appearance of any printed piece is based on three things: the quality of the light source, the subtractive effect of the ink/paper combination and the acuity of the observer. Our eyes are most sensitive to the additive primaries of red, green and blue, so we print with inks designed to control the reflection of those frequencies. Magenta is part of the process color ink set because it filters out green light; cyan ink filters away red light and yellow filters out blue.

So printing with red ink won't increase the gamut of available colors, as the red ink is simultaneously filtering out blue and green light frequencies. Even popular hi-fi systems that include fluorescent orange have only a small impact on the overall gamut; to truly expand the printable gamut requires ever more effective filtration of RGB light (i.e. CMY inks of greater purity).

What these additional ink colors do provide is super-smooth transitions between colors. In earlier inkjets, relatively coarser droplets combined with stochastic screening lead to “noisy” gradients. LUCIA's expanded palette blends colors more effortlessly than any litho press I've ever seen—for stunningly realistic results.

We can expect more high-resolution inkjet innovation in the future. Canon already sells desktop devices producing 1-picoliter droplets. Researchers at the University of Illinois claim to have developed a 10,000-dpi printhead. Something tells me it will hit the market in five years and use 21 colors.