ISO/IEC TR 29158:2011

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

ISO/IEC TR 29158:2011 is an engineering document intended for verifier manufacturers and application specification developers. It describes modifications which are to be considered in conjunction with 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 grading of certain parameters, and the reporting of the grading results. ISO/IEC TR 29158:2011 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 may also be applied 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• Status: Withdrawn
• Publication Date: 05-Oct-2011
• Withdrawal Date: 05-Oct-2011
• ICS: 35.040 - Information coding
• 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: 9599 - Withdrawal of International Standard
• Completion Date: 14-Dec-2020

Relations

• Revised: ISO/IEC 29158:2020 - Information technology — Automatic identification and data capture techniques — Direct Part Mark (DPM) Quality Guideline
• Effective Date: 05-Nov-2015

Standards Content (Sample)

TECHNICAL ISO/IEC
REPORT TR
29158
First edition
2011-10-15


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 TR 29158:2011(E)
©
ISO/IEC 2011

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ISO/IEC TR 29158:2011(E)

COPYRIGHT PROTECTED DOCUMENT


©  ISO/IEC 2011
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
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Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail [e-mail]
Web www.iso.org
Published in Switzerland

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ISO/IEC TR 29158:2011(E)
Contents Page
Foreword . iv
Introduction . v
1  Scope . 1
2  Normative references . 1
3  Terms and definitions . 1
4  Abbreviated terms . 2
5  Overview of methodology . 3
5.1  Process differences from 15415 . 3
5.2  Lighting. 3
6  Obtaining the image . 3
6.1  Orientation of the symbol to the camera . 3
6.2  Lighting. 4
6.3  Image focus . 4
6.4  Reflectance calibration . 4
6.5  Initial image reflectance level of the symbol under test . 5
7  Obtaining the test image . 5
7.1  Binarize image . 5
7.2  Apply Reference Decode Algorithm . 5
7.3  Connect areas of the same colour . 6
7.4  Final image adjustment . 7
8  Determine contrast parameters . 7
8.1  Calculate Cell Contrast (CC) . 8
8.2  Calculate Cell Modulation (CM) . 8
8.3  Calculate % Reflectance of Symbol (Rtarget) . 8
9  Grading . 8
9.1  Cell Contrast (CC) . 8
9.2  Minimum Reflectance . 8
9.3  Cell Modulation (CM) . 8
9.4  Fixed pattern damage . 9
9.5  Final grade . 9
10  Communicating grade requirements and results . 9
10.1  Communication from Application to Verifier . 9
10.2  Communicating from Verifier to Application . 9
10.3  Communicating Lighting . 9
10.4  Communicating the use of a proprietary decode . 10
Annex A (normative) Threshold determination method . 11
Annex B (informative) Communicating the grade . 15
Annex C (informative) Cross-reference to ISO/IEC 15415 . 18

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ISO/IEC TR 29158:2011(E)
Foreword
ISO (the International Organization for Standardization) and IEC (the International Electrotechnical
Commission) form the specialized system for worldwide standardization. National bodies that are members of
ISO or IEC participate in the development of International Standards through technical committees
established by the respective organization to deal with particular fields of technical activity. ISO and IEC
technical committees collaborate in fields of mutual interest. Other international organizations, governmental
and non-governmental, in liaison with ISO and IEC, also take part in the work. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national bodies casting a vote.
In exceptional circumstances, when the joint technical committee has collected data of a different kind from
that which is normally published as an International Standard (“state of the art”, for example) it may decide to
publish a Technical Report. A Technical Report is entirely informative in nature and shall be subject to review
every five years in the same manner as an International Standard.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights.
ISO/IEC TR 29158 was prepared jointly by Joint Technical Committee ISO/IEC JTC 1, Information technology,
Subcommittee SC 31, Automatic identification and data capture techniques.

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ISO/IEC TR 29158:2011(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, ink jet, 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.
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. 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 applicator to define the appropriate
parameters of this guideline for use in conjunction with a particular application.



