SIST-TS CEN/TS 14826:2022
(Main)Postal services - Automatic identification of items - Two dimensional bar code symbol print quality specification for machine readable Digital Postage Marks
Postal services - Automatic identification of items - Two dimensional bar code symbol print quality specification for machine readable Digital Postage Marks
This document:
- specifies a methodology for the measurement of defined print quality attributes of Digital Postage Marks in the form of two-dimensional bar code symbols on mail-pieces;
- defines methods for grading the results of these measurements and deriving an overall symbol quality grade as a guide to estimating the readability of the Digital Postage Marks;
- provides guidelines for printing and gives information on possible causes of deviation from high grades to assist users in taking appropriate corrective action;
- defines a test procedure for the assessment of printing systems for the production of Digital Postage Marks.
These provisions apply to the Digital Postage Mark blocks as they appear on fully produced mail items when remitted to postal operators, including the characteristics resulting from operations other than printing per se that affect their appearance to a mail processing system (covering, inserts into transparent window envelopes, affixed Digital Postage Mark labels).
This document does not define the qualification tests or sampling requirements necessary to determine the practical feasibility of any specific read rate.
Although this document is not intended for barcodes (other than Digital Postal Marks) which can be printed on mail pieces for item identification or additional services, a similar methodology can be applied.
Postalische Dienstleistungen - Automatische Identifizierung von Sendungen - Druckqualität von zwei-dimensionalen Strichcodes für Digitale Freimachungsvermerke
Dieses Dokument
— spezifiziert eine Methodik für die Messung festgelegter Druckqualitätsattribute von Digitalen Freimachungsvermerken in Form von zwei dimensionalen Strichcodesymbolen auf Sendungen,
— legt Verfahren zur Einstufung der Messergebnisse und zur Ermittlung einer Gesamtsymbolqualität fest, die als Leitfaden für die Abschätzung der Lesbarkeit Digitaler Freimachungsvermerke dient,
— liefert Leitlinien für den Druck und gibt Informationen zu möglichen Ursachen für eine Abweichung von hohen Qualitätseinstufungen, um Anwender beim Ergreifen geeigneter Korrekturmaßnahmen zu unterstützen und
— legt ein Prüfverfahren für die Beurteilung von Drucksystemen für die Herstellung Digitaler Freimachungs¬vermerke fest.
Diese Bestimmungen gelten für Digitale Freimachungsvermerkblöcke, wie sie auf vollständig fertiggestellten Sendungen bei der Anlieferung beim Postbetreiber erscheinen, einschließlich der Merkmale, die aufgrund anderer Verfahren als dem eigentlichen Drucken entstehen und die das Erscheinungsbild für ein Postbearbeitungssystem beeinflussen (Hüllen, Einlagen in Umschlägen mit transparenten Sichtfenstern, Aufklebeetiketten mit Digitalen Freimachungsvermerken).
Dieses Dokument legt keine Qualifikationsprüfungen oder Probenahmeanforderungen fest, die zur Ermittlung der praktischen Erreichbarkeit einer spezifischen Leserate erforderlich sind.
Auch wenn dieses Dokument nicht für Strichcodes (ausgenommen Digitale Freimachungsvermerke) gedacht ist, die für die Sendungsidentifizierung oder für zusätzliche Dienstleistungen auf Sendungen gedruckt werden können, kann für diese eine ähnliche Methodik verwendet werden.
Services postaux - Identification automatique des envois postaux - Mesure de la qualité d'impression des Marques d'Affranchissement Digitales sous la forme de symboles de codes à barres bidimensionnels lisibles par une machine
Poštne storitve - Avtomatska identifikacija pošiljk - Specifikacija kakovosti tiska dvodimenzionalnega simbola črtne kode za strojno branje digitalne poštne označbe
Ta dokument:
– določa metodologijo za merjenje opredeljenih lastnosti kakovosti tiska digitalnih poštnih označb v obliki dvodimenzionalnih simbolov črtne kode na poštnih pošiljkah;
– opredeljuje metode za razvrščanje rezultatov teh meritev in izpeljavo splošne kategorije kakovosti simbola kot vodilo pri ocenjevanju berljivosti digitalnih poštnih označb;
– podaja smernice za tiskanje in informacije o možnih vzrokih za odstopanje od visokih kategorij kakovosti, ki so uporabnikom v pomoč pri sprejemanju ustreznih popravnih ukrepov;
– opredeljuje preskusni postopek za ocenjevanje sistemov tiskanja, namenjenih za izdelavo digitalnih poštnih označb.
