Graphic technology — Prepress digital data exchange — Part 3: CIELAB standard colour image data (CIELAB/SCID)

This document specifies a set of standard large gamut colour images (encoded as 16-bit CIELAB digital data) that can be used for the evaluation of changes in image quality during coding, image processing (including transformation, compression and decompression), displaying on a colour monitor and printing. These images can be used for research, testing and assessing of output systems such as printers, colour management systems and colour profiles.

Technologie graphique — Échange de données numériques de préimpression — Partie 3: Données d'images en couleur normalisées CIELAB (CIELAB/SCID)

Grafična tehnologija – Izmenjava digitalnih podatkov v grafični pripravi – 3. del: Standardni podatki CIELAB za barvne slike (CIELAB/SCID)

General Information

Status
Published
Publication Date
11-Aug-2022
Current Stage
6060 - International Standard published
Due Date
09-May-2023
Completion Date
12-Aug-2022

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INTERNATIONAL ISO
STANDARD 12640-3
Second edition
2022-08
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 12640-3:2022(E)
© ISO 2022
---------------------- Page: 1 ----------------------
ISO 12640-3:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

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
© ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 12640-3:2022(E)
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 document ........................................................................................................................... 3

5.2.1 Image data encoding ....................................................................................................................................................... 3

5.2.2 Image data arrangement ............................................................................................................................................. 3

5.2.3 CIELAB image data (16 bits per channel) .................................................................................................... 3

5.2.4 CIELAB image data (8 bits per channel) ....................................................................................................... 4

5.3 Natural images........................................................................................................................................................................................ 4

5.4 Synthetic images ................................................................................................................................................................................... 7

5.4.1 Colour charts ......................................................................................................................................................................... 7

5.4.2 Vignettes .................................................................................................................................................................................... 9

5.4.3 Synthetic image format ............................................................................................................................................. 10

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) Checksum 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 .............................................................................................................................................................................................................................34

iii
© ISO 2022 – All rights reserved
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ISO 12640-3:2022(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.

This second edition cancels and replaces the first edition (ISO 12640-3:2007), of which it constitutes a

minor revision. The changes are as follows:
— CIE Publication 15:2004 has been changed to CIE Publication 15 Colorimetry;

— in 3.4, the definition of colour space has been updated based on revision to CIE Publication 17 in

2020;

— in the Bibliography, CIE S 17:2020 ILV has been updated to International lighting vocabulary, 2nd

edition.
A list of all parts in the ISO 12640 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.
© ISO 2022 – All rights reserved
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ISO 12640-3:2022(E)
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.

ISO 12640-1 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.

ISO 12640-2 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

© ISO 2022 – All rights reserved
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ISO 12640-3:2022(E)

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 document 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 document 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 gamut obtainable by printing, and

that of a group of German photographic printing experts. The similarity of these led to the conclusion

that it is desirable to reconcile them into a single gamut that would be taken as the reference colour

gamut for this document. 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 vignettes show the reference colour

gamut (in CIE Lab colour space) in cross-sections for 16 and 8 hue angles, respectively.

0.4 File format of the digital test images
* * *

All of the images consist of pixel interleaved data (L then a then b ) with the data origin at the upper

left of the image, as viewed naturally, and organized by rows. These data are available as individual

files, which are a normative part of this part of this document. The image file format is as specified

in ISO 12639:2004, Annex H, with BitsPerSample set to 16, 16, 16. The images can be imported and

manipulated as necessary by a wide variety of imaging software tools and platforms commonly in

general use in the industry. See Annex D for details of the TIFF header.
All colour charts and vignettes consist of files in Adobe® PDF format.

1) This information is given for the convenience of users of this document and does not constitute an endorsement

by ISO of the product named.
© ISO 2022 – All rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 12640-3:2022(E)
Graphic technology — Prepress digital data exchange —
Part 3:
CIELAB standard colour image data (CIELAB/SCID)
1 Scope

This document specifies a set of standard large gamut colour images (encoded as 16-bit CIELAB digital

data) that can be used for the evaluation of changes in image quality during coding, image processing

(including transformation, compression and decompression), displaying on a colour monitor and

printing. These images can be used for research, testing and assessing of output systems such as

printers, colour management systems and colour profiles.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 12639:2004, Graphic technology — Prepress digital data exchange — Tag image file format for image

technology (TIFF/IT)

ISO 13655, Graphic technology — Spectral measurement and colorimetric computation for graphic arts

images

ISO 22028-1, Photography and graphic technology — Extended colour encodings for digital image storage,

manipulation and interchange — Part 1: Architecture and requirements

PDF Reference: Adobe Portable Document Format, Version 1.4 3rd edition., Adobe Systems Incorporated,

