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FLEXO Magazine : August 2009
TECHNOLOGIES & TECHNIQUES of each of them. There are two categories of targets that will need to be on the test form: mechanical and process control. Mechanical targets include: • Impression and slur targets. • Plate exposure guides. • Registration targets. • Solid ink color patches. • Vignettes. • Flat tints. Process control targets include: • Solid ink color patches. • Gray balance patches. • Overprint trap patches. • Tone scales. • Vignettes. • Bar codes. • Line and type elements. The press trial must be conducted under normal operating conditions, so it is representative of future production runs. It should be run at target production run speed with the proper materials and settings as defi ned during the optimization activity. Decisions and adjustments will be made based on this run, so if special things are done that won’t be on future runs, the overall success of these efforts will be jeopardized. ICC CHARACTERIZATION For those that are looking to engage in full-blown ICC-based color management, a form will need to be run that includes a characterization, or profi ling, target. For CMYK profi ling, FIRST 4.0 recommends using the IT8.7/4 target, which contains 1,617 individual CMYK patches of different tone levels and combinations to effectively sample the CMYK color space. Two versions of the target are available: one in an ordered layout; and a second in a randomized, or scrambled, layout (see below). The randomized layout is preferred. If possible, it’s a good idea to include a second target at 90-degrees orientation to the fi rst one. Within a press form, there are spatial uniformity issues from side-to-side and front-to-back, and those differences need to be captured as best as possible. There are also characterization targets and approaches for fi ve-plus color printing/expanded gamut scenarios, like the one described in this hypothetical example. This is often called “n-color profi ling.” This gets a bit trickier and requires a custom target with many more patches to adequately sample the nowlarger number of color combinations with the additional inks. Individual software vendors will have their own solutions for this. With so many patches to measure on a characterization target, the task can seem daunting. But these days there are very fast scanning spectrophotometers that make light work of it, so don’t short-change the sampling by using one sample to measure and build the profi le from. It’s a good idea to take random samples from at least 10 impressions over some reasonable timeframe, once the process is in a steady-state, i.e. no further adjustments are being made to the press or inks. Also, be sure that version of the IT8.7/4 target used on the test form is compatible with the scanning spectrophotometer and supporting software. Depending on the spectrophotometer, there may need to be black blocks, diamonds, or something IT8.7/4-2005 Visual Two versions of the IT8.7/4 characterization target. 34 FLEXO AUGUST 2009 www.flexography.org IT8.7/4-2005