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FLEXO Magazine : October 2013
The goal in this first process is to build a dot gain charac- teristic that will match General Requirements for Applica- tions in Commercial Offset Lithography (GRACoL) Standards (ranging from 18 percent to 25 percent dot gain). This process will be better defined after creating a 4-color fingerprint. buiLding in 4-coLor Once a curve has been built, the dot percentages should translate across all channels. We then print a 4-color finger- print to create International Color Consortium (ICC) Profiles for proofing and monitor calibration. In this process, the goal is to get the printer to G7 standards using CMY-to-black con- version patches. A typical target is a Color IT8 7.4 . We then measure the 4-color fingerprint to verify dot gain, wet traps and overprint for the purpose of building a profile for that specific press, substrate, ink and so on. ICC profiles are then built to define the achievable color gamut of the press with a 4-color process. The next step is to correlate the relationship between the input data and the printed result and develop a proof that can match the press consistently. What is most important to realize—and this is where most ICC Profiling falls short—is that just because a proofing target is within G7 (or any other proofing standard) specification, the proof may not be up to standards visually. Even if all colors are within a Delta E of +/-2 , seeing the visual deficiencies and adjusting the proof to fix those deficiencies requires specific levels of expertise. This is why including common graphics and images is important in a 4-color fingerprint file: To allow calibration of proofs for a visual match in addition to a specifi- cation match. There are many challenges in this step. For instance, building a profile from a paper proof to a paper print is much easier than understanding how proofing on clear material overlaid on the printer’s substrate (like foil) will translate to the printed piece. This is where experience comes into play. Building a proof, when proofing onto the printed substrate isn’t always an option, is tricky. The knowledge of an experi- enced specialist is essential to create a match. eXPAnded gAMut FingerPrinting As more and more printers start to print using a standard- ized 7-color process, fingerprinting best practices remain as important as ever. Continuity and consistent horizontal density across the press sheet and from corner to corner is key for consistent fingerprinting with expanded gamut. This is important because in a 7-color process, inconsistent densities magnify just as much, or more than, traditional CMYK. The evaluation process is similar in expanded gamut, but due to the complexity, specialized software is required to build the achievable color space and develop proofing processes to match the press. It is important when switching to expanded gamut to choose auxiliary colors that best match the color gamut of what is typically printed: Choose from green, orange, red, violet and blue to achieve the widest color gamut. Also, develop gray component replacement standards on prepress files to minimize ink density on the printed piece. Files that contain large Pantone solids and vector art are gray 72 FLeXo OCTOBER 2013 www.flexography.org C M Y CM MY CY CMY K Roland_LEC_Order_Flexo.pdf 1 7/3/13 12:02 AM Continuity and consistent density horizontally across the press sheet and from corner to corner is the key for consistent fingerprinting with expanded gamut.