Information technology -- Automatic identification and data capture techniques -- Bar code symbol print quality test specification -- Two-dimensional symbols

ISO/IEC 15415:2011 specifies two methodologies for the measurement of specific attributes of two-dimensional bar code symbols, one of these being applicable to multi-row bar code symbologies and the other to two-dimensional matrix symbologies; defines methods for evaluating and grading these measurements and deriving an overall assessment of symbol quality; gives information on possible causes of deviation from optimum grades to assist users in taking appropriate corrective action. ISO/IEC 15415:2011 applies to those two-dimensional symbologies for which a reference decode algorithm has been defined, but its methodologies can be applied partially or wholly to other similar symbologies. While ISO/IEC 15415:2011 can be applied to direct part marks, it is possible that better correlation between measurement results and scanning performance will be obtained with ISO/IEC TR 29158 in combination with ISO/IEC 15415:2011.

Technologies de l'information -- Techniques automatiques d'identification et de capture des données -- Spécification de test de qualité d'impression des symboles de code à barres -- Symboles bidimensionnels

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Status
Published
Publication Date
14-Dec-2011
Current Stage
6060 - International Standard published
Start Date
24-Oct-2011
Completion Date
15-Dec-2011
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INTERNATIONAL ISO/IEC
STANDARD 15415
Second edition
2011-12-15
Information technology — Automatic
identification and data capture
techniques — Bar code symbol print
quality test specification — Two-
dimensional symbols
Technologies de l'information — Techniques automatiques
d'identification et de capture des données — Spécification de test de
qualité d'impression des symboles de code à barres — Symboles
bidimensionnels
Reference number
ISO/IEC 15415:2011(E)
ISO/IEC 2011
---------------------- Page: 1 ----------------------
ISO/IEC 15415:2011(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2011

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,

electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or

ISO's member body in the country of the requester.
ISO copyright office
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Published in Switzerland
ii © ISO/IEC 2011 – All rights reserved
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ISO/IEC 15415:2011(E)
Contents Page

Foreword ............................................................................................................................................................. v

Introduction ........................................................................................................................................................ vi

1  Scope ...................................................................................................................................................... 1

2  Normative references ............................................................................................................................ 1

3  Terms and definitions ........................................................................................................................... 2

4  Symbols and abbreviated terms .......................................................................................................... 3

5  Quality grading ...................................................................................................................................... 3

5.1  General ................................................................................................................................................... 3

5.2  Expression of quality grades ............................................................................................................... 4

5.3  Overall Symbol Grade ........................................................................................................................... 4

5.4  Reporting of symbol grade ................................................................................................................... 5

6  Measurement methodology for two-dimensional multi-row bar code symbols ............................. 5

6.1  General ................................................................................................................................................... 5

6.2  Symbologies with cross-row scanning ability ................................................................................... 6

6.2.1  Basis of grading .................................................................................................................................... 6

6.2.2  Grade based on analysis of scan reflectance profile ........................................................................ 6

6.2.3  Grade based on Codeword Yield ......................................................................................................... 7

6.2.4  Grade based on unused error correction ........................................................................................... 8

6.2.5  Grade based on codeword print quality .............................................................................................. 9

6.2.6  Overall symbol grade .......................................................................................................................... 10

6.3  Symbologies requiring row-by-row scanning .................................................................................. 11

7  Measurement methodology for two-dimensional matrix symbols ................................................. 11

7.1  Overview of methodology .................................................................................................................. 11

7.2  Obtaining the test images................................................................................................................... 12

7.2.1  Measurement conditions .................................................................................................................... 12

7.2.2  Raw image ............................................................................................................................................ 12

7.2.3  Reference grey-scale image ............................................................................................................... 12

7.2.4  Binarised image ................................................................................................................................... 13

7.3  Reference reflectivity measurements ................................................................................................ 13

7.3.1  General requirements ......................................................................................................................... 13

7.3.2  Light source ......................................................................................................................................... 13

7.3.3  Effective resolution and measuring aperture ................................................................................... 13

7.3.4  Optical geometry ................................................................................................................................. 14

7.3.5  Inspection area .................................................................................................................................... 16

7.4  Number of scans ................................................................................................................................. 16

