ISO/IEC 29158:2020

INTERNATIONAL ISO
STANDARD 29158
First edition
Information technology — Automatic
identification and data capture
techniques — Direct Part Mark (DPM)
Quality Guideline
Technologies de l'information — Techniques automatiques
d'identification et de capture de données — Ligne directrice de
qualité du marquage direct sur pièce (DPM)
PROOF/ÉPREUVE
Reference number
ISO 29158:2020(E)
©
ISO 2020

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ISO 29158:2020(E)

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© ISO/IEC 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 29158:2020(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Overview of methodology . 2
5.1 Process differences from ISO/IEC 15415. 2
5.2 Lighting . 3
5.3 Tilted coaxial lighting and camera position (TCL) . 3
6 Obtaining the image . 4
6.1 Camera position and symbol orientation. 4
6.1.1 Symbol placement . 4
6.1.2 Camera position in a 90 ° camera angle set up . 5
6.1.3 TCL setup . 5
6.2 Lighting environments . 5
6.2.1 General. 5
6.2.2 Perpendicular coaxial (90) . 5
6.2.3 Diffuse off-axis (D) . 5
6.2.4 Four direction (angle Q) . 5
6.2.5 Two direction (angle T) . 5
6.2.6 One direction (angle S) . 6
6.2.7 TCL Setup . 6
6.3 Image focus . 6
6.4 Depth of field . 6
6.5 System response adjustment and reflectance calibration . 6
7 Verifying a symbol . 7
7.1 Initial image reflectance. 7
7.1.1 General. 7
7.1.2 Initialize aperture size . 7
7.1.3 Create initial histogram. 7
7.1.4 Compute mean . 7
7.1.5 Optimize image . 7
7.2 Obtaining the test image . 7
7.2.1 Matrix symbologies . 7
7.2.2 Binarize image . 7
7.3 Apply Reference Decode Algorithm . 8
7.3.1 General. 8
7.3.2 Repeat if necessary . 8
7.3.3 Continue until end . 8
7.4 Final image adjustment . 8
7.4.1 General. 8
7.4.2 Determine grid-point reflectance with two apertures . 8
7.4.3 Create a grid-point histogram . 8
7.4.4 Measure mean light (M ) . 8
L
7.4.5 Record parameters . . 8
7.4.6 Create binarized images for the symbology reference decode . 9
7.4.7 Decode . 9
8 Determine contrast parameters . 9
8.1 Initialize aperture size . 9
8.2 Calculate cell contrast (CC) . 9
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ISO 29158:2020(E)

8.3 Calculate cell module modulation (CMOD) . 9
8.4 Calculate minimum reflectance (R ) . 9
target
9 Grading .10
9.1 Cell contrast (CC) .10
9.2 Minimum reflectance (R ) .10
target
9.3 Cell modulation (CM) .11
9.4 Fixed pattern damage (FPD) .11
9.5 Final grade .12
10 Communicating grade requirements and results .12
10.1 General .12
10.2 Communication of application requirements .12
10.3 Communicating from verifier to application .12
10.4 Communicating the use of a proprietary decode .12
Annex A (normative) Threshold determination method .14
Annex B (informative) Evaluation of image at virtual 90° camera position from real tilted
camera position .18
Annex C (normative) Continuous grading for ISO/IEC 15415 parameters .22
Annex D (normative) Dot connecting algorithm .27
Annex E (informative) Communicating the grade .29
Annex F (informative) Cross reference to ISO/IEC 15415 .32
Bibliography .33
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ISO 29158:2020(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.
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).
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. Details of any patent rights identified during the development of the document will be in the
Introduction and/or on the ISO list of patent declarations received (see www .iso .org/ patents) or the
IEC list of patent declarations received (see https:// patents .iec .c).
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.
This document was prepared by Joint Technical Committee ISO/TC JTC 1, Information Technology,
Subcommittee SC 31, Automatic identification and data capture techniques.
This first edition cancels and replaces ISO/IEC TR 29158:2011, which has been technically revised.
The main changes compared to the previous edition are as follows:
— inclusion of continuous grading;
— expanded grading levels for minimum reflectance (R );
target
— inclusion of a tilted lighting and camera position;
— reorganized proposed lighting options.
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.
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ISO 29158:2020(E)

