Closed-Loop Color: The Next Big Thing

Automated in-line color control for web presses, featuring closed-loop ink key control technology, is becoming an integral component within today's digital workflows. It can provide a link to a digital, color-managed, color reproduction workflow, and, when coupled with computer-to-plate (CTP) imaging and the ability to digitally preset ink fountains on the press, enables print shops to compress delivery schedules while improving quality.

"Closed-loop color control systems are required for quantification of feedback to optimize precise control of perceived color in today's digital workflow environment," says Evan Fitzgerald, director, domestic sales/technical service, Web Printing Controls Company (WPC) Inc. "The ability to analyze and archive the digital information presented to the press gives the printer the ability to become more proactive in the repeatability and predictability of the product."

"The more complete the digital workflow is from design through production, the better the chance of profitability and customer satisfaction," says Mark O'Connell, technical marketing manager for Graphics Microsystems, Inc. (GMI).

"Closed-loop color gives us the ability to preset ink fountains on press with the same digital data used during plating," explains Rich Magnetta, pressroom manager for magazine printer St. Ives Hollywood (Fla.).

Automated, closed-loop color control systems use a video densitometer and/or spectrophotometer to scan color bars on a moving web, measuring and evaluating solid ink densities, color gamut, dot gain, trapping, and three-color gray balance. Depending on the system used, up to 30 different variables can be measured. The real-time data is used to adjust ink settings to achieve target color values.

Closed-loop color systems also provide statistical process control (SPC) reports, which verify for clients color accuracy and consistency during the press run.

"Closed-loop technology precludes press operator adjustments, which tend to repeatedly overshoot and undershoot required values," says industry consultant Bob Erbstein. "It also eliminates subjectivity differences between different press operators, and eliminates the human tendency to adjust the color. The systems free press operators to focus on other issues such as setting tension or folders, thus further reducing start-up waste."

Erbstein, the president of Graphic Transitions LLC, spoke in November in Chicago at the 27th annual Pressroom Conference held by the Research & Engineering Council of the Graphic Arts Industry.

Erbstein estimates that currently in North America 273 web presses are equipped with closed-loop color control. Of these, 36% are used for publication printing, 25% for general commercial work, 15% for catalog output, and 14% for direct-mail printing.

The most popular closed-loop color systems are manufactured by GMI, Perretta Graphics Corporation, QTI (formerly Quad/Tech International), and WPC.

GMI's ColorQuick system uses video for location and inspection, and a spectrophotometer to measure color. The system—which measures color gamut, density, dot gain, and contrast—locks in and maintains the optimum color gamut match throughout the press run; density is allowed to vary to maintain the best color gamut match.

St. Ives Hollywood, one of four St. Ives plants in the U.S., prints average run lengths of 50,000 weekly and monthly magazines with splits for direct marketing. The plant has been investing in closed-loop technology to ensure that color within each version of a magazine will be the same.

In September 1999, it installed the first two GMI closed-loop systems on an eight-unit Heidelberg M-1000BE press. "We were able to reduce makeready waste and time, and generate less run waste," says Magnetta. "We also were able to reduce our paper consumption on repeat forms. In July and August 2000, we installed four more systems on the remaining eight-unit M-1000BE presses."

Magnetta adds, "This August, we'll complete the project and be the first magazine printer to have closed-loop color control on all our web presses."

"Closed-loop color lets us give our customers uniform color throughout the run and from form to form," he says. "We can review graphs of actual print history. This gives us greater control of each job and assures the customer of fewer color variations within the run. ColorQuick has eliminated crossover problems, because the same density is set on press and the color holds throughout the run."

Magnetta reports that St. Ives's customers have been impressed with the ability of this equipment to start fast and maintain uniform color. "In fact, 30% of our work runs without color proofs of any kind," he states. "We simply take the digital signal to press with preset and ColorQuick, and then run to SWOP standards. This saves the customer money, and we have fewer customers in the plant for color approvals."

QTI's Color Control System (CCS) utilizes video densitometry to update press operators with color measurements of solid ink density, print contrast, trapping, and dot gain while providing solid ink density closed-loop color control.

In partnership with System Brunner, QTI's CCS also measures and controls three-color gray balance. System Brunner's Process Aviator evaluates print quality, measuring and monitoring three-color gray balance in midtones and solids, as well as individual CMY midtone and solid ink balance. The Process Aviator tool is now a part of QTI's basic CCS package.

QTI and System Brunner also offer CCS with Instrument Flight, which utilizes System Brunner's patented evaluation and control algorithm to analyze more than 30 process variables, including three-color gray and midtone balance, while calculating the optimal inking recommendations.

The system then automatically adjusts the press's ink keys to meet these color recommendations in a completely closed-loop configuration.

"With QTI and System Brunner, we not only are providing color management on press with in-line color control, but we are using these tools to work back into prepress and measure and evaluate the proofs, plates, and print," says Andy Hollis, web press in-line color control operations director for System Brunner.

Hollis adds, "The workflow is evaluated and controlled by dot gain and CMY balance, not solid ink density as with other systems."