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TECHNICAL REPORT ISO/IEC TR 29158:2011(E)

Information technology — Automatic identification and data
capture techniques — Direct Part Mark (DPM) Quality Guideline
1 Scope
This Technical Report is an engineering document intended for verifier manufacturers and application
specification developers.
This Technical Report describes modifications which are to be considered in conjunction with 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 grading of
certain parameters, and the reporting of the grading results.
This Technical Report 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 may also be applied 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 referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO/IEC 15415, Information technology — Automatic identification and data capture techniques — Bar code
print quality test specification — Two-dimensional symbols
ISO/IEC 15416, Information technology — Automatic identification and data capture techniques — Bar code
print quality test specification — Linear symbols
ISO/IEC 19762-1, Information technology — Automatic identification and data capture (AIDC) techniques —
Harmonized vocabulary — Part 1: General terms relating to AIDC
ISO/IEC 19762-2, Information technology — Automatic identification and data capture (AIDC) techniques —
Harmonized vocabulary — Part 2: Optically readable media (ORM)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/IEC 15415, ISO/IEC 15416,
ISO/IEC 19762-1, ISO/IEC 19762-2 and the following apply.
3.1
MLcal
mean of the light lobe from a histogram of the calibrated standard
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ISO/IEC TR 29158:2011(E)
3.2
MLtarget
mean of the light lobe from the final grid-point histogram of the symbol under test
3.3
reference symbol
high-contrast printed calibration card
EXAMPLE The GS1 Data Matrix calibrated conformance standard test card.
3.4
Rcal
reported reflectance value, Rmax, from a calibration standard
3.5
Rtarget
measured percent reflectance of the light elements of the symbol under test relative to the calibrated standard
3.6
SRcal
system response parameters (such as exposure and/or gain) used to create an image of the calibration
standard
3.7
SRtarget
system response parameters (such as exposure and/or gain) used to create an image of the symbol under
test
3.8
stick
line segment comprised of image pixels that is used to connect areas of the same colour that are near to each
other
3.9
T1
threshold created using a histogram of the defined grey-scale pixel values in a circular area twenty times the
aperture size in diameter, centred on the image centre using the algorithm defined in Annex A
3.10
T2
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
4 Abbreviated terms
CM Cell Modulation
CC Cell Contrast
FPD Fixed pattern damage
LED Light emitting diode
MD MeanDark
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ISO/IEC TR 29158:2011(E)
5 Overview of methodology
5.1 Process differences from 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.
- A different process for determining the Modulation and Reflectance Margin parameter renamed Cell
Modulation.
- A different process for determining the Symbol Contrast parameter which has been renamed Cell Contrast.
- A difference process for computing Fixed Pattern Damage
- A new parameter called Minimum Reflectance.
This guideline explains how to both specify and report quality grades in a manner complementary to, yet
distinct from, the method in ISO/IEC 15415.
5.2 Lighting
This guideline recommends three specific lighting environments consisting of two forms of diffuse lighting
(non-directional):
- diffuse on-axis illumination uses a diffuse light source illuminating the symbol nominally
perpendicular to its surface (nominally parallel to the optical axis of the camera).
- diffuse off-axis illumination uses light from an array of LEDs reflected from the inside of a diffusely
reflecting surface of a hemisphere, with the symbol at its centre, to provide even incident illumination
from all directions.
- Directional illumination is oriented at a low angle (approximately 30 degrees) to the mark surface.
6 Obtaining the image
6.1 Orientation of the symbol to the camera
6.1.1 Camera position
The camera is positioned such that the plane of the image sensor is parallel to the plane of the symbol area.
6.1.2 Orienting the symbol
The part is placed such that the symbol is in the centre of the field of view and oriented so that the horizontal
lines in the symbol are parallel with a line formed by the edge of the image sensor to within +/- 5 degrees.
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ISO/IEC TR 29158:2011(E)
6.2 Lighting
Two lighting environments each with sub-options are defined in this document. The defined lighting
environments are denoted in the reported grade using the format defined in ISO/IEC 15415 using the angle
specifier with a combination of numbers and letters as defined below.
Note: This does not limit the prerogative of an Application Specification to choose different lighting
environments based on application requirements. Alternate lighting environments should include specifiers
consistent with the format of those below which can be used for communicating quality requirements and
quality grades.
6.2.1 Diffuse perpendicular (on-axis/bright field) (90)
A flat diffusing material is oriented such that the plane of the material is parallel to the plane of the symbol
area. The symbol is uniformly illuminated with diffuse light incident at 90 +/- 15 degrees relative to the optical
axis to the plane of the symbol. The angle specifier shall be 90 to denote this lighting environment.
6.2.2 Diffuse off-axis (D)
A diffusely reflecting dome is illuminated from below so that the reflected light falls non-directionally on the
part and does not cast defined shadows. This is commonly used for reading curved parts. The angle specifier
shall be D.
6.2.3 Low angle, four direction (30Q)
Light is aimed at the part at an angle of 30 +/- 3 degrees from the plane of the surface of the symbol from four
sides such that the lines describing the centre of the beams from opposing pairs of lights are co-planar and
the planes at right angles to each other. One lighting plane is aligned to be parallel to the line formed by a
horizontal edge of the image sensor to within +/- 5 degrees. The lighting shall illuminate the entire symbol
area with uniform energy. The angle specifier shall be 30Q.
6.2.4 Low angle, two direction (30T)
Light is aimed at the part at an angle of 30 +/- 3 degrees from two sides. The light may be incident from either
of the two possible orientations with respect to the symbol. The lighting plane is aligned to be parallel to the
line formed by one edge of the image sensor to within +/- 5 degrees. The lighting shall illuminate the entire
