ISO/IEC 15415:2024

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

This document - specifies two methodologies for the measurement of specific attributes of two-dimensional bar code symbols – one of which applies to multi-row bar code symbologies and the other to two-dimensional matrix symbologies; - specifies 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 document applies to two-dimensional symbologies for which a reference decode algorithm has been defined, however the methodologies in this document can be applied partially or wholly to other similar symbologies. NOTE While this document can be applied to direct part marks, better correlation between measurement results and scanning performance can be obtained with ISO/IEC 29158 in combination with this document.

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

General Information

• Status: Published
• Publication Date: 18-Dec-2024
• ICS: 35.040.50 - Automatic identification and data capture techniques
• Technical Committee: ISO/IEC JTC 1/SC 31 - Automatic identification and data capture techniques
• Drafting Committee: ISO/IEC JTC 1/SC 31/WG 1 - Data carrier
• Current Stage: 6060 - International Standard published
• Start Date: 19-Dec-2024
• Due Date: 08-Dec-2024
• Completion Date: 19-Dec-2024

Relations

• Revises: ISO/IEC 15415:2011 - Information technology - Automatic identification and data capture techniques - Bar code symbol print quality test specification - Two-dimensional symbols
• Effective Date: 23-Apr-2020

Overview

ISO/IEC 15415:2024 - Automatic identification and data capture techniques - Bar code symbol print quality test specification - Two-dimensional symbols - is the third edition of the international standard for assessing the print quality of two-dimensional (2D) bar code symbols. It defines objective measurement and grading methodologies for both multi-row bar code symbologies (stacked/row-based) and two-dimensional matrix symbologies (matrix/module-based). The standard specifies how to obtain and process test images, compute parameter scores, derive an overall symbol grade, and interpret deviations to support corrective action.

Key topics and technical requirements

• Two measurement methodologies: one for multi-row (stacked) symbologies and one for matrix symbologies; methodologies can be applied fully or partially to similar symbologies where a reference decode algorithm exists.
• Image acquisition and optical setup: requirements for obtaining test images, measuring aperture convolution, inspection area and measurement conditions.
• Reference and processed images: guidance on raw, reference grey-scale and binarized images used for grading.
• Grading parameters: includes symbol contrast (Rmin/Rmax), modulation, reflectance margin, fixed pattern damage, axial and grid non-uniformity, unused error correction, print growth, and additional image assessment parameters.
• Grading methods: continuous (decimal) grading introduced in this edition, procedures for per-parameter grading and computation of an overall symbol grade.
• Decode considerations: use of a reference decode algorithm and decode-based grading (e.g., codeword yield, unused error correction).
• Guidance and diagnostics: annexes provide thresholding algorithms, interpretation of scan vs. symbol grades, selection of grading parameters, substrate characteristics, and parameter overlays.
• Applicability to DPM: can be applied to direct part marks, but better correlation with scanning performance is achieved when combined with ISO/IEC 29158.

Practical applications and users

ISO/IEC 15415:2024 is used for:

• Quality control and verification of 2D barcode production (labels, packaging, tickets, documents).
• Verifier manufacturers to implement compliant measurement and grading functionality.
• Equipment integrators and system developers ensuring barcode print/read reliability in supply chains, logistics, retail, healthcare and manufacturing.
• Application specifiers and auditors defining acceptable symbol grades for operational requirements.
• Process improvement: diagnosing printing defects and guiding corrective actions via parameter-level feedback.

Related standards

• ISO/IEC 15416 - Linear barcode print quality (related principles)
• ISO/IEC 15426-1 / 15426-2 - Verifier performance requirements
• ISO/IEC 29158 - Direct Part Mark (DPM) verification guidance (recommended when verifying DPM together with 15415)

Keywords: ISO/IEC 15415:2024, 2D barcode, two-dimensional symbols, barcode print quality, barcode verification, matrix symbols, multi-row symbology, barcode grading, barcode verifier.

