ISO/DTR 26478

ISO /TC 42
Secretariat: ANSI
Date: 2026-03-25xx
Digital imaging – — Skin tone representation for use in photographic
testing, including test charts and test spectra

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'sISO’s member body in the country of the requester.
ISO Copyright Officecopyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email:
E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland.
ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Image capture standards . 3
4.1 General . 3
4.2 Printing and image permanence . 3
5 Skin tone spectra . 4
6 Test charts and colour palettes with skin tone patches. 6
6.1 General . 6
6.2 ColorChecker classic test chart . 6
6.3 ColorChecker digital SG test chart . 8
6.4 Fitzpatrick skin types . 8
6.5 L’Oréal skin type chart . 9
6.6 IT8 chart . 10
® TM
6.7 PANTONE SkinTone guide . 11
6.8 PERLA colour palette . 12
6.9 Monk skin tone scale . 13
6.10 Colorimetric skin tone scale . 15
7 Spectral data corresponding to representative skin tone swatches . 16
8 Considerations . 16
8.1 Considerations for scene-referred image capture standards . 16
8.2 Considerations for output-referred image evaluation standards . 17
8.3 Considerations for perceptual validation and cross-cultural inclusivity . 18
Annex A (informative) Digital image capture standards including skin tones . 19
Annex B (informative) Image permanence and printing standards including skin tones . 26
Annex C (informative) Reasons for differences between laboratory, in-situ and rendered image
surface colour measurements (including skin tone measurements) . 30 ®
Annex D (informative) Macbeth & Xrite ColorChecker comparison . 34
Bibliography . 36

iii
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 documentsdocument 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 drawnISO draws attention to the possibility that some of the elementsimplementation of this
document may beinvolve the subjectuse of (a) patent(s). ISO takes no position concerning the evidence,
validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this
document, ISO had not received notice of (a) patent(s) which may be required to implement this document.
However, implementers are cautioned that this may not represent the latest information, which may be
obtained from the patent database available at www.iso.org/patents. 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 ).
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 42, Photography
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
Introduction
Photography is widely used to depict a wide range of human subjects, and thus a wide range of skin tones. It
is important that photographic systems appropriately represent and reproduce this wide range of skin tones.
ISO/TC42 – Photography,TC 42 has developed numerous standards which include colour patches or spectral
data intended to represent various skin tones. (See Reference [12][12] Wueller)) These include standards for
characterizing digital cameras and for image permanence.
This report documents some of the work of an ISO/TC 42 Ad Hoc Group (AHG) created in the fall of 2023 to
consider the test chart skin tone patches used in ISO/TC 42 standards. One goal of this AHG was to provide
information for TC 42 working groups to consider regarding the use of skin tone representations for
ISO/TC 42 related work. For example, when colour patches for skin tones are used in TC 42 standards, it is
important that they be inclusive and represent a broad range of skin types. (See Reference [12].)
The AHG reviewed all ISO standards developed by TC 42 and identified eight relevant documents which
include patches or spectra that could be considered to represent skin tones. The relevant image capture-
related standards and technical reports are listed in 4.1 and discussed in Annex A, and the relevant image
permanence and printing related standards and technical reports are listed in 4.2 and discussed in Annex B.
Ideally, the colour patches and spectral reflectance data intended to represent skin tones in TC42TC 42
standards would be inclusive and represent a broad range of skin types. This technical reportdocument
provides information which is helpful when selecting skin tones for use in image capture testing of digital
imaging devices (e.g. digital cameras), specifically test charts which include skin tone patches and test spectra
which represent skin tones. It also provides links to spectral reflectance data intended to represent a broad
range of skin types.
., digital cameras), specifically test charts which include skin tone patches and test spectra which represent
skin tones. It also provides links to spectral reflectance data intended to represent a broad range of skin types.
