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

ISO 12640-3:2007 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
02-Jul-2007
Current Stage
9092 - International Standard to be revised
Start Date
09-Nov-2021
Completion Date
09-Nov-2021

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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 12640-3:2007(E)
ISO 2007
---------------------- Page: 1 ----------------------
ISO 12640-3:2007(E)
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.

COPYRIGHT PROTECTED DOCUMENT
© 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
---------------------- Page: 2 ----------------------
ISO 12640-3:2007(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

© ISO 2007 – All rights reserved iii
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ISO 12640-3:2007(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.

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
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ISO 12640-3:2007(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 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

© ISO 2007 – All rights reserved v
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ISO 12640-3:2007(E)

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 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. 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.
vi © ISO 2007 – All rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 12640-3:2007(E)
Graphic technology — Prepress digital data exchange —
Part 3:
CIELAB standard colour image data (CIELAB/SCID)
1 Scope

This part of ISO 12640 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 for the application 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 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 15:2004, Colorimetry

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

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

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

(ISBN 0-201-75839-3)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
check sum

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

NOTE Often, only the least significant bits are summed.
© ISO 2007 – All rights reserved 1
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ISO 12640-3:2007(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]
3.3
colour sequence
order in which the colours are stored in a data file
3.4
colour space
geometric representation of colours in space, usually of three dimensions
[CIE Publication 17-1987 (845-03-25)]
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 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 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
NOTE Other forms of colour data interleaving are line and plane.
4 Requirements

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

of ISO 12640. 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.
2 © ISO 2007 – All rights reserved
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ISO 12640-3:2007(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 part of ISO 12640 is based on the large gamut defined in Annex B. Image sets

contained in other parts of ISO 12640 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 12640
5.2.1 Image data encoding

The image data encoding is defined in accordance with ISO 22028-1 requirements as follows.

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 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⎜⎟65 535
16bit
100
aa=×round (256 ) (1)
16bit
bb=×round (256 )
16bit
* * * * * *
where L , a and b represent normalised 16-bit values of L , a and b .
16bit 16bit 16bit
© ISO 2007 – All rights reserved 3
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ISO 12640-3:2007(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 signed

16bit 16bit 16bit 16bit 16bit
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
bb= round ( )
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
* * *
16 bits/channel L , a and b , with respect to illuminant D50 (defined as
* * *

Colour values media-relative, i.e. such that a white in the image has the L , a and b values

of 100, 0, 0)
ISO 12639:2004, Annex H, with BitsPerSample set to 16, 16, 16
File format
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.
4 © ISO 2007 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 12640-3:2007(E)

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.
Table 2 — Natural images
Aspect,
Name Description and typical usage
image size

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

2 560 × 2 048 Used to evaluate the rendering of human skin tones and neutral colours,

especially highlights and shadows.
pixels

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

leather couch. Used to evaluate the colour rendering of extremely colourful
2 560 × 2 048
pixels objects in the presence of skin tones and neutrals.

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

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

pixels

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

2 560 × 2 048 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

appearances of metallic objects.
pixels

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

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

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

of details in highly chromatic areas.
2 560 × 2 048
pixels

N8 Fruits Square, Image of a range of fruits and vegetables. The memory colours of

2 024 × 2 024 strawberries, oranges, lemons, green grapes, apples, pears, tomatoes and

bell peppers are particularly suitable for the evaluation of the naturalness of
pixels
colour re-rendering processes.
© ISO 2007 – All rights reserved 5
---------------------- Page: 11 ----------------------
ISO 12640-3:2007(E)
a) N1 Bride and groom b) N2 People
c) N3 Cashew nuts d) N4 Meal
e) N5 Mandolin f) N6 Tailor scene
Figure 1 (continued)
6 © ISO 2007 – All rights reserved
---------------------- Page: 12 ----------------------
ISO 12640-3:2007(E)
g) N7 Wool h) N8 Fruits
Figure 1 — Reduced size sRGB reproductions of the natural images
5.4 Synthetic images
5.4.1 Colour charts

There are eight colour charts, each of which consists of a number of colour patches that sample the reference

colour gamut. Each chart contains a number of patches at two hue angles, with each pair separated by 180°.

The design intent was to provide samples at hue angle intervals of 22,5° (from 0° to 337,5°). However, the

limitations imposed by 8-bit data means that the intended hue angles can only be approximated to within ±1°.

* *

The colour charts show all the samples within the reference colour gamut at L intervals of 10 (from L = 0 to

* * * *
* *

L = 100) and C intervals of 10 (from C = 0 to the C value above the maximum C value for that L

ab ab ab ab

value from the reference colour gamut). These maximum C values are given in Table 3, and are derived

from the reference colour gamut described in Annex B of this part of ISO 12640, rounded to the nearest value.

Again, the limitations of the 8-bit data mean that the intended values shown in Table 3 can only be

* *

approximated. The L values achieved are to within ±0,2, and the C values to within ±1 C

ab ab

Because of this design, the maximum and minimum L values, and maximum C values, in the charts lie

outside the reference colour gamut. This ensures that the whole of the reference colour gamut can be

evaluated (within the patch sampling limitations of the charts). The CIELAB values for each patch in the charts

are given in Annex G.

