ISO/PAS 18940-1:2025

Publicly
Available
Specification
ISO/PAS 18940-1
Second edition
Imaging materials — Image
2025-05
permanence specification of
reflection photographic prints for
indoor applications —
Part 1:
Test methods
Matériaux pour l'image — Spécification relative à la permanence
de l’image des tirages photographiques par réflexion pour
applications intérieures —
Partie 1: Méthodes d'essai
Reference number
© ISO 2025
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ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviations . 2
3.1 Terms and definitions .2
3.2 Abbreviations .2
4 Requirements . 2
5 Test procedures . 2
5.1 Outline .2
5.2 Test target .2
5.3 Light stability test . .4
5.4 Ozone gas stability test .4
5.5 Thermal stability test .4
5.6 Humidity fastness test in high humidity condition .4
6 Measurement . 4
7 Data processing and graph creation . 5
7.1 Data processing.5
7.2 Calculation of colour difference .5
7.3 Graph reporting .6
7.3.1 General .6
7.3.2 Light stability .7
7.3.3 Ozone gas stability .8
7.3.4 Thermal stability .9
7.3.5 Humidity fastness in high humidity conditions .10
8 Reporting .11
8.1 Internal recording .11
8.2 Reporting for external communications . 12
Bibliography . 14

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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use 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.
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.
This second edition cancels and replaces the first edition (ISO/PAS 18940-1:2023), which has been
technically revised.
The main changes are as follows:
— editorial modifications for clarification based on the comments on the DPAS of the first edition.
A list of all parts in the ISO 18940 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
Introduction
Test methods for measurement of the image permanence for four important environmental stress factors
for indoor use of photographs are described in the following International Standards:
— ISO 18936 for thermal stability;
— ISO 18937 (all parts) for light stability;
— ISO 18941 for ozone gas stability;
— ISO 18946 for humidity fastness;
— ISO 18949 for low humidity testing.
Humidity testing according to ISO 18946 specifies high humidity test conditions to test for image fastness
(resistance to colorant migration). Humidity testing according to ISO 18949 specifies low humidity test
conditions, which can be observed in hot arid climates and during winter in continental climates. The
importance of low humidity depends on the environmental conditions of the specific usage case. Testing
according to ISO 18949 is optional.
NOTE It is acknowledged that other environmental stress factors can be present during indoor use of photographs
than the four mentioned before. Examples are other atmospheric gases, including SO and NO , the presence of which
x x
depends on local factors such as traffic, industry and heating. Mechanical stresses are also not considered here,
as these are typically considered to be low in the context of indoor consumer use of photographs as compared to
[3]
commercial applications (see ISO/TS 21139-1 ).
Each document includes variants of the test methods, test conditions and data analysis procedures to cover
different purposes. For the purpose of an overall specification for indoor image permanence performance, it
is necessary to specify which method, which condition and which data analysis procedure to select.
This document specifies the test methods, the test conditions and details of the data analysis. This document
also specifies how to communicate the results obtained by these test methods.
This document specifies which test method, test conditions and data analysis procedure are selected from
those listed in ISO 18936, ISO 18937 (all parts), ISO 18941, and ISO 18946.
In addition, this document also specifies the first level reporting of the results from the aforementioned
test methods in terms of data plots, which is the most generic reporting method. Graphical reporting
addresses the needs of communication on various levels, including technical product information on
datasheets, internet home pages, leaflets and posters distributed at trade shows. Graphic reporting is a key
for this document, as it provides the foundation for defining end-point criteria and specifications of image
permanence in other parts of this document.
Additional parts of the ISO 18940 series are being envisaged as future work to define standardized evaluation
point criteria on one hand and typical environmental conditions on the other, so that 'typical' expectations
for colour changes in the use profile 'consumer home' are taken into consideration. These additional parts
acknowledge that the actual expectations, use conditions (display and/or storage, including a certain level of
protection) as well as the actual environmental conditions in a specific instance of the use profile may vary.
More information on the image permanence issues of the consumer home environment can be found in
[2]
ISO/TR 18942 .
v
Publicly Available Specification ISO/PAS 18940-1:2025(en)
Imaging materials — Image permanence specification of
reflection photographic prints for indoor applications —
Part 1:
Test methods
1 Scope
This document specifies the test methods, test conditions, test target design, and analysis procedures for
the evaluation of the image permanence performance of photographic reflection prints. Tests based on
ISO 18936, ISO 18937 (all parts), ISO 18941, and ISO 18946 characterize the thermal stability, the light
stability, the ozone stability, and the humidity stability of photographic prints, respectively.
This document is applicable to any photographic reflection print produced through a digital step in the
workflow. It includes prints created by chromogenic silver halide, inkjet, electrophotography, thermal
diffusion, and other technologies. With reference to monochrome prints, this document is relevant
to photographic prints where the print material contains colorants. This document is not relevant to
monochrome silver halide prints, often known as black and white prints.
The document specifies the content and procedure for graphical reporting of test results as a first level data
collection for basic technical communication of image permanence performance of photographic prints.
This document does not include application-specific end-points, environmental conditions during
preservation and display of photographic prints, and test doses (durations, intensity).
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 13655, Graphic technology — Spectral measurement and colorimetric computation for graphic arts images
ISO 18924, Imaging materials — Test method for Arrhenius-type predictions
ISO 18936:2020, Imaging materials — Processed colour photographs — Methods for measuring thermal
stability
ISO 18937-2:2023, Imaging materials — Methods for measuring indoor light stability of photographic prints —
Part 2: Xenon-arc lamp exposure
ISO 18941, Imaging materials — Colour reflection prints — Test method for ozone gas fading stability
ISO 18944, Imaging materials — Reflection colour photographic prints — Test print construction and
measurement
ISO 18946, Imaging materials — Reflection colour photographic prints — Method for testing humidity fastness
ISO/CIE 11664-1, Colorimetry — Part 1: CIE standard colorimetric observers
ISO/CIE 11664-4, Colorimetry — Part 4: CIE 1976 L*a*b* colour space