The validity of a set of reference skin tones for photographic testing depends on its validation against criteria
appropriate for the photographic-imaging application. For photographic systems that capture and reproduce
images for viewing by humans, these criteria are not limited to spectral and colorimetric accuracy, which are
necessary for spectral-domain applications but not sufficient for applications in which the reproduced image
is judged perceptually by diverse human viewers across diverse populations of subjects. For applications in
photographic testing of skin tone reproduction, additional relevant criteria include perceptual validation
across diverse perceivers, cross-cultural inclusivity in the populations against which perceptual validation has
been established, comparative discriminative validity against alternative references in independent
evaluation, and documented validation in use.
This report supports UN Sustainable Development Goal SDG 10 (Reduced Inequalityinequality) by providing
information related to the selection of an inclusive set of colour patches.
v
Digital imaging – — Skin tone representation for use in photographic
testing, including test charts and test spectra
1 Scope
This document provides information related to the representation of skin tones for use in photographic testing
in order to be inclusive and represent a broad range of skin types. This includes the selection of colour patches
intended to represent skin tones and spectral reflectance data intended to represent skin tones.
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 22028-1, Photography and graphic technology — Extended colour encodings for digital image storage,
manipulation and interchange — Part 1: Architecture and requirements
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminologicalterminology 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 3.1
digital camera
device which incorporates an image sensor and produces a digital signal representing a picture
Note 1 to entry: A digital camera is typically a portable, hand-held device. The digital signal is usually recorded on a
removable or an internal memory.
3.2
opto-electronic conversion function
OECF
relationship between the log of the input levels and the corresponding digital output levels for an opto-
electronic digital image capture system
3.2 3.3
output-referred image state
image state associated with image data that represents the colour-space coordinates of the elements of an
image that has undergone colour-rendering appropriate for a specified real or virtual output device and
viewing conditions
Note 1 to entry: When the phrase “output-referred” is used as a qualifier to an object, it implies that the object is in an
output-referred image state. For example, output-referred image data are image data in an output-referred image state.
Note 2 to entry: Output-referred image data are referred to the specified output device and viewing conditions. A single
scene can be colour-rendered to a variety of output-referred representations depending on the anticipated output-
viewing conditions, media limitations, and/or artistic intents.
Note 3 to entry: Output-referred image data may become the starting point for a subsequent reproduction process. For
example, sRGB output-referred image data are frequently considered to be the starting point for the colour re-rendering
performed by a printer designed to receive sRGB image data.
3.3 3.4
photography
acquisition, processing, or reproduction of optically formed images using chemical or electronic technologies
3.4 3.5
scene-referred image state
image state associated with image data that represents estimates of the colour-space coordinates of the
elements of a scene
Note 1 to entry: When the phrase “scene-referred” is used as a qualifier to an object, it implies that the object is in a
scene-referred image state. For example, scene-referred image data are image data in a scene-referred image state.
Note 2 to entry: Scene-referred image data can be determined from raw digital camera image data before colour-
rendering is performed. Generally, digital cameras do not write scene-referred image data in image files, but some may
do so in a special mode intended for this purpose. Typically, digital cameras write standard output-referred image data
where colour-rendering has already been performed.
Note 3 to entry: Scene-referred image data typically represent relative scene colorimetry estimates. Absolute scene
colorimetry estimates may be calculated using a scaling factor. The scaling factor can be derived from additional
information such as the image OECF, FNumber or ApertureValue, and ExposureTime or ShutterSpeedValue tags.
Note 4 to entry: Scene-referred image data may contain inaccuracies due to the dynamic range limitations of the capture
device, noise from various sources, quantization, optical blurring and flare that are not corrected for, and colour analysis
errors due to capture device metamerism. In some cases, these sources of inaccuracy can be significant.
Note 5 to entry: The transformation from raw digital camera image data to scene-referred image data depends on the
relative adopted whites selected for the scene and the colour space used to encode the image data. If the chosen scene
adopted white is inappropriate, additional errors will be introduced into the scene-referred image data. These errors
may be correctable if the transformation used to produce the scene-referred image data are known and the colour
encoding used for the incorrect scene-referred image data has adequate precision and dynamic range.
