Seeing the Light: New Xerox Spectrophotometer-based Control System Will Let Digital Printers Calibrate Themselves, Deliver Consistent Color
Nabisco wants every Oreo® cookie on its conveyor belt in every bakery to look and taste exactly the same. Commercial printing professionals have the same requirement for printed pages. If the color is even slightly wrong, page-to-page or machine-to-machine, it's a print they can't sell. In fact, color is one of the toughest things to get consistently right because there are so many variables in the printing process, whether it is digital or traditional offset.
But scientists at Xerox Corporation's Webster research center have invented and patented an ultra-fast, low-cost spectrophotometer that's expected to streamline and simplify color printing. And the spectrophotometer - a system to measure color as seen by the human eye - has potential uses in other fields that demand precise color matching, including fabrics, paint, wallpaper, plastics and interior design, according to L.K. Mestha, a Xerox principal scientist.
Today, color printing - whether digital or offset - involves significant prepress work so that the printed output matches what the creative designer specifies. Specialists use spectrophotometers costing thousands of dollars to measure and duplicate the exact colors.
Once printing begins, densitometers on the presses calculate optical density of colors on a gray scale, measuring whether the device has applied the correct amount of ink. Densitometers are colorblind; they can only note changes in density. They are not "smart" enough to identify colors or see if a color deviates from the original with, for example, an unwanted pink or yellow tone.
In fact, the printing process has as many variables as a bakery, or more. Different papers and inks, variations in atmospheric humidity and temperature, and, in digital printers, internal changes in variables such as materials, static electricity, age of the parts - all can change colors subtly.
So although the colors may have been matched precisely in the prepress stage, they can drift as image after image is churned out. And even when it's right on one press, matching the same color on different machines is a real challenge.
Xerox's invention is a breakthrough in both measurement and control. Scientists designed a spectrophotometer that costs less than one-sixth the price of current models. It will be embedded inside a digital printer to make full color measurements on each passing page in a few milliseconds. In that brief time, the spectrophotometer shines light of different colors from several LED's onto tiny color patches on paper moving at the speed of the printer, analyzes the reflected light, and determines its color makeup "on the fly."
With Xerox-proprietary control algorithms, the digital printer can compare the color of each patch to the color in the original image. While the machine is running, the system can make minute adjustments to all the pixels in the image at the machine printing speed - no human involvement will be required. It's like automatically sampling cookies on the conveyor belt and changing the recipe while more cookies are in the oven.
"When machines can regulate themselves, they won't have to be designed with micron-level precision, parts will last longer, they will be able to tolerate differences in materials and operating environments, and the result will be fewer service calls. Printing professionals will be able to minimize prepress work and operator interventions, yet deliver more saleable prints," Mestha said.
The technology, in the research labs now, is expected to show up in stages in next-generation digital color printers within two years. It is also available for licensing.
Xerox Corporation, one of the world's top technology innovators, operates research and technology centers in the United States, Canada and Europe that conduct work in color science, computing, digital imaging, work practices, electromechanical systems, novel materials and other disciplines connected to Xerox's expertise in printing and document management. Xerox consistently builds its inventions into business by embedding them in superior Xerox products and solutions, using them as the foundation of new businesses, or licensing or selling them to other entities. For more information, visit www.xerox.com/innovation
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