ISO/TS 21830:2018

SLOVENSKI STANDARD
SIST-TS ISO/TS 21830:2020
01-april-2020
Barvno upravljanje slikovne tehnologije - Kompenzacija črne točke za n-
barvne ICC-profile
Image technology colour management - Black point compensation for n-colour ICC
profiles
Technologie de l'image - BPC pour profil à n couleurs
Ta slovenski standard je istoveten z: ISO/TS 21830:2018
ICS:
17.180.20 Barve in merjenje svetlobe Colours and measurement of
light
37.100.01 Grafična tehnologija na Graphic technology in
splošno general
SIST-TS ISO/TS 21830:2020 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST-TS ISO/TS 21830:2020

---------------------- Page: 2 ----------------------
SIST-TS ISO/TS 21830:2020
TECHNICAL ISO/TS
SPECIFICATION 21830
First edition
2018-09
Image technology colour
management — Black point
compensation for n-colour ICC profiles
Technologie de l'image — BPC pour profil à n couleurs
Reference number
ISO/TS 21830:2018(E)
©
ISO 2018

---------------------- Page: 3 ----------------------
SIST-TS ISO/TS 21830:2020
ISO/TS 21830:2018(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2018
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
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

---------------------- Page: 4 ----------------------
SIST-TS ISO/TS 21830:2020
ISO/TS 21830:2018(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Extension of black point compensation to n-colour ICC profiles . 1
4.1 Constraints . 1
4.2 Computation. 2
4.2.1 General. 2
4.2.2 Computing the SourceBlackPoint . 3
4.2.3 InitialLAB Calculation . 3
Bibliography . 4
© ISO 2018 – All rights reserved iii

---------------------- Page: 5 ----------------------
SIST-TS ISO/TS 21830:2020
ISO/TS 21830:2018(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.
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 2018 – All rights reserved

---------------------- Page: 6 ----------------------
SIST-TS ISO/TS 21830:2020
ISO/TS 21830:2018(E)

Introduction
The xCLR ICC profiles that are used in digital printing applications are often CMYK ICC profiles
extended with red, orange, green, blue and/or violet colourants. Hence there is a need to specify
black point compensation (BPC) for a well-defined class of xCLR ICC profiles, where xCLR refers to a
device-dependent colour space defined in ISO 15076-1 and ICC.1:2001-04, specified for 3 to 15 device
colourants wherein the value of x is a hexadecimal digit within the range 3 to F inclusive. Such xCLR ICC
profiles are also commonly referred to as n-colour profiles.
To guarantee continuity of the black point compensation procedure between CMYK devices and
printing devices with extended colourant sets, xCLR ICC profiles follow the constraints and calculation
of output-capable CMYK ICC profiles wherever possible, as specified in ISO 18619:2015.
Limiting xCLR ICC profiles to CMYK plus combinations from the set of red, orange, green, blue and
violet colourants is a logical extension of the CMYK colourant set to enhance the printing gamut as
applied in digital print.  Some of the key additional assumptions which will likely result in predictive
and expected behaviour for black point compensation calculations include:
— in a similar fashion to most CMYK colourants, the colourants chosen for use with the xCLR ICC
profiles should result in a colour gamut featuring a large range of neutral colours;
— the physical colourants should be sufficiently transparent with well-saturated CMY primaries in
order to keep the gamut shell well-formed and permit the black point compensation algorithm to
work correctly;
— a well-behaving forward model can be constructed near the darkest neutral, with a well-defined
darkest colour, thus guaranteeing a good approximation using curve-fitting as defined by
ISO 18619:2015, 4.2.5.5.
In the case of 4CLR ICC profiles, which are constrained by ISO 15076-1 as well as ICC.1:2001-04 to not
refer to CMYK device-dependent colour spaces, the 4CLR colour space should behave similarly to CMYK
device-dependent colour spaces, and conforms to the requirements defined by the key assumptions
given above for other xCLR ICC profiles.
An additional class of xCLR ICC profiles for consideration by this document are 3CLR and CMY ICC
profiles. For 3CLR ICC profiles, the colourants should be CMY-like in the sense of being chromatic
colourants with widely-spaced hue angles (as distinct from achromatic colourants such as grey or
black). As a result, BPC for 3CLR ICC profiles is defined by this document, and follows the same approach
as for CMY ICC profiles.
The BPC method described in this document does not give meaningful results for most 2CLR ICC
profiles, hence these types of ICC profiles are excluded from this document.
In addition, this document extends the BPC method for the ICC v4 profile types with the device-
dependent colour spaces described above for corresponding ICC v2 profile
...