ISO 18946:2023

INTERNATIONAL ISO
STANDARD 18946
Second edition
2023-12
Imaging materials — Reflection colour
photographic prints — Method for
testing humidity fastness
Matériaux pour l'image — Tirages photographiques en couleurs par
réflexion — Méthode d'essai de la solidité à l'humidité
Reference number
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements . 2
5 Outline of test procedure .2
6 Sample preparation .3
6.1 General . 3
6.2 Test target . 4
6.3 Printer driver setting . 5
6.4 Printing conditions . 5
6.5 Sample conditioning . 5
7 Humidity exposure .6
7.1 Equipment and calibration . 6
7.2 Test environment control . . . 6
7.3 Method A — Fixed humidity condition . 7
7.4 Method B — Multiple humidity conditions . 7
8 Colorimetric measurement . 7
9 Data analysis . 8
10 Test report . 9
10.1 General . 9
10.2 Samples information . 9
10.3 Test conditions . 9
10.4 Results . . 9
10.4.1 General . 9
10.4.2 Method A . . . 10
10.4.3 Method B . . 10
Annex A (informative) Correspondence to psychophysical evaluation .11
Annex B (informative) Test target for humidity fastness test — RGB values of input signal
in 8 bit .12
Bibliography .13
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 18946:2011), which has been technically
revised.
The main changes are as follows:
— Low humidity test has been removed, since the low humidity test was separated from ISO 18946
and published as ISO 18949.
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
This document addresses the methods and procedures for testing the humidity fastness of reflection
colour photographic prints exposed to high humidity. This is of particular relevance to dye-based ink-
[11][12][13][14][15][16][17]
jet prints or dye diffusion process prints .
Some types of colour photographic prints suffer from changes in image appearance when exposed to a
high relative humidity environment. The observed changes relate to colour, tone and loss of sharpness
caused by horizontal and vertical diffusion of colorants as a result of exposure to elevated humidity.
The elevated humidity can arise from:
a) exposure to high relative humidity of the environment of the display area or storage space;
b) trapped moisture as a result of stacking prints, or inserting them into albums, in a high relative
humidity environment;
c) trapped moisture as a result of stacking prints, or inserting them into albums, before sufficient dry
time has elapsed.
Note For the investigation of cases b) and c), the “sealed bag” method within the thermal test ISO 18936 can
be adopted.
Therefore, humidity based on meteorological data and users’ behaviour was considered in determining
the appropriate test conditions for the humidity fastness test. The test method stipulated in this
document is validated for case a).
Image deterioration of dye-based prints caused by high humidity is often detectable by the following
characteristics.
— Blur (sharpness loss), change of colour and/or tone is observed.
— The deterioration is observed in higher humidity, commonly over 80 % RH or over 90 % RH.
— The deterioration can occur in a relatively short time, even within one or two weeks.
— Higher density images, or images that contain more secondary or mixed colours, are generally
more affected. The largest change is usually observed at the boundary of different colours, or with
images that have contrasting background colours. The size of the higher density area also affects
the deterioration because the solvent and water of the ink diffuses to the adjacent lower density
area when the higher density area is small.
It is important to take into account these characteristics when determining the appropriate test chart
and test conditions.
This document makes use of a checkerboard pattern that allows assessment of humidity-induced blur
[12]
by means of a relatively simple colorimetric measurement .
v
INTERNATIONAL STANDARD ISO 18946:2023(E)
Imaging materials — Reflection colour photographic prints
— Method for testing humidity fastness
1 Scope
This document describes test methods for evaluating reflection colour photographic prints with regard
to changes in image appearance resulting from exposure to high relative humidity.
NOTE Testing under low humidity conditions is described in ISO 18949.
The observed changes relate to colour, tone and loss of sharpness caused by horizontal and vertical
diffusion of colorants from exposure to elevated humidity levels. Other humidity-related factors, such
as mould and mildew growth, and physical damage, such as curl, cockle, cracking or delamination due
to humidity cycling, are outside the scope of this test method.
