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Understanding Machine
Vision Verification of
1D and 2D Barcodes
Basics of Ensuring Barcode Readability
for Reliable Process Operation
Technology White Paper
Product Line Card
Technology White Paper
Why Verify?
Barcode quality is integral to the success of an automated
system. In a process where quality barcodes accurately store
and communicate data – from code to reader to central system
– little manual intervention is required. Thanks to quality bar-
codes, the unique benets of an automated system are realized:
lower costs, higher productivity, and fewer errors. Poor quality
barcodes, however, render the system almost as inefcient as
using no automation at all. Unreadable barcodes may require
re-labeling, re-scanning, or even manual entry of critical informa-
tion by a human operator – disrupting the productivity of the
process and causing a signicant loss of time. Bad barcodes
may prevent error-tracking, causing a domino effect of failures
down the line and resulting in costly scrap and rework. All told,
these effects completely counteract the benets of implement-
ing an automated system, the result being inated cost, loss of
productivity, and increased errors.
The purpose of barcode verication is to prevent this outcome
and preserve the intended benets of the automated system.
Verication systems evaluate a barcode’s quality against pub-
lished quality standards for 1D and 2D barcodes using precision
instruments such as barcode veriers or machine vision sys-
tems. A veried barcode ensures consistent readability, support-
ing 100% accurate automated data capture.
When Should You Verify?
To ensure that errors are prevented as early in the automated
system as possible, verication must occur before a part enters
the system. A verication step should occur after a part is
marked or labeled with a barcode and before the part reaches
the station where the barcode is rst read.
Proper verication ensures that every part is processed and
shipped with a high-quality barcode, despite the fact that mark-
ing and labeling systems will degrade over time. A verication
system is much more accurate than a standard barcode reader
at identifying low-quality barcodes early in the process, be-
fore parts with bad barcodes make it through the line and are
shipped to end customers. When barcode quality degradation is
identied early, the marking or labeling system may be adjusted
or replaced before unreadable barcodes are ever produced.
Understanding Machine Vision Verication of 1D/2D Barcodes
Legible, accurate barcodes have never been more important than they are today, when automated supply chains depend on data accuracy
to ensure the reliable performance of global operations. Machine vision verification is one tool that can be used to ensure that barcodes
meet a consistent level of quality for readability in an automated process, and that bad codes are identified before they result in costly fail-
ures. This white paper introduces 1D and 2D barcode verification and identifies parameters for verifying codes against published standards.
- Why Verify?
- When Should You Verify?
- Validation vs. Verification
- What Kind of Hardware Is Required?
- Verification Evaluation Parameters
- Verification Grades
- Verification with AutoVISIONTM
Microscan Systems, Inc.
1 www.microscan.com
Barcode
Marking
Station
Verication Barcode
Reading
Station
Barcode Quality Over Time Using a Verication
System to Check Quality
0 5000 10000 15000 20000
Number of Parts Marked/Labeled
A
B
C
D
F
NO
READ
Barcode Quality Over Time Using
a Reader to Check Quality
0 5000 10000 15000 20000
Number of Parts Marked/Labeled
A
B
C
D
F
NO
READ
With verication, bad barcodes are prevented from being applied
to the product, eliminating the chance for future failures.
Without verication, bad barcodes are not identied until they
are unreadable. By the time a bad barcode is identied, several
poor-quality barcodes may have already escaped down the line.
Technology White Paper
Validation vs. Verication
Depending on the requirements of a particular process, industry,
company, or customer, there are two levels of quality grading
for ensuring barcode readability: validation (sometimes called
process control) and true verication.
Validation/Process Control: Process control is a means of
ensuring that barcodes are readable throughout a particular
internal or internal/external process. Process control does not
check barcodes for compliance to a published barcode qual-
ity standard. Instead, it provides objective measurements for
barcode quality when verication to a standard is not possible
or not desired. If you are not concerned with meeting published
barcode quality standards in your application, you may opt to use
a subset of the default verication parameters in the verication
system as the criteria for passing codes.
Verification: Verication ensures that a barcode complies with
published barcode quality standards, such as ISO 15415, ISO
15416, and AIM DPM. To ensure compliance, all evaluation
parameters in the machine vision system must be enabled dur-
ing the verication process. Fully-conforming verication systems
provide reports as evidence of barcode compliance, which can
be sent to customers or other invested parties to provide the
highest assurance of barcode quality and consistency.
What Kind of Hardware Is Required?
More precise quality grading requires higher-performance hard-
ware. If a symbol must meet parameters for internal/external
process control only, a machine vision system with integrated
lighting may be adequate for performing validation. However,
barcodes that must comply with published barcode quality stan-
dards must be veried by a system with superior optics, such
as a C-mount lens, and with complete and uniform lighting by an
ISO/AIM-compliant light to produce an undistorted image.
