​​ISO 15415 2D Code Grading Process: Optimizing Barcode Quality for Business Success​

​​From healthcare to retail and manufacturing, 2D barcode grading plays a key role in ensuring compliance, accuracy, and efficiency across industries. That’s because poor scans can cause delays, reprints, wasted products, and costly chargebacks – issues that barcode grading standards are designed to prevent.

​ISO 15415 barcode grading standard provides guidelines for evaluating barcode labels based on critical factors such as clarity, size, contrast, symbol edge definition, and modulation to guarantee accurate machine reads in production. Making sure your barcodes are up to par streamlines operations, maximizes efficiency, and minimizes errors.  

ISO/IEC 15415 is specific to 2D codes printed on labels. Other common grading systems include ISO/IEC 15416 for 1D barcodes and ISO/IEC 29158 for 2D DPM codes. By interpreting diagnostic data from verification software, users can optimize aperture size or adjust lighting to improve scan quality or make changes to the barcode printing process to improve readability.  

​Understanding the decode and grade process

​​The barcode verification process begins with decoding. During this step, the verification software reads the barcode to extract the encoded information. A successful decode ensures the data can be properly interpreted by a scanner. The software then moves on to grading the barcode’s quality.  

• ​If a code cannot be decoded, the verifier will return an “F” grade and state “NO DECODE.”
• ​If the barcode is successfully decoded, the lowest grade received will become the overall grade for the code. For example, if all other parameters are graded “A” but axial non-uniformity receives a “B,” the grade for that barcode will be a “B”.

​Improving the grade starts with identifying the parameters causing the lower score. A closer inspection of the code will reveal the specific modules responsible for the issue, enabling targeted adjustments. High-quality barcodes exhibit sharp contrast between black and white modules, crisp edges, and precise proportions. Even minor imperfections can create decoding challenges.  

​The data matrix symbology offers a clear example of how barcodes are graded. One of the most common 2D codes, they’re known for their ability to store the highest data density per module, making grading quality essential, especially for small symbols.  

• ​Data matrix codes feature a finder pattern with solid left and bottom sides forming an "L" shape, with horizontal and vertical clocking patterns (or tracks) on opposite sides of the "L".
• ​The clocking pattern specifies the number of modules in the matrix and is used to decode the grid on which the modules are placed.  
• The matrix size determines the symbol size, encoding, and error correction.

​Following the ISO 15415 standards helps keep barcode quality in check, making sure your codes are easy to decode and work seamlessly across systems. 

​A step-by-step guide to reading and grading a 2D code 

1. ​The verifier captures an image.
2. The software blurs the image to remove background noise.
3. A global threshold is calculated to determine cell brightness.
4. The image is converted to black or white based on this threshold.
5. The software identifies the "L" finder pattern and clocking pattern.
6. A reference grid is generated using the clock pattern.
7. Each grid intersection is analyzed for light values, forming a binary sequence.
8. ​Reed-Solomon error correction is applied to the sequence.
9. The correct sequence is converted to ASCII values, revealing the encoded data. 

​Importance of aperture size for 2D code accuracy  

​For 2D codes, aperture refers to the circular sample captured at grid intersections, which the software uses to determine if a cell is dark or light. If the sample circle captures both dark and light cells, it will create a shade of gray. Ideally, the aperture should be centered within a cell that is the correct color. Cells without crisp edges or with other cell colors bleeding into them will likely result in gray. The decode process will convert the image to binary, so anything that was gray will have to be converted into either black or white – leaving room for inaccuracies. An improperly sized aperture, either too large or too small, will lower the grade’s accuracy.  

In the ISO 15415 standard for 2D codes printed on a label, you must set the aperture size in accordance with your application standard. Typically, that standard will set the aperture size to be 80% of the smallest module size allowed within the application. For instance, in a GS1 application, which provides global standards for supply chains, the X-dimensions can range from 10 MIL to 20 MIL with a specified aperture size of 8 MIL. This ensures consistent and accurate scanning, aligning with GS1’s guidelines for barcode quality and performance.