Te določbe se uporabljajo za bloke digitalnih poštnih označb, kot so prikazani na dokončanih poštnih pošiljkah ob predaji poštnim operaterjem, vključno z značilnostmi, ki niso posledica samega tiskanja, temveč izhajajo iz drugih postopkov, ki vplivajo na njihov videz v sistemu za obdelavo pošte (pokrivanje, vstavljanje v ovojnice s prozornim okencem, pritrditev nalepke digitalne poštne označbe). Ta dokument ne določa preskusov ustreznosti ali zahtev za vzorčenje, ki so potrebni za določitev praktične izvedljivosti katere koli določene hitrosti branja.
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-september-2022
Nadomešča:
SIST-TS CEN/TS 14826:2005
Poštne storitve - Avtomatska identifikacija pošiljk - Specifikacija kakovosti tiska
dvodimenzionalnega simbola črtne kode za strojno branje digitalne poštne
označbe
Postal services - Automatic identification of items - Two dimensional bar code symbol
print quality specification for machine readable Digital Postage Marks
Postalische Dienstleistungen - Automatische Identifizierung von Sendungen -
Druckqualität von zwei-dimensionalen Strichcodes für Digitale Freimachungsvermerke
Services postaux - Identification automatique des envois postaux - Mesure de la qualité
d'impression des Marques d'Affranchissement Digitales sous la forme de symboles de
codes à barres bidimensionnels lisibles par une machine
Ta slovenski standard je istoveten z: CEN/TS 14826:2022
ICS:
03.240 Poštne storitve Postal services
35.040.50 Tehnike za samodejno Automatic identification and
razpoznavanje in zajem data capture techniques
podatkov
35.240.69 Uporabniške rešitve IT pri IT applications in postal
poštnih storitvah services
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
CEN/TS 14826
TECHNICAL SPECIFICATION
SPÉCIFICATION TECHNIQUE
July 2022
TECHNISCHE SPEZIFIKATION
ICS 03.240; 35.040.50; 35.240.69 Supersedes CEN/TS 14826:2004
English Version
Postal services - Automatic identification of items - Two
dimensional bar code symbol print quality specification
for machine readable Digital Postage Marks
Services postaux - Identification automatique des Postalische Dienstleistungen - Automatische
envois postaux - Mesure de la qualité d'impression des Identifizierung von Sendungen - Druckqualität von
Marques d'Affranchissement Digitales sous la forme de zwei-dimensionalen Strichcodes für Digitale
symboles de codes à barres bidimensionnels lisibles Freimachungsvermerke
par une machine
This Technical Specification (CEN/TS) was approved by CEN on 6 June 2022 for provisional application.
The period of validity of this CEN/TS is limited initially to three years. After two years the members of CEN will be requested to
submit their comments, particularly on the question whether the CEN/TS can be converted into a European Standard.
CEN members are required to announce the existence of this CEN/TS in the same way as for an EN and to make the CEN/TS
available promptly at national level in an appropriate form. It is permissible to keep conflicting national standards in force (in
parallel to the CEN/TS) until the final decision about the possible conversion of the CEN/TS into an EN is reached.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN/TS 14826:2022 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Symbols and abbreviations . 8
5 Requirements . 8
6 Basic measurement methodology . 10
7 Verification requirements for Digital Postage Marks. 10
8 Grading implications for individual symbol attributes . 13
9 Additional grading parameters - Quiet zone . 15
10 Qualification of printing systems for Digital Postage Marks . 15
Annex A (normative) Test procedure for printing systems for Digital Postage Marks . 16
Annex B (informative) Light sources and spectral response characteristics for verification of
Digital Postage Marks . 18
Annex C (informative) Symbol parameters measured in accordance with ISO/IEC 15415 . 21
Annex D (informative) Characteristics of Digital Postage Mark printing and reading
environments that affect print quality . 23
Annex E (informative) Possible causes of low parameter grades in the Digital Postage Mark
environment . 26
Bibliography . 30
European foreword
This document (CEN/TS 14826:2022) has been prepared by Technical Committee CEN/TC 331 “Postal
Services”, the secretariat of which is held by NEN.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes CEN/TS 14826:2004.
Organisations contributing to the development of the document include:
— Universal Postal Union;
— ISO/IEC JTC 1/SC 28 “Office equipment”;
— ISO/IEC JTC 1/SC 31 “Automatic identification and data capture techniques”;
It is intended that this document is adopted by ISO/IEC JTC 1/SC 28, in the work programme of which the
project has been assigned project number ISO/IEC NP 18050.
For compatibility between CEN and UPU versions of this document, the term 'document' is used. In a CEN
context, this is interpreted as being equivalent to the deliverable mentioned on the title page of this
document. In a UPU context, this is interpreted as being equivalent to 'standard'.
In comparison with the previous edition, the following technical modifications have been made:
— EN 14615 has been added as a normative reference.