(ISBN 0-201-75839-3)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
checksum

sum of the digits in a file that can be used to check if a file has been transferred properly

Note 1 to entry: Often, only the least significant bits are summed.
3.2
colour gamut

solid in a colour space, consisting of all those colours that are present in a specific scene, artwork,

photograph, photomechanical or other reproduction; or are capable of being created using a particular

output device and/or medium
[SOURCE: ISO 12640-4:2011]
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ISO 12640-3:2022(E)
3.3
colour sequence
order in which the colours are stored in a data file
3.4
colour space
geometric representation of colour in space
Note 1 to entry: A colour space is usually of three dimensions
Note 2 to entry: This entry was numbered 845-03-25 in IEC 60050-45:1987

[SOURCE: CIE S 17:2020 ILV: International Lighting Vocabulary, 2nd edition, modified]

3.5
colour value
numeric values associated with each of the pixels
3.6
data range
range of integers for a given variable in between a minimal and maximal value
3.7
global colour change

change to the colours in an image (often selectively by colour region) applied consistently to all parts of

the image

Note 1 to entry: This is in contrast to a local colour change where selected spatial areas of an image are changed

separately from the rest of the image area.
3.8
orientation

specifies the origin and direction of the first line of data with respect to the image content as viewed by

the end user

Note 1 to entry: The codes used to specify orientation are contained in ISO 12639.

3.9
pixel
smallest discrete picture element in a digital image file
3.10
pixel interleaving
* * *

colour data organized such that the L , a and b colour space values for one pixel are followed by the

same sequence of colour values for the next pixel; the specific order of colour components is determined

by the ColorSequence tag as defined in ISO 12639
Note 1 to entry: Other forms of colour data interleaving are line and plane.
4 Requirements

This document consists of the images contained in the 18 image data files which are part of this

document. Their file names are listed in Table 4. The image characteristics of these data are described

in Clause 5 and the electronic data structure in Clause 6.
© ISO 2022 – All rights reserved
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ISO 12640-3:2022(E)
5 Data description and definition
5.1 Data set definition

The set of standard colour image data consists of eight natural (photographed) images and ten synthetic

images created digitally on a computer. The synthetic images consist of eight colour charts consisting

of various patches, each 10 mm square, and two colour vignettes. The natural images are identified as

N1 to N8, and each of them also has a descriptive name derived from the picture content (e.g. bride and

groom). The synthetic images are identified as CC1 to CC8, CV1 and CV2.

The images are identified by the designation CIELAB/SCID. The co-ordinates of the text insertion are

provided in Annex E.

NOTE The image set defined in this document is based on the large gamut defined in Annex B. Image sets

contained in other document are based on different gamuts and can be more suitable for use in evaluation of

other applications.
5.2 Colour encoding used in this document
5.2.1 Image data encoding

The image data encoding shall be in accordance with the requirements of ISO 22028-1.

[10]

The image data are the desired CIELAB colorimetry defined by CIE Publication 15 , and measured in

accordance with ISO 13655, of reproductions of the images on the reference medium, with the reference

medium white point selected as the colour space white point. The image data are output-referred,

[11]

having been rendered to the reference medium of the ICC.1:2004-04 perceptual rendering intent,

which is defined as a hypothetical print on a substrate specified to have a neutral reflectance of 89 %

(the reference medium white point) and the darkest printable colour on this medium is assumed to have

a neutral reflectance of 0,347 31 % of the substrate reflectance (the reference medium black point). The

rendering target colour gamut for the reference medium is specified in Annex B. The reference viewing

environment is based on standard viewing condition P2, as specified for graphic arts and photography

in ISO 3664, but extended in the following way: the surfaces immediately surrounding the image are

assumed to be a uniform matt grey with a reflectance of 20 %. The reference viewing environment is

also assumed to have a viewing flare of 0,75 % of the luminance of the reference white. The CIELAB

image data are encoded as specified in 5.2.3 and 5.2.4.
5.2.2 Image data arrangement
* * *

The image data are pixel-interleaved in the colour sequence of L then a then b (16 bits) for the natural

* * *

images and L then a then b (8 bits) for the colour charts and the vignettes. The arrangement of data

follows the scanning of each image from the upper left corner to the upper right, then moving to the

next lower horizontal line. The resolution is 12 pixels/mm for every natural image.

