Dependent Aims
It’s well known that when using 7-color EG, it is not possible to match the entire Pantone book. It’s less well known that even when using spot colors mixed in an inkroom, it’s not possible to match the entire Pantone book. The effects of substrate color and limitations on ink film thickness limit the ability of both spot color printing and EG printing to reproduce the entire Pantone book. And while it’s true that, in most cases, you can match more Pantone spot colors using custom-mixed inks, EG offers an advantage that spot color workflows do not—color predictability. Based only on the 7-color press characterization, we can predict the closest achievable color for all 1,898 colors in the Pantone+ Solid Coated Ink book in a matter of seconds.
The ability to know ahead of time whether a color is achievable or not—and how close of a color match can be achieved—is invaluable to both the brand and the converter. Figure 6 shows the color build book of the 18 spot colors in the three items of the “FIRST in Motion” job. Most of these saturated colors from the Pantone+ Solid Coated Ink book are slightly out of the gamut of the wide web flexo press on which the production job was printed. In fact, seven of the 18 colors are out of gamut by more than 2.0 Delta E 2000. Even if the production run printed exactly like the press characterization run, Pantone 185 would be off by 1.9 Delta E 2000. Add reasonable press variation of 1.5 Delta E 2000 and you could expect this color to be off by about 3.5 Delta E when compared to the “master standard.”
Take Pantone 185 as an example. Aiming to match the “master standard” of Pantone 185 from the Pantone+ Solid Coated Ink book is an irrational aim. We know ahead of time (as soon as we have created the press profile) that we cannot match it to less than 1.9 Delta E. With the power of color science, however, we can derive the closest “in-gamut” color to Pantone 185. This “closest in-gamut” color is called the “dependent aim.” Theoretically, we can match this color at 0.0 Delta E 2000. Add reasonable press variation of 1.5 Delta E 2000 and you could expect this color to be off by about 1.5 Delta E. Referring to Figure 7, aiming at L48.4 a72.6 b45.7 (the dependent aim) instead of L49.8 a77.5 b49.2 (the master standard) enables reasonable expectations to be established from the beginning of the process.
Comparing the spot colors in this job that were reproduced with EG color builds to the depended aims, we see a very accurate color match. The color difference ranged from a Delta E 2000 of 0.46 to a Delta E 2000 of 1.63 with an average Delta E 2000 of 1.10.
The Synchronized Profile
It’s often said your production run must match your press characterization run as closely as possible. A more accurate statement would be your production run must match your press profile as closely as possible. This implies there is a difference between the press characterization data and the profile data. In the case that your press profile has been synchronized to your print specification (e.g. G7 for CMYK; SCTV for OGV), there is a difference.
A synchronized profile is one in which curves have been applied to the profile to obtain as close of a match as possible to your print specification. In the absence of the ability to synchronize a profile, it was a requirement that the press characterization run be a near-perfect match—solids and tints—to your print specification. As it is extremely difficult to get the tints to match the print specification, converters were forced to conduct multiple press characterization runs with curve adjustments in an attempt to hit the specification. This process was expensive, time consuming and, given that a press is a moving target, of limited accuracy.
Instead of conducting multiple press characterization runs, it’s possible to conduct a “Virtual Press Run.” This process simulates the results that would be achieved if a second “real” press characterization were run with new curves applied to match the tints to your specification as closely as possible. It is effectively done at no cost and is more accurate than performing a second “real” press characterization run.
The result of a “Virtual Press Run” is a “Synchronized Press Profile.” It is a profile that has been “synchronized” to your print specification. It should be noted that the “Virtual Press Run” or “synchronization” process affects only the tints and not the solids. The process works best when your curve software can access information from your profile software. On an ongoing basis, the goal of the proof and production pressrun is to match the synchronized profile as closely as possible.
Note: The term “Virtual Press Run” is from Chromix and the term “Synchronized Press Profile” is from Esko.
Proofing
The dependent aim concept is based on the acceptance of digital values as a way to communicate color. While digital values are certainly increasing in acceptance, the ability to actually “see” the color as it will appear when printed and in the context of the actual design will always be highly valued. One of the biggest advantages of EG printing is proof-to-press match. When properly color managed, today’s inkjet proofers offer color match accuracy for EG that far exceeds the color match accuracy for spot colors.
Visual Comparison: Proof vs Press Sheet
For the purposes of this article, we’re going to break a basic principle of proof-to-press color assessment. While such judgments should only be made in person while in a viewing booth under standard viewing conditions, we wanted to share a visual example of the proof-to-press match quality achieved using FIRST specifications on this project. Figure 8 is a picture of the proof (left) and the press sheet (right) placed side by side in a viewing booth. Even with the camera metamerism and the glare of the film print samples compared to the paper proof, the visual match between proof and press sheet is evident.
In Conclusion
This article wraps up the series of articles chronicling the “FIRST in Motion” project. The general consensus that the EG work looked better than the spot color work is a side conclusion that was not the true purpose of the project. The main conclusion is that printing to the numbers works. And if you are going to print to the numbers, using FIRST makes the process far easier and less ambiguous.
About the Author: Mark Samworth began his career with DuPont, where he held numerous positions in the areas of flexographic plates and electronic imaging. Mark joined Esko in 1997 and is currently focused on consulting in screening, calibration, G7, color management and expanded gamut. He holds 11 patents in digital imaging, including FlexoCal, Hybrid Screening, Plate Cell Patterning, Concentric Screening, Equinox expanded gamut technology and PressSync. He has authored numerous articles in the industry’s major trade publications and presented many papers at the industry’s major trade forums. In May of 2011, Mark was inducted as the 49th member of the FTA Hall of Fame. Mark received his bachelor of science from RIT and his MBA from the University of Delaware. He lives in Wilmington, DE.