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FLEXO Magazine : September 2010
FFTA’s 2010 FAll ConFerenCe & TAbleTop exhibiTion Looking to drive efficiencies, improve customer satisfaction and gain a high return of profitability? november 8-10 Hyatt Regency | Louisville, KY Chair: Cayleigh NiChols, Prairie state grouP Co-Chair: riChard BlaCk, all PriNtiNg resourCes, iNC. www.flexography.org A rate idea: The future of flexo & process improvement FallCon10_FLEXOBrochure.indd 1 8/31/10 1:42 PM Technologies & Techniques Bar Width Growth. Like traditional UPC, bar width growth, or better put, the prevention of it, is critical to successful printing of these new types of bar codes. However, perhaps surprisingly, these bar codes are actually more immune to bar width growth than UPCs. This is because one of the most difficult parts of the grading of a UPC symbol, called decod- ability, is severely affected by bar width growth. On the other hand, the design of GS1-DataBar is more tolerant of bar width growth (assuming it is uniform). However, there is a threat of narrow spaces becoming so small that it is hard for the scan- ner to optically resolve it. This problem would be reported as modulation when the print quality is measured. The matrix codes do not even have a parameter called decodability but they do have modulation. Line Width. In principle, the line width (also known as the X dimension) of a UPC code can be any size. In practice, it is limited by standard specifications to a minimum size of 0.010in. (0.25mm). The standard size for a UPC keeps this dimension at 0.013in. and allows larger sizes if space permits. The minimum size allowed for GS1-DataBar is 0.008in. The largest size allowed is .016in. But, remember the driving force behind the use of these types of bar codes is small size. The matrix symbols are inherently smaller than the multi- row symbols anyway, so there is rarely a need for such small feature sizes to be used when printing them. Pitfalls to avoid The major pitfall to avoid is in prepress. Aside from even having software with which to generate the graphics for these new types of bar codes, graphic designers need to know enough about the symbologies to be effective at driving the software. There are seven versions of GS1 DataBar (we have seen only two of them above) and several possible sizes and shapes (essentially square or rectangular for Data Matrix). Aside from knowing the type of symbol to create, much like with regular bar codes, prepress providers must watch out for pixel round off. It is essential to create your bar code with the resolution of your output device—your photo plotter, for example—in mind. This becomes even more important with today ’s direct-to-plate technology. The resolution of those devices makes the pixel round off more significant. To avoid this problem, set the X dimension to an integer multiple of the dot-pitch of the output raster, and then do not scale the image in your graphics software. Also, you should not distort the image of the bar code (to compensate for wrap- ping around a cylinder), even though it would seem that doing so would be important for a two-dimensional symbology. I have found that the amount of distortion is well handled by the bar code decoding process itself, whereas the pixel round-off that can occur is less forgiving. Print Quality MeasureMent Mutli-row symbols are measured using a similar process to UPC. However, each row is analyzed as a separate bar code and then the results are combined. Whereas a single row UPC is measured on 10 scans which are averaged, each row of a multi-row bar code is measured 10 times, and these scans are averaged. That means that a multi-row bar code could have 20, 30 or more scans used to compute the overall grade. A Data Matrix symbol is measured in a completely different way. An image of the two dimensional code is captured by a camera, using very controlled lighting, to obtain a high resolu- tion and calibrated image. Then the image is processed to decode the symbol and determine the coordinates of the centers of each cell in the code. Then the color of each cell is measured and used to derive the overall grade. The grade consists of measurements of the border pattern which is the key to locating the symbol and the grid of cells. Also, mea- surements are taken of each cell in the interior of the symbol, which encodes the data bits. so Much More to say This article is a very brief introduction to a very broad topic. There is more detail about these new bar codes than can fit in a short article. Indeed, there are hundreds of pages of technical specifications published by ISO on the various symbologies and print quality methods employed. Under normal circumstances, your software, scanners and verifiers should hide all that technical detail from you. Hopefully, this article was a good introduction to the world of new bar code symbologies. n ABOUT THE AUTHOR: Glenn Spitz is president of Webscan Inc. a manufacturer of bar code verifiers, a member of bar code standards committees and presenter of a bar code semi- nar entitled Demystifying Bar Codes. figure 4. A rectangular version of Data Matrix. 52 FLeXO septeMber 2010 www.flexography.org FLX_Sept2010_mech.indd 52 9/1/10 9:45 AM