About four years ago, Quad/Graphics began retrofitting each of its web presses with closed-loop color control systems. "We now have about 95% of our presses equipped with CCS," explains Mike Popp, director of press operations for Quad/Graphics, Pewaukee, Wis.

"Looking at the future of our pressroom, we knew we had to tighten up the window of variability as it relates to color fluctuation throughout the run," says Popp. "While trying to be a low-cost, high-quality producer, we also try to do things at high speed and with fewer people. To do this, we need automated machines that will help the press operator maintain consistency throughout the run."

He continues, "With closed-loop color control, there's no need for someone to keep visual watch over the color, to make adjustments as the presses run. The operator can focus on other press duties, such as compensation, bundle quality, and registration."

Sacramento, Calif.-based high-end commercial printer Dome Printing, a much smaller shop than industry giant Quad/Graphics, also uses QTI's CCS. Running a color-managed workflow from prepress to the pressroom, Dome uses CCS with Instrument Flight for closed-loop color control on its six-unit Heidelberg M-130 heatset web.

Dome, one of the first shops in California to implement CTP and now 100% digital, finds that closed-loop color control is an integral part of its digital workflow. "It's a part of the digital process, along with CTP and digital proofing," says company president Tim Poole. "There a lot of variations in the analog world. The digital infrastructure, with capabilities like closed-loop color control, brings a level of consistency."

Poole explains that Dome uses CCS because it controls color based on dot gain and gray balance rather than just density. "There are problems with just measuring density," states Andy Poole, Dome's vice president of manufacturing. "We can have a straight-line density across the press sheet and still be out of gray balance."

Says Tim Poole, "After using this system for 18 months, we found that we occasionally run solid ink density because a particular job might warrant it. But with closed-loop color with gray balance, we have accurate color almost twice as fast, and find that corrections happen a lot quicker on press.

"CCS also brings a lot of value to our marketability," he adds. "It validates what we do. Every client on that press understands what we do; it is as much a marketing tool as a pressroom tool."

The latest color control offering from Perretta Graphics, Dynascan II, is designed to operate at any press speed, including those exceeding 3,000 feet per minute. It offers continuous in-line scanning of the web (both sides simultaneously), and also can read a control bar with a width of less than two mm. The module provides automatic ink correction, SPC output to existing data management networks, and a comprehensive data bank to provide reporting of key color control attributes.

Courier Graphics Corporation, Phoenix, installed its first Perretta Graphics CLC Dynascan closed-loop color control system in mid-1997 on a six-color Heidelberg M-1000 web press. In early 2000, the commercial printer installed on a five-color M-1000 the Dynascan II system, which was set up to lock into target density values in three to five scans and maintain a tight tolerance of ±.03 points.

"With our first Perretta CLC system, we found that we cut our makeready waste in half," reports Ed Farnum, vice president of operations for Courier. "Later, as we became more used to the equipment, we found that our quality levels went up throughout the run."

Moreover, says Farnum, "We've cut our makeready time drastically. That has to figure into the equation on payback."

Courier found that its Perretta system provided a return-on-investment (ROI) rate of less than 24 months. According to Farnum, part of the quick ROI came about via Courier's large amount of makereadies; Farnum estimates that the firm completed 1,600 makereadies last year (three to four makereadies per crew per day on each web).

The WPC Mictrotrak CLC microdensitometer system measures and reports print contrast, dot gain, and ink trapping, automatically adjusting a press's ink keys to maintain density levels. CLC Plus uses CCD sensor technology to combine the functions of closed-loop color technology and color register in one system.

Process Manager software extracts data from CIP3 Print Production Format (PPF) files and dispatches job configuration and preset data to all WPC systems in use, including register, closed-loop color control, ribbon alignment, and web guides.

Quebecor World Loveland (Colo.) installed a WPC system in September 2000 on one of its eight-unit Baker Perkins G-16 web presses, which it uses to print telephone directories.

"The biggest benefits from our closed-loop system are the real-time data that we can provide to our clients, the savings on makeready time, and the consistency that we are giving our customers," says Brad Johnson, manufacturing manager for Quebecor World Loveland. "Our clients demand that we keep to a certain tolerance."

Adds Johnson, "We provide to our customers a score card on a book-by-book basis, which includes color density and dot gain readings. The closed-loop system not only increases our book score, but we are able to download the data from the Process Manager."

With the WPC system, Quebecor World Loveland is able to preset all 16 ink fountains in approximately 30 seconds, as well as all of the auxiliary systems from the Process Manager, in just one step, states Johnson. "This saves us a lot of time on makeready," he asserts.

With its closed-loop color system in place, Johnson says that Quebecor World can be within the customer's acceptable quality density range in about 1,500 impressions. "We can start pulling color OKs, which have a density range of plus-or-minus .03 points, at about 5,000 impressions," he says. "On our presses, which are manually adjusted by operators, it normally takes a minimum of 15,000 impressions to get to that density range."

Johnson sees closed-loop color control coming into the printing industry the same way registration control did nearly 10 years ago. "More and more printers will turn to closed-loop color control, especially as we continue to see a downturn in the craftsmanship we once had," Johnson says.