Wide-Format Color Management: So Many Variables, So Little Time

In the world of commercial print, device-to-device color matching is fairly straightforward. Inks and substrates are standardized, target densities and Lab values, as well as paper white tolerances, are defined (GRACoL, SWOP, FOGRA. etc.). Even with UV offset, where media such as plastics can present some challenges, it is still pretty much standardized.

But in the world of wide-format output, it’s a different story, with device-to-device color matching a struggle, with some unique issues. To begin with, in the attempt to color match from one device to another, there are many more variables to be controlled.

There are over 20 different printer brands, as well a host of media types and ink systems— solvent, UV curable, latex, dye sublimation and aqueous, Bart Fret, GMG’s Director of Sales - Large Format, explained.

Each type of ink also presents it own unique imaging characteristics. “The different inks may also image at distinctly different resolutions and may not target a common output condition, like offset print processes,” said Ray Cheydleur, X-Rite’s Printing and Imaging Product Portfolio Manager.

There is also no standard on ink colors. Depending on the manufacturer, inks might be strong or weak in specific primary colors.

“That’s not all,” added Fret. “There are different lighting conditions to be taken into account, and front and backlit prints to consider, for example.”

The most difficult challenge of matching across the wide format production process has to do with substrates, stated Ron Ellis, principal, Ron Ellis Consulting. “The issue is both the consistency of substrates themselves, as well as difference in color between many substrates. Designers are often designing using common print specifications such as GRACoL or SWOP. These print specs are what they are seeing on the screen as they design – and each of these print specifications contains a paper color as well. Most fast wide-format devices can easily achieve G7, but often do not have the full gamut to exactly match these specs, and when the paper color is different than the print spec the designer has in mind it can cause color issues.“

According to Ellis, basically all of the color moves with the color of the substrate. “There are ways to manage this but it requires knowledge and the right toolset,” he said. “I train my customers on substrate correction methods that help mitigate these issues. Often multiple pieces for the same customer may run across multiple substrates, such as an SBS board and a styrene. While these substrates have very different colors, using color management we can usually make both of these match by making one of the substrates be the substrate relative target, and having the other substrate use a matching paper tint.”

Also, while the print quality of a 15-year old offset press is not too different from one manufactured today, a wide-format digital press from 15 years ago is dramatically different from more recent devices. “Older printers generate much larger dots; a digital press built today outputs smaller—and often variable—dots,” said Fret. There has been an evolution in print quality and many companies operate presses that run the range from one year old to 10 years old, with vastly different gamuts and a wide range of quality.

“The scope is much wider and as such the difficulty in matching printers is much higher,” Fret explained.

Adding monitors to the equation heightens the level of complication; the inherent nature of a monitor compared to print is already a challenge. The basic dilemma is the comparison of an additive color system (monitors) versus a subtractive color system (printer).

How to show the additional variables in wide-format imaging is also a challenge. With high-quality offset at 200 lpi, you rarely see dots, said Fret. “However, imagine print on a structured material from a 15-year old printer. There is a grainy effect, and adding additional variables are hard to simulate on a monitor—visible dots or graininess and specific defects, materials and structure of the material. Even more challenging, many people think that they can match colors with different RIPs driving different printers on the same print floor—each with different color management systems.”

To make it work, communication, calibration and quality control are in order. “Best practices start with setting the proper expectations,” Cheydleur noted. “This means good communication is critical.”

The customer and printer need to communicate regarding the targeted print condition. “Without knowing the target print condition it is impossible for a print supplier to match the desired output,” Ellis reported. “The print provider can help the customer understand the print conditions that can be achieved on specific equipment and substrates. Once a print condition has been agreed upon, calibration becomes important.”

Monitor-to-output matching issues require that both monitors and output devices are properly profiled and calibrated.

“All stakeholders should be working with calibrated devices, monitors, local proofers (even if they are design proofs) and, of course, final contract proofs and output devices,” said Cheydleur. “This requires ICC color management software and a spectrophotometer for print profiling. This provides for proper expectation setting right from the initial creation stage.”