Note 6 to entry: The scene may correspond to an actual view of the natural world or may be a computer-generated
virtual scene simulating such a view. It may also correspond to a modified scene determined by applying modifications
to an original scene to produce some different desired scene. Any such scene modifications should leave the image in a
scene-referred image state and should be done in the context of an expected colour-rendering transform.
3.5 3.6
skin tone
The perceived colour of the surface of human skin
Note 1 to entry: A colour is expressed by the CIELAB colour space and characterized by lightness, hue, and chroma.
3.6 3.7
test chart
arrangement of test patterns designed to test particular aspects of an imaging system
3.7 3.8
test pattern
specified arrangement of spectral reflectance or transmittance characteristics used in measuring an image
quality attribute
4 Background
This report documents some of the work of an ISO/TC42 Ad Hoc Group (AHG) created in the fall of 2023 to
consider the test chart skin tone patches used in ISO/TC42 standards. One goal of this AHG was to provide
information for TC42 working groups to consider regarding the use of skin tone representations for ISO/TC42
related work. For example, when colour patches for skin tones are used in TC42 standards, it is important that
they be inclusive and represent a broad range of skin types. (See [12] Wueller)
The AHG reviewed all ISO standards developed by TC42 and identified eight relevant documents which
include patches or spectra that could be considered to represent skin tones. The relevant image capture-
related standards and technical reports are listed in 4.1 and discussed in Annex A, and the relevant image
permanence and printing related standards and technical reports are listed in 4.2 and discussed in Annex B.
54 Image capture standards
4.1 General
The following published ISO standards or technical reportsTechnical Reports developed by ISO/TC42TC 42
relate to digital image capture and include test patches or spectra intended to represent skin tones. These
standards are described in Annex Aannex A.:
— ISO 19093:2018 Photography — Digital cameras — Measuring low-light performance;
ISO 17321-1:2012 Graphic technology and photography — Colour characterisation of digital still cameras
(DSCs) — Part 1: Stimuli, metrology and test procedures
ISO/TR 17321-2:2012 Graphic technology and photography — Colour characterisation of digital still
cameras (DSCs) — Part 2: Considerations for determining scene analysis transforms
ISO 19264-1:2021 Photography — Archiving systems — Imaging systems quality analysis — Part 1:
Reflective originals
— ISO 17321-1:2012;
— ISO/TR 17321-2:2012;
— ISO/TR 19263-1:2017;
— ISO 19264-1.
Except for ISO 19093, these four documents use only two skin tone patches, a “dark skin” patch and a “light
skin” patch, from the ColorChecker colour rendition chart first defined in 1976. (See Reference [7][7]
McCamy.)).
5.14.2 Printing and image permanence
The following image permanence and printing standards or technical specifications were reviewed by experts
from WG 5. These standards are described in Annex Bannex B.:
ISO/PAS 18940-1:2023 Imaging materials — Image permanence specification of reflection photographic
prints for indoor applications — Part 1: Test methods
ISO/TS 21139-22:2023 Permanence and durability of commercial prints - Part 22: Backlit display in indoor
or shaded outdoor conditions - Light stability
ISO 18946:2023 Imaging materials — Reflection colour photographic prints — Method for testing humidity
fastness
— ISO/PAS 18940-1:2023;
— ISO/TS 21139-22:2023;
— ISO 18946:2023;
— ISO/TS 20791-2:2021 Photography — Photographic reflection prints - Part 2: Evaluation of colour variation
in printing;
One of these documents uses only two relevant patches, a lighter patch and a darker patch similar to those
defined for the original Macbeth ColorChecker test chart in 1976 as discussed above. (See Reference [7][7]
McCamy.)). Two more recent standards documents use the same two patches along with a third, darker brown
patch. The fourth document uses a total of 6 different light brown patches, intended to represent brownish
colours from many origins, such as landscape, leather, fur, but no dark brown patches.
