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FLEXO Magazine : November 2008
TECHNOLOGIES & TECHNIQUES FIGURE 1. Deviations from the absolute value for seven devices of the same brand. How Accurate Are Your Spectrophotometers? VIGC Study Reveals Instrument Consistency Can be a Nightmare Q uality assessment in the graphic arts industry depends mostly on the use of spectrophotometers. Printers use them to check their production processes. Customers use them to evaluate the print job for acceptance. Quality demands are getting stricter every year; the spectrophotometer decides whether a job is accepted or not. But when VIGC, the Flemish Innovation Center for Graphic Communications, did a study on the accuracy of those devices, they found deviations up to a delta E of nearly 4! “Color quality is the biggest challenge in the printing industry,” said Eddy Hagen, managing director and trend watcher of VIGC. “Graphic arts companies will try everything to get the colors as desired by the customer. Those customers will use it as the most important criterion to accept, or reject, a print job. This makes the devices to measure that color quality quite essential. So you would expect that the quality of those devices is top class. But it isn’t.” After having experienced some issues with different devices, VIGC started its first tests to compare multiple devices in the summer of 2007. “We saw some deviations between the different spectrophotometers that we use ourselves,” explained Fons Put, senior consultant with VIGC. “So we set up a procedure to check 28 F LEXO and compare different devices. As the reference we used the GretagMacBeth NetProfiler test chart. This is a test chart which comes with a certificate stating the L*a*b*-values of the different patches, measured with three spectrophotometers under ideal conditions. The certificate is valid for 12 months only, so it needs to be renewed every year. And then we measured the 13 patches on the test chart with different spectrophotometers. For two patches we also measured the repeatability of the devices, mean- ing 10 measurements in a row.” DEVIATIONS DETAILED Over the past year, VIGC has tested over 20 different devices. Most were currently in use by printing companies working in cooperation with VIGC. This is in contrast with similar, smaller studies that have been done in the past. Other studies used de- vices acquired directly from the vendors. VIGC tested devices that are out in the field, that are used on a daily basis by companies in the industry. This gives them a very interesting overview of the capabilities of spectrophotometers in daily life. Those capabilities are not what people think. When a customer demands a maximum delta E of 2, which is often the case for NOVEMB E R 20 0 8 www. f l e x o g r a p h y. o r g