5.2.3 CIELAB image data (16 bits per channel)

The CIELAB data for the natural images are encoded as 16-bit integers per channel, derived by

* * *

multiplying the L , a and b values for each pixel with the corresponding value for the data range.

 
L =×round 65535
 
16bit
 
100
 
* *
aa=×round()256 (1)
16bit
* *
b =×round()256 b
16biit
* * * * * *
where L , a and b represent normalised 16-bit values of L , a and b .
16bit 16bit 16bit
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ISO 12640-3:2022(E)
The data range of the values is:
* * *
L ∈{0..100}, a ∈{−128..+127} and b ∈{−128..+127},
* * * * *
L ∈{0..65 535}, a ∈{−32 768..+32 512} and b ∈{−32 768..+32 512}, a and b are
16bit 16bit 16bit 16bit 16bit
signed integers.
NOTE −32 678 = −128 × 256, and 32 512 = 127 × 256.
5.2.4 CIELAB image data (8 bits per channel)

The CIELAB data for the colour charts are encoded as 8-bit integers per channel, derived by multiplying

* * *

the L , a and b values for each pixel with the corresponding value for the data range.

 
L =×round 255
 
8bit
 
100
 
* *
aa=round() (2)
8bit
* *
b =round(bb )
8bit
* * * * * *
where L , a and b represent normalised 8 bit values of L , a and b .
8bit 8bit 8bit
The data range of the values is:
* * *
L ∈{0..100}, a ∈{−128..+127} and b ∈{−128..+127},
* * * * *

L ∈{0..255}, a ∈{−128..+127} and b ∈{−128..+127}, the a and b are signed integers.

8bit 8bit 8bit 8bit 8bit
5.3 Natural images

The characteristics of the eight natural images, shown in Figure 1, are given in Table 1.

Table 1 — Characteristics for natural images
Parameter Characteristics
Resolution 12 pixels/mm
* * *

Colour values 16 bits/channel L , a and b , with respect to illuminant D50 (defined as

* * *
media-relative, i.e. such that a white in the image has the L , a and b
values of 100, 0, 0)
File format ISO 12639:2004, Annex H, with BitsPerSample set to 16, 16, 16
This format also readable with TIFF 6.0 with extension, photometric
interpretation tag 8, CIELAB, signed encoding.
Label on image CIELAB/SCID

Image data orientation Horizontal scanning starting from top left and ending at bottom right

NOTE The natural images have been colour-rendered to produce the desired image colorimetry on the

reference print medium as described in Annex B. For the most part, the image colours will be within the reference

colour gamut. However, it is possible for some image colours to be slightly outside (this is somewhat dependent

on how the convex hull of the gamut is constructed). It is sometimes necessary to gamut map the results of colour

rendering and re-rendering processing to exactly fit the destination device colour gamut.

The description and typical usage of the natural images are given in Table 2. The descriptive names

of these images are given following the identification code. Figure 1 shows reduced size sRGB

reproductions of the natural images. Statistical and gamut data for each of the natural images are

* * *

shown in Annex F, as histograms of the L values and a versus b plots for each image, respectively.

© ISO 2022 – All rights reserved
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ISO 12640-3:2022(E)
Table 2 — Natural images
Name Aspect, image Description and typical usage
size

N1 Bride and groom Horizontal, Image of a bride wearing white clothes and groom wearing black

2 560 × 2 048 clothes. Used to evaluate the rendering of human skin tones and neu-

pixels tral colours, especially highlights and shadows.

N2 People Horizontal, Image consisting of five people wearing colourful clothes, sitting on a

2 560 × 2 048 dark leather couch. Used to evaluate the colour rendering of extreme-

pixels ly colourful objects in the presence of skin tones and neutrals.

N3 Cashew nuts Vertical, Image of dried fruits and filled containers used to evaluate tonal

2 048 × 2 560 and colour rendering, in particular adjustments for grey component
pixels replacement.

N4 Meal Horizontal, Image with widely recognizable cooked food and pastel colours. Used

2 560 × 2 048 to evaluate high-key tonal rendering and food memory colours.
pixels

N5 Mandolin Vertical, Image of goods, including metallic objects, used to evaluate the

2 048 × 2 560 reproduction of colours, as well as the reproduction of the lustrous

pixels appearances of metallic objects.

N6 Tailor scene Horizontal, Still-life image of textile used to evaluate the tone reproduction in a

2 560 × 2 048 range of neutrals and textile structures (object moiré).
pixels

N7 Wool Horizontal, Image of different coloured balls of wool used to evaluate the repro-

2 560 × 2 048 duction of details in highly chr
...