Standards Content (Sample)

International
Standard
ISO/IEC 15415
Third edition
Automatic identification and data
2024-12
capture techniques — Bar code
symbol print quality test specification
— Two-dimensional symbols
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 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
© ISO/IEC 2024 – All rights reserved
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms. 3
4.1 Symbols .3
4.2 Abbreviated terms .3
5 Quality grading . 4
5.1 General .4
5.2 Expression of quality grades . .4
5.3 Symbol grade.4
5.4 Specifying the symbol grade requirement in an application specification .5
5.5 Reporting of symbol grade .5
5.6 Optical setup and obtaining the test images .6
5.6.1 General requirements .6
5.6.2 Convolving with the measuring aperture .7
5.6.3 Geometry of the optical setup .7
5.6.4 Inspection area .9
5.6.5 Measurement conditions .9
6 Measurement methodology for two-dimensional multi-row bar code symbols .10
6.1 General .10
6.2 Symbologies with cross-row scanning ability.10
6.2.1 Basis of grading .10
6.2.2 Grade based on analysis of scan reflectance profile .10
6.2.3 Grade based on codeword yield .11
6.2.4 Grade based on unused error correction . 12
6.2.5 Grade based on codeword print quality . 13
6.2.6 Overall symbol grade . 15
6.3 Symbologies requiring row-by-row scanning . 15
7 Measurement methodology for two-dimensional matrix symbols .16
7.1 Overview of methodology .16
7.2 Test images.16
7.2.1 Raw image .16
7.2.2 Reference grey-scale image .16
7.2.3 Binarised image .16
7.3 Reference reflectivity measurements .17
7.3.1 Application specification defines the aperture size .17
7.4 Grading procedure .17
7.5 Image assessment parameters and grading .18
7.5.1 Use of reference decode algorithm .18
7.5.2 Decode .18
7.5.3 Computing R and R .18
max min
7.5.4 Symbol contrast .19
7.5.5 Modulation and related measurements .19
7.5.6 Fixed pattern damage . 22
7.5.7 Axial nonuniformity . 22
7.5.8 Grid nonuniformity . 23
7.5.9 Unused error correction . 23
7.5.10 Print growth .24
7.5.11 Additional grading parameters . 25
7.6 Symbol grade. 25

© ISO/IEC 2024 – All rights reserved
iii
8 Measurement methodologies for composite symbologies .25
Annex A (normative) Thresholding algorithm based on histogram .27
Annex B (informative) Interpreting the scan and symbol grades .31
Annex C (informative) Guidance on selecting grading parameters in application specifications .33
Annex D (informative) Substrate characteristics .39
Annex E (informative) Parameter grade overlay applied to two-dimensional symbologies . 41
Annex F (informative) Explanation of the main changes in this edition of this document .42
Bibliography .45

© ISO/IEC 2024 – All rights reserved
iv
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of document should be noted. This document was drafted in accordance with the editorial rules of the ISO/
IEC Directives, Part 2 (see www.iso.org/directives or www.iec.ch/members_experts/refdocs).
ISO and IEC draw attention to the possibility that the implementation of this document may involve the
use of (a) patent(s). ISO and IEC take no position concerning the evidence, validity or applicability of any
claimed patent rights in respect thereof. As of the date of publication of this document, ISO and IEC had not
received notice of (a) patent(s) which may be required to implement this document. However, implementers
are cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents and https://patents.iec.ch. ISO and IEC shall not be held
responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www.iso.org/iso/foreword.html.
In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 31, Automatic identification and data capture techniques.
This third edition cancels and replaces the second edition (ISO/IEC 15415:2011) which has been technically
revised.
The main changes are as follows:
— a continuous (or decimal) grading has been introduced;
— a more optimal threshold calculation has been introduced;
— a more stable symbol contrast calculation has been introduced;
— a definition of grading for print growth has been added;
— modulation and reflectance margin have been combined into a single measurement.
Any feedback or questions on this document should be directed to the user’s national standards
body. A complete listing of these bodies can be found at www.iso.org/members.html and
www.iec.ch/national-committees.

© ISO/IEC 2024 – All rights reserved
v
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
subdivided 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. Some matrix codes are comprised of
unconnected dots, in which the individual modules do not directly touch their neighbours but are separated
from them by a clear space.
Unless explicitly specified otherwise, the term “symbol” in this document refers 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 specifications 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, also known as verifiers, is covered
in ISO/IEC 15426-1 and ISO/IEC 15426-2.
The methodology described in this document is intended to achieve comparable results to the linear bar
code symbol quality standard ISO/IEC 15416, the general principles of which this document has followed.
It should be read in conjunction with the symbology specification applicable to the bar code symbol being
tested, which provides symbology-specific details 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. The
procedures described in this document must necessarily be augmented by the reference decode algorithm
and other measurement details within the applicable symbology specification, and they may also be altered
or overridden as appropriate by governing symbology or application specifications.
The method of quality assessment described in this document is most applicable to reading environments
wherein printed and otherwise marked symbols are read predominantly by diffuse reflection. For direct part
mark applications, in which symbols and substrates may be glossy, specular, low contrast, etc., a modified
and extended version of the methodology defined in this document has been defined in ISO/IEC 29158 and

