Fundamentals of ANSI/ISO Bar Code
by George Wright IV, vice president, Product Identification & Processing Systems Inc.
Return to article: Bar Coding Rules
Whatever the bar coding application, standardized bar code print quality verification is essential.
Healthcare bar code application guidelines from EAN.UCC and HIBCC require a minimum overall symbol print quality grade of C. This is the equivalent of 1.5 on the 0.0ï¿½4.0 numeric scale. The grade is determined according to the globally accepted standard for calculating bar code print quality: ISO/IEC 15416, Information technologyï¿½Automatic identification and data capture techniquesï¿½Bar code print quality test specificationï¿½Linear symbols. This ISO standard supersedes ANSI X3.182-1990.
Here are some important points to consider when selecting a verifier and developing a bar code print quality verification protocol.
Scanning is not verification. A bar code scanner is a data collection tool. Its purpose is to decode or read the data encoded in the symbol and to pass this information on to a computer system. Ideally, it should do this easily and quickly, even on poorer quality bar codes. A bar code print quality verifier is a quality assessment instrument. It is intended to evaluate, measure, and report with accuracy and repeatability specific physical characteristics of a bar code to quantify the likelihood that it will be readily decoded. A verifier should perform in strict accordance with globally accepted ISO specifications.
Not all scanners are created equal. Some scanners may rely only on the simplest optics and the published reference decode algorithm (the recipe) for reading a given symbology. Such scanners have limited abilities to read poorer quality bar codes and generally operate well only over a limited range. Other scanners incorporate extra processing power, enhanced decode algorithms, special optics, and secret tricks of the trade to read even very low quality symbols at varying depths of field.
Because scanners differ in their capabilities, bar codes must be printed to accommodate (within limits) the lowest common denominator. Thus, it is essential to be able to accurately predict how readily a bar code can be decodedï¿½even by the least sophisticated scanners. Grading symbols according to the ISO 15416 specification is the globally accepted method of quantifying this scannability.
ISO 15416 defines a rigorous methodology for print quality verification. Depending on the symbology and application, it specifies 7 or more parameters to be graded. Some are pass-fail, while others are graded on an integer scale from 4 (highest) to 0 (failure). The lowest grade for any parameter in a single scan is the grade for that scan. The overall symbol grade is the arithmetic mean (average) to one decimal place of the individual scan grades for 10 scans taken from top to bottom of the symbol in the inspection band.
It is this 10-scan average grading that gives ISO 15416 its robustness. The height of a linear bar code gives it ï¿½vertical redundancy,ï¿½ providing multiple possible scan paths, any one of which might provide the decode necessary for data capture. By averaging 10 scans, the methodology allows for a reasonable amount of nonuniformity in the printing process. At the same time, it ensures a final grade that is fairly determined and representative of overall symbol quality.
Generally, it is preferable to record and refer to the numeric overall grades rather than the less-precise letter grades. Whereas a grade of 2.5 is a B, a 2.4 is a C. Yet there is virtually no qualitative difference in these two grades. In addition, the standard is quite specific about when a symbol is to be verified: ï¿½Whenever possible, measurements shall be made on the bar code symbol in its final configuration, i.e., the configuration in which it is intended to be scanned.ï¿½
One ANSI/ISO verifier is not the same as another. Not all verifiers marketed as following or compliant with the ANSI/ISO methodology are the same. Some units are handheld and portable, while others are laboratory-type desktop instruments. Some models have fully automated scanning motion left to right and vertically through the inspection band. With others, this is a completely manual process. And some verifiers perform additional application-specific data format checks beyond what is required by ISO 15416.
In addition to understanding the feature differences between verifiers, it is essential to determine exactly how closely any ï¿½ANSI/ISOï¿½ verifier conforms to the relevant ISO standards for verifier methodology and accuracy. ISO 15416 specifies the methodology by which a symbol is to be graded. Equally important, and arguably more so, is the accuracy and repeatability with which the verifier performs these calculations.
It is essential to ï¿½verify the verifier.ï¿½ ISO/IEC 15426-1, Information technologyï¿½Automatic identification and data capture techniquesï¿½Bar code verifier conformance specification: Part 1: Linear symbols specifies the accuracy with which a verifier must derive and report the specified parameter grades under ISO 15416. It is critical to determine that a verifier grades with the required level of accuracy. To do this, one needs to test the verifierï¿½s performance against a set of certified symbols with known values for the parameters being tested. It is also important to test a verifier for conformance on a regular basis after putting the unit into use. This is not the same as calibrating a verifier for high and low reference reflectance values, a relatively simple calibration function somewhat analogous to the process of zeroing a scale.
Although a verifier manufacturer may offer test symbols against which its instrumentï¿½s performance may be judged, EAN.UCC System Calibrated Conformance Standard Test Cards from the Uniform Code Council (UCC) are the globally accepted tools for this purpose. These precision-engineered ï¿½primary reference test symbolsï¿½ are manufactured to the strict specifications of UCC, and each symbol is individually measured using a specialized, custom-built scanning micro-densitometer. Known as The Judge, this ultrahigh-precision bar code verifier is traceable to the U.S. National Institute of Standards and Technology.
No one verification setup does it all. Bar code print quality verification needs vary from application to application. This is true even when all the applications require grading according to the methodology of ISO 15416 and verifier conformance to ISO 15426-1 requirements for accuracy. At the most fundamental level, the verifier optical scanning unitï¿½s aperture must be matched to the narrow bar/space width (the ï¿½X-dimensionï¿½) of the symbol being verified. This requirement is specified by the governing application guideline or by ISO 15416 in the absence of such a guideline.
As with most technologies, bar code print quality verification equipment evolves constantly, with different manufacturers emphasizing a variety of different features and benefits. Still to come for some of the newest symbologies (such as RSS/Composite and Data Matrix) are certain bar code print quality verification tools that many companies would like to have. Proven, high-speed, in-line ISO verification on a pharmaceutical packaging line is one example. These new tools are in the works from a number of companies. And although there are always trade-offs between features and cost, the essential performance characteristics to look for remain constant: adherence to the methodology of ISO 15416 and conformance to the requirements for accuracy specified in ISO 15426-1.
ISO standards can be purchased on-line at www.iso.org. UCC.EAN System Calibrated Conformance Standard Test Cards, standards, and application guidelines can be purchased on-line at www.uc-council.org. HIBCC application standards are freely available at www.hibcc.org. Helpful information about bar code print quality verification is available from the Association for Automatic Identification and Mobility (AIM) at www.aimglobal.org. Questions or comments to the author should be addressed to George Wright IV at firstname.lastname@example.org.