Perfecting Proofing

The goal of an effective proofing system is to ensure predictable, repeatable results throughout a print run by achieving the closest possible match between the proof and the printing press using color management and screening techniques. An effective proofing system will be able to accurately reproduce trap and overprint characteristics, together with the fine lines and text that are critical in package and label design. Inks or dyes, media, RIPs, and color management tools all will play important supporting roles.

As is the case with any worthy goal, getting there is the challenge. With proofing, it requires shifting our attention to process control and calibration as the keys to achieving the best possible press-to-proof match. "Chasing" the proof on-press has always been problematic—not to mention time-consuming and expensive—for the simple reason that proofing devices typically behave much differently than printing presses. Absent appropriate process controls, errors in packaging preproduction can be carried through and multiplied across the various print disciplines, substrates, and color sets employed to identify a given brand and its extensions. This could have disastrous—and costly—consequences in terms of time, labor, waste, and rework.

State-of-the-art 
proofing in action

Fourth-generation, family-owned Hammer Packaging is among the largest and most forward-thinking producers of high-end packaging decorating in North America. Roughly 70 percent of Hammer's capacity supports the production of litho-based labels for the food and beverage industry, with web offset and flexo-printed labels accounting for the remaining 30 percent. The company also is said to be the world's largest producer of premium seed packets. Customers include Gatorade, Coca-Cola, Pepsi, Campbell's, and many other well-known brands. The $100 million company employs more than 400 people at three plants in the Rochester, N.Y. area.

Hammer operates both Epson inkjet (with GMG RIP for color management) and Kodak Approval digital halftone proofing systems. The company uses off-the-shelf conventional and UV sheetfed inks by the Flint Group that conform to the ISO 12647-2 ink specification defining the L*a*b* colorimetric values for CMYK and RGB overprints. Plates are imaged on a Kodak Magnus VLF platesetter, which anchors the company's EskoArtwork prepress workflow. While the company produces some inkjet contract proofs, it more often relies on its Kodak Approval to generate hard copy contract proofs/mockups on the actual substrate to be used in production.

In Hammer Packaging's fast-paced world, says Prepress Manager Bill Pope, state-of-the-art proofing denotes "having the capability to proof accurately on a wide variety of substrates, targeting all the printing systems and ink sets we use."

In Hammer's case, the effort extends to the entire lineup of the company's 12 conventional and UV web, sheetfed, and narrow-web UV flexo presses. In sum, it reflects a process of continuous improvement driven by Hammer's expansion in terms of new presses, job mix, ink sets, and substrates—especially the 2 to 3.2 mil film stock (clear, white, metalized polypropylene, etc.) it uses for a significant amount of its label and shrink sleeve applications. "The biggest issue for us is substrates," Pope confirms. "What prints well on paper may not print well on film."

The company currently is engaged in the re-calibration of its presses using the G7 calibration methodology to accommodate the significant volume of work that moves back and forth between its web offset and flexo presses. To date, the company has sent three people through the G7 Professional Certification training (representing prepress, offset pressroom, and flexo pressroom) and is currently in the process of calibrating its multiple printing press platforms on various substrates with different screening (AM and FM) towards the aim of achieving "G7 Master Printer" status.

"The industry continues to fight proof/press issues and excess waste in materials, time, and labor," Pope says. "The name of the game is process control. We view our latest effort as an opportunity to improve how well our presses can match the proof. One of the keys is to level the playing field as much as possible by using the same 'crayons', so to say, on all our output devices. If the color of your process colorants is different from device to device, you have a potentially significant uphill battle in terms of achieving a match. Process control and good calibration techniques give us a real opportunity to leverage this capability against the competition."

Practically speaking, it doesn't make sense for Hammer—or any packaging printer with multiple jobs moving among multiple presses, for that matter—to create color separations for each process it plans to use, Pope explains. "It's cumbersome, time-consuming and ultimately counterproductive, and it results in expensive on-press tweaking," he says. "Rather, there is a huge benefit in bringing each press to a common printing condition, by which I mean a commercially acceptable visual match (within certain tolerances), regardless of ink set, substrate, or printing device, such that all that remains is to predetermine plate curves to help achieve that condition."

The main benefit of the G7 specification is that it produces a more visually consistent printed appearance—with calibration curves alone—than can be achieved with traditional dot-based calibration methods. The simple explanation for this is that dot size alone is not a reliable indicator of visual appearance, because it doesn't consider other factors like ink hue, ink film thickness, and trapping. With G7, widely different printing processes can share not only common gray balance, but also common tonal contrast and image weight, regardless of paper type, ink quantity, screening type, or imaging technology. This "shared appearance" concept offers a significant new default compatibility benefit when exchanging files between different imaging systems. G7 is currently being applied to many types of printing including commercial and publication printing, newsprint, and even flexo and gravure.

The fact is, Pope continues, "If you're looking to run one product on a dedicated press all the time, you probably don't need the G7 specification. However, if you need to run the same product or graphics on different printing devices and/or processes, you need to maintain a common grey balance between them all in order to achieve a good visual match. And if you can get them all to print similarly, one file will fit all."

Quality commitment

For professionals like those at Hammer Packaging that take their commitment to quality seriously, the aim of color process control is to produce a proof that can be more easily matched on press because both processes are calibrated. Color calibration encompasses calibrating all processes and devices to a predetermined specification, and is a prerequisite for color process control, which aims to maintain those processes and devices in their appropriately calibrated state.

The logic is unassailable: IF you have a process or device that is properly calibrated, AND you are using good process control for consistency, THEN the same process can be profiled and that profile can be used to make prepress proofing devices match actual printing processes, thus ensuring accurate color communication and reproduction. In the end, Pope says, the aim is a matter of achieving a realistic subjective visual appearance across a broad range of printing types, within tolerances the customer can live with. pP