Modulation and Decodability

 In 301

Modulation and decodability are easy to understand if you are familiar with the Scan Reflectance Profile or SRP. This is discussed in previous articles in this blog. The Scan Reflectance Profile is a powerful diagnostic tool for gauging what is going on with a barcode symbol.

The SRP makes it easier to talk about reflectivity attributes of the ANSI grading system.

Modulation grades well when the Scan Reflectance Profile is symmetrical

Modulation is beautifully illustrated graphically with the SRP. The north-to-south symmetry of the SRP is Modulation.

 The modulation graph should be about six increments tall. The equatorial line is talled the global threshold or GT and each bar and space must penetrate the GT for the scanner to count the elements and determine the symbology and decode.

 

Modulation is downgraded when the SRP is asymmetrical. When modulation problems become extreme, some elements (bars or spaces) will fail to peneetrate the GT–this is almost occuring on the SRP shown belowm

 

 

Modulation is downgraded most often due to excessive gain or spread of the barcode image. Several factors contribute to excessive gain or spread, including ink thickness or thinness, characteristics of the substrate and roller pressure. Modulation can also be impacted by a highly shiny or glossy ink or substrate.

 Modulation probems are usually due to press gain

This as a good time to talk about Defects. This can also cause modulation problems. Now that you’re familiar with the SRP you can easily see how Defects throw a wrench into the works of a scanner.

 

 

SRP for Bad Defects

 

Defects in a barcode are either voids in the bars or artifacts in the spaces. They could be caused by dirt or oils on the substrate that cause the inknot to adhere or particulate in the printing environment. When the scanner does the bar-space count at the GT, a void in a wide bar could be counted as two narrow bars; an artifact in a space could be counted as an extra bar. This can contribute to a modulation problem if a defect is detected but doesn’t intersect with the GT. Either way it throws the count off, making it impossible for the scanner to determine what the symbol is.

Moduation is tested and graded based on the same formula for every symbology. Decodability is calculated differently for each symbology. UPC uses a different formula than Code 128. In general, decodability is a measurement of the accuracy of the printed symbol as compared to its engineering specification—in other words, to its perfect form.

Decodability grades the symbol according to how much of the engineering tolerance (margin of error) is left for the scanner, after all the design, pre-press and on-press and post production activity (such as product packaging, shrink wrapping, etc.

Modulation measures reflectance; Decodability measures tolerance available for the scanner

Whereas modulation is a matter of reflectance, decodabiity can be a much more difficult fo figure out. Design mistakes can be a subtle and stealthy cause of decodability problems. A barcode that is designed at a resolution that is incompatible with the resolution of the output device (printer) it can cause bars and spaces locations and widths to be interpolated—moved around or re-sized. You can imagine how this messes up the engineering of the barcode.

 

Decodability Macrophoto Image

 

Here you see a portion of a printed barcode with decodability problems compared to a precision photo image of the same barcode with no decodability issues. Notice how the printer has attempted to compensate for a resolution discrepancy by adjusting the width of some bars and by moving the location of some bars.

ANSI-compliant verification and grading of barcodes—as comprehensive as it is—still does not cover all the bases when it comes to controlling barcode-related risk. There are other factors that can bite you. For example, what could possibly go wrong when a barcode receives a consistent ANSI A grade—but still fails at point-of-sale?

We will discuss some of these in future postings.

Please comment, ask questions and add stories of your own experiences.

John helps companies resolve current barcode problems and avoid future barcode problems to stabilize and secure their supply chain and strengthen their trading partner relationships.

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Showing 10 comments
  • Barcodes
    Reply

    Thanks for this clear explanation. We had a customer asking about this (he had low modulation result for his barcode) and it was helpful to be able to point him to your blog.
    One thing – I couldn’t find the post on SRP you mention in this article – can you point me to it or link to it from this post? Thanks

    • John Nachtrieb
      Reply

      You are correct–I have not posted anything specifically about the SRP–I will do so very soon. There is a mention of SRP in the posting aboaut colors–the post can be found here: http://www.barcode-test.com/barcode-tutorial/barcode-colors-%E2%80%93-what-works-and-what-doesn%E2%80%99t/. My apologies for inadvertently misleading you. The SRP is a very interesting phenomenon–visually very appealing but of limited value as a diagnostic tool. Many verifier manufacturers include it in the verification report because it suggests something of great scientific authority and profound importance. It isn’t meaningless but it is not the best tool for figuring out what’s going on with a problematic barcode. Thanks for your comments.

      • John Nachtrieb
        Reply

        Take a look at today’s new posting on the Scan Reflectance Profile. The SRP is a most interesting symbol reflectance reporting tool. Does this help you?

  • Barcodes
    Reply

    Thanks for this clear explanation. We had a customer asking about this (he had low modulation result for his barcode) and it was helpful to be able to point him to your blog.
    One thing – I couldn’t find the post on SRP you mention in this article – can you point me to it or link to it from this post? Thanks

    • John Nachtrieb
      Reply

      You are correct–I have not posted anything specifically about the SRP–I will do so very soon. There is a mention of SRP in the posting aboaut colors–the post can be found here: http://www.barcode-test.com/barcode-tutorial/barcode-colors-%E2%80%93-what-works-and-what-doesn%E2%80%99t/. My apologies for inadvertently misleading you. The SRP is a very interesting phenomenon–visually very appealing but of limited value as a diagnostic tool. Many verifier manufacturers include it in the verification report because it suggests something of great scientific authority and profound importance. It isn’t meaningless but it is not the best tool for figuring out what’s going on with a problematic barcode. Thanks for your comments.

      • John Nachtrieb
        Reply

        Take a look at today’s new posting on the Scan Reflectance Profile. The SRP is a most interesting symbol reflectance reporting tool. Does this help you?

  • China
    Reply

    If there is a reading of 62% and another at 69% decodability of a UPC label, what is the industry standard? We have these UPC’s that don’t scan with two different scanners and we do not know why it is not scanning. We got the results from the Label person about the decodability but passed with a “A” rating.

    • John Nachtrieb
      Reply

      The Decodability threshold for an ANSI A grade is 62% so your symbols are apparently right at the threshold. I don’t understand what you are asking regarding the industry standard. Most brand owners accept an ANSI C grade as the minimum acceptable, but the final grade is comprised of other parameters too, not just Decodability. I cannot comment on why one scanner is decoding the symbol and another is not without seeing the full verification report. Please send it and I will examine it and comment. Send to lab@barcode-test.com. Thank you.

  • China
    Reply

    If there is a reading of 62% and another at 69% decodability of a UPC label, what is the industry standard? We have these UPC’s that don’t scan with two different scanners and we do not know why it is not scanning. We got the results from the Label person about the decodability but passed with a “A” rating.

    • John Nachtrieb
      Reply

      The Decodability threshold for an ANSI A grade is 62% so your symbols are apparently right at the threshold. I don’t understand what you are asking regarding the industry standard. Most brand owners accept an ANSI C grade as the minimum acceptable, but the final grade is comprised of other parameters too, not just Decodability. I cannot comment on why one scanner is decoding the symbol and another is not without seeing the full verification report. Please send it and I will examine it and comment. Send to lab@barcode-test.com. Thank you.

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