In addition, ISO 18944:2018 Imaging materials — Reflection colour photographic prints — Test print
construction and measurement 18944 specifies requirements and recommendations for the digital test file
content used to generate target prints for image stability testing of reflection colour photographic prints. ISO
18944:2018 is currently being revised to include skin tone patches which are consistent with ISO /PAS 18940-
1 and ISO 12647-7.
The image permanence test targets defined in the standards described above were designed to cover the
printed colour space in general and are not intended to spectrally reproduce any specific natural colours such
as skin tones, blue sky or the colours of other natural objects. Photographic prints are based on a limited
number of pigments or dyes and therefore cannot spectrally match the wide range of colours of the natural
world but typically provide metameric matches. Therefore, a typical set of test patches for image permanence
contains single and mixed colorant patches to study the stability of the colorants separately or in combination.
These test targets have been validated by inter-laboratory comparison tests and have been used for many
years, providing a database of comparable permanence data for contemporary and historical photographic
material. If a permanence test is developed to specifically probe colour permanence of skin tones, this report
can provide relevant information regarding how to select such patches.
65 Skin tone spectra
A large percentage of photographs depict at least one person, and people are very sensitive to skin tone
reproduction errors in photography, so properly capturing and reproducing a diverse range of skin tones is
very important. (See Reference [10][10] Wueller)). Examples of the relative radiance spectra of real skin tones
are shown in Figure 1Figure 1 below. (See Reference [11][11] Wueller)).
26478_ed1fig1.EPS
Key
X wavelength
Y relative radiances
Figure 1 — Examples of the relative radiance spectra of real skin tones
In addition, a set of 100 spectral measurements of human skin reflectance is available from the US National
[3] [3]
Institute of Standards and Technology (NIST), as described in Cooksey, et al. . See .
The text file posted at this URL was converted to Excel format, and the spectra are shown in Figure 2
(see Reference [2]Figure 2 below (See [2] Burns).). Note that the spectral reflectance values range between
250 nm and 2 500 nm, in 3 nm intervals. The wide wavelength range of the posted data was based on a range
of potential uses, including medical applications, that are beyond our area of focus.
26478_ed1fig2a.EPS 26478_ed1fig2b.EPS

a)a)  NIST 100 reflectance spectra (250 to 1 400) nm b)b)  Visible wavelengths (400 to 700) nm
Key
X wavelength
Y reflectance
Figure 2 — a) NIST 100 reflectance spectra (250-1 400 nm), b) visible wavelengths (400-700 nm)
CIE Technical Committee 1-92 has developed and published a Human Skin Colour Database (CIE 256:2025)
which provides valuable data for research and applications related to skin colour measurement. This database
is available at: https://www.cie.co.at/publications/measuring-skin-colour/dataset1-
humanskincolourdatabase
[9][9] [13] [13]
In addition, skin tone spectral data has been reported by Wang, et. al and Xiao, et. al. . Kaida Xiao has
published a version of the skin tone database at https://www.kaidaxiao.co.uk/about-1
76 Test charts and colour palettes with skin tone patches
6.1 General
Over the last fifty years, various colour test charts and colour palettes have been developed which include
patches intended to represent skin tones. These palettes serve different purposes. Some are designed for
medical use, some for cosmetics, and others to represent skin tones in print, display and image capture. These
charts and palettes are described in 6.2 to 6.10below.
7.16.2 ColorChecker Classicclassic test chart
The original design of the most widely used colour test chart was described in a 1976 publication.
1 1)
(See Reference [7][7] McCamy).). The original name for this test chart was the “Macbeth ColorChecker” , ,
which was also referred to as the “Macbeth chart”. The current version of the test chart, now known as the
Calibrite ColorChecker Classic test chart, is shown in Figure 3Figure 3. The 24 patches are surrounded by a
black border and include 6 patches in a grey lightness scale and saturated red, green, blue, cyan, magenta and
yellow patches in the two bottom rows of the chart. The original spectral reflectances of the colour patches in
the top two rows were chosen to approximate natural objects such as blue sky and green foliage.