If the desire is to match a specific target or brand color, use a well-qualified color references like the PANTONE Matching System, which has both physical guides and digital references to help both designers and printers, Cheydleur added. “If you need to match with offset and offset is using a standard reference profile, then making sure that all devices are targeting this final output space right from the start is also critical. Training and qualification, such as the Pantone Certified Printer program, which looks at the entire print communication process, is a simple way to make sure that all parts of the workflow are aligned.”

Added Ellis, “To achieve the end goal of color matching, I train customers on involve methods of rapidly calibrating substrates and devices to achieve print conditions. Rapid is important, because if it takes too long to calibrate a device then operators will ignore it because it is too disruptive. Ideally an operator should be able to calibrate a device within 10-15 minutes, and should be able to quickly handle new substrates. There are specific methods and standard operating procedures for achieving quick results. Once calibrated, it is important to be able to maintain the calibration.”

Quality control tells an operator if he or she is okay to print, or if they will need to recalibrate. Many of Ellis’ customers have a routine where they read a control strip prior to printing a job. If the control strip passes they print. If it fails they recalibrate. “Knowing your print specification, a quick calibration method, and quality control procedures are keys to productive high quality print,” said Ellis.

Without the software to make the processes match each other, you are in trouble, said Fret. “Quality control includes assuring that printers are calibrated often to verify whether they are drifting or not,” he said. “The first step to good color management is to use the software correctly and compensate for the machine differences. Then you can train customers to submit files within a certain way. Unfortunately, most software designed for RIPping, even including color management, cannot get two of the same printers on the same material to completely match.”

Tools and technology need to be customized for wide-format printers. “For example, while many designers design to GRACoL a large number of wide-format devices when operating in high-speed mode cannot achieve the gamut of GRACoL,” Ellis said. “They can however achieve G7 Gray, which provides the gray balance, tonality and visual appearance of GRACoL. So these tools need to be able to be customized so that they are less offset-centric, and more tuned in to the capabilities and needs of wide format devices.”

X-Rite Pantone’s solution includes the I1Display Pro for calibrating the display monitor. The solution features hardware and flexible software for both creation and production, and it also provides tools to track display quality and performance.

The PANTONE family of products offers both designers and printers a common language for special colors and brand colors, Cheydleur explained. These are available within design applications, as various physical samples in the Pantone guides, and digitally through products like Pantone Color Manager, which can soft proof colors directly within the application and create project palettes.

“X-Rite’s i1Pro2 combined with the i1iO scanning table is a measurement solution that provides flexibility and automation that can handle a wide variety of substrate thicknesses and finishes in a simple automated fashion,” said Cheydleur.

“i1Publish software provides a full solution for all parts of the ICC color management workflow,” he continued. “This product not only builds standard RGB and CMYK output ICC profiles but also includes device-link profiles and CMYK + N color profiling. Other tools in this suite offer display profiling, scanner profiling, target creation and proofing qualification.”

“GMG ColorServer provides a consistent, color-matched file, to any device,” Fret remarked. “Each output system can be calibrated to the same, known reference standard. With a common reference point, all remote systems can use the same color transformation profiles (GMG’s mx4 profile technology) that define the color match between the target data and output proof. Several printers can be aligned and matched, even if they are using different substrates. With this GMG MX technology, even spot colors can be matched precisely to the printer’s color gamut and remains consistent even if the printer shifts. The base calibration is more elaborate and consistent than ICC linearization. This is what makes the difference.”

GMG’s controls in its color management profiles are designed to result in greater accuracy and assure that printers will match visually to one another, even when considering different variables, like UV or solvent inks, or different substrates. “With the control we have on our profile and gamut compression technology, we can even provide a color match between wide format digital devices and offset presses,” Fret Said. “In addition, GMG can offer the creation of a correct color reference file right from the designer's desk with GMG ColorMaster. This provides a master image file that matches the color gamut of any output device—digital press, traditional press, or monitor.”