What are the ISO Standards for Barcode Verification?
The International Organization for Standardization (ISO) founded in 1947 is a standard-setting body composed of representatives from various national standards organizations. There are hundreds of ISO standards, some of which pertain to barcodes—how the data is put in a barcode, how to decode it, how to determine the size of the barcode, and more. There are only three ISO standards that pertain to barcode quality. These three standards are: ISO 15416 for 1D barcodes, ISO 15415 for 2D label-based barcodes, and ISO/IEC TR 29158, or AIM DPM, for 2D DPM codes.
This 1D barcode ISO standard requires 10 individual scan lines be taken throughout the height of a code and a grade assigned to each scan line. Scan line grades are determined by many different parameters. If a scan line fails minimum reflectance, decode, or minimum edge contrast, the line automatically receives an “F” grade. If all three pass, the software grades symbol contrast, modulation, defects, and decodability parameters. Each are graded on a scaleof A to F. Once every scan line has been graded, the 10 scans are averaged to generate a formal grade for the barcode.
|Minimum Reflectance checks whether the bars are dark enough to meet the required ratio of light that is reflected off of the spaces.
Bars too light
|Edge Contrast measures the difference between adjacent bars and spaces.
Background too dark
|Modulation refers to local variations in contrast.
|Decode checks to see whether the code can be read using the standard reference decode algorithm.
Symbol read? Y/N
|Defects include printing errors, dirt, or markings that affect one single bar or space.
|Decodability grades the accuracy of bar and space widths compared to their ideal size. A barcode with bar width growth or distortion will score a low decodability grade.
Bar Width Growth/Loss or Distortion
This standard grades 2D barcodes against 8 different parameters. The lowest individual grade becomes the overall grade for the code. The grading process begins with a pass/fail test. If the code can be decoded, it passes the first test. If it cannot, it is automatically assigned an “F” grade. Some questions to ask to determine reasons for a no decode include:
- Are you using the right aperture, ISO standard, and lighting angle?
- Is the symbology enabled? Is the camera in focus?
- Is the code in the center of the field of view?
- Do the cell sizes look proportionate to one another?
- Are all the components of the finder pattern present?
After a code is decoded, the following parameters are then graded.
|Symbol Contrast refers to the difference between the darkest and the lightest modules.
|Modulation measures local variations in contrast.
|Fixed Pattern Damage includes errors with the L sides or clock pattern or quiet zone.
|Axial Non-uniformity refers to the uneven scaling of the code.
|Grid Non-uniformity measures the biggest deviation from the grid.
ISO/IEC TR 29158 (AIM DPM)
The quality parameters and grading process for DPM codes are similar to ISO 15415, with a few key differences. The first is the way the global threshold is determined. Global threshold is essentially the dividing line between light and dark cells. Where that line is drawn is very important, since it defines whether a cell is closer to light or dark. To accommodate a variety of background surfaces, AIM DPM calculates global threshold using a more sophisticated algorithm than ISO 15415. Modulation typically improves as a result. AIM DPM also allows the use of 30-, 45-, 90-degree, and dome lighting. This makes verification on parts that are curved, reflective, or marked using dot peen possible.
Some industry committees have also developed application standards that specify which one of these ISO standards to grade against. These industries include medical device, retail, transportation, food service, and the US department of defense.
To learn more about ISO standards and understanding verification results, watch the free on-demand webinar: Understanding Barcode Verification Results.