QR Code Failure: Ten Reasons Your QR Code Fails–and how you can avoid it
This article is about printing the QR Code–not the management of the data, the compatibility of the symbol with the smartphone OS, whether or not there is web accessibility where the QR Code is displayed, or any of the myriad other post-print factors that can cause the QR Code to fail.
This article discussed QR Code failure due to imaging or printing problems–not data management or web connectivity
The Ten Reasons are listed in no particular order, but module size is probably the most frequent cause of QR Code failure.
Here they are:
- The modules are too small or the density is too high. Reduce the amount of data or enlarge the module (and symbol) size. The modules are the dark and light squares that comprise the symbol. In digital and thermal or thermal transfer printing, each module is usually comprised of at least two pixels and sometimes more.
- The quiet zones are violated. Yes QR Code does have quiet zones—that blank space around the symbol, and so do other 2D symbologies. The quiet zone must be at least two modules wide on all four sides of the symbol—four modules is recommended. It performs a critical function and it must be there.
- QR Code is designed to be square, not rectangular. Square makes it scannable from any angle.
- Reverse printing (a light image in a dark field) is technically allowed by the ISO specification, but not universally supported by the scanning devices (smartphones). Therefore a dark image in a light field is highly recommended.
- Colors are also allowed in the specification, but again, not all colors are supported by all scanning devices (smartphones). What works on one smartphone may not work on another. Black on white is recommended. Yes, the ISO specification can lead you astray.
QR Code failure can occur even when the symbol is compliant to the ISO specification
- The squareness of the QR Code is important. All modules must fall on design grid lines and must not be distorted.
- Fixed pattern damage. While the QR Code does a remarkable job of “forgiving” printing errors and pattern damage, if the fixed pattern damaged, the symbol fails. The fixed pattern is comprised of a finder pattern and a timing pattern, basically those three square patterns in the corners of the QR Code.
- QR Code can allow some printing distortion, but it cannot exceed module size tolerances and the modules must be uniform in both width and height. QR Code, like all 2D or matrix symbols, is sensitive to “rogue” or “widow” modules that are very different in size than the other modules.
QR Code failure occurs when module size is non-uniform
- When printing QR Code on a thermal or thermal transfer printer such as a Zebra® make sure the head temperature is properly adjusted so the pixels blend together to form closed modules—but not so high they encroach on the unprinted areas (clear or light reflectance modules).
- Verify! A very least scan your QR Code with as wide a variety of smartphones as you can get your hands on—not just The press operator’s iPhone®! Use an Android® and a Windows® Mobile phone and a RIM Blackberry® and a Nokia Symbian® and…..and if you possibly can, use a real ISO-compliant verifier. Get a third party test lab to do it for you or if you’re going to use QR Code a lot, by an ISO compliant verifier.