ISO TC 130 N 4703
Date: 2022-01-2504-29
ISO/FDIS 12640-3:2022(E)
ISO TC 130/WG 2
ISO TC 130/WG 2
Secretariat: SAC
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)
---------------------- Page: 1 ----------------------
ISO/FDIS 12640-3:2022(E)
ISO/FDIS 12640-3:2022(E)
© ISO 2022

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-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland.
© ISO 2022 – All rights reserved
ii © ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 12640-3:2022(E)
ISO/FDIS 12640-3:2022(E)
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 .................................................................................................................................................................................... iv

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

1 Scope .................................................................................................................................................................................. 9

2 Normative references ......................................................................................................................................................... 9

3 Terms and definitions ......................................................................................................................................................... 9

4 Requirements .................................................................................................................................................................... 11

5 Data description and definition .......................................................................................................................................... 11

5.1 Data set definition ..................................................................................................................................................... 11

5.2 Colour encoding used in this document ...................................................................................................................... 11

5.2.1 Image data encoding .............................................................................................................................................. 11

5.2.2 Image data arrangement ........................................................................................................................................ 11

5.2.3 CIELAB image data (16 bits per channel) ................................................................................................................. 11

5.2.4 CIELAB image data (8 bits per channel) ................................................................................................................... 12

5.3 Natural images .......................................................................................................................................................... 12

5.4 Synthetic images ........................................................................................................................................................ 17

5.4.1 Colour charts ......................................................................................................................................................... 17

5.4.2 Vignettes ............................................................................................................................................................... 20

5.4.3 Synthetic image format .......................................................................................................................................... 22

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6 Electronic data ................................................................................................................................................................... 22

6.1 Image file characteristics ............................................................................................................................................ 22

6.2 Image file formats ...................................................................................................................................................... 23

Annex A (normative) Guidance for use of digital data ................................................................................................................ 24

Annex B (informative) Definition of the reference colour gamut ................................................................................................ 28

Annex C (normative) Checksum data ......................................................................................................................................... 36

Annex D (informative) Typical TIFF file headers used for image data .......................................................................................... 38

Annex E (informative) Text insertion ......................................................................................................................................... 43

Annex F (informative) Histogram and gamut plots ..................................................................................................................... 46

Annex G (informative) CIELAB values in colour charts ................................................................................................................. 1

Bibliography ................................................................................................................................................................................ 9

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ISO/FDIS 12640-3:2022(E)
ISO/FDIS 12640-3:2022(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/directiveswww.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/patentswww.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.htmlwww.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 130, Graphic technology.

TheThis second edition of ISO 12640-3 is a minor revision which cancels and replaces the first edition (ISO 12640-

3:2007). The scope of the document remains unchanged.

), of which it constitutes a minor revision. The changes are editorial as shown belowfollows:

Normative reference: — CIE Publication 15:2004 washas been changed to CIE Publication 15 Colorimetry;

Definition— in 3.4, the definition of colour space: has been updated based on revision to CIE Publication 17 in 2020.

— in the Bibliography:, CIE S 17:2020 ILV washas been updated to: International lighting vocabulary, 2nd edition.

A list of all parts in the ISO 12640 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.htmlwww.iso.org/members.html.

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ISO/FDIS 12640-3:2022(E)
ISO/FDIS 12640-3:2022(E)
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 12640-1 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 12640-2 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

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ISO/FDIS 12640-3:2022(E)
ISO/FDIS 12640-3:2022(E)

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 12640document 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 12640document 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 gamut obtainable by printing, and that of a group of German photographic

printing experts. The similarity of these led to the conclusion that it would beis desirable to reconcile them into a

single gamut that would be taken as the reference colour gamut for this part of ISO 12640.document. 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

vignettes show the reference colour gamut (in CIE Lab colour space) in cross-sections for 16 and 8 hue angles,

respectively.
0.4 File format of the digital test images
* * *

All of the images consist of pixel interleaved data (L then a then b ) with the data origin at the upper left of the

image, as viewed naturally, and organized by rows. These data are available as individual files, which are a

normative part of this part of this part of ISO 12640.document. The image file format is as specified in ISO

12639:2004, Annex H, with BitsPerSample set to 16, 16, 16. The images can be imported and manipulated as

necessary by a wide variety of imaging software tools and platforms commonly in general use in the industry. (See

Annex D for details of the TIFF header.).
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ISO/FDIS 12640-3:2022(E)
ISO/FDIS 12640-3:2022(E)
All colour charts and vignettes consist of files in Adobe® PDF format.

