Graphic technology -- Image quality evaluation methods for printed matter

This document defines a measurement method for the evaluation of distortions in the macroscopic uniformity of printed areas that are oriented in the horizontal and vertical direction, such as streaks and bands. It provides requirements for the layout of the test form, the use of a colour measurement device taking measurements in a 2D sampling grid, and the formula to compute the Macro-Uniformity-Score. This document does not cover any non-adjacent or non-horizontal nor vertical patterns. Due to the used spatial frequency, the Macro-Uniformity-Score does not measure high frequency (fine) patterns such as missing nozzles.

Technologie graphique - Méthodes d'évaluation de la qualité d'image pour les imprimés

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Published
Publication Date
19-Nov-2020
Current Stage
9092 - International Standard to be revised
Start Date
12-Jul-2021
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ISO/TS 18621-21:2020 - Graphic technology -- Image quality evaluation methods for printed matter
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TECHNICAL ISO/TS
SPECIFICATION 18621-21
First edition
2020-11
Graphic technology — Image quality
evaluation methods for printed
matter —
Part 21:
Measurement of 1D distortions of
macroscopic uniformity utilizing
scanning spectrophotometers
Technologie graphique - Méthodes d'évaluation de la qualité d'image
pour les imprimés —
Partie 21: Mesure des distorsions 1D d'uniformité macroscopique à
l'aide de spectrophotomètres à balayage
Reference number
ISO/TS 18621-21:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO/TS 18621-21:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 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 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TS 18621-21:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Requirements .......................................................................................................................................................................................................... 2

4.1 Principles ..................................................................................................................................................................................................... 2

4.2 Apparatus .................................................................................................................................................................................................... 2

4.2.1 General...................................................................................................................................................................................... 2

4.2.2 Measurement condition ........................................................................................................................................... .. 3

4.3 Procedure .................................................................................................................................................................................................... 3

4.3.1 Test pattern .......................................................................................................................................................................... 3

4.3.2 Printing and measuring ............................................................................................................................................. 3

4.4 Evaluation .................................................................................................................................................................................................... 4

4.5 Reporting ..................................................................................................................................................................................................... 5

Annex A (informative) Recommended tone value combinations ........................................................................................... 6

Bibliography ................................................................................................................................................................................................................................ 7

© ISO 2020 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO/TS 18621-21:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

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 ISO documents 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 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).

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 Technical Committee ISO/TC 130, Graphic technology.

A list of all parts in the ISO 18621 series can be found on the ISO website.

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.
iv © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/TS 18621-21:2020(E)
Introduction

The subject of image quality is broad and complex, due to its multidimensionality and the apparent

characteristics of human vision. Many different methods can be available to provide a measure of a

particular visual attribute in some particular viewing context and aimed at a particular printing

technology. It is a challenge to have image quality evaluation methods that are independent of the

marking technology, i.e. correlate with human perception to provide visual significance to measured

differences across many printing technologies. The evaluation of perceived image quality is an active

field of research.

The uniformity that can be achieved, or in fact the lack thereof, is an important factor in the evaluation of

the overall print quality. Uniformity refers to the subjective impression of the homogeneity of the colour

in extended areas up to the document size. Colour uniformity refers to all types of unintended but visible

variations in colour, that may go in any direction in colour space and may have any spatial pattern. Spatial

patterns include 1D, 2D, periodic, aperiodic, localized, large-scale and small-scale variations. They can be

identified as streaks or streakiness, banding, gradients, mottle, moiré and others.

When evaluating perceived uniformity, the intended viewing distance should be taken into account. For

practical application it is also common practice to distinguish 2 categories of uniformity that depend on

the spatial frequency (or actually the angular frequency as seen by the eye):

— Microscopic uniformity such as graininess that is related to the imaging process and generally

consists of a 2D random noise pattern. It is visually relevant for image objects as small as few square

mm in size in case of normal reading distance (40 cm).

— Macroscopic uniformity involves distortions in the homogeneity that extend beyond few mm in one

or both geometric dimensions. It is generally visible across the document page size with examples

called banding, cording stripes or streaks.

This document focuses on the macroscopic uniformity that exhibits 1D type patterns that extend more

or less across the printed area of a page. It uses well established colour measurement instruments as

the basic measurement device, especially systems that can be combined with automated XY-tables for

performing well defined measurements in a complete 2D grid of measurement locations in an easy

way. These systems generally have a minimum pitch in both dimensions of 6 mm. This method takes

a much more rigorous approach than the 9-point sample method that is defined in ISO 12647-7 that is

applicable to proofing systems.

The measurement method derives a single valued Macro-Uniformity-Score on a scale that ranges

from 100 (“perfect uniformity”) to 0 (“extremely poor uniformity”). It is based on the evaluation of

the average colour differences that occur in horizontal and vertical rows separately and adds them up

to arrive at a single value. Then a formula is applied to compute the Macro-Uniformity-Score that is

shown to correlate well with the perception of representative streaks or stripes of toner-based printing

systems as well as inkjet based systems.

This document describes a methodology in such a way that other documents can apply it for specific

use cases. Such documents will typically need to apply additional constraints on test pages and process

control in order to ensure that the resulting Macro-Uniformity-Score can be compared between

different printing devices, substrates and ink sets.
© ISO 2020 – All rights reserved v
---------------------- Page: 5 ----------------------
TECHNICAL SPECIFICATION ISO/TS 18621-21:2020(E)
Graphic technology — Image quality evaluation methods
for printed matter —
Part 21:
Measurement of 1D distortions of macroscopic uniformity
utilizing scanning spectrophotometers
1 Scope

This document defines a measurement method for the evaluation of distortions in the macroscopic

uniformity of printed areas that are oriented in the horizontal and vertical direction, such as streaks

and bands.