© ISO/IEC 2024 – All rights reserved
vi
provides for lighting arrangements and enhanced algorithms which more closely match reading equipment
commonly used in DPM applications.
NOTE The Bibliography provides official and industry standards containing symbology specifications, among
other references, to which this document applies. However, the Bibliography does not provide an exhaustive list of
symbology specifications.
© ISO/IEC 2024 – All rights reserved
vii
International Standard ISO/IEC 15415:2024(en)
Automatic identification and data capture techniques —
Bar code symbol print quality test specification — Two-
dimensional symbols
1 Scope
This document
— specifies two methodologies for the measurement of specific attributes of two-dimensional bar code
symbols – one of which applies to multi-row bar code symbologies and the other to two-dimensional
matrix symbologies;
— specifies 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 document applies to two-dimensional symbologies for which a reference decode algorithm has been
defined, however the methodologies in this document can be applied partially or wholly to other similar
symbologies.
NOTE While this document can be applied to direct part marks, better correlation between measurement results
and scanning performance can be obtained with ISO/IEC 29158 in combination with this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements 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 15416, Information technology – Automatic identification and data capture techniques — Bar code
print quality test specification — Linear symbols
ISO/IEC 15426-2, Information technology — Automatic identification and data capture techniques — Bar code
verifier conformance specification — Part 2: Two-dimensional symbols
ISO/IEC 19762, Information technology — Automatic identification and data capture (AIDC) techniques —
Harmonized vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 19762, ISO/IEC 15416 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/

© ISO/IEC 2024 – All rights reserved
3.1
binarised image
binary (black/white) image created by applying a threshold to the pixel (3.7) values in the reference grey-
scale image (3.9)
3.2
effective resolution
resolution obtained on the surface of the symbol under test and calculated as the resolution of the image
capture element multiplied by the magnification of the optical elements of the measuring device
Note 1 to entry: The effective resolution is normally expressed in pixels (3.7) per mm (or pixels per inch).
3.3
error correction capacity
number of codewords, or units of data, in a symbol (or error control block) assigned for erasure and error
correction, minus the amount reserved for error detection
3.4
inspection area
portion of an image 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 (3.1) is inverted from its intended state
3.7
pixel
individual light-sensitive element in an array
EXAMPLE Charge coupled device (CCD), complementary metal oxide semiconductor (CMOS) 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 (3.7) 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 (3.7) of the light-sensitive array by convolving the raw image (3.8)
with a synthesised aperture (3.10)
3.10
synthesised aperture
convolutional kernel used to blur an image