This information is given for the convenience of users of this document and does not constitute an endorsement by ISO of the product

named.
vii
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ISO/FDIS 12640-3:2022(E)

Graphic technology — Prepress digital data exchange — Part 3: CIELAB standard colour

image data (CIELAB/SCID)
1 Scope

This part of ISO 12640document specifies a set of standard large gamut colour images (encoded as 16-bit CIELAB

digital data) that can be used for the evaluation of changes in image quality during coding, image processing

(including transformation, compression and decompression), displaying on a colour monitor and printing. These

images can be used for research, testing and assessing of output systems such as printers, colour management

systems and colour profiles.
2 Normative references

The following referenced documents are indispensable forreferred to in the applicationtext in such a way that some

or all of their content constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 3664, Viewing conditions — Graphic technology and photography

ISO ISO 12639:2004, Graphic technology — Prepress digital data exchange — Tag image file format for image

technology (TIFF/IT)

ISO 13655, Graphic technology — Spectral measurement and colorimetric computation for graphic arts images

ISO 22028--1, Photography and graphic technology — Extended colour encodings for digital image storage,

manipulation and interchange — Part 1: Architecture and requirements
CIE Publication 15, Colorimetry

ICC.1:2004-04, Image technology colour management — Architecture, profile format, and data structureT IFF,

Revision 6.0 Final, Aldus Corporation (now Adobe Systems Incorporated), June 3, 1992

PDF Reference: Adobe Portable Document Format, Version 1.4 3rd edition., Adobe Systems Incorporated, (ISBN 0-

201-75839-3)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
check sum
checksum

sum of the digits in a file that can be used to check if a file has been transferred properly

NOTENote 1 to entry: Often, only the least significant bits are summed.
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ISO/FDIS 12640-3:2022(E)
3.2
colour gamut

solid in a colour space, consisting of all those colours that are present in a specific scene, artwork, photograph,

photomechanical or other reproduction; or are capable of being created using a particular output device and/or

medium
[ISO 12231]
[SOURCE: ISO 12640-4:2011]
3.3
colour sequence
order in which the colours are stored in a data file
3.4
colour space

geometric representation of colour in space [CIE S 17:2020 ILV: International Lighting Vocabulary, 2nd edition]

Note 1 to entry: A colour space is usually of three dimensions
Note 2 to entry: This entry was numbered 845-03-25 in IEC 60050-45:1987

[SOURCE: CIE S 17:2020 ILV: International Lighting Vocabulary, 2nd edition, modified]

3.5
colour value
numeric values associated with each of the pixels
3.6
data range
range of integers for a given variable in between a minimal and maximal value
3.7
global colour change

change to the colours in an image (often selectively by colour region) applied consistently to all parts of the image

NOTE Note 1 to entry: This is in contrast to a local colour change where selected spatial areas of an image are changed

separately from the rest of the image area.
3.8
orientation

specifies the origin and direction of the first line of data with respect to the image content as viewed by the end user

NOTE Note 1 to entry: The codes used to specify orientation are contained in ISO 12639:2004.

3.9
pixel
smallest discrete picture element in a digital image file
3.10
pixel interleaving
* * *

colour data organized such that the L , a and b colour space values for one pixel are followed by the same sequence

of colour values for the next pixel; the specific order of colour components is determined by the ColorSequence tag

as defined in ISO 12639
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ISO/FDIS 12640-3:2022(E)

NOTE Note 1 to entry: Other forms of colour data interleaving are line and plane.

4 Requirements

This part of ISO 12640document consists of the images contained in the 18 image data files which are part of this

part of ISO 12640.document. Their file names are listed in Table 4. The image characteristics of these data are

described in Clause 5 and the electronic data structure in Clause 6.
5 Data description and definition
5.1 Data set definition

The set of standard colour image data consists of eight natural (photographed) images and ten synthetic images

created digitally on a computer. The synthetic images consist of eight colour charts consisting of various patches,

each 10 mm square, and two colour vignettes. The natural images are identified as N1 to N8, and each of them also

has a descriptive name derived from the picture content (e.g. bride and groom). The synthetic images are identified

as CC1 to CC8, CV1 and CV2.

The images are identified by the designation CIELAB/SCID. The co-ordinates of the text insertion are provided in

Annex E.