NOTE Applications that show the CIELAB values when these files are opened are likely to show the L values as the

integer value gi
...

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 12640-3:2007(E)
ISO 2007
---------------------- Page: 1 ----------------------
ISO 12640-3:2007(E)
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.
COPYRIGHT PROTECTED DOCUMENT
© 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
...

SLOVENSKI STANDARD
SIST ISO 12640-3:2008
01-januar-2008

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6WDQGDUGQLSRGDWNL&,(/$%]DEDUYQHVOLNH &,(/$%6&,'

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

image data (CIELAB/SCID)
Ta slovenski standard je istoveten z: ISO 12640-3:2007
ICS:
35.240.30 Uporabniške rešitve IT v IT applications in information,
informatiki, dokumentiranju in documentation and
založništvu publishing
37.100.99 'UXJLVWDQGDUGLY]YH]L] Other standards related to
JUDILþQRWHKQRORJLMR graphic technology
SIST ISO 12640-3:2008 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SLOVENSKI STANDARD
SIST ISO 12640-3:2008
01-januar-2008

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

image data (CIELAB/SCID)
Ta slovenski standard je istoveten z: ISO 12640-3:2007
ICS:
35.240.30 Uporabniške rešitve IT v IT applications in information,
informatiki, dokumentiranju in documentation and
založništvu publishing
37.100.01 *UDILþQDWHKQRORJLMDQD Graphic technology in
VSORãQR general
SIST ISO 12640-3:2008 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ISO 12640-3:2008
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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 12640-3:2007(E)
ISO 2007
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SIST ISO 12640-3:2008
ISO 12640-3:2007(E)
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ii © ISO 2007 – All rights reserved
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SIST ISO 12640-3:2008
ISO 12640-3:2007(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

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SIST ISO 12640-3:2008
ISO 12640-3:2007(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.

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
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SIST ISO 12640-3:2008
ISO 12640-3:2007(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 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

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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 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. 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.
vi © ISO 2007 – All rights reserved
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SIST ISO 12640-3:2008
INTERNATIONAL STANDARD ISO 12640-3:2007(E)
Graphic technology — Prepress digital data exchange —
Part 3:
CIELAB standard colour image data (CIELAB/SCID)
1 Scope

This part of ISO 12640 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 for the application 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 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 15:2004, Colorimetry

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

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

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

(ISBN 0-201-75839-3)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
check sum

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

NOTE Often, only the least significant bits are summed.
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ISO 12640-3:2007(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]
3.3
colour sequence
order in which the colours are stored in a data file
3.4
colour space
geometric representation of colours in space, usually of three dimensions
[CIE Publication 17-1987 (845-03-25)]
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 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 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
NOTE Other forms of colour data interleaving are line and plane.
4 Requirements

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

of ISO 12640. 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.
2 © ISO 2007 – All rights reserved
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ISO 12640-3:2007(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 part of ISO 12640 is based on the large gamut defined in Annex B. Image sets

contained in other parts of ISO 12640 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 12640
5.2.1 Image data encoding

The image data encoding is defined in accordance with ISO 22028-1 requirements as follows.

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 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⎜⎟65 535
16bit
100
aa=×round (256 ) (1)
16bit
bb=×round (256 )
16bit
* * * * * *
where L , a and b represent normalised 16-bit values of L , a and b .
16bit 16bit 16bit
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ISO 12640-3:2007(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 signed

16bit 16bit 16bit 16bit 16bit
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
bb= round ( )
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
* * *
16 bits/channel L , a and b , with respect to illuminant D50 (defined as
* * *

Colour values media-relative, i.e. such that a white in the image has the L , a and b values

of 100, 0, 0)
ISO 12639:2004, Annex H, with BitsPerSample set to 16, 16, 16
File format
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.
4 © ISO 2007 – All rights reserved
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SIST ISO 12640-3:2008
ISO 12640-3:2007(E)

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.
Table 2 — Natural images
Aspect,
Name Description and typical usage
image size

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

2 560 × 2 048 Used to evaluate the rendering of human skin tones and neutral colours,

especially highlights and shadows.
pixels

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

leather couch. Used to evaluate the colour rendering of extremely colourful
2 560 × 2 048
pixels objects in the presence of skin tones and neutrals.

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

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

pixels

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

2 560 × 2 048 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

appearances of metallic objects.
pixels

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

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

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

of details in highly chromatic areas.
2 560 × 2 048
pixels

N8 Fruits Square, Image of a range of fruits and vegetables. The memory colours of

2 024 × 2 024 strawberries, oranges, lemons, green grapes, apples, pears, tomatoes and

bell peppers are particularly suitable for the evaluation of the naturalness of
pixels
colour re-rendering processes.
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ISO 12640-3:2007(E)
a) N1 Bride and
...

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