G7 Qualification Helps Digital and Offset Printers Achieve Color Consistency

By Erik Cagle

ISO 12647 vs. G7

There is a lot of confusion in the market about ISO 12647 and G7. Are they competing standards? Are they regional standards? Are they standards at all? Let me explain the relationship and some history for context.

ISO 12647 is a series of international printing standards, which describe “Process Control for Production of Halftone Color Separations, Proofs and Production Print.” There are currently seven standards covering parameters and measurements, offset, coldset, publication gravure, screen printing, flexo and proofing from digital data. There is an eighth standard going through the development process that covers print process from digital data.

These standards describe in great detail the proper methods and materials to be used, and the ways to monitor and measure the various printing processes. The one thing they don’t implicitly do is specify a resultant color characterization set. This is due to the variability inherent in the process itself—different papers, machine characteristics, etc.

As the globalization of business communication increases, so does the need to do work in a distributed way through the use of multiple printing processes across many countries, while achieving the same visual results. This increases the need for standard color characterization (color target definition) sets. Since there is already a set of printing standards, one would think that there should be an easy way to develop an agreed upon set of color characterizations by process and substrate.

However, since there is also a lot of technology available, there are actually many ways to not only develop color characterizations, but also many ways to achieve the same color characteristics. Currently there are a number of regionally developed color characterization sets available. These include GRACoL and SWOP, developed in the United States; a series of PSO sets developed in Germany; and many others around the globe.

The original ISO 12647 standards specify “tone value curves” as a way to control print. However since the original standards were developed, two more ways have been introduced to control print—color profiles and near neutral scales. To accommodate these additional methods, there was an ISO Technical Standard developed, ISO-TS 10128. It describes “methods of adjustment of the color reproduction printing system to match a set of characterization data.”

As a result of preference, the GRACoL and SWOP sets were created using “near neutral curves” (G7), while the PSO sets were created using tone value curves. Ultimately, the end result is an almost identical appearance when the comparable GRACoL and PSO sets are judged.

The G7 process, which was developed by IdeAlliance, is a method for producing near neutral curve sets. In essence, it is used as a calibration method that can be used in a print production process. While it is not an ISO standard in itself, G7 is method that conforms to ISO-TS 10128.

So the short answer is that there are many ways to get you to the same color place depending on your process preferences, and in the end, whichever option you choose relative to ISO-TS 10128 should allow you to achieve successful print production if you follow the process laid out in ISO 12647.

—Dave Zwang, principal consultant of Zwang & Co., a firm specializing in process analysis, and strategic development of firms in the fields of electronic publishing, design, prepress, and printing.

Just mention the term G7 certification and you can hear a collective cringe coming from the folks at IDEAlliance, the printing industry association unofficially tasked with governing printing methodologies, specifications and standards. G7 is a “qualification” program; the law sees a difference between the terms. IDEAlliance is working on a certification program.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 All Next »

1 Comment

View Comments

Erik Cagle Author's page

G7 Qualification : The Art of Maintaining Color