NOTE The image set defined in this part of ISO 12640document is based on the large gamut defined in Annex B. Image sets

contained in other parts of ISO 12640document are based on different gamuts and can be more suitable for use in evaluation of

other applications.
5.2 Colour encoding used in this part of ISO 12640document
5.2.1 Image data encoding

The image data encoding is definedshall be in accordance with ISO 22028-1the requirements as followsof

ISO 22028-1.
[10]

The image data are the desired CIELAB colorimetry as defined by CIE Publication 15, , and measured in

accordance with ISO 13655, of reproductions of the images on the reference medium, with the reference medium

white point selected as the colour space white point. The image data are output-referred, having been rendered to

[11]

the reference medium of the ICC.1:2004-04 perceptual rendering intent, which is defined as a hypothetical print

on a substrate specified to have a neutral reflectance of 89 % (the reference medium white point) and the darkest

printable colour on this medium is assumed to have a neutral reflectance of 0,347 31 % of the substrate reflectance

(the reference medium black point). The rendering target colour gamut for the reference medium is specified in

Annex B. The reference viewing environment is based on standard viewing condition P2, as specified for graphic

arts and photography in ISO 3664, but extended in the following way: the surfaces immediately surrounding the

image are assumed to be a uniform matt grey with a reflectance of 20 %. The reference viewing environment is also

assumed to have a viewing flare of 0,75 % of the luminance of the reference white. The CIELAB image data are

encoded as specified in 5.2.3 and 5.2.4.
5.2.2 Image data arrangement
* * *

The image data are pixel-interleaved in the colour sequence of L then a then b (16 bits) for the natural images

* * *
and L then a then b (8 bits) fo
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 12640-3
ISO/TC 130
Graphic technology — Prepress digital
Secretariat: SAC
data exchange —
Voting begins on:
2022-05-16
Part 3:
Voting terminates on:
CIELAB standard colour image data
2022-07-11
(CIELAB/SCID)
Technologie graphique — Échange de données numériques de
préimpression —
Partie 3: Données d'images en couleur normalisées CIELAB (CIELAB/
SCID)
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 12640-3:2022(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2022
---------------------- Page: 1 ----------------------
ISO/FDIS 12640-3:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

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
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ISO/FDIS 12640-3:2022(E)
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 document ........................................................................................................................... 3

5.2.1 Image data encoding ....................................................................................................................................................... 3

5.2.2 Image data arrangement ............................................................................................................................................. 3

5.2.3 CIELAB image data (16 bits per channel) .................................................................................................... 3

5.2.4 CIELAB image data (8 bits per channel) ....................................................................................................... 4

5.3 Natural images........................................................................................................................................................................................ 4

5.4 Synthetic images ................................................................................................................................................................................... 7

5.4.1 Colour charts ......................................................................................................................................................................... 7

5.4.2 Vignettes .................................................................................................................................................................................... 9

5.4.3 Synthetic image format ............................................................................................................................................. 10

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) Checksum 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 .............................................................................................................................................................................................................................34

iii
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ISO/FDIS 12640-3:2022(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.

This second edition cancels and replaces the first edition (ISO 12640-3:2007), of which it constitutes a

minor revision. The changes are as follows:
— CIE Publication 15:2004 has been changed to CIE Publication 15 Colorimetry;

— in 3.4, the definition of colour space has been updated based on revision to CIE Publication 17 in

2020;

— in the Bibliography, CIE S 17:2020 ILV has been updated to International lighting vocabulary, 2nd

edition.
A list of all parts in the ISO 12640 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.
© ISO 2022 – All rights reserved
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ISO/FDIS 12640-3:2022(E)
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.

ISO 12640-1 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.

ISO 12640-2 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

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---------------------- Page: 5 ----------------------
ISO/FDIS 12640-3:2022(E)

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 document 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 document 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 gamut obtainable by printing, and

that of a group of German photographic printing experts. The similarity of these led to the conclusion

that it is desirable to reconcile them into a single gamut that would be taken as the reference colour

gamut for this document. 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 vignettes show the reference colour

gamut (in CIE Lab colour space) in cross-sections for 16 and 8 hue angles, respectively.

0.4 File format of the digital test images
* * *

All of the images consist of pixel interleaved data (L then a then b ) with the data origin at the upper

left of the image, as viewed naturally, and organized by rows. These data are available as individual

files, which are a normative part of this part of this document. The image file format is as specified

in ISO 12639:2004, Annex H, with BitsPerSample set to 16, 16, 16. The images can be imported and

manipulated as necessary by a wide variety of imaging software tools and platforms commonly in

general use in the industry. See Annex D for details of the TIFF header.
All colour charts and vignettes consist of files in Adobe® PDF format.