7.5  Basis of scan grading ......................................................................................................................... 16

7.6  Grading procedure .............................................................................................................................. 16

7.7  Additional reflectance check over extended area ............................................................................ 17

7.8  Image assessment parameters and grading .................................................................................... 17

7.8.1  Use of reference decode algorithm ................................................................................................... 17

7.8.2  Decode .................................................................................................................................................. 17

7.8.3  Symbol Contrast .................................................................................................................................. 18

7.8.4  Modulation and related measurements ............................................................................................. 18

7.8.5  Fixed Pattern Damage ......................................................................................................................... 21

7.8.6  Axial Nonuniformity ............................................................................................................................ 21

7.8.7  Grid Nonuniformity .............................................................................................................................. 22

7.8.8  Unused error correction ..................................................................................................................... 23

7.8.9  Additional grading parameters .......................................................................................................... 23

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ISO/IEC 15415:2011(E)

7.9  Scan grading ........................................................................................................................................23

7.10  Overall Symbol Grade .........................................................................................................................24

7.11  Print growth ..........................................................................................................................................24

8  Measurement methodologies for composite symbologies .............................................................24

9  Substrate characteristics ....................................................................................................................25

Annex A (normative) Symbology-specific parameters and values for symbol grading ............................26

Annex B (informative) Symbol grading flowchart for two-dimensional matrix symbols ...........................30

Annex C (informative) Interpreting the scan and symbol grades ................................................................31

Annex D (informative) Guidance on selection of grading parameters in application specifications .......33

Annex E (informative) Substrate characteristics ...........................................................................................39

Annex F (informative) Parameter grade overlay applied to two-dimensional symbologies ......................41

Bibliography ......................................................................................................................................................42

iv © ISO/IEC 2011 – All rights reserved
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ISO/IEC 15415:2011(E)
Foreword

ISO (the International Organization for Standardization) and IEC (the International Electrotechnical

Commission) form the specialized system for worldwide standardization. National bodies that are members of

ISO or IEC participate in the development of International Standards through technical committees

established by the respective organization to deal with particular fields of technical activity. ISO and IEC

technical committees collaborate in fields of mutual interest. Other international organizations, governmental

and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information

technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of the joint technical committee is to prepare International Standards. Draft International

Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as

an International Standard requires approval by at least 75 % of the national bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.

ISO/IEC 15415 was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,

Subcommittee SC 31, Automatic identification and data capture techniques.

This second edition cancels and replaces the first edition (ISO/IEC 15415:2004), which has been technically

revised. It also incorporates the Technical Corrigendum ISO/IEC 15415:2004/Cor.1:2008.

© ISO/IEC 2011 – All rights reserved v
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ISO/IEC 15415:2011(E)
Introduction

The technology of bar coding is based on the recognition of patterns encoded, in bars and spaces or in a

matrix of modules of defined dimensions, according to rules defining the translation of characters into such

patterns, known as the symbology specification. Symbology specifications may be categorised into those for

linear symbols, on the one hand, and two-dimensional symbols on the other; the latter may in turn be

sub-divided into “multi-row bar code symbols”, sometimes referred to as “stacked bar code symbols”, and

“two-dimensional matrix symbols”. In addition, there is a hybrid group of symbologies known as “composite

symbologies”; these symbols consist of two components carrying a single message or related data, one of

which is usually a linear symbol and the other a two-dimensional symbol positioned in a defined relationship

with the linear symbol.

Multi-row bar code symbols are constructed graphically as a series of rows of symbol characters, representing

data and overhead components, placed in a defined vertical arrangement to form a (normally) rectangular

symbol, which contains a single data message. Each symbol character has the characteristics of a linear bar

code symbol character and each row has those of a linear bar code symbol; each row, therefore, may be read

by linear symbol scanning techniques, but the data from all the rows in the symbol must be read before the

message can be transferred to the application software.

Two-dimensional matrix symbols are normally square or rectangular arrangements of dark and light modules,

the centres of which are placed at the intersections of a grid of two (sometimes more) axes; the coordinates of

each module need to be known in order to determine its significance, and the symbol must therefore be

analysed two-dimensionally before it can be decoded. Dot codes are a subset of matrix codes in which the

individual modules do not directly touch their neighbours but are separated from them by a clear space.