The two colour patches in the upper left were intended to represent dark skin and light skin. The designers of
the original Macbeth ColorChecker test chart contended that the lightest human skin being photographed is
practically white, due to the use of talcum powder, while the darkest human skin is practically black, and that
both have nearly uniform spectral reflectances. They also contended that the characteristic spectrum of
human skin is primarily due to absorption by melanin and hemoglobin, such that the spectra for all types of
human skin form a continuous homologous series. The medium light skin and medium dark skin patches were
selected to test the ability of systems to reproduce the colour associated with this typical spectrum at two
different exposure levels. (See Reference [7][7] McCamy).).

Macbeth ColorChecker, Gretag-Macbeth ColorChecker, X-rite ColorChecker, and Calibrate ColorChecker Classic are
examples of commercially available products. This information is given for the convenience of users of this document
and does not constitute an endorsement by ISO of this product.
1)
Macbeth ColorChecker, Gretag-Macbeth ColorChecker, X-rite ColorChecker, and Calibrate ColorChecker Classic are
examples of commercially available products. This information is given for the convenience of users of this document
and does not constitute an endorsement by ISO of this product.

26478_ed1fig3.EPS
Figure 3 — ColorChecker Classicclassic test chart
The selection and arrangement of colour patches in the Macbeth ColorChecker was based on an earlier colour
chart developed by Kodak Research Labs, which was reported in 1957. See Reference [1][1] Breneman. The
Kodak chart had 24 patches arranged in a (6 x× 4) grid. Each patch was produced by applying pigments to 2x2
inch(2 × 2) in pieces of cover glass which were held in a wooden frame. The chart included six neutral patches
(including a titanium white patch with 78 % reflectance and an ivory black patch with 0,22 % reflectance),
nine highly saturated colours, and several “familiar” colours including foliage, blue sky, and flesh. While it
included only a single “flesh” patch (produced using a combination of cadmium red, strontium yellow,
ultramarine blue, and titanium white pigments with 32 % reflectance), it also included a “brown” patch
(produced using burnt umber, burnt sienna, yellow ochre, and zinc oxide with 2,7 % reflectance),
see Reference [1]). See [1].
In 1997, the Gretag Color Control System Division merged with the Macbeth division of Kollmorgen
Instruments to form Gretag-Macbeth, which sold the similar Gretag-Macbeth ColorChecker chart. In 2006, X-
Rite acquired the holding company which owned Gretag-Macbeth and began selling the X-rite ColorChecker.
In 2021, X-Rite photo and video products were transferred to a new company named Calibrite, which currently
sells the Calibrite ColorChecker Classic test chart.
The ISO TC42/TC 42 standards described earlier in 4.14.1 and 4.24.2 that include dark skin and light skin
patches are based on the spectral reflectances of the original Macbeth ColorChecker described in
Reference [7]reference [7]. A comparison of this original ColorChecker chart and an X-Rite ColorChecker
chart was made using a SpectraScan PR-740 Spectroradiometer. The data is provided in Annex DAnnex D. It
shows that the spectral data in the TC42TC 42 standards provides a reasonably accurate representation of the
original Macbeth ColorChecker test chart. However, several colour patches on the X-Rite ColorChecker are
substantially different from the ISO data and the original Macbeth ColorChecker test chart. In particular,
Patches 1 (dark skin), 3 (blue sky), 4 (foliage), 5 (blue flower), 8 (purplish blue), and 13 (blue) of the X-Rite
ColorChecker are significantly different than the original Macbeth ColorChecker test chart. While the original
test chart appears to mimic these items spectrally, the X-Rite ColorChecker test chart seems to only mimic
them colorimetrically. Patches 2 (light skin), 6 (bluish green), 7 (orange), 10 (purple), 14 (green), and 17
(magenta), are slightly different, while the remaining colour patches are essentially the same.