1) This information is given for the convenience of users of this document and does not constitute an endorsement

by ISO of the product named.
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 12640-3:2022(E)
Graphic technology — Prepress digital data exchange —
Part 3:
CIELAB standard colour image data (CIELAB/SCID)
1 Scope

This document specifies a set of standard large gamut colour images (encoded as 16-bit CIELAB digital

data) that can be used for the evaluation of changes in image quality during coding, image processing

(including transformation, compression and decompression), displaying on a colour monitor and

printing. These images can be used for research, testing and assessing of output systems such as

printers, colour management systems and colour profiles.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 12639:2004, Graphic technology — Prepress digital data exchange — Tag image file format for image

technology (TIFF/IT)

ISO 13655, Graphic technology — Spectral measurement and colorimetric computation for graphic arts

images

ISO 22028-1, Photography and graphic technology — Extended colour encodings for digital image storage,

manipulation and interchange — Part 1: Architecture and requirements

PDF Reference: Adobe Portable Document Format, Version 1.4 3rd edition., Adobe Systems Incorporated,

(ISBN 0-201-75839-3)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
checksum

sum of the digits in a file that can be used to check if a file has been transferred properly

Note 1 to entry: Often, only the least significant bits are summed.
3.2
colour gamut

solid in a colour space, consisting of all those colours that are present in a specific scene, artwork,

photograph, photomechanical or other reproduction; or are capable of being created using a particular

output device and/or medium
[SOURCE: ISO 12640-4:2011]
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ISO/FDIS 12640-3:2022(E)
3.3
colour sequence
order in which the colours are stored in a data file
3.4
colour space
geometric representation of colour in space
Note 1 to entry: A colour space is usually of three dimensions
Note 2 to entry: This entry was numbered 845-03-25 in IEC 60050-45:1987

[SOURCE: CIE S 17:2020 ILV: International Lighting Vocabulary, 2nd edition, modified]

3.5
colour value
numeric values associated with each of the pixels
3.6
data range
range of integers for a given variable in between a minimal and maximal value
3.7
global colour change

change to the colours in an image (often selectively by colour region) applied consistently to all parts of

the image

Note 1 to entry: This is in contrast to a local colour change where selected spatial areas of an image are changed

separately from the rest of the image area.
3.8
orientation

specifies the origin and direction of the first line of data with respect to the image content as viewed by

the end user

Note 1 to entry: The codes used to specify orientation are contained in ISO 12639.

3.9
pixel
smallest discrete picture element in a digital image file
3.10
pixel interleaving
* * *

colour data organized such that the L , a and b colour space values for one pixel are followed by the

same sequence of colour values for the next pixel; the specific order of colour components is determined

by the ColorSequence tag as defined in ISO 12639
Note 1 to entry: Other forms of colour data interleaving are line and plane.
4 Requirements

This document consists of the images contained in the 18 image data files which are part of this

document. Their file names are listed in Table 4. The image characteristics of these data are described

in Clause 5 and the electronic data structure in Clause 6.
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ISO/FDIS 12640-3:2022(E)
5 Data description and definition
5.1 Data set definition

The set of standard colour image data consists of eight natural (photographed) images and ten synthetic

images created digitally on a computer. The synthetic images consist of eight colour charts consisting

of various patches, each 10 mm square, and two colour vignettes. The natural images are identified as

N1 to N8, and each of them also has a descriptive name derived from the picture content (e.g. bride and

groom). The synthetic images are identified as CC1 to CC8, CV1 and CV2.

The images are identified by the designation CIELAB/SCID. The co-ordinates of the text insertion are

provided in Annex E.

NOTE The image set defined in this document is based on the large gamut defined in Annex B. Image sets

contained in other document are based on different gamuts and can be more suitable for use in evaluation of

other applications.
5.2 Colour encoding used in this document
5.2.1 Image data encoding

The image data encoding shall be in accordance with the requirements of ISO 22028-1.

[10]

The image data are the desired CIELAB colorimetry defined by CIE Publication 15 , and measured in

accordance with ISO 13655, of reproductions of the images on the reference medium, with the reference

medium white point selected as the colour space white point. The image data are output-referred,

[11]

having been rendered to the reference medium of the ICC.1:2004-04 perceptual rendering intent,

which is defined as a hypothetical print on a substrate specified to have a neutral reflectance of 89 %

(the reference medium white point) and the darkest printable colour on this medium is assumed to have

a neutral reflectance of 0,347 31 % of the substrate reflectance (the reference medium black point). The

rendering target colour gamut for the reference medium is specified in Annex B. The reference viewing

environment is based on standard viewing condition P2, as specified for graphic arts and photography

in ISO 3664, but extended in the following way: the surfaces immediately surrounding the image are

assumed to be a uniform matt grey with a reflectance of 20 %. The reference viewing environment is

also assumed to have a viewing flare of 0,75 % of the luminance of the reference white. The CIELAB

image data are encoded as specified in 5.2.3 and 5.2.4.
5.2.2 Image data arrangement
* * *

The image data are pixel-interleaved in the colour sequence of L then a then b (16 bits) for the natural

* * *

images and L then a then b (8 bits) for the colour charts and the vignettes. The arrangement of data

follows the scanning of each image from the upper left corner to the upper right, then moving to the

next lower horizontal line. The resolution is 12 pixels/mm for every natural image.