Introduction
Direct Part Marking (DPM) is a technology whereby, generally, an item is physically altered to produce
two different surface conditions. This alteration can be accomplished by various means including, but
not limited to, dot peen, laser mark, ink jetting, and electro-chemical etch. The area of the alteration
is called "the mark." The area that includes the mark and background as a whole, when containing a
pattern defined by a bar code symbology specification, is called "a symbol."
When light illuminates a symbol, it reflects differently depending on whether it impinges on the
background of the part or on the physical alteration. In most non-DPM bar code scanning environments,
light is reflected off a smooth surface that has been coloured to produce two different diffuse reflected
states. The DPM environment generally does not fit this model because the two different reflected
states depend on at least one of the states having material oriented to the lighting such that the angle
of incidence is equal to the angle of reflection. Sometimes the material so oriented produces a specular
(mirror like) reflectance that results in a signal that is orders of magnitude greater than the signal from
diffuse reflectance.
In addition, from the scanner point-of-view, some marking and printing methods generate dots and are
not capable of producing smooth lines. This is important for symbologies such as Data Matrix, which
is specified to contain smooth continuous lines, but can be marked with disconnected dots in DPM
applications.
Current specifications for matrix symbologies and two-dimensional print quality are not exactly suited
to reading situations that have either specular reflection or unconnected dots or both. Additionally,
symbologies specified to consist of smooth continuous lines may appear with unconnected dots. This
is intended to act as a bridge between the existing specifications and the DPM environment in order
to provide a standardized image-based measurement method for DPM that is predictive of scanner
performance.
As with all symbology and quality standards, it is the responsibility of the application to define the
appropriate parameters of this guideline for use in conjunction with a particular application.
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INTERNATIONAL STANDARD ISO 29158:2020(E)
Information technology — Automatic identification and
data capture techniques — Direct Part Mark (DPM) Quality
Guideline
1 Scope
This document is an engineering document intended for verifier manufacturers and application
specification developers.
This document describes modifications to the symbol quality methodology defined in ISO/IEC 15415
and a symbology specification. It defines alternative illumination conditions, some new terms and
parameters, modifications to the measurement and subsequent grading of certain parameters and the
reporting of the grading results.
This document was developed to assess the symbol quality of direct marked parts, where the mark is
applied directly to the surface of the item and the reading device is a two-dimensional imager.
When application specifications allow, this method is also potentially applicable to symbols produced
by other methods. This is appropriate when direct part marked (DPM) symbols and non-DPM symbols
are being scanned in the same scanning environment. The symbol grade is reported as a DPM grade
rather than as an ISO/IEC 15415 grade.
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 15415, Information technology — Automatic identification and data capture techniques — Bar
code symbol print quality test specification — 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 and ISO/IEC 15415
and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
reference symbol
high-contrast printed calibration card for which results are traceable back to national or international
standards and for which the supplier supplies a calibration certificate
3.2
stick
line segment comprised of image pixels that is used to connect areas of the same colour that are near to
each other
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4 Symbols and abbreviated terms
CM cell modulation
CC cell contrast
CMOD cell module modulation
FPD fixed pattern damage
M mean of the grid-centre point histogram of the dark elements
D
M mean of the grid-centre point histogram of the light elements
L
M mean of the light lobe from a histogram of the calibrated standard
Lcal
M mean of the light lobe from the final grid-point histogram of the symbol under test
Ltarget
R reported reflectance value, Rmax, from a calibration standard
cal
R measured percent reflectance of the light elements of the symbol under test relative to the
target
calibrated standard
NOTE R is graded and reported as the parameter named “Minimum Reflectance”.
target
S system response parameters (such as exposure and/or gain) used to create an image of the
Rcal
calibration standard
S system response parameters (such as exposure and/or gain) used to create an image of the
Rtarget
symbol under test
T threshold created using a histogram of the defined grey scale pixel values in a circular area
1
20 times the aperture size in diameter, centred on the image centre using the algorithm
defined in Annex A
T threshold created using the histogram of the reference grey scale image pixel values at
2
each intersection point of the grid using the method defined in Annex A
T current minimum threshold in the calculation of the optimal threshold according Annex A
min
T current maximum threshold in the calculation of the optimal threshold according Annex A