Verication Evaluation Parameters
There are a number of verication evaluation parameters that
determine barcode quality and they may be used for either true
verication or validation/process control. Published barcode
quality standards, such as ISO 15415, ISO 15416, and AIM
DPM, require that a designated set of these parameters be
met to ensure that a barcode is veried to the standard, while
process control grading may require that a barcode meet only a
subset of these parameters. Parameters for 1D and 2D barcode
evaluation are shown below.
1D Verification Evaluation Parameters
High Quality Symbol:
Parameter Description Example ISO
15416
Decodability Legibility per a
reference de-
code algorithm ü
Defects Voids in bars or
spots in spaces ü
Edge
Determination
Detection of
all bars and
spaces using a
global threshold
ü
Minimum
Edge
Contrast
Minimum
reectance
difference for
any bar/space
combination
ü
Minimum
Reflectance
Reectance of
the darkest bar
and the lightest
space ü
Modulation Relation
between wide
and narrow
elements in the
symbol
ü
Symbol
Contrast
Difference in
reectance
between the
darkest bar
and the lightest
space
ü
Quiet Zone Size of the
quiet zone ü
2 www.microscan.com
Machine Vision System with Integrated Lighting
Machine Vision System with C-Mount Optics
and External Lighting
Product Line Card
Technology White Paper
2D Verification Evaluation Parameters
High Quality Symbol:
Parameter Description Example ISO
15415
AIM
DPM
Axial Non-
Uniformity
Amount of de-
viation along a
symbol’s major
axes
Y
Xü ü
Symbol
Contrast
Difference in
reectance be-
tween light and
dark symbol
elements
ü
Cell Contrast Difference in
grayscale value
between light
and dark sym-
bol elements
ü
Modulation Difference in
reectance of
light and dark
symbol
elements
ü
Cell
Modulation
Deviation in
grayscale val-
ues of symbol
elements
ü
Decodability Legibility per a
reference de-
code algorithm ü ü
Fixed Pattern
Damage
Damage to the
quiet zone,
nder pattern,
or clock pattern ü ü
Grid Non-
Uniformity
Amount of
deviation of grid
intersection
Y
Xü ü
Minimum
Reflectance
Minimum
reectance of
light elements ü
Parameter Description Example ISO
15415
AIM
DPM
Reflectance
Margin
Degree to which
each module
is correctly
distinguishable
in comparison
to the global
threshold
ü
Unused Error
Correction
Remaining error
correction avail-
able ü ü
Print Growth Variation of ele-
ment size that
could impede
readability
For Reference
Only
Verication Grades
Barcodes are graded by verication equipment like barcode veri-
ers and machine vision systems, which assign values 0-4/A-F to
the barcode for each of the above-listed evaluation parameters.
A barcode’s overall grade is determined by the worst result for
each parameter, so the barcode is always as good as its poorest
parameter. Typically, a barcode with a grade A, B, or C is consid-
ered acceptable quality, while a grade D or F signies a poorly-
marked or poorly-printed barcode.
Verication with AutoVISION™
Microscan’s AutoVISION Machine Vision Software
provides powerful tools for both text quality veri-
cation (OCV or Optical Character Verication) and
barcode quality verication. Using AutoVISION and
high-performance smart cameras and lighting, you
can set up a complete verication system to de-
termine barcode quality at any level of quality grading, including
conformance to three published barcode quality standards:
ISO 15415 AIM DPM ISO 15416
Clear and concise values are provided via the AutoVISION user
interface to grade 1D and 2D barcodes for each parameter
required by a particular barcode quality standard. AutoVISION
assigns values 0-4/A-F to the barcode for each parameter and
then the barcode receives an overall grade for meeting the qual-
ity standard.
3 www.microscan.com
Technology White Paper
www.microscan.com
North America (Corporate Headquarters)
Email: info@microscan.com
Europe
Email: emea@microscan.com
Asia Pacific
Email: asia@microscan.com
4
Default parameters in AutoVISION are pre-set to grade barcodes
against published barcode quality standards (ISO 15415, ISO
15416, and AIM DPM), but can be adjusted in the AutoVISION
Symbol Quality Verication Tool to enable process control grading
for barcodes that must meet application-specic criteria only.
Microscan Meets Verication Needs
From 2D barcode veriers to complete, scalable machine vision
systems like AutoVISION, Microscan offers a range of products
to ensure that automation systems operate at peak performance
thanks to quality and compliant barcodes. For engineers tasked
with meeting quality control or global standards in marking and
labeling, Microscan provides project evaluations to nd the right
barcode verication solution for any project.
More Microscan product information and training resources are
available at www.microscan.com.
©2013 Microscan Systems, Inc. 04/13
A Data Matrix 2D barcode is veried against the AIM DPM quality standard
using Microscan’s AutoVISION machine vision software.
Verication evaluation parameters are adjusted in the
AutoVISION Symbol Quality Verication Tool to grade a
barcode for internal process control.