7.26.3 ColorChecker Digitaldigital SG test chart
2 2)
The ColorChecker Digitaldigital SG chart , , currently available from Calibrite, is shown in Figure 4Figure 4.
This test chart is A4-sized and features 140-patches designed for digital camera calibration and ICC Profile
determination.
26478_ed1fig4.EPS
Figure 4 — ColorChecker Digitaldigital SG test chart
The target includes the same 24 patches from the ColorChecker Color Rendition Chartcolour rendition chart,
including the light skin and dark skin patches. It also includes 14 additional skin tone patches. The outer edge
of the test chart is composed of white, black and neutral patches, which can be used to assess the uniformity
of the lighting. This test chart is designed to be used with Calibrite PROFILER software. See
https://calibrite.com/us/product/colorchecker-digital-sg/
7.36.4 Fitzpatrick skin types
The Fitzpatrick skin types were developed by American dermatologist Thomas Fitzpatrick in 1975, to estimate
the response of different skin types to ultraviolet (UV) light. Fitzpatrick skin types classify human skin based
on how the skin responds to UV exposure according to six phototypes which were determined by responses
to survey questions. It originally included only the first four skin tones and was expanded to include the two
darker tones in 1988. (See Reference [4][4] Fitzpatrick).).
The Fitzpatrick skin type is widely used for skin phototyping, based on a person's tendency to sunburn and
ability to tan, which are correlated to skin melanin content and therefore skin tone. The Fitzpatrick skin types
were not designed to classify skin tones, and no standard relationship exists between Fitzpatrick skin types
and skin tones.
The Calibrate ColorChecker Digital SG chart is an example of a commercially available product. This information is given
for the convenience of users of this document and does not constitute an endorsement by ISO of this product.
2)
The Calibrate ColorChecker Digital SG chart is an example of a commercially available product. This information is
given for the convenience of users of this document and does not constitute an endorsement by ISO of this product.

The Fitzpatrick skin type was not intended to be a colour scale, but it has been treated as such by some
dermatologists, as depicted in Figure 5Figure 5. See https://www.newbeauty.com/how-to-use-fitzpatrick-
scale/
26478_ed1fig5.EPS
Figure 5 — Fitzpatrick Scale Classificationscale classification of 6 Skin Typesskin types
Although some research has interpreted the Fitzpatrick skin types as skin tone labels in machine learning
applications, this is not a recommended practice.
7.46.5 L’Oréal skin type chart
A more diverse skin tone representation, the 66-patch skin type chart shown in Figure 6Figure 6,, was
33)
developed by L'Oréal to enable matching skin tones to appropriate cosmetic products. (See Reference [6][6]
L’Oréal).). The L'Oréal chart shows skin tone patches with variations in two dimensions: skin lightness on the
x-axis, and skin hue on the y-axis. Representing this two-dimensional variation in skin tones is more inclusive
than a single lightness-darkness gradient. (See Reference [8][8] Thong).).

The L'Oréal skin type chart is an example of a commercially available product. This information is given for the
convenience of users of this document and does not constitute an endorsement by ISO of this product.
3)
The L'Oréal skin type chart is an example of a commercially available product. This information is given for the
convenience of users of this document and does not constitute an endorsement by ISO of this product.

26478_ed1fig6.EPS
Figure 6 — L'Oréal 66-patch skin type chart
The colour values of the L’OrealL’Oréal chart are not publicly available. The number of patches contained on
this chart limit its use as a calibration chart in some applications in photography and print.
7.56.6 IT8 chart
A colour rendition test chart, commonly known as the “IT8 chart”, was first standardized in 1993 as ANSI
standard IT8.7/2 - 1993 Graphic technology - Color reflection target for input scanner calibration. Currently,
this standard is known as ANSI CGATS/ISO 12641-1:2018 Graphic technology - Prepress digital data exchange
- Colour targets for input scanner calibration - Part 1: Colour targets for input scanner calibration. The target
includes 264 colour patches in a grid of 22 columns x 12 rows, along with 24 grey patches, as shown in
Figure 7Figure 7. It enables a graphic arts colour input scanner to be calibrated for the dye set used to create
the target.
