ISO 12641-1:2016

INTERNATIONAL ISO
STANDARD 12641-1
First edition
2016-05-01
Graphic technology — Prepress digital
data exchange — Colour targets for
input scanner calibration —
Part 1:
Colour targets for input scanner
calibration
Technologie graphique — Échange de données numériques de
préimpression — Cibles de couleur pour étalonnage à l’entrée du
scanner
Reference number
©
ISO 2016
© ISO 2016, Published in Switzerland
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ii © ISO 2016 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 4
4.1 Target design . 4
4.2 Transmission targets . 4
4.2.1 Target layout and physical characteristics . 4
4.2.2 Patch size . 9
4.2.3 Colour gamut mapping . 9
4.2.4 Neutral and dye scale values .10
4.2.5 Neutral scale mapping .11
4.3 Reflection targets .11
4.3.1 Target layout and physical characteristics .11
4.3.2 Patch size .13
4.3.3 Colour gamut mapping .14
4.3.4 Neutral and dye scale values .14
4.3.5 Neutral scale mapping .15
4.4 Allowable tolerances on patch values .15
4.4.1 Uncalibrated targets .15
4.4.2 Calibrated targets .16
4.5 Spectral measurement and colorimetric calculation .16
4.6 Data reporting .16
4.7 Data file format .16
4.7.1 File format .16
4.7.2 Keyword syntax and usage .16
4.7.3 Data format identifiers .17
4.8 Useable target life .19
Annex A (informative) Gamut mapping — Computational reference .20
Annex B (informative) Application notes .22
Bibliography .25
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).
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For an explanation on the meaning of ISO specific terms and expressions related to conformity
assessment, as well as information about ISO’s adherence to the WTO principles in the Technical
Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 130, Graphic technology.
This first edition of ISO 12641-1 cancels and replaces ISO 12641:1997, which has been technically revised
to take account of the technical advancements in the related fields and the associated equipment.
ISO 12641 consists of the following parts, under the general title Graphic technology — Prepress digital
data exchange:
— Part 1: Colour targets for input scanner calibration
An additional part dealing with advanced colour targets for input scanner calibration is planned.
Annexes A and B are for information only.
iv © ISO 2016 – All rights reserved

Introduction
The technical requirements of this part of ISO 12641 are identical to the American National Standards
IT8.7/1-1993 and IT8.7/2-1993. These Standards resulted from the joint efforts of an international
industry group that included participants representing a broad range of prepress vendors, film
manufacturers, and users. This group, initially identified as the digital data exchange standards (DDES)
committee, later became the founders of the ANSI IT8 (Image Technology) accredited standards
committee which is responsible for electronic data exchange standards in graphic arts prepress.
Purpose of this part of ISO 12641
Colour input scanners do not all analyse colour the same way the human eye does. These devices are
designed to optimize the signal generated when typical materials are scanned. Colour reflection and
transparency products use various combinations of proprietary dye sets to achieve visual responses
that simulate the colour appearance of natural scene elements. The ability to achieve the same
colour appearance from different combinations of dyes is referred to as metamerism. Because both
photographic dyes and input scanner sensitivities vary from product to product, there is variability
in the input scanner response to metameric colours produced by the various materials. The intent of
this part of ISO 12641 is to define an input test target that will allow any colour input scanner to be
calibrated with any film or paper dye set used to create the target. This part of ISO 12641 is intended
to address the colour reflection and transparency products which are generally used for input to the
preparatory process for printing and publishing.
The target was designed to be useable for calibration by visual comparison and as a numerical data
target for electronic systems and future development. The target design made use of a uniform colour
space to optimize the spacing of target patches. The tolerances developed for individual coloured
patches meet the values needed for both numerical and visual analysis.
Design of the target
The CIE 1976 (L*a*b*) or CIELAB colour space was chosen as the space to be used for the design of the
colour calibration target. Uniform spacing in hue angle, lightness and chroma, and tolerancing in terms
of differences in these parameters (∆E* ) is believed to provide a reasonable distribution of coloured
ab
patches in the most effective manner. Although CIELAB was defined with reference to reflection
viewing conditions, tolerancing in terms of vector differences (∆E* ) does provide a reasonable error
ab
estimate for transmission materials as well, although the uniformity of the space is dependent upon the
conditions of viewing.
The design goal was to define a target that would have, as its main part, as many common coloured
patches as was practical, regardless of the dye set used. The remainder of the target is intended to
define the unique colour characteristics of the particular dye set used to create a specific target; the
values for each target patch is to be established using a common procedure.
To provide a reasonable measure of the colour gamut that is within the capability of modern colour
papers and films, all manufacturers of these products were invited to provide colour dye data along
with the necessary minimum and maximum density data for each of their image forming colour dye
sets. Data were provided by Agfa Company, Eastman Kodak Company, Fuji Photo Film Company, and
Konica Corporation. These data were then used to estimate the CIELAB colour gamut that each paper
and film dye set could produce. This estimate was achieved by mathematical modelling (by several of
the participating companies) using methods which were different but gave very similar results. Annex A
provides additional reference material concerning the method used in selecting aim values.
The following documents provide reference information on the computational methods used in gamut
determination.
1. N. Ohta, “The Color Gamut Obtainable by the Combination of Subtractive Color Dyes. V. Optimum
Absorption Bands as Defined by Nonlinear Optimization Technique.” Journal of Imaging Science, 30,
[1]
9-12 (1986) .
2. M. Inui, “Fast Algorithm for Computing Color Gamuts,” Colour Research and Application, 18, 341-348
[4]
(1993) .
All computations were based upon the use of the CIE 2 degree observer and D illuminant. All
transmission measurements were made using diffuse/normal or normal/diffuse geometry as defined
for total transmittance. All reflection measurements were made using 0°/45° or 45°/0° geometry
as defined in ISO 13655. The reference white was assumed to be a perfect diffuser. The use of an
absolute reference allows all colours on similar media (reflection or transmission) that have the same
colorimetric definition to also look the same when viewed at the same time.
The gamut plots developed
...