Since barcode quality grading is becoming a hot topic - and believe me it is - here are eight things to remember when the topic turns to 1D or 2D code verification.
- Verification or Validation?
The Two V's mean very different things. In conversation, I have heard the terms "Verification" and " Validation" used interchangeably. In the world of auto ID and labeling, however, they mean very different things. Verification means grading a 1D or 2D code against a specific standard with the intention of predicting how easy it will be to read - or whether it will read at all. Validation means checking the format of the content of the code to see if the agreed formatting standard has been applied. Put simply Verification is Penmanship while Validation is Grammar and Content.
The tips in this blog address verification (can it be read?), which is sometimes called grading.
- Keeping up with Standards: ANSI, ISO, and AIM.
The thing to remember is that there is a single standard for 1D code grading - ISO 15416. It used to be called ANSI grading and use letter grades (A to F). Now ISO 15416 specifies that 1D barcode quality should be reported using number grades (4.0 to 0.0). Of course everybody still uses letter grades - old habits die hard. But in a true verification report for ISO 15416, numbers will always accompany letter grades.
There are two possible standards for 2D code (i.e. Data Matrix) grading - ISO 15415 and AIM DPM-2006-1. By and large, ISO 15415 is applicable to printed codes while AIM DPM-2006-1 is aimed (sorry) at direct part mark (DPM) codes. Both report numerical grades.
- Making an Image
The ISO and AIM standards exist to provide reliable and repeatable means of predicting the ability of a reader to successfully decode a code at the point of use. The standards therefore have a lot to say about how a verifier captures an image of a code. The basic rule is " light it like it will be lit when it is being read" - but if you do not know how that will be, the standards offer their own guidelines, strongly recommending certain lighting and imaging geometries and favoring red light.
Image resolution is also important. There must be at least eight pixels on the narrow bar of a 1D code or in each cell of a 2D Data Matrix symbol.
- Calibration and Reflectance
Barcode verification systems work in the world of reflectance, which is the measurement of how much light that hits a surface bounces off again. Black things have low reflectance, while white things have high (but never 100%) reflectance. Machine vision systems measure grayscale which means pixel values between 0 and 255, where 255 is as white as the camera can cope with and 0 is black. A verification system must be able to transform grayscale values into reflectance values (somewhere between the 0% for pure black and 100% for pure white) and this is where Reflectance Calibration comes in.
In Microscan's AutoVISION „¢ software, Reflectance Calibration is achieved by imaging a calibration card on which the black areas and the white areas of a target are of a known reflectance. The typical values are 4% (black) and 82% (looks like white to me). Once calibration is performed, the system knows how to transform grayscale levels into reflectance values to use in the grading calculation.
- Making a Report
The amount of information required to prove code quality depends on the problem being solved. An inline system may only need to produce a go/no-go signal that indicates whether the minimum grade was achieved. An offline system may need to be able to save a nice, comprehensive report that includes the fine details about how a code measured up against specific grading parameters along with an image of the code. Starting with the recently-released software version 2.1.1, AutoVISION has the capability to save PDF or plain text files of detailed Verification Reports for 1D and 2D grading. This is in addition to AutoVISION's on-screen reporting capability and built-in I/O capability.
Explore AutoVISION Verification Reports in the latest AutoVISION software.
- Free-Form Verification
Each barcode verification standard specifies eight or nine different individual measurements results against which a code is graded. The overall grade is basically the lowest grade on these individual measurements. Grading against the full set of these results is required for " hand on the heart," true verification to published ISO or AIM standards, but may not be right for grading that is aimed at monitoring a particular process, such as printer performance.
In the latter case, a subset of the standard ISO/AIM measurements might be the best indicators of the health of a printer or marking system. For example, in the case of a dot peen system for direct part marking (DPM), measurements for Modulation and Grid Uniformity may be the best indication of whether the needle that does the printing (actually it is stamping) is in good shape. In AutoVISION and Visionscape ® machine vision software, you can selectively switch off ISO/AIM measurements or adjust them to allow your code's grade to be based on only the measurements of interest.
To learn more about ISO/AIM grading parameters for 1D/2D codes, check out Microscan's white paper: Understanding Machine Vision Verification of 1D and 2D Barcodes.
- Ready-to-Go Kits
As with any other machine vision-based system, a verification system consists of a camera, one or more lights, and the hardware to keep them in the right geometrical relationship. To make life a little bit easier, Microscan has assembled three Verification Kits that include smart cameras, lights, and brackets to support common verification applications and in pre-configured geometries to satisfy AIM and ISO requirements. The kits are:
Check out all of Microscan's complete barcode verification solutions: www.microscan.com/Products/BarcodeVerificationSolutions.aspx
- Why Does Verification Matter?
Why does all of this matter? Well the fact is that 1D and 2D barcodes are becoming ever more important in commerce. As a case-in-point, consider how " big box" retailers are increasingly using automated scanning systems at their receiving points for incoming goods, and how the smooth operation of these systems rely on reasonably legible barcodes on their product cases. To make sure this happens, big box retailers such as Lowe's Inc., a major US DIY retailer, published a Barcode Guidelines document that explicitly states that its vendors can be fined for supplying Lowe's with cases marked with " poor quality non-scanable barcodes." Money talks, so expect scenarios like these to drive a lot more interest in code quality and grading in the future.
So there you are - eight quick tips about barcode verification.
To make it happen, always remember to verify/grade as soon after printing or marking as you can. Good scanning and reading to you all!
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