Unless the context requires otherwise, the term “symbol” in this International Standard may refer to either type

of symbology.

The bar code symbol must be produced in such a way as to be reliably decoded at the point of use, if it is to

fulfil its basic objective as a machine-readable data carrier.

Manufacturers of bar code equipment and the producers and users of bar code symbols therefore require

publicly available standard test specifications for the objective assessment of the quality of bar code symbols

(a process known as verification), to which they can refer when developing equipment and application

standards or determining the quality of the symbols. Such test specifications form the basis for the

development of measuring equipment for process control and quality assurance purposes during symbol

production as well as afterwards.

The performance of measuring equipment for the verification of symbols (verifiers) is the subject of a separate

International Standard (ISO/IEC 15426, Parts 1 and 2).

This International Standard is intended to achieve comparable results to the linear bar code symbol quality

standard ISO/IEC 15416, the general principles of which it has followed. It should be read in conjunction with

the symbology specification applicable to the bar code symbol being tested, which provides symbology-

specific detail necessary for its application. Two-dimensional multi-row bar code symbols are verified

according to the ISO/IEC 15416 methodology, with the modifications described in Clause 6; different

parameters and methodologies are applicable to two-dimensional matrix symbols.

There are currently many methods of assessing bar code quality at different stages of symbol production. The

methodologies described in this International Standard are not intended as a replacement for any current

process control methods. They provide symbol producers and their trading partners with universally

standardized means for communicating about the quality of multi-row bar code and two-dimensional matrix

symbols after they have been printed. The procedures described in this International Standard must

necessarily be augmented by the reference decode algorithm and other measurement details within the

vi © ISO/IEC 2011 – All rights reserved
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ISO/IEC 15415:2011(E)

applicable symbology specification, and they may also be altered or overridden as appropriate by governing

symbology or application specifications.

Alternative methods of quality assessment may be agreed between parties or as part of an application

specification.

For direct part mark applications, a modified version of the methodology defined in this International Standard

has been defined in ISO/IEC TR 29158.
© ISO/IEC 2011 – All rights reserved vii
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INTERNATIONAL STANDARD ISO/IEC 15415:2011(E)
Information technology — Automatic identification and data
capture techniques — Bar code symbol print quality test
specification — Two-dimensional symbols
1 Scope
This International Standard

 specifies two methodologies for the measurement of specific attributes of two-dimensional bar code

symbols, one of these being applicable to multi-row bar code symbologies and the other to two-

dimensional matrix symbologies;

 defines methods for evaluating and grading these measurements and deriving an overall assessment of

symbol quality;

 gives information on possible causes of deviation from optimum grades to assist users in taking

appropriate corrective action.

This International Standard applies to those two-dimensional symbologies for which a reference decode

algorithm has been defined, but its methodologies can be applied partially or wholly to other similar

symbologies.

While this International Standard can be applied to direct part marks, it is possible that better correlation

between measurement results and scanning performance will be obtained with ISO/IEC TR 29158 in

combination with this International Standard.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.

ISO/IEC 19762-1, Information technology — Automatic identification and data capture (AIDC) techniques —

Harmonized vocabulary — Part 1: General terms relating to AIDC

ISO/IEC 19762-2, Information technology — Automatic identification and data capture (AIDC) techniques —

Harmonized vocabulary — Part 2: Optically readable media (ORM)
ISO 7724-2:1984, Paints and varnishes — Colorimetry — Part 2: Colour measurement

ISO/IEC 15416, Information technology — Automatic identification and data capture techniques — Bar code

print quality test specification — Linear symbols

NOTE The Bibliography lists official and industry standards containing specifications of symbologies to which (inter

alia) this International Standard is applicable.
© ISO/IEC 2011 – All rights reserved 1
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ISO/IEC 15415:2011(E)
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO/IEC 19762-1, ISO/IEC 19762-2,

