SIST ISO 20654:2018

INTERNATIONAL ISO
STANDARD 20654
First edition
2017-08
Corrected version
2018-01
Graphic technology — Measurement
and calculation of spot colour tone
value
Technologie graphique — Mesurage et calcul de la valeur de tons des
couleurs d'accompagnement
Reference number
ISO 20654:2017(E)
©
ISO 2017

---------------------- Page: 1 ----------------------
ISO 20654:2017(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 20654:2017(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 2
4.1 Calculation of spot colour tone value . 2
4.2 Steps for obtaining SCTV from spectral reflectance measurements . 3
4.3 Steps for obtaining SCTV from CIELAB measurements . 3
Bibliography . 5
© ISO 2017 – All rights reserved iii

---------------------- Page: 3 ----------------------
ISO 20654:2017(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 on 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 the following
URL: www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 130, Graphic technology.
This corrected version of ISO 20654:2017 incorporates the following corrections:
— Introduction: final paragraph removed;
— Formula (6) revised.
iv © ISO 2017 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 20654:2017(E)

Introduction
This document defines a new metric Spot Colour Tone Value (SCTV) for the determination of the tone
value of a spot colour ink. Spot colours in this document are defined as non-process colours (process
colours being the CMYK 4-colour primary inks). This method produces approximately uniform visual
spacing of the tones between the unprinted substrate and the 100% coverage, known as the solid ink.
This metric is calculated from either the measured spectral reflectance factors or from colorimetric
values computed from the same spectral data.
Historically, spot colours have been managed by measuring the solid ink value only, with no clear
guidelines or methodology for measuring intermediate halftones. For artwork that only incorporates
the spot ink at full coverage, this can be a reasonable practice; however, for artwork that includes
gradations of the spot colour, which can print alone or in combination with the other inks, a formal
strategy for managing the spot colour tone is required. This solution has been to print linear scales and
use those values as a reference tone for alignment. This practice renders different results from each
print supplier.
In the past, spot colour tones have been measured using the standard process colour tones methodology
based on ISO status density measurement using a set of spectral products optimised for cyan, magenta
and yellow inks. This method does not work well with intermediate tones of spot colours and in many
cases produced a tone scale far from being perceptually uniform. Hence, there is a need for a new metric
that will quantify the intermediate tones of spot colours in a more perceptually uniform way.
© ISO 2017 – All rights reserved v

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 20654:2017(E)
Graphic technology — Measurement and calculation of
spot colour tone value
1 Scope
This document defines a metric for assessing intermediate tones of a spot ink. This method for
the calculation of Spot Colour Tone Value (SCTV) produces approximately uniform visual spacing
of tones between substrate and solid. It can be c
...

SLOVENSKI STANDARD
SIST ISO 20654:2018
01-februar-2018
*UDILþQDWHKQRORJLMD0HUMHQMHLQL]UDþXQEDUYQHWRQVNHYUHGQRVWL
Graphic technology - Measurement and calculation of spot colour tone value
Technologie graphique - Mesurage et calcul de la valeur de tons des couleurs
d'accompagnement
Ta slovenski standard je istoveten z: ISO 20654:2017
ICS:
17.180.20 Barve in merjenje svetlobe Colours and measurement of
light
37.100.01 *UDILþQDWHKQRORJLMDQD Graphic technology in
VSORãQR general
SIST ISO 20654:2018 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------

SIST ISO 20654:2018

---------------------- Page: 2 ----------------------

SIST ISO 20654:2018
INTERNATIONAL ISO
STANDARD 20654
First edition
2017-08
Graphic technology — Measurement
and calculation of spot colour tone
value
Technologie graphique — Mesurage et calcul de la valeur de tons des
couleurs d’accompagnement
Reference number
ISO 20654:2017(E)
©
ISO 2017

---------------------- Page: 3 ----------------------

SIST ISO 20654:2018
ISO 20654:2017(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

---------------------- Page: 4 ----------------------

SIST ISO 20654:2018
ISO 20654:2017(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 2
4.1 Calculation of spot colour tone value . 2
4.2 Steps for obtaining SCTV from spectral reflectance measurements . 3
4.3 Steps for obtaining SCTV from CIELAB measurements . 3
Bibliography . 5
© ISO 2017 – All rights reserved iii

---------------------- Page: 5 ----------------------

SIST ISO 20654:2018
ISO 20654:2017(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 on 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 the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 130, Graphic technology.
iv © ISO 2017 – All rights reserved

---------------------- Page: 6 ----------------------

SIST ISO 20654:2018
ISO 20654:2017(E)

Introduction
This document defines a new metric Spot Colour Tone Value (SCTV) for the determination of the tone
value of a spot colour ink. Spot colours in this document are defined as non-process colours (process
colours being the CMYK 4-colour primary inks). This method produces approximately uniform visual
spacing of the tones between the unprinted substrate and the 100% coverage, known as the solid ink.
This metric is calculated from either the measured spectral reflectance factors or from colorimetric
values computed from the same spectral data.
Historically, spot colours have been managed by measuring the solid ink value only, with no clear
guidelines or methodology for measuring intermediate halftones. For artwork that only incorporates
the spot ink at full coverage, this can be a reasonable practice; however, for artwork that includes
gradations of the spot colour, which can print alone or in combination with the other inks, a formal
strategy for managing the spot colour tone is required. This solution has been to print linear scales and
use those values as a reference tone for alignment. This practice renders different results from each
print supplier.
In the past, spot colour tones have been measured using the standard process colour tones methodology
based on ISO status density measurement using a set of spectral products optimised for cyan, magenta
and yellow inks. This method does not work well with intermediate tones of spot colours and in many
cases produced a tone scale far from being perceptually uniform. Hence, there is a need for a new metric
that will quantify the intermediate tones of spot colours in a more perceptually uniform way.
This document is the result of work done by many people in developing and testing a range of candidate
metrics. In particular, significant contributions were made by William B. Birkett, Charles Spontelli and
Hanno Hoffstadt.
© ISO 2017 –
...