— Clauses 5, 7.4.2 and A.3 have been modified to take into account the latest edition of ISO/IEC 15415.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN/CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to announce this Technical Specification: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United
Kingdom.
Introduction
Digital Postage Marks (or franking marks), sometimes abbreviated to DPM, are used to evidence the
payment of postage and/or other fees related to services requested by mailers. Digital Postage Marks are
represented by symbols imprinted on the envelope, the label or the insert. Digital Postage Marks
produced by different vendors’ systems are generated with a variety of symbols and graphical images.
The symbologies used for these images are primarily two-dimensional bar codes of both multi-row
(PDF417) and matrix types (e.g. Data Matrix), as specified in UPU standard S28. However, postal
operators can also use other symbologies, e.g. OCR or 4-state codes for these purposes. The two-
dimensional bar code symbologies offer advantages for the machine-readable representation of data
strings of the order of 80 or more bytes in length, due to their high information density characteristics.
Public postal operators and private carriers in Europe have a high interest in automatically reading and
validating these marks, preferably at high speed. It is essential that these symbols are read reliably by
postal processing equipment. The highest practicable read rate is desired by users of such equipment in
order to ensure efficient automation of this process, and any shortfall in the read rate can have as its
consequence a loss of revenue to the operator.
This document has been designed to customise the generic method of measuring the print quality of two-
dimensional bar code symbols to the needs of the postal application and to recommend appropriate print
quality levels that should contribute to the achievement of the read rates desired by the authorities
responsible for validation of the Digital Postage Marks and by postal operators; it is also intended to
provide guidelines for printing machine readable Digital Postage Marks on mail items. The Technical
Specification will provide mailers, postal operators and their suppliers with a practical, quantitative, and
objective way to measure and communicate to each other basic print quality parameters of machine-
readable Digital Postage Marks. Since all attributes do not contribute uniformly to the readability of a
Digital Postage Mark, the Technical Specification identifies five levels of criticality for an attribute (graded
0 to 4, in ascending order of quality), and a grading scheme that assesses the overall symbol quality based
on averaging the results of multiple scans.
The document can be used in the following ways:
— it allows an estimate to be made of the readability of a Digital Postage Mark without actually
submitting it to any postal validation and the qualification of said symbol as acceptable or not
acceptable for readability purposes;
— it allows an estimate to be made of the quality levels potentially achievable by a printing system with
particular substrates;
— it provides a tool for process control in the operation of Digital Postage Mark printing systems.
The document applies the measurement methodology defined in ISO/IEC 15415 for print quality
attributes that tend to influence the readability of two-dimensional bar codes. This methodology is
derived from a view of the current state-of-the-art in two-dimensional bar code scanning technologies.
Yet, such a state-of-the-art is not a perfectly defined concept. First, it is likely to evolve with time towards
improved recognition capabilities. Second, an automatic identification and data capture system is always
the result of a compromise between recognition power and cost. This is why the Technical Specification
is expressed in the form of guidelines rather than prescriptions. However, it is not technically possible to
define guidelines concerning solely the printing of Digital Postage Marks without taking into account the
manufacturing of the mail item as a whole. The readability of the Digital Postage Mark is a function not
only of the inherent quality of printing, i.e. the interaction of the ink, substrate and printing mechanism
together with the effects of the shape of the mail-piece and its transport through the printing system on
the production of the mark, but also of the effects of environmental and handling factors in transit
between the production point and the point at which it is to be read. For example, the symbol contrast of
Digital Postage Marks is not only that provided by the printer/paper combination under defined
illumination conditions. It also results from a variety of other factors among which the covering of the
mail item or the material of the transparent window through which the Digital Postage Mark can be seen.
As a consequence, the guidelines described in this document apply to the Digital Postage Mark blocks of
fully assembled mail items. It is the responsibility of the users of the Technical Specification to achieve
compliance with the guidelines by controlling the effects of the physical elements resulting in the relevant
attributes.
The guidelines are primarily a tool for predicting the level of Digital Postage Mark readability with respect
to current scanning technologies, and compliance with them should result in a high level of Digital
Postage Mark readability. The guidelines are aimed at facilitating the relations between postal operators
and customers, vendors of mail generation and printing equipment and suppliers of mail reading and
sorting equipment. In particular, equipment vendors need firm and precise guidance in designing print
systems and formats for machine readability. Therefore, a quantitative specification of print quality is
critical to the development of products that meet the needs of mailers and postal operators.