max
TCL tilted coaxial lighting and camera position
5 Overview of methodology
5.1 Process differences from ISO/IEC 15415
All parameters in the symbology and print quality specifications apply except for:
— a different method for setting the image contrast;
— a different method for creating the binary image;
— a new method for choosing the aperture size;
— an image pre-process methodology for joining disconnected modules in a symbol (where applicable);
— a different process for determining the modulation and reflectance margin parameter renamed cell
modulation (CM);
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— a different process for determining the symbol contrast parameter which has been renamed cell
contrast (CC);
— a different process for computing FPD;
— A new parameter called minimum reflectance (R ).
target
Axial nonuniformity, grid nonuniformity and unused error correction are applied with their continuous
grading grades as defined in Annex C, so long as ISO/IEC 15415 does not provide information on
continuous grading for these parameters. If/when ISO/IEC 15415 does provide continuous grading
on these parameters, that information will be used. This document explains how to both specify and
report quality grades in a manner complementary to, yet distinct from, the method in ISO/IEC 15415.
NOTE Annex F gives a cross reference comparison of this document to ISO/IEC15415.
5.2 Lighting
Lighting environments shall be reported according to 6.2 and 10.2. The lighting environment(s) shall be
selected by the application standard in consideration of the properties of the mark and the requirements
of the reading equipment and environment of the application.
5.3 Tilted coaxial lighting and camera position (TCL)
TCL is useful for DPM applications that use a geometrical mark which is peened, drilled or carved into a
surface. Reading camera and unidirectional illumination are located at a coaxial position with a known
fixed tilt angle and object rotation angle and position.
To read dot-peened codes, there are multiple reading setups possible. This document defines several
camera and lighting setups in order to address various dot peen geometries.
This specific TCL environment is focussing on the system response of the mark (e.g. the image a camera
[2]
sees). SAE Standard AS9132 takes a different approach to specify the mark geometry.
Figure 1 illustrates the setup. The essential parameter is the camera reading angle. Typical camera
reading angles include 30°, 45° or 60° in relation to the plane of the mark.
NOTE 1 The camera angle is defined in a compatible way to the lighting angle of ISO/IEC 15415:2011, Figure 3.
NOTE 2 Within the dot peen industry, it is common to specify the stylus angle which is twice the camera angle
given in Figure 1.
NOTE 3 In practice, the condition "coaxial lighting" may be implemented by an approximate setup like a high
distance ring. The light angle tolerance of ±3° should be respected.
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Key
c camera and coaxial lighting
m light beam in mark is reflected to camera
o light beam outside mark is reflected away
α camera reading angle
p peened mark
m marked object
Figure 1 — Tilted coaxial lighting and camera setup
This setup is referenced by the abbreviation "TCL" in the following text.
It is not feasible to grade this setup with a camera angle of 90°. The result will not be significant for this
application, as other features of the marked object are measured.
Note that a general-purpose verifier device may not cover this application, as it requires a special
construction.
6 Obtaining the image
6.1 Camera position and symbol orientation
6.1.1 Symbol placement
Camera to object position is described in this subclause. By default, the horizontal and vertical axis of
the symbol are parallel to a line formed by the edge of the image sensor within ± 3° (i.e. nominally no
rotation). This symbol orientation should be maintained unless an application specification requires
or allows a different orientation. An application specification may specify a different symbol rotation.
Since the symbol rotation is determined after decoding, the actual rotation angle should be reported
so that the setup can be reproduced easily. In applications in which the rotation angle is specified, the
rotation angle shall be reported to confirm conformance to specified requirements.
The part is placed such that the symbol is in the centre of the field of view.
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6.1.2 Camera position in a 90 ° camera angle set up
The camera is positioned such that the plane of the image sensor is parallel to the plane of the symbol
area. This is identical to a 90° camera angle.
6.1.3 TCL setup
Within the TCL setup, camera and symbol position differs in the following points.
— The camera is positioned in the camera angle defined by the application.
— The raw image is geometrically transformed to correspond to a test image with a virtual camera
position with a 90° camera angle, as described in Annex B.
— The symbol rotation angle needs to be specified by the application and shall be respected by ± 5°.
6.2 Lighting environments
6.2.1 General
The lighting environment is specified by the application. This shall include a direction specifier or an
angle or both. The format is an extension of the angle specifier used in ISO/IEC 15415. Several examples
are given in the following subclauses.
6.2.2 Perpendicular coaxial (90)
The symbol is illuminated with diffuse light such that the specular reflection from the entire field of
view is nominally uniform.
...