Expanded Gamut Study Evaluates Spot Color Reproduction in Multicolor Printing

Ink Build

In EG printing, there are many different colorant combinations that can make the same color. There is considerable redundancy in creating an ink build—Think of the UCR/GCR black channel, but now with seven colors! EG printing allows for many different combinations and permutations. Some ink builds can be more stable on press. The OGV primaries can be nearer to the color to be reproduced, so a small drift of ink density on press is less noticeable, leading to more accurate printing and easier process control. Some ink builds can dispense with very low ink values, which may be difficult to hold in flexo printing.

The separations and ink recipe of each system were evaluated for example, for an orange color:

  • PANTONE 2433 C. Alwan, CGS ORIS and ColorLogic create a very similar build, with emphasis on orange and yellow for what is an orange spot color
  • Kodak and GMG Color created a CMYK-only build with no EG colorants
  • Heidelberg violated a golden rule of limiting the build to three channels, and used five channels, but with the least TAC

It is interesting to note that all of these builds were accurate to CIE Delta E 2000 < 1, so all of these builds essentially created the same color when printed.

Figure 3: In a sophisticated test, the whole PANTONE+ Solid Coated library was placed into a three-page PDF and analyzed in PACKZ. PACKZ (pronounced “packs”) is a native PDF editor for packaging production.

Issues Illustrated

Adobe and Pantone provide everyday commercial tools for EG jobs and workflows. The study identified some issues with products from these companies that could confuse a less-skilled user in a busy press shop.

When using a file with a large number of spot channels in Acrobat Pro, in Tools -> Print Production -> Output Preview, only the first 30 or so spot color names are displayed. The remaining spot channels in the file are not discarded, but are shown to the user as CMYK equivalents, creating an extremely confusing situation. This was brought to Adobe’s attention and the company said, “Expect it to be resolved in an upcoming version of Acrobat.” In Photoshop, there are a number of well-known issues including color accurate display of spot colors and spot color tints.

The Pantone swatch books and digital libraries have long been a source of confusion, with different versions, variation in swatch books and different values being used. This confusion continues to plague us in the current study. A $99 user application called the Pantone Color Manager was used in this study to export a digital library as a CxF file. But that CxF file has a different number of entries and different L*a*b* values, compared to the digital library provided directly to vendors under their license agreement.

Figure 4: A practical tolerance in package printing is 2 Delta E, so the percentage of spot colors that are within this limit is tabulated for each system. The reader can clearly see EG printing for spot color reproduction works, and works very well.

The primary function of the Color Manager is for a user to keep the digital libraries up to date, but the program itself has a bug where a progress indicator appears to never complete its own update, leaving the user to wonder if an update has been completed or not.

In this research, the issues with Adobe and Pantone products had to be discovered and workarounds found. In a commercial environment, in a busy press shop with less skilled users, these issues are likely to pose a bigger challenge. We also note that none of these products are freeware or shareware or public domain—they are all paid-for applications. If these high-profile products were the Boeing 737, they would be grounded.

Building Confidence in Expanded Gamut

A study of this nature is most applicable to an early technology area that has affordable systems, delivered and implemented at customer sites, yet the market remains nervous. The lack of wider adoption means many printers are not availing themselves of the benefits of the technology. This independent study with practical, real-world examples provides a benchmark to the industry, feedback to the vendors and data that guides printers and would-be adopters of the new technology.

The findings show that EG printing can replace cumbersome conventional spot color workflows and create considerable savings and advantages, especially for label and packaging printers. The conclusion of the study is that EG solutions for spot color printing are ready, here and now.

Advisor to the study, Marc Levine, director, enterprise print quality for Schawk Inc, notes that, “Many printers want to move to EG, but face obstacles related to technology unknowns. With this study, we seek to remove some of those unknowns so that printers who wish to move ahead with EG are more empowered to do so.”

Acknowledgements: A special thanks to David Palmieri of CGS ORIS, whose X GAMUT software was used to create and measure the spot color test form. HP’s Paul McCarthy and Doug Blake provided generous access to the Indigo 7900 digital press, and Epson America provided roll media for use on the Epson P9000 printer. We salute the bravery of the vendors that entered this study and allowed their data to be made public and openly discussed and debated. Advisors to the study were Roger Breton, Marc Levine, Bill Pope and John Seymour.

About the Author

headshot Abhay Sharma
Dr. Abhay Sharma is a professor at Ryerson University in Toronto, and author of a new book, Understanding Color Management, Second Edition. Download the free, 50-page Expanded Gamut Study and contact Abhay for more information.