The IT8.7/2 standard does not specify any colour patches that are intended to represent skin tones. However,
the colours in columns 20 through 22 are not specified in the standard and can be any colours chosen by the
chart manufacturer. Some manufacturers have decided to include colour patches representing skin tones, as
shown in column 22 of Figure 7Figure 7.
26478_ed1fig7.EPS
Figure 7 — IT8 Colour reflection target for input scanner calibration
® TM
7.66.7 PANTONE SkinTone guide
® TM 44)
The PANTONE SkinTone guide is a collection of 138 separate skin tone patches arranged in a fan, as
shown in Figure 8Figure 8. Digital values for each patch are available. The colour of each patch is identified
by a unique Pantone Number which represents both the tone and the “undertone”, which is a value used by ®
PANTONE that reflects the hue of a skin tone on a red-yellow axis. The guide is designed for representing
skin tones in print, to be viewed using D65 (Daylight 6 500 K) illumination. It is said to have been “created by
scientifically measuring thousands of actual skin tones across the full spectrum of human skin types” and
“specially formulated to be the closest physical representations” of skin colours, that is to attempt a spectral
match between printed ink and measured skin tone.
See: https://www.pantone.com/products/fashion-home-interiors/skintone-guide

4 ® TM
The PANTONE SkinTone guide is an example of a commercially available product. This information is given for the
convenience of users of this document and does not constitute an endorsement by ISO of this product.
4) ® TM
The PANTONE SkinTone guide is an example of a commercially available product. This information is given for the
convenience of users of this document and does not constitute an endorsement by ISO of this product.

26478_ed1fig8.EPS
® TM
Figure 8 — PANTONE SkinTone guide
7.76.8 PERLA Color Palettecolour palette
The Project on Ethnicity and Race in Latin America (PERLA) was formed in 2008 to empirically examine race
and ethnicity across Latin America. The 11 colour patches in the PERLA colorcolour palette, shown in
Figure 9figure 9 below,, came from internet photographs to cover the range of colours found in Latin American
survey respondents. The methods for selecting the colour patches and their colour coordinates are not
publicly available.
See: https://perla.princeton.edu/perla-color-palette/
26478_ed1fig9.EPS
Figure 9 — PERLA Color Palettecolour palette
7.86.9 Monk skin tone scale
The Monk skin tone scale, shown as swatches in Figure 10Figure 10,, is designed for machine learning
applications. It was developed by Dr. Ellis Monk at Harvard University to address the biases in the Fitzpatrick
scale, which is skewed towards lighter skin tones that are more UV sensitive. The 10 skin tones in the Monk
skin tone scale represent a diverse range of tones, while using a manageable number of patches.
(See Reference [5][5] Google).).
26478_ed1fig10.EPS
Figure 10 — Monk skin tone scale swatches
The Monk skin tone scale is often depicted using orbs, as shown in Figure 11Figure 11. The orbs depict how
each skin tone may appear in both the real world and in images. This is a helpful reminder that a person's skin
does not appear to be a single, uniform colour. Rather, it can exhibit a range of shades across the complex
surfaces that comprise a person’s face and body.
26478_ed1fig11.EPS
Figure 11 — Monk skin tone scale orbs
The Monk skin tone scalerepresentation matched to each application class is intendeddescribed above: for
applications such as developing and testing face recognition algorithms. As a result, the Monk skin tone scale
is represented using rendered sRGB values which are designed to be displayed on a monitor. This means that
the Monk skin tone scale is in an sRGB output-referred image state, and the sRGB values represent output
workflows (rather than scene-referred image data,state workflows) as described in ISO 22028-1. The Monk
skin tone scale values, the values listed in Table 1 are appropriate; for printed-reference and spectral
applications, the Pantone physical swatches and corresponding spectroradiometric data are also provided as
LAB values, and boththe appropriate references; for applications requiring the full chromatic and dimensional
representation of human skin, the continuous reference orbs (Figure 11) are the primary representation.