© ISO/IEC 2024 – All rights reserved
4 Symbols and abbreviated terms
4.1 Symbols
E error correction capacity of the symbol
cap
D distance across or width of an element in a symbol
D expected or nominal width of an element in a symbol
NOM
e number of erasures
M measure of the difference in reflectance between a module and the threshold
MOD
M measure of axial nonuniformity
ANU
M measure of grid nonuniformity
GNU
M measure of unused error correction, accounting for the number of errors, erasures and capacity
UEC
R reflectance
R indicative reflectance of the brightest area of a symbol
max
R indicative reflectance of the darkest area of a symbol
min
ΔR symbol contrast, i.e. the difference in reflectance between R and R
SC max min
t number of errors
T threshold
X average spacing of modules in the horizontal axis
AVG
Y average spacing of modules in the vertical axis
AVG
4.2 Abbreviated terms
ANU axial nonuniformity
CU contrast uniformity
FPD fixed pattern damage
GNU grid nonuniformity
MOD modulation
PG print growth
SC symbol contrast
UEC unused error correction
© ISO/IEC 2024 – All rights reserved
5 Quality grading
5.1 General
The measurement of two-dimensional bar code symbols is designed to yield a quality grade, reported as the
symbol grade, indicating the overall quality of the symbol. This can be used by producers and users of the
symbol for diagnostic and process control purposes and is broadly predictive of the read performance to be
expected of the symbol. The process requires the measurement and grading of defined parameters, from
which the symbol grade is derived. The symbol grade is sometimes called the “overall symbol grade” when
used in a context in which the modifier “overall” helps to clarify and distinguish the symbol grade from
other parameter grades.
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 between different real-world applications. Application specifications should
therefore define the required symbol quality in terms of aperture, light (angle, orientation and wavelength),
and minimum symbol grade in accordance with this document. The guidelines in Annex C are provided
as an aid in writing application specifications according to this document. Annex D provides additional
information regarding substrate properties. When this document is used without an applicable application
specification, suitable choices for aperture, light (angle and wavelength), and minimum grade, must be made
by the user. However, if these choices are not suited to the intended application, then the achieved symbol
grade cannot be relied upon as an indicator of reading performance in the intended application. Thus, it is
highly preferred to follow an agreed upon application specification when using this document (such as a
specification mutually agreed upon or published by an industry standards body or regulatory authority).
This document 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 document.
NOTE Information on sampling plans can be found in ISO 3951-1, ISO 3951-2, ISO 3951-3, ISO 3951-5 and
ISO 28590.
5.2 Expression of quality grades
This document specifies a numeric basis for expressing quality grades on a descending scale from 4,0 to 0
in steps of 0,1. The highest quality is represented by 4,0. Alphabetic grades are not formal and should not be
reported as the formal grade. The link between numeric and alphabetic grades is given in Table 1. Numeric
grades are more precise because they express a grade with ten steps within each letter grade range. Overall
numeric grades should not be rounded to the nearest whole number. When using alphabetic grades for
convenience they shall be accompanied by a numerical grade.
Table 1 shows the correspondence between alphabetic and numeric grades.
Table 1 — Correspondence between numeric and historical alphabetic quality grades
Numeric range Alphabetic grade
≥3,5 (i.e. 3,5; 3,6; 3,7; 3,8; 3,9; 4,0) A
2,5 to 3,4 B
1,5 to 2,4 C
0,5 to 1,4 D
≤0,4 (i.e. 0,0; 0,1; 0,2; 0,3; 0,4) F
5.3 Symbol grade
The symbol grade shall be calculated in accordance with 6.2.6 or 6.3 or 7.6 or Clause 8 and as applicable to
the type of symbol.
© ISO/IEC 2024 – All rights reserved
5.4 Specifying the symbol grade requirement in an application specification
An application specification shall specify the minimum grade requirement as well as the grading conditions,
shown in the format:
grade/aperture/light/angle
where
grade indicates the minimum grade required;
aperture indicates 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 aperture defined
in 5.6.2;
light indicates the numeric value of the peak light wavelength (i.e. the illumination) in nanometres
(for narrow band illumination); the alphabetic character W indicates broadband (nominally,
“white light”), the spectral response characteristics of which must imperatively be defined or
specified in kelvin in parenthesis after the W designated by a number followed by the letter K,
or have their source specification clearly referenced;
angle indicates the angle of incidence (an additional parameter) in degrees (relative to the plane
of the symbol) of the illumination from four sides (as a default, unless another orientation is
specified by an application) – see Figure 1 and Figure 2.
The angle shall be included in the specification of grading requirements when the angle of incidence is other
than 45°. While it may be included for 45°, its absence indicates that the specified angle of incidence is 45° by
default. Application specifications may specify a different angle of incidence instead of leaving it blank.
The orientation of light refers to the number of directions, the default being four. Light from only two sides
may be specified by appending the letter "T" to the angle, such as 30T. The letter "S" may be used to indicate
only one side. The letter "Q "may be used to indicate four sides, but omitting it implies four sides so 45Q is
equivalent to 45 but 45Q is explicit regarding the orientation.
EXAMPLE 1 An application specification can specify a symbol quality requirement as 1,5/05/660 to indicate that
the required symbol quality is 1,5 or higher obtained using an aperture size of 0,125 mm (reference number 05) with
660 nm light incident from 45° from four sides.
EXAMPLE 2 Using a white light with 5400 K, the light source is 1,5/05/W(5400 K).
Other lighting options are defined in ISO/IEC 29158 which can be more appropriate for direct part marking
applications, especially in applications which utilize symbols marked on reflective substrates. Therefore,
ISO/IEC 29158 should be specified by an application specification as the method of grading when such
lighting options are preferred in an application.
5.5 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
© ISO/IEC 2024 – All rights reserved
where
grade indicates the symbol grade as defined in 5.3;
aperture indicates the aperture reference number (from ISO/IEC 15416 for linear scanning techniques,
or the diameter in thousandths of an inch (expressed to the nearest thousandth or a to higher
precision) of the aperture defined in 5.6.2;
light indicates the numeric value indicates the peak light wavelength (i.e. the illumination) in nano-
metres (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 indicates the angle of incidence (an additional parameter, relative to the plane of the symbol)
of the illumination from four sides.
The angle shall be included in the reporting of the overall symbol grade when the angle of incidence differs
from the default orientation of 45° from four sides. While it may be included for the default orientation, its
absence indicates that the angle of incidence is 45° from four sides.
The notation used to specify a minimum grade that is required in an application is similar to the notation
used to report a grade result, but the grading requirement specifies a minimum for the grade in an
application, whereas the result specifies a specific occurrence of a grade produced by verifying a symbol.
EXAMPLE 1 2,8/05/660 indicates that the overall grade was 2,8 and was obtained with the use of a 0,125 mm
aperture (reference number 05) and a 660 nm light source, incident at 45° from four sides.
EXAMPLE 2 2,8/10/W/30Q indicates that the grade of a symbol was 2,8 and was obtained with broadband light,
measured with light incident at 30° from four sides and using a 0,250 mm aperture (reference number 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.
EXAMPLE 3 2,8/10/670 indicates that the grade of a symbol was 2,8 and was obtained using a 0,250 mm aperture
(reference number 10), and a 670 nm light source, incident at 45° from four sides.
NOTE The previous edition of this document defined the use of a * to indicate the presence of extreme reflectance
in or near the symbol. This has been removed in this edition of this document.
5.6 Optical setup and obtaining the test images
5.6.1 General requirements
Equipment for assessing the quality of symbols in accordance with this clause shall comprise a means of
measuring and analysing the variations in the reflectivity of a symbol on its substrate over an inspection
area which shall cover the full height and width of the symbol including all quiet zones. All measurements on
a two-dimensional matrix symbol shall be made within the inspection area defined in accordance with 5.6.4.
The measured reflectance values shall be expressed in percentage terms by means of calibration to a
reference reflectance standard traceable to National Measurement Institutes.
NOTE Maximum white diffuse reflectance is taken as 100 %.
The peak light wavelength or, in the case of applications designed for the use of broadband illumination,
the reference spectral response characteristics, should be specified in the application specification to
suit the intended scanning environment. Light sources may either have inherently narrow band or near-
monochromatic characteristics or have broad bandwidths. Special care is necessary when making
measurements with broadband illumination. The overall spectral response of the measurement and reading
systems shall be defined and matched in order to make accurate and repeatable measurements of the
grey-scale reflectance of a sample area that correlate with the intended system. Overall spectral response
includes the spectral distribution of the light source, the response of the detector and any associated filter
characteristics.
© ISO/IEC 2024 – All rights reserved
Refer to Annex C for guidance on the selection of the light source.
5.6.2 Convolving with the measuring aperture
The measuring aperture is specified by the application specification to suit the X dimensions of the symbols
in the application and the intended scanning environment. The measuring aperture is applied by convolving
the raw image with a synthetic aperture and defined by a kernel of equal weights within a round area and
zero outside. The purpose of applying an aperture is
a) to reduce the effect of small imperfections in the symbol, such as substrate texture and printing defects, and
b) to standardize the operation of verification devices, independent of the pixel density (resolution) of
each device.
NOTE The aperture can be a physical one, as is common for implementations of ISO/IEC 15416. In any case, this
convolving aperture is not to be confused with an aperture of a lens.
5.6.3 Geometry of the optical setup
A reference optical geometry is defined for reflectivity measurements and consists of:
— flood incident illumination, uniform across the inspection area, from a set of four light sources arranged
at intervals of 90° around a circle concentric with the inspection area and in a plane parallel to that of
the inspection area, at a height which allows incident light to fall on the centre of the inspection area at
an angle of 45° (or another angle if specified for the application) to its plane, and
— a light collection device, the optical axis of which is perpendicular to the inspection area and passes
through its centre, and which focuses an image of the test symbol on a light-sensitive array.
The light reflected from the inspection area (see 5.6.4) shall be collected and focussed on the light-sensitive array.
Two principles govern the design of the optical set-up.
— First, the test image’s grey-scale shall be nominally linear and not be enhanced in any way (such as a
gamma correction). Filters which modify the spectral characteristics of the light source should only be
used to remove unwanted ambient light and/or to produce the spectral characteristics of illumination
specified for an application (such as a particular narrow band). Other filters should be avoided or used
only when they are consistent with an application specification (see C.1.1) in which case it shall be
reported along with the grade. A filter that merely restricts the spectral components to the specified
wavelength need not be reported, but one which introduces special effects, such as a UV (ultraviolet)
filter, shall be reported. In any case where the use of a filter significantly affects a measurement, the
usage of the filter shall be reported along with the grade.
— Second, the image resolution shall be adequate to produce consistent readings. Implementations
should have sufficient resolution irrespective of the rotation, unless the manufacturer defines handling
instructions which restricts the angle of the symbol in relation to the camera sensor orientation.
NOTE 1 The conformance requirements in ISO/IEC 15426-2 are useful for confirming adequate resolution.
Alternative optical arrangements may be used in an implementation, provided that the measurements
obtained with them can be correlated with the use of the reference or the specified optical arrangement. In
particular, the tolerances specified in ISO/IEC 15426-2 shall be met. Furthermore, application specifications
can establish alternative optical arrangements, in accordance with 5.4, which are better aligned to an
application and thus can result in different results than the reference optical arrangement.
Figures 1 and 2 illustrate the principle of the optical arrangement but are not intended to represent actual
devices; the magnification of the device in particular is likely to differ from 1:1.