Although the method and procedures described in this document can be used to test any colour
hardcopy technology, it is particularly appropriate to systems where the colorants are applied by a
mechanism involving the diffusion of colorant into image-receiving layers (for example inkjet or dye
diffusion processes) or applied onto uncoated fibrous materials such as paper.
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 18913, Imaging materials — Permanence — Vocabulary
ISO/TR 18931, Imaging materials — Recommendations for humidity measurement and control
ISO 18941, Imaging materials — Colour reflection prints — Test method for ozone gas fading stability
ISO 13655, Graphic technology — Spectral measurement and colorimetric computation for graphic arts
images
ISO/CIE 11664-4, Colorimetry — Part 4: CIE 1976 L*a*b* colour space
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 18913 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
colour fringing
area of anomalous colour, most visible around a printed edge
Note 1 to entry: The cause is colorants that diffuse laterally at different rates. It is visually analogous to chromatic
aberration effects seen in images from simple lens systems.
3.2
operational fluctuation
positive and negative deviations from the setting of the sensor at the operational control set point
during equilibrium conditions in a laboratory accelerated weathering device
Note 1 to entry: Operational fluctuations are the result of unavoidable machine variables and do not include
measurement uncertainty. Operational fluctuations apply only at the location of the control sensor and do not
imply uniformity of conditions throughout the test chamber.
[SOURCE: ASTM G113-22]
3.3
operational uniformity
range around the operational control point for measured parameters within the intended exposure
area, within the limits of the intended operational range
[SOURCE: ASTM G113-22]
4 Requirements
This document specifies a set of recommended test methods with associated requirements for permitted
reporting. Data from these tests shall not be used to make life expectancy claims, such as time-based
print lifetime claims, either comparative or absolute. Conversion of data obtained from these methods
for the purpose of making public statements regarding product life shall be in accordance with the
applicable International Standards for specification of print life.
The test methods in this document might be useful as stand-alone test methods for comparison of
the stability of image materials with respect to one specific failure mode. Data from the test methods
of this document may be used in stand-alone reporting of the absolute or comparative stability of
image materials with respect to the specific failure mode dealt with in this document, when reported
in compliance with the reporting requirements of this document. Caution shall be exercised when
comparing test results for different materials. Comparisons shall be limited to test cases that use
equipment with matching specifications and matching test conditions.
5 Outline of test procedure
[12]
The checkerboard pattern shown in Figure 1 shall be printed at (23 ± 2) °C and in an environment of
(50 ± 10) % RH.
The test samples shall be conditioned, positioned with unrestricted airflow, for (24 ± 2) h at (23 ± 2) °C
and (50 ± 5) % RH.
The printed samples shall be exposed to high humidity as specified in Clause 7.
The colour patches shall be measured using CIELAB colorimetry before and after the humidity
∗
exposures. The colour difference ΔE for the patches of the checkerboard pattern shall be calculated
ab
according to Formula (1) in Clause 9.
This document stipulates two test methods: A and B.
∗
Method A demonstrates the degree of the deterioration (ΔE of the printed image) quantitatively in a
ab
fixed humidity condition, i.e. 25 °C and 85 % RH, for a given period of time. Four weeks is the
recommended duration. One, two or eight weeks durations can be used. Method A is most useful for
research and development of printing systems or printing materials where the humidity fastness of
many samples can be screened and closely compared.
Method B demonstrates the limitations of printing systems and materials by analysing data from tests
at various levels of humidity, i.e. 25 °C for two weeks at three or more humidity levels chosen from 60 %
RH, 65% RH, 70 % RH, 75 % RH, 80 % RH, 85 % RH, 90 % RH and 95 % RH, and showing where each
∗
sample starts to show significant changes with respect to the average ΔE of 84 patches. Method B is
ab
especially useful for communicating with end users who will be able to recognize the high humidity
limitations for each product tested.
The test procedures are summarized in Table 1.