5.2.3 CIELAB image data (16 bits per channel)

The CIELAB data for the natural images are encoded as 16-bit integers per channel, derived by

* * *

multiplying the L , a and b values for each pixel with the corresponding value for the data range.

 
L =×round 65535
 
16bit
 
100
 
* *
aa=×round()256 (1)
16bit
* *
b =×round()256 b
16biit
* * * * * *
where L , a and b represent normalised 16-bit values of L , a and b .
16bit 16bit 16bit
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ISO/FDIS 12640-3:2022(E)
The data range of the values is:
* * *
L ∈{0..100}, a ∈{−128..+127} and b ∈{−128..+127},
* * * * *
L ∈{0..65 535}, a ∈{−32 768..+32 512} and b ∈{−32 768..+32 512}, a and b are
16bit 16bit 16bit 16bit 16bit
signed integers.
NOTE −32 678 = −128 × 256, and 32 512 = 127 × 256.
5.2.4 CIELAB image data (8 bits per channel)

The CIELAB data for the colour charts are encoded as 8-bit integers per channel, derived by multiplying

* * *

the L , a and b values for each pixel with the corresponding value for the data range.

 
L =×round 255
 
8bit
 
100
 
* *
aa=round() (2)
8bit
* *
b =round(bb )
8bit
* * * * * *
where L , a and b represent normalised 8 bit values of L , a and b .
8bit 8bit 8bit
The data range of the values is:
* * *
L ∈{0..100}, a ∈{−128..+127} and b ∈{−128..+127},
* * * * *

L ∈{0..255}, a ∈{−128..+127} and b ∈{−128..+127}, the a and b are signed integers.

8bit 8bit 8bit 8bit 8bit
5.3 Natural images

The characteristics of the eight natural images, shown in Figure 1, are given in Table 1.

Table 1 — Characteristics for natural images
Parameter Characteristics
Resolution 12 pixels/mm
* * *

Colour values 16 bits/channel L , a and b , with respect to illuminant D50 (defined as

* * *
media-relative, i.e. such that a white in the image has the L , a and b
values of 100, 0, 0)
File format ISO 12639:2004, Annex H, with BitsPerSample set to 16, 16, 16
This format also readable with TIFF 6.0 with extension, photometric
interpretation tag 8, CIELAB, signed encoding.
Label on image CIELAB/SCID

Image data orientation Horizontal scanning starting from top left and ending at bottom right

NOTE The natural images have been colour-rendered to produce the desired image colorimetry on the

reference print medium as described in Annex B. For the most part, the image colours will be within the reference

colour gamut. However, it is possible for some image colours to be slightly outside (this is somewhat dependent

on how the convex hull of the gamut is constructed). It is sometimes necessary to gamut map the results of colour

rendering and re-rendering processing to exactly fit the destination device colour gamut.

The description and typical usage of the natural images are given in Table 2. The descriptive names

of these images are given following the identification code. Figure 1 shows reduced size sRGB

reproductions of the natural images. Statistical and gamut data for each of the natural images are

* * *

shown in Annex F, as histograms of the L values and a versus b plots for each image, respectively.

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ISO/FDIS 12640-3:2022(E)
Table 2 — Natural images
Name Aspect, image Description and typical usage
size

N1 Bride and groom Horizontal, Image of a bride wearing white clothes and groom wearing black

2 560 × 2 048 clothes. Used to evaluate the rendering of human skin tones and neu-

pixels tral colours, especially highlights and shadows.

N2 People Horizontal, Image consisting of five people wearing colourful clothes, sitting on a

2 560 × 2 048 dark leather couch. Used to evaluate the colour rendering of extreme-

pixels ly colourful objects in the presence of skin tones and neutrals.

N3 Cashew nuts Vertical, Image of dried fruits and filled containers used to evaluate tonal

2 048 × 2 560 and colour rendering, in particular adjustments for grey component
pixels replacement.
N4 Meal Horizontal, Image with widely recognizable cooked food
...

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