Recently, color management has become a more important requirement for wide-format signs and displays. The technology is maturing, becoming easier to use, and customers are more aware of the advantages in delivering consistent, accurate color.
There are two key components to wide-format color management. One is accuracy—the ability to replicate colors to a standard or the brand and product colors for cosmetics, fashion, etc. The other key is consistency between printers. One digital printer is comparatively easy to color manage, but multiple printers are a challenge. When using multiple, different digital printers, a flexo press and an offset press, the objective is still consistency between the print processes, but the task becomes insurmountable without the right tools.
Science Replaces Skill
Many companies become experts in image editing in order to output consistent color. This method requires lots of skill. The operator outputs a proof, goes into the ‘adjust image’ function of a photo editing program, and experiments with the image until the output matches the required colors. This interactive, skills-based approach takes an inordinate amount of time and many operators don’t have such skills. Meanwhile, as the operator fixes some colors in the image, something else in the image gets ‘broken’. The whole approach is based on subjective visual assessment and no one ever gets all the ‘stars’ to line up.
Similarly, when printing with different inks (solvent, aqueous, etc.), on different machines, with different RIPs (Colorburst, EFI, Onyx, and others), centralized color management is far better than individual printer-based systems. Ultimately, after the system is up and running, all a printer needs is a spectrophotometer and a measuring process that virtually anyone can follow.
A good centralized color management system also supports using a single, standards-based, color corrected image file that can be safely sent to any printer as a PDF file. This approach also delivers files more ‘forgiving’ to changing conditions. Some color management systems additionally deliver customized separations optimized to the specific printer, ink, and media. This produces more consistency, ink savings, improved drying and better adhesion to the substrate.
Because a centralized color-managed system is based on scientific measurement, it is more reliable. Once installed, anyone can run the system. The incremental costs are for software, an automated spectrophotometer, hardware (an existing computer may be suitable), installation and training.
How it’s Done
The workflow is quite simple:
The first step shuts off color management on all RIPs. The RIPs will receive color-managed files, so they do not need to perform this function. However, the RIP still performs basic printer to media calibration for each media type. This involves printing a tone scale for each color, and making adjustments to optimize the match between requested and printed values. Once calibration is complete, the device is linearized.
The final step is creating a reference or “fingerprint” of the printer or press. A reference chart is printed and ‘read’ with a spectrophotometer. This allows the software to understand both what colors your printer can reproduce as well as how it produces them. Good color management software takes the printer color output, compares it to a preferred standard (GRACoL, for example) and creates a link to correlate the printer’s color capabilities to the color standard. Printers with a broader range of colors (gamut) support a better match to the color standard or original color being matched.
With the right software and training, you can deal with special circumstances. For example, some customers print the backside of polycarbonate then laminated over the print with a white film. The resulting color gamut is considerably smaller than GRACoL. In this type of case it is possible to compress the input color range to fit the available gamut.
Where’s the Proof?
Creating a “proof” from a wide-format production printer is very disruptive. Whatever job is running must be halted, in many circumstances the media has to be replaced, and just one copy is printed as a proof—not a very efficient process. Using a different, smaller printer to show what a job will look like is high desirable. However, when a company cannot achieve accurate, consistent color between different printers, it can’t rely on a “proof” to represent what the final job.
If all of the printers—wide-format and digital printers used for proofs—are linked and managed to the same standard, a proof can be printed on any device (such as a smaller Epson or HP printer), and it will be accurate.
Recently at one of our customer sites there were nine jobs in the print cue. Seven were proofs on a wide-format roll-fed printer, and only two were real production jobs. The customer complained that they had to move media, output a one-up sample, replace the media and do the same thing again. After we tied a standard (GRACoL) to their printers they now use a smaller, less expensive printer. The proof may not be on the same production material, but it still accurately predicts the color of the final job. More importantly, the wide-format press is outputting paying work only, without frequent media changes. With a minimal investment, offline proofing doubled their productivity and the company does not have to buy another production printer, delivering much better utilization of capital equipment.
Fingerprinting the press, building a device link between the press and the standard, and calibrating the RIP on a regular basis, allows a shop to centralize their workflow and achieve consistent color.
Maintaining Your Balance
The final challenge is maintaining a system consistently over time. Because media, inks and even printers change over time, a good system must compensate for this variation. Daily, real-time recalibration provides a solution. Test charts (e.g. IT8 or ECI 2002) and a test page with images (IDEAlliance, for example) provide the data and visual references for evaluation. Just load the media and print the test form. Compare this print to the standard. Visual comparisons are often a sufficient litmus test if conditions haven’t changed dramatically. If small corrections are required, the printer can be recalibrated, while larger changes and weekly numeric performance evaluations would require use of the test chart and measurement with the spectrophotometer. This can be done while the current job is running, producing an updated profile by the time the next job is output.
Running the Gamut of Scientific Color Management
This article has described using a centralized color management system to achieve accurate, consistent color, making color predictable both day to day and between different machines and printing processes. We have also described how to maximum productivity by using a single, standards-based color file as well as maximizing productivity using off-line proofing.
These approaches are best practices possible with scientific, measurement-based color management. This moves the operator from a subjective, skills and color judgment-based approach to one where different operators can output the same file, on different machines, yet achieve the same results. Additionally, optimum color management takes maximum advantage of the available color gamut, achieving the best quality possible with the given printers and their capabilities.
What once required a time-consuming, difficult to teach, and often inconsistent skill has become an efficient, productive process. Both you and your customers will take notice.