symbol area with uniform energy. The angle specifier shall be 30T.
6.2.5 Low angle, one direction (30S)
Light is aimed at the part at an angle of 30 +/- 3 degrees from one side. The light may be incident from any of
the four possible orientations with respect to the symbol. The plane perpendicular to the symbol surface
containing the centre of the beam is aligned to be parallel to the line formed by one edge of the image sensor
to within +/- 5 degrees. The lighting shall illuminate the entire symbol area with uniform energy. The angle
specifier shall be 30S.
6.3 Image focus
The camera is adjusted such that the symbol is in best focus.
6.4 Reflectance calibration
Using a high-contrast, nationally traceable printed calibration card (such as the GS1 Data Matrix calibrated
conformance standard test card) calibrated using a known aperture, take an image of the calibration card.
Using the known aperture size, sample the centre of every element in the image, not including the outer
spaces, and pick the highest reflectance of the target.
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ISO/IEC TR 29158:2011(E)
Set the system response so that the mean of the light elements is in the range of 70% to 86% of the maximum
grey scale (MLcal) and the black level (no light) is nominally equal to zero. The system response is the linear
relationship between the reflectivity of the target and the pixel intensity values in the image as a result of
several factors (e.g. shutter speed, imager sensitivity, f-stop, gain, illumination intensity.) This procedure
requires the ability to adjust at least one of these factors in order to adjust the system response.
Record the system response as the Reference System Response (SRcal) and record MLcal.
6.5 Initial image reflectance level of the symbol under test
6.5.1 Initialize aperture size
Set the aperture to 0.8 of the minimum X-dimension of the application, and apply it to the original image to
create a reference greyscale image.
6.5.2 Create initial histogram of symbol under test
Create a histogram of the reference grey-scale pixel values in a circular area 20 times the aperture size in
diameter, centred on the image centre, and find the Threshold, T1, using the algorithm defined in Annex A.
The threshold divides the histogram into two portions: a portion less than the threshold which contains dark
pixels and a portion greater than the threshold which contains light pixels (called the “light lobe”).
6.5.3 Compute mean
Compute the mean of the light lobe.
6.5.4 Optimize image
Adjust the system response by taking new images and repeating steps 6.5.1 and 6.5.2 until the mean of the
light elements is in the range of 70% to 86% of the maximum grey scale.
7 Obtaining the test image
The referenced matrix symbologies all require the locating of continuous modules in their reference decode
algorithms. Some marking technologies are not capable of producing symbols with smooth, continuous lines
when viewed by an imager. For example, dot peened symbols often produce unconnected dots. This section
includes a method of pre-processing the image that will connect disconnected modules so that the standard
reference decode algorithms can operate successfully.
Once the grid of the symbol is determined, the location information is transferred to the evaluation of the
reference greyscale image and subsequent processing occurs using the reference greyscale image.
7.1 Binarize image
Compute a reference greyscale image using the current aperture size. Using T1, binarize the entire image.
7.2 Apply Reference Decode Algorithm
Attempt to find and process the symbol using the symbology Reference Decode Algorithm and the current
aperture size. If the attempt fails, go to 7.3. If successful go to 7.4.
Note: where a symbology has a reference decode algorithm that operates successfully on nominally
disconnected modules (e.g. “dot” codes) the process of connecting modules is inappropriate. With these
symbologies, if the application of the Reference Decode Algorithm fails then go to 7.3.4 (not 7.3).
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ISO/IEC TR 29158:2011(E)
7.3 Connect areas of the same colour
This process is called the "stick function" and operates on the binarized image. The output is used for the
initial decode using the reference decode algorithm. The steps below seek to connect areas in the image that
are separated by less than one module, while not connecting areas which are separated by a distance of a
module or more, for example alternating "clock teeth" modules.
7.3.1 Initializing stick size and module colour
Since a module size is not known during the execution of this algorithm, successively larger distance guesses
are used within a range from the size of 50% of the smallest X-dimension to 110% of the largest X-dimension
allowed by the application specification.
In addition, knowledge of the colour of “on” versus “off” modules is also required by the algorithm. Generally
the “on” colour is dark for bright field illumination and light for dark field illumination. (For instance, the "on"
colour is the colour of the “L” pattern of a Data Matrix symbol.) If a verifier does not “know” the colour of "on",
the algorithm may need to be repeated for each case.
Note: Implementers are free to optimize this algorithm (such as by attempting a better first guess of the
correct stick size by analyzing the image), as long as the equivalent result is obtained.
7.3.2 Connect like colours
1. Prepare by:
a) Setting every pixel in the output image to the background (off) colour.
b) Selecting an initial stick size equal to 50% of the minimum X of the application.
2. Starting on the row of the image one half-stick length down from the top, and the column one half-stick
length in from the left:
a) If the colour of the pixel is the “on” colour, set the pixel in the same position in the output image to the
“on” colour, and continue at step 2e.
b) Find the two pixels which are one-half stick distance to the left and one-half the stick distance to the
right and the two pixels that are one-half stick distance above and below.
c) If both of the horizontal or vertical pixels found in step 2b are the “on” colour, then go to step 2d else
continue to step 2e.
d) For each pixel on the line or lines between the two "on" pixels found in step 2b (a line equal in length
to the stick), set the correspondingly positioned pixels in the output image to the “on” colour.
e) Move to the next pixel and go to step 2a. (If the position of the current pixel is one half-stick length in
from the right, the next pixel is at the start of the column one half-stick length in from the left of the
next row. If the position of the current pixel is on the row one half stick length up from the bottom, and
one half stick length in from the right, exit since the image is completely processed.)

