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FLEXO Magazine : August 2009
TECHNOLOGIES & TECHNIQUES Opportunity Has Knocked: How Will You Get Ready? The Case for Fingerprinting & Characterization By Bill Pope and Michelle Beuscher Art courtesy EskoArtwork. Authors’ Note: This is the second in a series of three articles covering an updated methodology for printing as detailed in the Print Section of FIRST (Flexographic Image Reproduction Specifi cations and Tolerances) 4.0. This CGATS (Committees for Graphic Arts Technology Standards)-endorsed approach is intended to help the printer become more successful through optimization, fi ngerprinting, characterization, process control, and process improvement. To read Part I, see FLEXO July page 18. hen we last checked in with our printing department manager, he was in the throes of trying to determine whether his plant could print a new item with complex graphics, a specialty ink, and an expanded color gamut ink system. Well, through the optimization process described in the July installment of this series, he and his staff were successful in reproducing the desired graphics on their equipment. Now they are ready for the second main part of the methodology: fi ngerprinting and characterization. W WHAT’S THE DIFFERENCE? Fingerprinting and characterization are terms that are often used interchangeably. However, in today’s printing environment, they have very different and distinct meanings. Fingerprinting, as detailed in section 19.2 of FIRST 4.0, is a term that’s been used for many years and has evolved in its meaning and application. In year’s past, the term encompassed so that a look-up table of CMYK versus L*a*b* values can be generated. These values lead to profi les and subsequent color management activities. This entire process is known as characterization. Now, not all printers employ ICC-based color management. Many printers use conventional dot gain compensation curves (cutback curves) that adjust for differences in dot gain between the press and something else: a proof, another printed sample, etc. In this case, fi ngerprinting is the way that information is gathered, so that curves can be generated. G7™, or near-neutral calibration, is another process control technique that might be employed. The G7 process and details are beyond the scope of this article, but the necessary target can be run as part of a fi ngerprinting and/or characterization run as well. PROCESS CONTROL DATA So you know you can print the job… now what? both the mechanical check-out of the printing press, color calibration efforts, and to an extent process control activities. But since the advent of color management, a newer term has come to represent the color calibration part of fi ngerprinting: characterization. In an ICC-based color management world, characterization is the activity of determining how a printing (or proofi ng) system reproduces various combinations and tone levels of CMYK values. A profi ling target (such as an IT8.7/4) is used that contains known CMYK values, then the output of the target is measured with a spectrophotometer, 30 FLEXO AUGUST Fingerprinting allows you to fi nd out and quantify how much a printing process varies, typically for a few key print attributes, such as: solid ink density, dot gain, and others. This information is then used to determine process control limits (upper and lower) so that, during future pressruns, an operator can determine when to take corrective action (and when not to). Additionally, printers can use it to develop customer release specifi cations that are realistic and based on factual data about the process. It is important to view the fi ngerprinting pressrun as “placing the stake in the ground,” meaning that all future pressruns will need to perform similarly to this one. The success of any color calibration efforts rely on this fact. FINGERPRINT AND PRESS TRIAL Now that the process has been optimized for this new job, as was reviewed in last month’s article, it’s time to take the identifi ed materials and settings, put them all back together, and print the fi ngerprint test form. Since this job utilizes a specialty ink and expanded color gamut ink system, the test form will need to include elements that allow for an evaluation 2009 www.flexography.org