1 Scope
This document:
— specifies a methodology for the measurement of defined print quality attributes of Digital Postage
Marks in the form of two-dimensional bar code symbols on mail-pieces;
— defines methods for grading the results of these measurements and deriving an overall symbol
quality grade as a guide to estimating the readability of the Digital Postage Marks;
— provides guidelines for printing and gives information on possible causes of deviation from high
grades to assist users in taking appropriate corrective action;
— defines a test procedure for the assessment of printing systems for the production of Digital Postage
Marks.
These provisions apply to the Digital Postage Mark blocks as they appear on fully produced mail items
when remitted to postal operators, including the characteristics resulting from operations other than
printing per se that affect their appearance to a mail processing system (covering, inserts into transparent
window envelopes, affixed Digital Postage Mark labels).
This document does not define the qualification tests or sampling requirements necessary to determine
the practical feasibility of any specific read rate.
Although this document is not intended for barcodes (other than Digital Postal Marks) which can be
printed on mail pieces for item identification or additional services, a similar methodology can be applied.
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.
EN 1556, Bar coding - Terminology
ISO/IEC 15415, Information technology — Automatic identification and data capture techniques — Bar
code symbol print quality test specification — Two-dimensional symbols
ISO/IEC 15416, Automatic identification and data capture techniques — Bar code print quality test
specification — Linear symbols
ISO/IEC 15419, Information technology — Automatic identification and data capture techniques — Bar
code digital imaging and printing performance testing
ISO/IEC 15426-2, Information technology — Automatic identification and data capture techniques — Bar
code verifier conformance specification — Part 2: Two-dimensional symbols
UPU standard S28 , Communication of Postal Information using Two-dimensional Symbols
UPU standard S44-1 , Colour and Durability Attributes of Franking Marks
UPU documents are available from the Universal Postal Union International Bureau.
3 Terms and definitions
For the purposes of this document, the terms and definitions given in in ISO/IEC 15415, ISO/IEC 15416,
EN 1556 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1
broad-band
descriptive of illumination in which the spectral distribution of the light is wide, with a bandwidth in
excess of 200 nm at the 50% power level
3.2
mail format
form taken by a finished mail-piece or other carrier of a Digital Postage Mark, e.g. envelope with or
without contents, or flat sheet of paper
3.3
narrow-band
descriptive of illumination in which the spectral power distribution is concentrated in a narrow band of
wavelengths, with a bandwidth of less than 200 nm at the 50% power level
3.4
overall symbol grade
measure of symbol quality calculated as arithmetic mean of scan grades from a number of individual
scans of the symbol
3.5
read rate
percentage representing the number of items carrying digital postage marks that have been successfully
read, out of all such items attempted to be read in a given period
3.6
scan grade
result of the assessment of a single scan of a symbol, derived by taking the lowest grade achieved for any
measured parameter in that scan
3.7
spectral response characteristic
integral response of the reading system, a function of wavelength across the spectral region of interest
and calculated for each wavelength as the product of the intensity of light emitted, the transmission
characteristic of any filters or coatings used, and the response of the sensor element at that wavelength
3.8
validation
technical process by which the authenticity, data integrity and uniqueness of a Digital Postage Mark are
confirmed or denied
3.9
verification
technical process by which a bar code symbol is measured to determine its conformance with the
specification for that symbol
3.10
verifier
device used to measure and analyse quality attributes of a bar code symbol such as element and quiet
zone dimensions, reflectances, and other aspects against a standard to which the bar code symbol
conforms
4 Symbols and abbreviations
For the purposes of this document, the following symbols apply:
dpi dots per inch (25,4 mm);
dpmm dots per millimetre;
°K degrees Kelvin;
UEC Unused Error Correction;
X nominal width of a narrow element (bar code) or of a module (matrix code);
Y nominal height of an element (bar code).
5 Requirements
The print quality requirement for a Digital Postage Mark, when measured in accordance with
ISO/IEC 15415 and the following clauses, is expressed in the form:
grade/aperture/light/angle, where:
— “grade” is the overall symbol grade, i.e. the arithmetic mean to one decimal place of the scan
reflectance profile or scan grades;
NOTE 1 Where the value is followed by an asterisk, it indicates that there are extremes of reflectance in the
symbol surroundings which can potentially interfere with reading.
— “aperture” is the aperture reference number (from ISO/IEC 15416 for linear scanning techniques, or
the diameter in thousandths of an inch (to the nearest thousandth) of the synthetic aperture defined
in ISO/IEC 15415);
— “light” defines the illumination: a numeric value indicates the peak light wavelength in nanometres
(for narrow- band illumination); the alphabetic character W indicates that the symbol has been
measured with broad-band illumination (sometimes referred to as “white light” although the terms
are not directly equivalent) the spectral response characteristics of which shall imperatively be
defined or have their source specification clearly referenced;
— “angle” is an additional parameter defining the angle of incidence (relative to the plane of the symbol)
of the illumination. It shall be included in the reporting of the overall symbol grade when the angle
of incidence is other than 45°. Its absence indicates that the angle of incidence is 45°.