ISO/IEC 15416 and the following apply.
3.1
binarised image

binary (black/white) image created by applying the Global Threshold to the pixel values in the reference grey-

scale image
3.2
effective resolution

resolution obtained on the surface of the symbol under test, normally expressed in pixels per millimetre or

pixels per inch, and calculated as the resolution of the image capture element multiplied by the magnification

of the optical elements of the measuring device
3.3
error correction capacity

number of codewords in a symbol (or error control block) assigned for erasure and error correction, minus the

number of codewords reserved for error detection
3.4
inspection area

rectangular area which contains the entire symbol to be tested inclusive of its quiet zones

3.5
grade threshold

boundary value separating two grade levels, the value itself being taken as the lower limit of the upper grade

3.6
module error

module of which the apparent dark or light state in the binarised image is inverted from its intended state

3.7
pixel

individual light-sensitive element in an array [e.g. CCD (charge coupled device) or CMOS (complementary

metal oxide semiconductor) device]
3.8
raw image

plot of the reflectance values in x and y coordinates across a two-dimensional image, representing the

discrete reflectance values from each pixel of the light-sensitive array
3.9
reference grey-scale image

plot of the reflectance values in x and y coordinates across a two-dimensional image, derived from the

discrete reflectance values of each pixel of the light-sensitive array by convolving the raw image with a

synthesised circular aperture
3.10
reflectance margin
measurement of modulation using error correction and known module colours
3.11
sample area

area of an image contained within a circle 0,8X in diameter, X being the average module width determined by

the application of the reference decode algorithm for the symbology in question or, where the application

permits a range of X dimensions, the minimum module width permitted by the application specification

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ISO/IEC 15415:2011(E)
3.12
scan grade

result of the assessment of a single scan of a matrix symbol, derived by taking the lowest grade achieved for

any measured parameter of the reference grey-scale and binarised images
4 Symbols and abbreviated terms
AN = Axial Nonuniformity
E = error correction capacity of the symbol
cap
e = number of erasures
FPD = Fixed Pattern Damage
GN = Grid Nonuniformity
GT = Global Threshold

MARGIN = a measure of the difference in reflectance between a module and the global threshold, the value of

which goes to zero for modules of the incorrect reflectance state

MOD = an absolute measure of the difference in reflectance between a module and the global threshold

R = highest reflectance in any element or quiet zone in a scan reflectance profile, or the highest reflectance

max
of any sample area in a two-dimensional matrix symbol

R = lowest reflectance in any element in a scan reflectance profile, or the lowest reflectance of any sample

min
area in a two-dimensional matrix symbol
SC = Symbol Contrast (equal to R - R )
max min
t = number of errors
UEC = Unused Error Correction
5 Quality grading
5.1 General

The measurement of two-dimensional bar code symbols is designed to yield a quality grade indicating the

overall quality of the symbol which can be used by producers and users of the symbol for diagnostic and

process control purposes, and which is broadly predictive of the read performance to be expected of the

symbol in various environments. The process requires the measurement and grading of defined parameters,

from which a grade for an individual scan (scan reflectance profile grade or scan grade) is derived; the grades

of multiple scans of the symbol are averaged to provide the overall symbol grade.

As a consequence of the use of different types of reading equipment under differing conditions in actual

applications, the levels of quality required of two-dimensional bar code symbols to ensure an acceptable level

of performance will differ. Application specifications should therefore define the required performance in terms

of overall symbol grade in accordance with this standard. The guidelines in Annex D.4 are provided as an aid

in writing application standards which employ this standard.

This standard defines the method of obtaining a quality grade for individual symbols. The use of this method in

high volume quality control regimes may require sampling in order to achieve desired results. Such sampling

plans, including required sampling rates are outside of the scope of this international standard.

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ISO/IEC 15415:2011(E)

NOTE Information on sampling plans may be found in the following: ISO 3951-1, ISO 3951-2, ISO 3951-3,

ISO 3951-5 or ISO 2859-10.
5.2 Expression of quality grades

Although this International Standard specifies a numeric basis for expressing quality grades on a descending

scale from 4 to 0, with 4 representing the highest quality, individual parameter grades and individual scan

grades may also be expressed on an equivalent alphabetic scale from A to D, with a failing grade of F, in

application standards with a historical link to ANSI X3.182.
Table 1 maps the alphabetic and numeric grades to each other.
Table 1 — Equivalence of numeric and alphabetic quality grades
Numeric grade Alphabetic Grade
4 A
3 B
2 C
1 D
0 F
5.3 Overall Symbol Grade

The overall symbol grade shall be calculated as defined in 6.2.6 or 7.10. Overall symbol grades shall be

expressed to one decimal place on a numeric scale ranging in descending order of quality from 4,0 to 0,0.

