SIST ISO 12640-3:2008

INTERNATIONAL ISO
STANDARD 12640-3
First edition
2007-07-15
Graphic technology — Prepress digital
data exchange —
Part 3:
CIELAB standard colour image data
(CIELAB/SCID)
Technologie graphique — Échange de données numériques de
préimpression —
Partie 3: Données d'images en couleur normalisées CIELAB
(CIELAB/SCID)
Reference number
©
ISO 2007
PDF disclaimer
This PDF file may contain embedded typefaces. In accordance with Adobe's licensing policy, this file may be printed or viewed but
shall not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading this file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create this PDF file can be found in the General Info relative to the file; the PDF-creation
parameters were optimized for printing. Every care has been taken to ensure that the file is suitable for use by ISO member bodies. In
the unlikely event that a problem relating to it is found, please inform the Central Secretariat at the address given below.

©  ISO 2007
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means,
electronic or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or
ISO's member body in the country of the requester.
ISO copyright office
Case postale 56 • CH-1211 Geneva 20
Tel. + 41 22 749 01 11
Fax + 41 22 749 09 47
E-mail copyright@iso.org
Web www.iso.org
Published in Switzerland
ii © ISO 2007 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Requirements . 2
5 Data description and definition. 3
5.1 Data set definition. 3
5.2 Colour encoding used in this part of ISO 12640. 3
5.3 Natural images . 4
5.4 Synthetic images . 7
6 Electronic data . 11
6.1 Image file characteristics. 11
6.2 Image file formats . 11
Annex A (normative) Guidance for use of digital data. 12
Annex B (informative) Definition of the reference colour gamut . 14
Annex C (normative) Check-sum data . 21
Annex D (informative) Typical TIFF file headers used for image data. 22
Annex E (informative) Text insertion. 24
Annex F (informative) Histogram and gamut plots. 25
Annex G (informative) CIELAB values in colour charts . 29
Bibliography . 33

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 12640-3 was prepared by Technical Committee ISO/TC 130, Graphic technology.
ISO 12640 consists of the following parts, under the general title Graphic technology — Prepress digital data
exchange:
⎯ Part 1: CMYK standard colour image data (CMYK/SCID)
⎯ Part 2: XYZ/sRGB encoded standard colour image data (XYZ/SCID)
⎯ Part 3: CIELAB standard colour image data (CIELAB/SCID)
The following parts are under preparation:
⎯ Part 4: Wide gamut display-referred standard colour image data (TBDencoded/SCID)
⎯ Part 5: Scene-referred standard colour image data (RIMM/SCID)