In view of the close correlation between print quality and reading performance, where maximum reading
performance is critical, a Digital Postage Mark represented by a two-dimensional bar code symbol shall
achieve a minimum overall symbol grade of 2,8 under the following measurement conditions:
— aperture diameter 0,25 mm (reference number 10), in the case of a Digital Postage Mark in the form
of a two- dimensional multi-row bar code symbol; or
— aperture diameter from 0,25 to 0,40 mm (reference number 10 to 16), in the case of a Digital Postage
Mark in the form of a two- dimensional matrix symbol;
and
— peak wavelength of 660 nm in the case of a Digital Postage Mark intended to be read under narrow-
band illumination; or
— light reference W, together with the specification of the spectral response characteristics used or a
reference to a source of this specification, in the case of a Digital Postage Mark intended to be read
under broad-band illumination.
NOTE 2 The aperture reference number represents the nominal diameter, in thousandths of an inch, of the
measuring aperture. For multi-row symbologies, ISO/IEC 15415 specifies that its diameter is to be determined by
the application specification; see 7.4.1. For matrix symbols, the measuring aperture diameter is a function of the
symbol X dimension; see 7.4.2.
In either case the angle of incidence of the light shall be 45°. These would be expressed as, for example,
2,8/16/W (with the spectral response specification, or an appropriate reference) for a Digital Postage
Mark in the form of a two-dimensional matrix symbol intended for reading in broad-band light, or
2,8/10/660 for a Digital Postage Mark in the form of a multi-row bar code symbol intended to be read in
narrow- band (visible red) light with a peak wavelength of 660 nm.
The illumination conditions used for verification shall imperatively be specified or clearly referenced
with the verification results.
In order to allow for the effect of less easily controllable substrates, where a somewhat lower read rate
can result (for example with Digital Postage Mark symbols printed on relatively low-reflectance
substrates that are unable to meet the preferred symbol contrast requirements), the overall symbol grade
requirement may be reduced to 1,8 provided that all measured parameters except Symbol Contrast are
consistent with the requirements of the higher grade of 2,8. A minimum overall symbol grade of 1,8
governed by any of the measured parameters would probably lead to a further reduction in read rate
performance. See Clause 8 for details, and Annex C for a description of the measurement parameters.
While the above grades are recommended as the minima to ensure an adequate read rate, postal
operators may determine their minimum recommended grades corresponding to the particular reading
requirements of their environment or to the read rate which they require.
An overall symbol grade of 2,8 can only be obtained as the arithmetic mean of scan grades from a number of
individual scans, for instance four scans with grade 3 (B) and one with grade 2 (C). Since it is no longer required to
measure a symbol at different orientations, such result could be achieved after five successive measurements of the
same symbol, or on a batch of five identical symbols produced in the same conditions (cf. Annex A).
Similarly, an overall symbol grade of 1,8 can only be obtained as the arithmetic mean of scan grades from a number
of individual scans, for instance four scans with grade 2 (C) and one with grade 1 (D).
6 Basic measurement methodology
Digital Postage Marks shall be measured according to the methodology defined in ISO/IEC 15415 for the
type of symbology concerned, either two-dimensional multi-row symbologies (e.g. PDF417 as defined in
ISO/IEC 15438) or two-dimensional matrix symbologies (e.g. DataMatrix as defined in ISO/IEC 16022).
The print quality requirements specified in ISO/IEC 15438 and ISO/IEC 16022, and in similar symbology
standards, which were published prior to the development of the generic methodologies defined in
ISO/IEC 15415 shall not be applied to the evaluation of Digital Postage Marks.
NOTE For two-dimensional multi-row symbols, ISO/IEC 15415 adapts (and supplements) the methodology for
the print quality assessment of linear bar code symbols defined in ISO/IEC 15416. For matrix symbols, the
methodology of ISO/IEC 15415 requires the capture of a two-dimensional grey-scale image of the symbol to be
verified, under defined and controlled illumination conditions, and the processing of the image to analyse its
specified parameters. ISO/IEC 15415 defines the reference optical arrangement to be used for measurement, and
the symbol attributes to be measured (see Annex C for a list of the measured parameters for each type of symbol).
ISO/IEC 15415 requires to be read in conjunction with the International Standard or other equivalent formal
specification of the symbology concerned and in particular makes use of the reference decode algorithm defined in
that specification as a common, standard basis for evaluation. It assigns grades on a five-step scale to each of the
parameters; there are four passing grades, from 4 to 1 in descending order of quality, and one failing grade of 0. It
provides for multiple scans of the symbol in different positions in order to derive an average assessment of the
symbol, and defines an overall grading scheme that takes account of the individual parameters and the results from
individual scans. It provides for applications to determine the minimum grade for acceptability for that application.
