Information technology -- Automatic identification and data capture techniques -- Direct Part Mark (DPM) Quality Guideline

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.

Technologies de l'information -- Techniques automatiques d'identification et de capture de données -- Ligne directrice de qualité du marquage direct sur pièce (DPM)

General Information

Status
Published
Publication Date
13-Dec-2020
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
16-Nov-2020
Completion Date
16-Nov-2020
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INTERNATIONAL ISO/IEC
STANDARD 29158
First edition
2020-12
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)
Reference number
ISO/IEC 29158:2020(E)
ISO/IEC 2020
---------------------- Page: 1 ----------------------
ISO/IEC 29158:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2020

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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/IEC 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

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

© ISO/IEC 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/IEC 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

iv © ISO/IEC 2020 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/IEC 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.
© ISO/IEC 2020 – All rights reserved v
---------------------- Page: 5 ----------------------
ISO/IEC 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.

vi © ISO/IEC 2020 – All rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO/IEC 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
© ISO/IEC 2020 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO/IEC 29158:2020(E)
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
M mean of the grid-centre point histogram of the light elements
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, R , from a calibration standard
cal max

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

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

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);
2 © ISO/IEC 2020 – All rights reserved
---------------------- Page: 8 ----------------------
ISO/IEC 29158:2020(E)

— 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.
© ISO/IEC 2020 – All rights reserved 3
---------------------- Page: 9 ----------------------
ISO/IEC 29158:2020(E)
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.
4 © ISO/IEC 2020 – All rights reserved
---------------------- Page: 10 ----------------------
ISO/IEC 29158:2020(E)
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.
6.2.3 Diffuse off-axis (D)
A diffusely reflecting dome is illuminated
...

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
---------------------- Page: 1 ----------------------
ISO 29158:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO/IEC 2020

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: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii PROOF/ÉPREUVE © ISO/IEC 2020 – All rights reserved
---------------------- Page: 2 ----------------------
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

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

© ISO/IEC 2020 – All rights reserved PROOF/ÉPREUVE iii
---------------------- Page: 3 ----------------------
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

iv PROOF/ÉPREUVE © ISO/IEC 2020 – All rights reserved
---------------------- Page: 4 ----------------------
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.
© ISO/IEC 2020 – All rights reserved PROOF/ÉPREUVE v
---------------------- Page: 5 ----------------------
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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ISO 29158:2020(E)
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
M mean of the grid-centre point histogram of the light elements
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

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

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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ISO 29158:2020(E)

— 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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ISO 29158:2020(E)
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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ISO 29158:2020(E)
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.
...

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