Where a specification defines overall symbol grades in alphabetic terms the relative mapping of the alphabetic

and numeric grades is as illustrated in Figure 1 below. For example, the range of 1,5 to immediately below 2,5

corresponds to grade C.
Figure 1 — Mapping of alphabetic and numeric overall symbol grades
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ISO/IEC 15415:2011(E)
5.4 Reporting of symbol grade

A symbol grade is only meaningful if it is reported in conjunction with the illumination and aperture used. It

should be shown in the format grade/aperture/light/angle, where:

 "grade" is the overall symbol grade as defined in 6.2.6 or 7.10, i.e. the arithmetic mean to one decimal

place of the scan reflectance profile or scan grades,

 "aperture" is the aperture reference number (from ISO/IEC 15416 for linear scanning techniques, or the

diameter in thousandths of an inch (to the nearest thousandth) of the synthetic aperture defined in 7.3.3),

 "light" defines the illumination: a numeric value indicates the peak light wavelength in nanometres (for

narrow band illumination); the alphabetic character W indicates that the symbol has been measured with

broadband illumination ("white light") the spectral response characteristics of which must imperatively be

defined or have their source specification clearly referenced,

 "angle" is an additional parameter defining the angle of incidence (relative to the plane of the symbol) of

the illumination. It shall be included in the reporting of the overall symbol grade when the angle of

incidence is other than 45°. Its absence indicates that the angle of incidence is 45°.

NOTE While illumination from four sides with an angle of incidence of 45° is the default, other angles of incidence

may be specified as requirements for grading by specifying the angle instead of leaving it blank. Other lighting

options are defined in ISO/IEC TR 29158 which may be more appropriate for direct part marking applications,

especially in applications which rely on symbols marked on reflectance substrates.

An asterisk following the value for "grade", in the case of a two-dimensional matrix symbol, indicates that the

surroundings of the symbol contain extremes of reflectance that may interfere with reading - see 7.6.

Examples

2,8/05/660 would indicate that the average of the grades of the scan reflectance profiles, or of the scan grades, was 2,8

when these were obtained with the use of a 0,125 mm aperture (ref. no. 05) and a 660 nm light source, incident at 45°.

2,8/10/W/30 would indicate the grade of a symbol intended to be read in broadband light, measured with light incident at

30° and using a 0,250 mm aperture (ref. no. 10), but would need to be accompanied either by a reference to the

application specification defining the reference spectral characteristics used for measurement or a definition of the spectral

characteristics themselves.

2,8*/10/670 would indicate the grade of a symbol measured using a 0,250 mm aperture (ref. no. 10), and a 670 nm light

source, and indicates the presence of a potentially interfering extreme reflectance value in the surroundings of the symbol.

NOTE The same notation is used to specify a minimum grade that is required in an application as is a grade that is

obtained by measuring a symbol in accordance with this standard. For example, an application standard may

specify a symbol quality requirement as 1.5/05/660 and this would be met by a measured grade of X.X/05/660

as long as X.X is a number that is greater or equal to 1.5. However, this requirement would not be met by

2.0/10/660 nor 3.0/05/W nor 3.5/05/660/30.
6 Measurement methodology for two-dimensional multi-row bar code symbols
6.1 General

The evaluation of two-dimensional multi-row bar code symbols shall be based on the application of the

methodology of ISO/IEC 15416, modified as described in 6.2.2 or 6.3, and if appropriate for the symbology, on

the application of the additional provisions described in 6.2.3, 6.2.4 and 6.2.5, to derive an overall symbol

grade. Ambient light levels shall be controlled in order not to have any influence on the measurement results.

The symbol shall be scanned using the light wavelength(s) and effective aperture size specified in the

appropriate application standard. When performing a measurement, the scan lines should be made

perpendicular to the h
...

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