It also allows for applications to establish additional parameters. In the case of Digital Postage Marks, the quiet zone
is an additional graded parameter (see Clause 9), and the spectral response characteristics of the system by which
the Digital Postage Mark is intended to be read need to be specified.
In each scan of the symbol a number of parameters is measured and graded, and the scan is given a scan
grade, which is equal to the lowest grade obtained for any parameter in that scan; the overall symbol
grade in accordance with ISO/IEC 15415 is the arithmetic mean, to one decimal place, of the scan grades.
However, for the purposes of this document, if any scan grade is 0, the overall symbol grade shall also be
regarded as 0. In this event it can be appropriate to perform the verification process a second time to
eliminate the possibility of a random or transient incident having affected one of the scans.
The overall symbol grades are only meaningful when reported in conjunction with additional parameters
defined in the application specification: the measuring aperture size, the illumination (peak wavelength
or spectral response characteristic), and the angle of incidence of the illumination.
7 Verification requirements for Digital Postage Marks
7.1 Verification equipment
Instruments to be used for the verification of Digital Postage Marks shall comply with the requirements
of ISO/IEC 15426-2. These devices provide a standardized means of measurement of two-dimensional
bar code symbols to enable consistent and repeatable measurements of symbol quality to be made. Their
basic configuration is intended to replicate a bar code reading device that uses image capture and
processing techniques, as is likely to be the case with mail processing equipment. ISO/IEC 15415 defines
a reference optical arrangement for reflectance measurements, with the results of which the reflectance
measurements obtained by a verifier should correlate. There is however no requirement that its
construction should follow the reference arrangement. The specification of certain components of the
device, described in the following subclauses, shall be matched to the defined requirements of the
application in which the bar code symbols are intended to be used. The instrument shall be calibrated
before use in accordance with the manufacturer's instructions.
For the verification of Digital Postage Mark symbols, the image capture component of the equipment
should preferably be a camera, and associated illumination, of the same type and spectral response
characteristics as the equipment expected to be used for operational reading of the mail-piece(s) to be
verified, with a mechanism, of a similar nature to that expected to be used, to transport the mail-pieces
past the measurement window. However, if such mechanism is not available, or differs from the intended
equipment in a manner that can affect scan grading significantly, measuring on standstill test samples
may be preferred.
If equipment precisely matching the spectral response characteristics of the mail processing equipment
expected to be used is not available, a device complying with the general requirements of ISO/IEC 15415
and ISO/IEC 15426-2 shall be used with a light source covering the spectral band indicated for the ink
colour in question in UPU S44-1. It should be noted that in this case the reflectance measurements (of ink
and paper) recorded may differ from those perceived by the operational mail processing equipment and
the results should be taken as indicative rather than predictive of the symbol contrast perceived by the
specific mail processor.
7.2 Optical geometry
ISO/IEC 15415 defines a default geometry for print quality assessment of two-dimensional symbols. This
consists of two elements. The first element is an annular light source, or a set of individual light sources
arranged in a circle, giving flood incident illumination which is uniform across the sample area. The light
source(s) shall be concentric with the sample area and shall lie in a plane parallel to that of the sample
area, at a height which will allow incident light to fall on the centre of the sample area at an angle of 45°
to its plane. The second component is a light collection device, the optical axis of which is perpendicular
to the sample area and passes through its centre, and which focuses an image of the test symbol on a
light-sensitive array. This arrangement is appropriate for the measurement of the diffusely reflected light
from the surface of a mail-piece and shall be used for the verification of Digital Postage Marks; another
arrangement may be used if its results can be correlated with those obtained by the use of the default
geometry.
7.3 Light source
The apparent reflectance of a sample area to a scanner or verifier is primarily a function of:
— response of the ink and substrate to the illumination (its absorption or reflection of incident light at
different wavelengths); and
— spectral response characteristics of the reading system, which in turn depend on:
— spectral distribution of the illumination (the intensity of light of different wavelengths emitted
across the spectrum);
— spectral characteristics of any filters in the optical path (the transmittance of light of different
wavelengths);
— spectral response of the photosensitive elements of the image capture device (their sensitivity
at different wavelengths).
When the light is not monochromatic, the apparent reflectance is the integrated response across the
image capture device's spectral band.
The illumination conditions used by mail processing systems generally require broad-band light (of
various colour temperatures, and the spectral response characteristics of the specific equipment may,
therefore, differ) to capture not only the image of the Digital Postage Mark but also the images of the
address block and other information which are not covered by this document. Hand-held reading
equipment for Digital Postage Marks may have a narrow-band red light source.
