Why Did My Code Fail the Decode Quality Parameter?


The first step in the barcode verification process is to check that the code can be decoded. Since decode is a pass/fail parameter,failing for decode can often feel like a dead end. Traditional verifiers will first test if a barcode can be decoded. If it can't be decoded, that parameter will receive an "F" grade and the verifier will not continue the verification grading process. This leaves users with an “F” grade but no explanation of why. A failure for decode really means that the code was not printed or marked well enough to be decoded by the standard reference decode algorithm.

What is the standard reference decode algorithm?

The standard reference decode algorithm is the algorithm listed in the ISO standard for each symbology type. It is the most simplistic decode algorithm for each symbology. A verifier uses it as the first test to ensure a code can be read. The main purpose of a verifier is to ensure that the majority of barcode readers or barcode scanners can decode the code. One way it does that is by confirming a code can be read without a sophisticated decode algorithm.

Generally, inexpensive barcode reader manufacturers don't spend time and money to develop their own decode algorithms and instead use the standard reference decode algorithm in their scanners. In contrast, more expensive barcode reader brands tend to develop proprietary, powerful decoding algorithms that can handle damaged or defective codes. This is their greatest advantage and a selling point for customers to choose their brand over another. Due to the differences in reader capabilities, testing using the standard reference decode algorithm is a way to ensure that the broadest range of barcode readers can decode your barcodes.


The value of barcode verifiers

While high-powered barcode readers may read your codes easily, if those same codes arrive at a facility that uses more basic readers they may not be read at all. Manufacturers and customers can go back and forth endlessly debating if a no read issue is with the code or the reader, and for that reason many manufacturers turn to verification. Verifiers not only calculate quality grades for barcodes, but they also generate a quality report for every code verified. Those reports are proof that codes can be read and the data can be decoded.  

What to try when your barcode Is failing the decode quality parameter

  • Are you using the correct aperture?
  • Are you using the right ISO standard?
  • Are you using the right lighting angle? 
  • Is the symbology enabled?
  • Is the symbol "mirrored"?
  • Is the camera in focus?
  • Is the code in the center of the FOV?
  • Do the cell sizes look proportionate to one another?
  • Are the edges of the cell crisp?
  • Are all the components of the finder pattern present? 
  • Is the inkjet nozzle blocked?
  • Is the thermal element faulty?
  • Try using less ink or a different kind of ink.
  • Change paper or substrate.
  • Adjust artwork to accommodate known growth. 
  • Clean print head.
  • Reduce thermal or laser heat.

Unlike other barcode verifiers on the market, Cognex barcode verifiers provide quality parameter grading even if a data matrix or QR code fails for the decode quality parameter, giving users an idea of where to start to improve code quality. For more information on barcode verification products at Cognex please visit, http://www.cognex.com/barcode-verifiers

Naomi Brown

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