It provides requirements for the layout of the test form, the use of a colour measurement device taking

measurements in a 2D sampling grid, and the
...

TECHNICAL ISO/TS
SPECIFICATION 18621-21
First edition
Graphic technology — Image quality
evaluation methods for printed
matter —
Part 21:
Measurement of 1D distortions of
macroscopic uniformity utilizing
scanning spectrophotometers
Member bodies are requested to consult relevant national interests in ISO/IEC

JTC 1/SC 28,ISO/TC 42 before casting their ballot to the e-Balloting application.

PROOF/ÉPREUVE
Reference number
ISO/TS 18621-21:2020(E)
ISO 2020
---------------------- Page: 1 ----------------------
ISO/TS 18621-21:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 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 2020 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/TS 18621-21:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 1

4 Requirements .......................................................................................................................................................................................................... 2

4.1 Principles ..................................................................................................................................................................................................... 2

4.2 Apparatus .................................................................................................................................................................................................... 2

4.2.1 General...................................................................................................................................................................................... 2

4.2.2 Measurement condition ........................................................................................................................................... .. 3

4.3 Procedure .................................................................................................................................................................................................... 3

4.3.1 Test pattern .......................................................................................................................................................................... 3

4.3.2 Printing and measuring ............................................................................................................................................. 3

4.4 Evaluation .................................................................................................................................................................................................... 4

4.5 Reporting ..................................................................................................................................................................................................... 5

Annex A (informative) Recommended tone value combinations ........................................................................................... 6

Bibliography ................................................................................................................................................................................................................................ 7

© ISO 2020 – All rights reserved PROOF/ÉPREUVE iii
---------------------- Page: 3 ----------------------
ISO/TS 18621-21:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

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 ISO documents 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 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).

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 Technical Committee ISO/TC 130, Graphic technology.

A list of all parts in the ISO 18621 series can be found on the ISO website.

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.
iv PROOF/ÉPREUVE © ISO 2020 – All rights reserved
---------------------- Page: 4 ----------------------
ISO/TS 18621-21:2020(E)
Introduction

The subject of image quality is broad and complex, due to its multidimensionality and the apparent

characteristics of human vision. Many different methods can be available to provide a measure of a

particular visual attribute in some particular viewing context and aimed at a particular printing

technology. It is a challenge to have image quality evaluation methods that are independent of the

marking technology, i.e. correlate with human perception to provide visual significance to measured

differences across many printing technologies. The evaluation of perceived image quality is an active

field of research.

The uniformity that can be achieved, or in fact the lack thereof, is an important factor in the evaluation of

the overall print quality. Uniformity refers to the subjective impression of the homogeneity of the colour

in extended areas up to the document size. Colour uniformity refers to all types of unintended but visible

variations in colour, that may go in any direction in colour space and may have any spatial pattern. Spatial

patterns include 1D, 2D, periodic, aperiodic, localized, large-scale and small-scale variations. They can be

identified as streaks or streakiness, banding, gradients, mottle, moiré and others.

When evaluating perceived uniformity, the intended viewing distance should be taken into account. For

practical application it is also common practice to distinguish 2 categories of uniformity that depend on

the spatial frequency (or actually the angular frequency as seen by the eye):

— Microscopic uniformity such as graininess that is related to the imaging process and generally

consists of a 2D random noise pattern. It is visually relevant for image objects as small as few square

mm in size in case of normal reading distance (40 cm).

— Macroscopic uniformity involves distortions in the homogeneity that extend beyond few mm in one

or both geometric dimensions. It is generally visible across the document page size with examples

called banding, cording stripes or streaks.

This document focuses on the macroscopic uniformity that exhibits 1D type patterns that extend more

or less across the printed area of a page. It uses well established colour measurement instruments as

the basic measurement device, especially systems that can be combined with automated XY-tables for

performing well defined measurements in a complete 2D grid of measurement locations in an easy

way. These systems generally have a minimum pitch in both dimensions of 6 mm. This method takes

a much more rigorous approach than the 9-point sample method that is defined in ISO 12647-7 that is

applicable to proofing systems.

The measurement method derives a single valued Macro-Uniformity-Score on a scale that ranges

from 100 (“perfect uniformity”) to 0 (“extremely poor uniformity”). It is based on the evaluation of

the average colour differences that occur in horizontal and vertical rows separately and adds them up

to arrive at a single value. Then a formula is applied to compute the Macro-Uniformity-Score that is

shown to correlate well with the perception of representative streaks or stripes of toner-based printing

systems as well as inkjet based systems.

This document describes a methodology in such a way that other documents can apply it for specific

use cases. Such documents will typically need to apply additional constraints on test pages and process

control in order to ensure that the resulting Macro-Uniformity-Score can be compared between

different printing devices, substrates and ink sets.
© ISO 2020 – All rights reserved PROOF/ÉPREUVE v
---------------------- Page: 5 ----------------------
TECHNICAL SPECIFICATION ISO/TS 18621-21:2020(E)
Graphic technology — Image quality evaluation methods
for printed matter —
Part 21:
Measurement of 1D distortions of macroscopic uniformity
utilizing scanning spectrophotometers
1 Scope

This document defines a measurement method for the evaluation of distortions in the macroscopic

uniformity of printed areas that are oriented in the horizontal and vertical direction, such as streaks

and bands.

It provides requirements for the layout of the test form, the use of a colour measurement device taking

measurements in a 2D sampling grid, and the formula to compute the Macro-Uniformity-Score.

This document does not cover any non-adjacent or non-horizontal nor ver
...

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