Ink specifications for the Digital Postage Mark are defined in UPU standard S44-1. For a given ink, its
reflectance will vary widely with different light sources. The ink reflectance will also depend on the ink
coverage, which is determined principally by the print mechanism. UPU standard S44-1 indicates the
reference spectral bands and the desirable contrast levels within these for the various ink colours on a
range of backgrounds. It also describes the use of a default set of spectral characteristics for the
assessment of reflectances, which may be correlated with those of a specific type of reading equipment
by the use of an appropriate correction factor. Individual postal operators may define the colours
permitted in their territory.
The substrates used may be of a variety of materials and colours, and their reflectances will also vary
widely with the light source.
It is therefore essential, in order to maximize the correlation between reflectance values as measured by
a verifier and their appearance to reading and mail processing equipment, that the spectral response
characteristics of the two types of equipment should match as closely as practicable. The print quality of
a Digital Postage Mark should be measured under the same spectral response conditions as are used in
the mail processing equipment expected to be used. Because the spectral response characteristics of
different equipment specified by postal operators may vary, the verifier shall either have the capability
to change the light source or image capture component, or have its particular set of spectral response
characteristics clearly identified.
Annex B describes the spectral response characteristics of a number of common types of light source used
for the reading of Digital Postage Marks.
7.4 Measuring aperture
7.4.1 General
The shape and dimensions of the measuring aperture shall be specified.
NOTE This is necessary in order that defects in the symbol are not given exaggeratedly high or unjustifiably
low importance, and secondly in order to maximize the measured contrast between dark and light elements. Defects
include voids in low reflectance areas and extraneous specks in high reflectance areas, which will tend to decrease
the modulation of the area by bringing the reflectance of the area closer to the Global Threshold (the midpoint
between the highest and lowest reflectances in the symbol, used to binarize the image into dark and light areas).
These goals are achieved by specifying a circular aperture whose diameter is slightly smaller than the width of the
smallest element specified for the application.
The measuring aperture may be either a real physical aperture in the optical path of the verifier or a
virtual one achieved by applying a mathematical process to integrate the reflectance values from a
number of adjoining pixels in the image capture device.
7.4.2 Measuring aperture for two-dimensional multi-row symbologies
For Digital Postage Mark symbols in the form of a two-dimensional multi-row symbol, complying with
UPU standard S28, with a minimum X dimension of 0,38 mm, the measuring aperture shall be a circular
aperture of diameter 0,250 mm (aperture reference number 10, as defined in ISO/IEC 15416).
ISO/IEC 15416 indicates that this aperture is appropriate for symbols with X dimensions up to 0,63 mm,
but it also states that the aperture to be used for verification shall be the aperture appropriate for the
smallest X dimension permitted by the application.
7.4.3 Measuring aperture for two-dimensional matrix symbologies
ISO/IEC 15415 defines the measuring aperture for these symbols as a circular aperture, synthesized from
the individual image pixels, from 0,5X to 0,8X in diameter (based on the smallest X dimension specified
for the application), and specifies that the resolution of the verifier shall be sufficient to ensure that the
parameter grading results are consistent irrespective of the rotation of the symbol. For Digital Postage
Mark symbols in the form of a two- dimensional matrix symbol, complying with UPU standard S28, which
specifies an X dimension of 0,508 mm or more, an aperture from 0,25 to 0,40 mm diameter (reference
number 10 to 16) is appropriate in accordance with ISO/IEC 15415.
NOTE Experience has shown that the imaging system used for verification can require an effective linear
resolution of 6 to 8 pixels per module (corresponding to 11,8 to 15,7 pixels per mm for an X dimension of 0,508 mm),
or 30 to 60 pixels per module on an area basis, to provide the required consistency of results. Annex D, D.2, indicates
that current mail processing systems typically use a resolution of approximately 8 to 10 pixels per mm for reading.
7.5 Mail format
The form in which the Digital Postage Mark is verified depends on the purpose for which it is being
measured and the point in the entire mailing process at which it is measured. As a general principle, the
capabilities of the production system dictate the highest quality that can be achieved, and the
introduction of other factors (substrate materials, filling of envelopes, window envelopes or overwraps,
handling in transit, etc.) will tend to reduce symbol quality, and allowance shall be made for this when
setting quality levels.
For testing the performance of printing equipment, it will normally be sufficient to test symbols printed
on to a flat substrate, in order to minimize the effect of external variables.
For process control of symbol production, it is appropriate to verify the symbol on the mail-piece in the
form in which it emerges from the printing system.