7.3.3 Apply the Reference Decode Algorithm
The referenced matrix symbologies all require the locating of continuous modules in their reference decode
algorithms. Some marking technologies are not capable of producing symbols with smooth, continuous lines
when viewed by an imager. For example, dot peened symbols often produce unconnected dots.
Once the primary lines of the symbol are determined, the location information is transferred to the evaluation
of the original image and subsequent processing occurs using the original image.
Using the connected image from 7.3.2, find the symbology reference lines with the symbology reference
decode algorithm. Note: for example, the symbology reference lines for Data Matrix comprise the "L."
Transfer the reference lines to the original binarized image. Perform the rest of the reference decode
algorithm. If successful, go to 7.4.
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ISO/IEC TR 29158:2011(E)
7.3.4 Repeat if necessary
If the decode attempt fails, choose a new stick size that is at least one pixel more in length and a new aperture
size equal to 0.8 stick size and go to 7.1.
7.3.5 Continue until end
Continue until the symbol is successfully decoded or the stick size exceeds the maximum stick size or one-
tenth of the maximum image dimension in pixels (if the maximum X-dimension is not known). If the lines are
not found, the symbol grade is Zero.
Note: This algorithm assumes that the symbol is oriented orthogonal to the image sensor, so that modules
that must be connected are aligned vertically and horizontally in the image. If this were not true, the stick
would need to be rotated through all angles, in addition to the vertical and horizontal directions.
7.4 Final image adjustment
This procedure uses only the nominal centres of modules to create a highly bi-modal histogram of the symbol
reflectance states.
7.4.1 Determine grid-point reflectance with two apertures
Re-compute the reference grey-scale image using two new aperture sizes equal to 0.5 and 0.8 of the
measured average grid spacing. Perform the following calculations and grading for both apertures.
7.4.2 Create a grid-point histogram
Create a histogram of the reference grey-scale image pixel values at each intersection point of the grid
determined from the decode and find T2 using the algorithm defined in Annex A.
7.4.3 Measure MeanLight
Measure the MeanLight of the grid-centre point histogram. If it is in the range of 70% to 86% of the maximum
grey scale then retain the values for MeanDark (MD) and MeanLight.
If not, adjust the system response and go to 7.4.1
7.4.4 Record parameters
Set MLtarget equal to MeanLight. Record the system response as SRtarget. Record the new T2.
7.4.5 Create binarized images for the Symbology Reference Decode
If the decode was achieved using the Stick Function then set the stick size to the average grid spacing and
apply the stick algorithm using T2 on the new reference grey-scale image to create the final binarized image.
Otherwise, binarize using T2.
7.4.6 Decode
Decode the final binary image using the steps of 7.3.3 through 7.4.5 using the symbology Reference Decode
Algorithm. Recalculate T2 using the grid centres of this decode. If this decode fails, apply the stick algorithm in
7.4.5 and decode again.
8 Determine contrast parameters
Calculate t
...