The CIELAB values listed in Table 1 below.
It is believed that the LAB values were determinedcalculated by converting the rendered sRGB values to D65
XYZ with the display black point scaled to zero and then using D65 as the white point for the CIELAB
calculations (with no chromatic adaptation). transform). This conversion supports display-referred (i.e.,
output-referred) sRGB workflows.
Table 1 — sRGB and CIELAB values for the Monk scale
Patch sRGB R sRGB G sRGB B CIELAB L* CIELAB a* CIELAB b*
Monk 01 246 237 228 94,211 1,503 5,422
Monk 02 243 231 219 92,275 2,061 7,280
Monk 03 247 234 208 93,091 0,216 14,205
Monk 04 234 218 186 87,573 0,459 17,748
Monk 05 215 189 150 77,902 3,471 23,136
Monk 06 160 126 86 55,142 7,783 26,740
Monk 07 130 92 67 42,470 12,325 20,530
Monk 08 96 65 52 30,678 11,667 13,335
Monk 09 58 49 42 21,069 2,69 5,964 0
Monk 10 41 36 32 14,610 1,482 3,525
Some of the Monk scale CIELAB skin tone patch values lie outside the measured skin tone gamut.
(See Reference [15][15] Cook).). The three brightest patches are above an L* value of 90, which is beyond what
a photographic print on paper can achieve. These Monk L* values are higher than the L* values of most papers,
especially those without optical brighteners.
In addition, the Monk skin tones are significantly more yellow than natural skin tones and do not show the red
component from the hemoglobin in the blood flowing through the skin. The skin tones in this scale are
rendered for a display with a reference white point of 6 500 K. For such a cool reference white, it appears that
the tones need to be turned into “warmer” tones in order to be perceived as natural.
7.96.10 Colorimetric skin tone scale
The colorimetric skin tone scale (CST) was developed based on 2,517 colorimetric facial skin tone
[14][14]
measurements from US research volunteers belonging to different demographic groups .
The CST scale provides methods to create skin tone patches based on a set of observed skin tone values. The
scale is created by estimating hue and chromaticity at evenly spaced increments of L* values from 20 to 70.
Hue and chromaticity are estimated as a function of L* using linear regression such that:

The colours shown in Figure 12Figure 12 and colour coordinates in Table 2Table 2 were computed using skin
[14]
tones measured by Reference [14] .
26478_ed1fig12.EPS
Figure 12 — Colorimetric skin tone scale
Table 2 — Colour coordinates of colorimetric skin tone scale
patchPatc L* a* b*
h
1 70,00 6,07 4,70
2 64,44 11,02 9,26
3 58,89 14,44 13,06
4 53,33 16,45 15,94
5 47,78 17,20 17,74
6 42,22 16,79 18,35
7 36,67 15,34 17,66
8 31,11 12,93 15,62
9 25,56 9,65 12,16
10 20,00 5,55 7,26
The authors reported that the colorimetric skin tone scale was more sensitive, consistent, and colorimetrically
accurate relative to the Monk skin tone scale.
87 Spectral data corresponding to representative skin tone swatches ®
Many of the Pantone skin colour patches show an excellent spectral match with the in-situ measured skin
reflectance data, as shown in Figure 13Figure 13. Such a spectral match has the additional benefit of providing
a colourimetric match under all types of light sources.
26478_ed1fig13a.EPS 26478_ed1fig13b.EPS

a)a)  Lightest and darkest patches b)b)  Medium dark patches
Key
X wavelength
Y reflectance ®
Figure 13 — Comparison of measured skin tones (solid lines) and Pan
...