© ISO/IEC 2024 – All rights reserved
The general test set-up defined in this optical geometry should work suitably for many open applications
with methodology described in this document. However, for direct part mark applications, application
specifications should consider using ISO/IEC 29158 instead.
NOTE 2 ISO/IEC 29158 establishes an extension of the methodology described in this document and is more
appropriate for many direct part marking applications.
This reference geometry is intended to provide a basis to assist the consistency of measurement and does
not necessarily correspond with the optical geometry of individual scanning systems. As stated in 5.4,
specialised applications, and especially those involving direct part marking which employs physical changes
to the surface of the substrate for the creation of the graphic image, can require the angle of illumination in
particular to be set to a different particular angle, such as 30°, to the plane of the symbol. If an angle and/
or orientation, other than the default is used, then the angle of incidence and orientation of the light shall be
stated as a fourth parameter when reporting the overall symbol grade, as described in 5.5.
The modified methodology that is specified in ISO/IEC 29158 intended for direct part marking applications
defines more illumination options and should be used in applications where diffuse lighting from four sides
does not provide adequate correlation with the requirements of a specialised application.
Key
1 light sensing element
2 lens providing 1:1 magnification (i.e. measurement A equals to measurement B)
3 inspection area
4 light sources
ϑ angle of incidence of light relative to plane of symbol (the default is equal to 45°, optionally 30° or 90° diffuse)
Figure 1 — Reference optical arrangement — Side view