Table 1 — Summary of test procedures
Steps Procedures and test conditions
Test target Checkerboard pattern shown in Figure 1
Sample preparation
Temperature
(23 ± 2) °C and (50 ± 10) % RH
and RH
Temperature
(23 ± 2) °C and (50 ± 5) % RH
and RH
Sample conditioning
Duration (24 ± 2) h, unrestricted airflow
25 °C and 85 % RH
Method A Recommended duration of 4 weeks
One, two or eight week durations can be used
Humidity exposure
25 °C for two weeks at three or more humidity levels chosen
Method B from 60 % RH, 65 % RH, 70 % RH, 75 % RH, 80 % RH, 85 % RH,
90 % RH and 95 % RH
Method CIE colorimetry conforming to measurement condition M0 of ISO 13655
Measurement
∗
Parameter
ΔE of 84 patches in Figure 1 before and after the humidity exposure
ab
Method A Measured deterioration at a fixed humidity
Report
Method B Highest limit humidity without significant deterioration
6 Sample preparation
6.1 General
The checkerboard pattern shown in Figure 1 shall be printed at (23 ± 2) °C and (50 ± 10) % RH.
The test samples shall be conditioned for (24 ± 2) h at (23 ± 2) °C and (50 ± 5) % RH before humidity
exposure, positioned with unrestricted airflow.
1)
The sample holding environment shall be substantially ozone-free [≤2 nl/l average ozone
concentration over any 24 h period] for ozone-sensitive samples, as determined in accordance with
ISO 18941. A material that is not sensitive to ozone shall have demonstrated no measurable D or
min
printed patch colour change at ambient ozone exposure levels and measurement condition temperature
and humidity, over time periods consistent with measurement and test-staging time periods.
At least two replicate prints are required for each test case. Replicates shall be located for testing in
different regions of the test chamber volume.
It is recommended that reference samples be included in every exposure test to track consistency of the
[10]
test procedures as well as unintended changes of test conditions .
−9
1) 1 nl/l = 1 ppb (1 × 10 ). Although the notation “ppb” (parts per billion) is widely used in the measurement and
reporting of trace amounts of pollutants in the atmosphere, it is not used in International Standards because it is
language-dependent.
6.2 Test target
The checkerboard test pattern (see Figure 1) shall be used as the test target. The ISO 18946 humidity
test target is contained in the image permanence test target collection that is available at https:// www
.imaging .org/ site/ IST/ IST/ Standards/ Image _Permanence _Targets .aspx
The standard humidity print stability digital test file shall be downloaded and maintained in the tiff file
format. No lossy image or file compression shall be applied to the target file. The digital file resolution
shall be maintained as 600 dpi. The humidity print stability digital test file is encoded in sRGB, defined
[8]
as per IEC 61966-2-1 , and uses the tiff format with the sRGB ICC profile embedded. After downloading,
the humidity print stability digital test file shall be retained in that format and encoding with the ICC
profile retained.
NOTE Other file formats that retain the state of exactly unchanged pixel encoding values, no lossy
compression, embedded sRGB ICC profile, and 600 dpi, can be treated as equivalent to the tiff format for internal
use in a test environment.
This test pattern contains all of the cyclic combinations of Y, M, C, R, G, B, white and black as a
checkerboard pattern. Rows 1, 7, 13 and 14 consist of solid-fill colour patches, which are used to evaluate
changes in colour quality. Rows 2 to 6 and 8 to 12 consist of colour patches with a fine checkerboard
pattern of interleaved colour squares which manifest colour changes that correlate well with loss of
line quality caused by lateral migration of colorants.
The RGB values for each patch of the test target are shown in Annex B, Table B.1.
This test target was created to measure both colour and tone change and blur of the checkerboard
pattern. The change in the CIELAB colorimetric value of each patch in Figure 1 caused by humidity
exposure shall be measured as specified in Clause 8. However, the measurement of the colorimetric
value of CIELAB of the checkerboard pattern is not always accurate in detecting line profile change as it
cannot detect image sharpness loss if there is no co
...