iv © ISO 2007 – All rights reserved

Introduction
0.1 Need for standard digital test images
Standard test images provide a set of data that can be used for any of the following tasks:
⎯ evaluating the colour reproduction of imaging systems;
⎯ evaluating colour image output devices;
⎯ evaluating the effect of image processing algorithms applied to the images;
⎯ evaluating the coding technologies necessary for the storage and transmission of high-definition image
data.
Because they exist as standard, well-defined, high-quality image data sets, typical of the range of image
content commonly encountered, they enable users to be confident that the images will produce good quality
reproductions, if properly rendered, and that they provide a reasonable test of the evaluation task being
undertaken. No limited set of images can fully test any system, but the sets provided give as reasonable a test
as can be expected from a limited image set. Furthermore, the existence of a standard image data set
enables users in different locations to produce comparisons without the need to exchange images prior to
reproduction.
However, different applications require that the standard image data be provided in different image states
using different image encodings (see ISO 22028-1). The user needs to select those appropriate to the
evaluation task being undertaken. Whilst transformation of the image data to another image state is always
possible, there is, in general, no agreement amongst experts as to how this is best done. Thus, it has been
considered preferable to provide data in three different image states in the various parts of ISO 12640.
Part 1 of ISO 12640 provides a set of 8-bits-per-channel data that is defined in terms of CMYK dot
percentages. The colours resulting from reproduction of CMYK data are strictly defined only at the time of
printing and, as such, the data are only applicable to evaluation of CMYK printing applications.
Transformations to other image states and colour encodings are not necessarily well defined. In fact, the data
might not even be useful for CMYK printing processes different from those typically found in traditional graphic
arts applications as the image data are defined to produce “pleasing” images when reproduced on systems
using “typical” inks and producing “typical” tone value rendering. Printing systems that use inks of a distinctly
different colour, or produce a very different tone value rendering, will not reproduce them as pleasing images
without a well-defined colour transformation. Moreover, with a bit depth of only 8 bits per channel, any colour
transformation employed will probably introduce artefacts.
Part 2 of ISO 12640 provides a set of test image data encoded both as XYZ tristimulus values with a depth of
16 bits per channel and as sRGB (defined in IEC 61966-2-1) with a bit depth of 8 bits per channel. (The higher
bit depth for the XYZ encoding is necessary because of the perceptual non-uniformity of the XYZ colour
space.) Both sets of data are optimized for viewing on a reference sRGB CRT display in the reference sRGB
viewing environment, and relative to CIE standard illuminant D65 for which the XYZ values were computed.
The images are mainly designed to be used on systems utilizing sRGB as the reference encoding, and as
such are mainly applicable to the consumer market and those systems for which the colour monitor is the
“hub” device. Although such systems are used for some applications in the graphic arts industry, sRGB is by
no means the most common image encoding. Furthermore, a particular drawback is the fact that the sRGB
colour gamut is quite different in shape than the colour gamut of typical offset printing. This difference can
necessitate fairly aggressive colour re-rendering to produce optimal prints from sRGB image data.
In order to be useful for applications where large, print-referred output gamuts are encountered, common in
graphic technology and photography, it was felt that it would be desirable to produce an image set in which
some colours are permitted to be encoded close to the boundary of the full colour gamut attainable with
surface colours. Furthermore, from the perspective of colour management it is advantageous if the images are
referenced to illuminant D50, which is the predominant reference illuminant used in graphic arts and
photography, both for viewing and measurement. For this reason it has also become the predominant
reference illuminant for most colour management applications.
The purpose of this part of ISO 12640 is, therefore, to provide a test image data set with a large colour gamut
related to illuminant D50. The bit depth of the natural images is 16 bits per channel, while the colour charts
and vignettes are 8 bits per channel.
0.2 Definition of the reference colour gamut
The reference colour gamut defined for this part of ISO 12640 originated from three quite separate sources.
However, it was noted that there was considerable similarity between the three. One definition came from
work within ISO/TC 130 itself, and this arose by consideration of various sets of published data, which
together were taken to define the colour gamut of surface colours. The other definitions arose from work within
Hewlett-Packard, which was focused on the colour gamuts obtainable by printing, and that of a group of
German photographic printing experts. The similarity of these led to the conclusion that it would be desirable
to reconcile them into a single gamut that would be taken as the reference colour gamut for this part of
ISO 12640. Full details of the reference colour gamut and its derivation are given in Annex B.
0.3 Characteristics of the test images
The performance of any colour reproduction system is normally evaluated both subjectively (by viewing the
final output image) and objectively (by measurement of control elements). This requirement dictated that the
test images include both natural scenes (pictures) and synthetic images (colour charts and colour vignettes).
Because the results of subjective image evaluation are strongly affected by the image content, it was
important to ensure that the natural images were of high quality and contained diverse subject matter.
However, by requiring images to look natural, it is difficult within a single, relatively small sample set to
produce elements in the scene that contain the subtle colour differences required in such test images and that
cover the full reference colour gamut defined. It is also important to have some images that contain subtle
differences in near-neutral colours. Thus, while most images contain colours that extend to the gamut
boundary, this is often only for a limited range of hues in each image. The full reference colour gamut can only
be explored by utilizing the synthetic colour chart.
A survey was conducted of all ISO/TC 130 member countries to identify desirable image content and to solicit
submission of suitable images for consideration. The image set that resulted consists of eight natural images,
eight colour charts and two colour vignettes. The natural images include flesh tones, images with detail in the
extreme highlights or shadows, neutral colours, brown and wood-tone colours that are often difficult to
reproduce, memory colours, complicated geometric shapes, fine detail, and highlight and shadow vignettes.
The colour charts and colour
...

INTERNATIONAL ISO
STANDARD 12640-3
First edition
2007-07-15
Graphic technology — Prepress digital
data exchange —
Part 3:
CIELAB standard colour image data
(CIELAB/SCID)
Technologie graphique — Échange de données numériques de
préimpression —
Partie 3: Données d'images en couleur normalisées CIELAB
(CIELAB/SCID)
Reference number
©
ISO 2007
PDF disclaimer
PDF files may contain embedded typefaces. In accordance with Adobe's licensing policy, such files may be printed or viewed but shall
not be edited unless the typefaces which are embedded are licensed to and installed on the computer performing the editing. In
downloading a PDF file, parties accept therein the responsibility of not infringing Adobe's licensing policy. The ISO Central Secretariat
accepts no liability in this area.
Adobe is a trademark of Adobe Systems Incorporated.
Details of the software products used to create the PDF file(s) constituting this document can be found in the General Info relative to
the file(s); the PDF-creation parameters were optimized for printing. Every care has been taken to ensure that the files are suitable for
use by ISO member bodies. In the unlikely event that a problem relating to them is found, please inform the Central Secretariat at the
address given below.
This CD-ROM contains:
1) the publication ISO 12640-3:2007 in portable document format (PDF), which can be viewed using
Adobe® Acrobat® Reader;
2) image files N1_16_LAB.tif, N2_16_LAB.tif, N3_16_LAB.tif, N4_16_LAB.tif, N5_16_LAB.tif,
N6_16_LAB.tif, N7_16_LAB.tif and N8_16_LAB.tif correspond to the natural images shown in
Figure 1;
3) image files CC1.pdf, CC2.pdf, CC3.pdf, CC4.pdf, CC5.pdf, CC6pdf, CC7.pdf and CC8.pdf
correspond to the colour charts shown in Figure 2;
4) image files CV1.pdf and CV2.pdf correspond to the vignettes shown in Figure 3.
Adobe and Acrobat are trademarks of Adobe Systems Incorporated.

©  ISO 2007
All rights reserved. The appropriate use, transmittal, and reproduction of the content of this CD-ROM are specified in Annex A of
ISO 12640-3:2
...