TECHWATCH tm: Real-World Color Specs Evolve

While it may seem counter-intuitive, standards sometimes have to change. Some measurement standards must evolve to account for changes in usage and applications. This is especially true in color measurement. The continuous emergence of the digitization of graphic arts is not just making production more efficient—it is simultaneously expanding the color range that we can produce.

As a result, it now requires new measurement tools. A computer display, to designers' frequent disappointment, can present many more colors than the printed page. Likewise, the color gamut or range of colors that toner-based print devices can produce exceeds that of traditional offset and other traditional processes such as flexo, screen and gravure. To adapt as the print industry grows its reproducible color range, Pantone has now announced, and is releasing, an improved, broader-range color specification system, called Goe. It launched Sept. 5 and was displayed at Graph Expo.

No doubt, many articles will address Goe because Pantone specifications are so pervasive to print industry operation. (See GAM September 2007, p.14, and blogs at graphicartsonline.com.) For present purposes, we'll look at an inside perspective from Pantone's standpoint. We spoke with the firm's chief technology officer, Brian Rooney, who provided perspective on how Goe addresses emerging color reproduction problems. First, let's discuss some current events in measuring color, then present Rooney's description of Goe's contribution.

To really specify an object's color, you need to define its spectral profile. Recently, our industry has witnessed the appearance of embedded spectrophotometers within closed-loop offset printing systems: Heidelberg Prinect Inpress in sheetfed offset and Graphic Microsystems ColorQuick for web offset are two examples. A spectrophotometer measures light waves reflecting from an object (in this case, a printed surface) to create the color's spectral profile. Onboard spectrophotometers are also migrating into digital print engines. We have seen them showing up in wide-format inkjet printers (see GAM October 2006, p.26; write us if you need a copy.)

Since printing processes provide constraints when reproducing the color we see in the real world, the management of these constraints is the key to faithful reproduction in the balancing act between paper (the so-called fifth color), colorant (ink) and reproduction process coming together in the image reproduction ballet. The CIE standard for color, set in 1931 by the CIE international standards body, has done a good job of coordinating the print product spectral profiles factoring in the viewing conditions of the observer, and the characteristics of the light source under which the object is being viewed.

Since there are many different objects, viewing conditions and light sources, we also have many mathematical transforms for converting standard CIE color into forms we work with every day. Some of the more common transforms are L*a*b, Adobe RGB, and standard RGB or sRGB. All these transforms are dependent on the conditions of the observer and the light source, so they can't easily be interchanged, at least not without adjusting for the differing conditions.

The pressure to interchange these transforms—say, as one moves a project between a preliminary short-run digital output and a full-run offset run—is an area that commonly raises problems in today's color reproduction world. Compounding this situation even further is the fact the majority of printing processes used today employ subtractive CMYK color. This places reproduction systems in an even more difficult position to correct for color differences and changes in viewing conditions.

Now, as mentioned, the electronic imaging and printing processes allow for a wider range of colors to be reproduced than ever before. Pantone's Goe system was designed to provide both the creative design community, and the production-oriented print processes, the ability to do more with color. This requires both science and human interface for the person working in an ever growing color world.

This becomes clearer as Pantone's Brian Rooney explains a bit more about the inner workings of the Goe system and the accuracy it can deliver when run to Pantone's specs.

Pantone color digital values are not theoretical, says Rooney. “They come from first physically measuring the spectral value for each and every Goe color, and then using the latest color science algorithms to translate those real-world measurements into digital equivalents.

“With the Goe System [and Matching System], Pantone also provides the same real-world spectral data and translations of that data into L*a*b [and other] data formats—each with a particular characteristic observer and light source condition—to our licensees to use in their particular internal color data model for their software,” he continues.

Also provided is a method for optimizing the reproduction of the Goe System for specific output devices. “We provide our digital device licensees with custom-tuned Look Up Tables (LUT's) that close the loop from 'real-world data' [the original Goe System printed swatches] through the digital realm [design software to RIP], and back to 'real-world output' [printed output from products like a NexPress, Indigo, iGen],” Rooney says.

These custom-tuned look-up tables are evaluated against the very same starting point as the printed swatches delivered by Pantone's specialized printing presses in its Carlstadt, NJ headquarters. Custom tuning also brings into play some sophisticated gamut mapping algorithms that work to optimize how to reproduce “out-of-device-space” colors. The end result equals accurate and repeatable production of Pantone colors on a wide variety of digital printing devices.

A Goe white paper is posted at graphicartsonline.com .