© ISO/IEC 2024 – All rights reserved
Key
L light source
S symbol
Figure 2 — Reference optical arrangement — Plan view
5.6.4 Inspection area
The inspection area for all measurements shall be an area framing the complete symbol, including quiet
zones. The centre of the inspection area shall be as close as practicable to the centre of the field of view.
NOTE The inspection area is not the same as the field of view of the verifier, which is often larger.
5.6.5 Measurement conditions
A test image of the symbol shall be obtained in a configuration that mimics the typical scanning situation
for that symbol, but with substantially higher resolution (see 5.6), uniform illumination and at best focus.
The reference optical arrangement is defined in 5.6.3. Alternative optical arrangements are also discussed
in 5.6.3.
Measurements shall be made with the light of a single peak wavelength or a set of spectral characteristics,
in accordance with 5.4. Ambient light levels shall be controlled to have no significant influence on the
measurement results.
Whenever possible, measurements shall be made on the symbol in its final configuration, i.e. the
configuration in which it is intended to be scanned. The geometry of the optical setup described in 5.6.3 is
intended to prevent extreme reflectance values outside the symbol area (e.g. when surrounded by free air or
a highly specular reflective surface) from distorting the symbol contrast measurements.

© ISO/IEC 2024 – All rights reserved
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 or
...