For predicting whether the readability of the Digital Postage Mark is likely to reach an acceptable level it
is appropriate to verify the symbol on the finished mail-piece in the form in which it is presented to the
postal service, or received at the mail processing point.
In the cases of process control and the prediction of readability of a complete mail piece, it can be
desirable to allow for the influence of factors such as the geometrical distortions caused by contents of
the mail-piece, the optical effects of window materials or film wraps through which the Digital Postage
Mark has to be read, and the effects of environmental conditions and handling while it is in transit.
These factors lead to the recommendation that the symbol quality at the point of production should,
wherever possible, be higher than the minimum required for acceptable readability at the point of
reading, to allow for possible degradation by these factors.
Annex D discusses a number of factors related to the printing and scanning process that can have an
impact on symbol quality.
8 Grading implications for individual symbol attributes
The minimum overall symbol grades specified in Clause 5 are based on averaging the profile (or scan)
grades of multiple scans of a symbol, which are in turn based on the lowest grade for any parameter in
each scan. It is not possible, therefore, to define a set of threshold values which have to be exceeded for
all parameters in every scan. However, it is possible to suggest, for guidance, that the average value of
each individual parameter for all scans should be within a limiting value which is derived from the
minimum overall symbol grade.
Tests have indicated that an overall symbol grade of 2,8 should result in a read rate in the region of
99,5 %. If the overall symbol grade is reduced to 1,8, the resulting read rate can be in the region of 95 %.
If, however, the values of all parameters except Symbol Contrast are consistent with an overall grade of
2,8 and those of the Symbol Contrast parameter with a grade of 1,8, the resulting read rate can be in the
region of 97 %. There is, however, no direct linkage between a particular quality grade and a particular
read rate, since read rates achieved in practice can be governed by a number of factors additional to print
quality that cannot be assessed simply by verifying the symbol.
Certain parameters (e.g. Decode) are graded only on a pass/fail basis, i.e. they can only have the grade 4
or 0; if graded 0 the scan grade shall also be 0 and the overall symbol grade will also be 0, in accordance
with the requirement in Clause 6. In consequence they shall pass the relevant test in every scan and the
limiting value is therefore an absolute one rather than a mean.
Tables 1 and 2 indicate the limiting mean values for two-dimensional multi-row and matrix symbols
respectively, corresponding to the grades and read rates indicated above.
Table 1 — Indicative limiting mean parameter values for two-dimensional multi-row symbols
Approx. desired read rate 99,5 % 97 % 95 %
Parameter Limiting mean value
Decode* Pass* Pass* Pass*
Minimum reflectance* ≥ 0,5R * ≥ 0,5R * ≥ 0,5R *
max max max
Min. edge contrast* ≥ 0,15* ≥ 0,15* ≥ 0,15*
Symbol contrast ≥ 0,52 ≥ 0,36 ≥ 0,36
Modulation ≥ 0,58 ≥ 0,58 ≥ 0,48
Defects ≤ 0,21 ≤ 0,21 ≤ 0,26
Decodability ≥ 0,475 ≥ 0,475 ≥ 0,35
Codeword yield ≥ 0,63 ≥ 0,63 ≥ 0,56
Unused error correction ≥ 0,48 ≥ 0,48 ≥ 0,36
Quiet zone* 3X* 3X* 3X*
NOTE Parameters indicated with an asterisk are pass/fail parameters, and the values
indicated are absolute values which shall be met in every scan of the symbol.
Table 2 — Indicative limiting mean parameter values for two-dimensional matrix symbols
Approx. desired read rate 99,5 % 97 % 95 %
Parameter Limiting mean value
Decode* Pass* Pass* Pass*
Symbol contrast ≥ 0,52 ≥ 0,36 ≥ 0,36
Fixed pattern damage grade 2,8 grade 2,8 grade1,8
Modulation ≥ 0,38 ≥ 0,38 ≥ 0,28
Axial non-uniformity ≤ 0,084 ≤ 0,084 ≤ 0,104
Grid non-uniformity ≤ 0,52 ≤ 0,52 ≤ 0,64
Unused error correction ≥ 0,48 ≥ 0,48 ≥ 0,35
Quiet zone* 3X* 3X* 3X*
NOTE Parameters indicated with an asterisk are pass/fail parameters, and the values
indicated are absolute values which shall be met in every scan of the symbol.
ISO/IEC 15415 gives general guidance on possible causes of low grades for individual parameters.
Annex E gives additional guidance on the possible causes of low grades that are more specifically related
to the production and reading environments for Digital Postage Marks.
NOTE The measurement of print growth, while important for process control, is not taken into account in
grading the symbol and no limiting value can therefore be defined for this parameter. Its effect is, to some extent,
reflected in the modulation parameter.
9 Additional grading parameters
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