3 Terms, definitions and abbreviations
3.1 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.2 Abbreviations
CIE Commission internationale de l'éclairage (International Commission on Illumination)
4 Requirements
To be in accordance with this document, the user shall provide graphical reporting of image permanence
testing associated with all four environmental stress factors required in this document, one at a time,
including light, heat, ozone, and humidity. If the result of one or more stress factors is not available, it shall
be reported that there is no result reported for that stress factor.
5 Test procedures
5.1 Outline
Sample strips with printed test targets shall undergo the light, ozone gas, thermal and humidity stress
tests described in 5.3, 5.4, 5.5, and 5.6 respectively. To maintain the accuracy and precision of each test, it is
crucial to adhere to the specified test conditions in each section. To ensure consistency in tests conducted
on different days, it is recommended to include a reference sample of the same type for each test.
5.2 Test target
For light, ozone and thermal stability tests, the test target shall consist of the 24 patches with sRGB values
defined in Table 1. The requirements for preparation, printing, handling and measurement of the test target
as defined in ISO 18944 apply. When preparing the test target prints, the sRGB values of Table 1 are used
to construct the test patches instead of the sRGB values defined in ISO 18944:2018, 5.3.2 and Annex A. Test
targets for high humidity testing are defined in ISO 18946.
An example of test target design is shown in Figure 1.
NOTE 1 This test target was created based on ISO 18944:2018, Table A.1. However, in order to reduce the test load,
the number of patches was reduced from 113 to 24, including three newly added brown patches.
Table 1 — Colour patch of the test target - RGB values of input signal in 8 bit
Number Name of colour patch Digital value in 8 bit
R G B
1 dark yellow 255 255 32
2 medium yellow 255 255 64
3 light yellow 255 255 128
4 dark magenta 255 32 255
5 medium magenta 255 64 255
6 light magenta 255 128 255
TTaabblle 1 e 1 ((ccoonnttiinnueuedd))
Number Name of colour patch Digital value in 8 bit
R G B
7 dark cyan 32 255 255
8 medium cyan 64 255 255
9 light cyan 128 255 255
10 dark blue 64 64 255
11 dark green 64 255 64
12 dark red 255 64 64
13 black 0 0 0
14 dark grey 32 32 32
15 medium grey-1 64 64 64
16 medium grey-2 128 128 128
17 light grey 192 192 192
18 white 255 255 255
19 dark brown 131 55 26
20 medium brown 204 115 77
21 light brown 230 179 179
22 light blue 128 128 255
23 light green 128 255 128
24 light red 255 128 128
NOTE The patch numbers in the figure are only given for information as to provide a visual association with the
sRGB values in Table 1 and are removed when printing.
Figure 1 — Example of the test target design
In addition to graphically reporting the measurement results from the fading of the solid patches, it is
...