Don’t Overlook Barcode Quality Basics
Many times—more than I can remember—people send us samples of bad barcodes and the problem that has confounded them turns out to be something very basic—and obvious to us at least. So this article will focus on some of those most basic attributes of a barcode, whether it be a 1D UPC symbol or a 2D QR or Data Matrix code.
One of the most prevalent mistakes is just making the barcode too small when there is plenty of real estate for a larger symbol. Regardless of whether it is a 1D barcode or a 2D symbol, the scanner sees them the same way: as reflective differences between the symbol and the substrate. Whether the scanner is a laser, a CCD or a digital camera, it has a minimum aperture that must be smaller than the X dimension in order to detect the reflective differences accurately. The X dimension of a 1D barcode is the narrow bar; in a 2D symbol it is the element or square building block. If the X dimension is the same size or smaller than the scanner’s aperture, it will be difficult if not impossible for the scanner to decode the symbol, and more likely it will mis-decode it.
This would suggest that the bigger the barcode the better, and there are certain benefits to making the 1D barcode as big as possible, within some common sense considerations. The pro argument is that a larger X dimension translates to more allowable margin of bar width error, both plus and minus of nominal. The con argument is that the larger barcode is often truncated to fit the available space. This makes the barcode scanning less omni-directional and more uni-directional: the barcode must be radially oriented to the scanner for it get a full pass through all the bars. Ignoring the aspect ratio of symbol width to height can easily wipe away any advantages of a larger barcode, and truncation of a 1D barcode is always discouraged.
Another very common basic mistake is to leave inadequate quiet zones or to encroach upon them with graphics, corners, folds or other reflectance variations. Many people seem to believe that 2D symbols do not need quiet zones—to their peril. A full surround quiet zone of at least 1 element width is required on all four sides of a Data Matrix Code. A quiet zone of at least 3 element widths is required on all four sides of a QR Code. There is an unwritten exception that QR Codes that are meant for scanning with a smart phone are allowed a 1 element side quiet zone. This is not specifically allowed in the ISO15415 specification but it has become a common, if ill-advised practice.
Not infrequently we see samples where either the barcode itself or the background has a pattern. Often this is the result of screening. Recently we received samples of barcodes that were rotogravure printed, and had a characteristic heavy waffle pattern which confused the scanner and caused the symbol to fail the decodability and defects ISO parameters.