TRADITIONAL
VERIFICATION
Since the introduction
of bar codes, there have been published standards on printing them.
Each bar code type, such as UPC or the Interleaved 2 of 5 "case
code" specifies a tolerance on the printed widths of bars and spaces,
and contrast between bars and spaces. Early verifiers were developed
to measure these characteristics and pass or fail bar codes accordingly.
This so-called "traditional" verification was a natural extension
of the printed bar code specifications.
The difficulty with traditional
verification is that the actual scanning experience by the end user
did not always correlate to verifier results. Many bar codes that
failed verification were actually very easily scanned by normal scanners
at the retail store. On the other hand, some bar codes that passed
traditional verification could not be scanned. The problem stems
from the fact that this verification method was far removed from the
way real scanners operate.
The traditional verification method
is based on comparing the printed bar widths to the specified bar width
within the published tolerance. As scanning systems improved they
could read bar codes that were more inaccurate than the published specification
allowed. Following the advice of the verifier either required
keeping tighter than necessary control over the printing, or throwing
away usable product.
Another limitation
of traditional verification is that it does not address defects within
the printed code, such as voids in bars. To address the issue
of defects, ambiguous statements such as "without any spots and
voids" were often specified along with the traditional measurement
criteria. This subjective means for identification of defects
is impossible to quantify and therefore the acceptability of the bar
codes cannot be validated.
ANSI VERIFICATION
In recent years
new standards and guidelines have been established by ANSI (American
National Standards Institute) and the UCC (Uniform Code Council).
These new standards measure bar code print quality according to the
way actual scanners work. ANSI verification is now relied upon
by suppliers and customers of packaging as a basis for ensuring compliance
because it addresses virtually all the aspects of print quality that
affect scanning.
Verification to the ANSI standard
provides printers and converters the benefits of the improved performance
to which scanning systems have evolved. Using ANSI grading you
do not have to print to tougher standards than are actually required.
At the same time, end users are provided protection from getting printing
defects in their material that traditional verfication could miss.
ANSI's "Bar Code Print Quality
Guideline", X3.182 published in 1990, established a procedure for
measuring bar code quality. The ANSI guideline provides a standard
measurement methodology and defines eight categories of print quality
to be measured. The output of the ANSI method is a grade for any
bar code on a scale of 0 to 4 or expressed as a letter grade (A,B,C,D,
or F) based on the measurements in each category. A grade of "C"
or better should scan on virtually any properly maintained scanner on
the first pass. Since better quality labels will scan more easily
and allow more margin of error, some package purchasers even specify
grade "B" or better codes.
The ANSI specification was adopted
by the UCC and applied to the most common bar code used in retail distribution,
the UPC. The resulting specification filled in some details particular
to UPC and also added a ninth criteria, checking the quiet zones.
The benefit
of the new standards is that they are closely related to the way scanners
work so they can predict scannability of a bar code consistently.
Because virtually all of the aspects of print quality that affect scanning
are measured, ANSI verification has become the basis for communication
between producers and users of printed bar coded products. With
these new meaningful standards available, purchasers of packaging are
asking for a specific level of bar code quality from their suppliers.
Converters are expected to be able to comply.
ANSI Information
