ISO 18909:2006

INTERNATIONAL ISO
STANDARD 18909
First edition
2006-07-15
Photography — Processed photographic
colour films and paper prints — Methods
for measuring image stability
Photographie — Films et papiers photographiques couleur traités —
Méthodes de mesure de la stabilité de l'image

Reference number
©
ISO 2006
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.

©  ISO 2006
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 2006 – All rights reserved

Contents Page
Foreword. v
Introduction . vi
1 Scope . 1
2 Normative references . 1
3 Test methods — General . 1
3.1 Sensitometric exposure . 1
3.2 Processing. 2
3.3 Densitometry . 3
3.4 Definition of density terms . 3
3.5 Density values to be measured . 3
3.6 Method of correction of density measurements for d changes . 3
min
3.7 Computation of image-life parameters. 8
3.8 Effects of dye fading and stain formation on the printing quality of colour negative
images. 9
4 Test methods — Dark stability . 10
4.1 Introduction . 10
4.2 Test conditions . 10
4.3 Number of specimens . 11
4.4 Test equipment and operation for specimens free-hanging in air . 11
4.5 Test equipment and operation for specimens sealed in moisture-proof bags . 12
4.6 Conditioning and packaging of specimens in moisture-proof bags. 12
4.7 Incubation conditions for specimens sealed in moisture-proof bags . 12
4.8 Computation of dark stability . 12
5 Test methods — Light stability . 12
5.1 Introduction . 12
5.2 Number of specimens . 13
5.3 Irradiance measurements and normalization of test results. 13
5.4 Backing of test specimens during irradiation testing. 13
5.5 Specification for standard window glass.14
5.6 High-intensity filtered xenon arc ID65 illuminant (50 klx to 100 klx) for simulated indoor
indirect daylight through window glass. 14
5.7 Glass-filtered fluorescent room illumination — Cool White fluorescent lamps (80 klx or
lower). 16
5.8 Incandescent tungsten room illumination 3,0 klx – CIE illuminant A spectral distribution. 18
5.9 Simulated outdoor sunlight (xenon arc) 100 klx – CIE D65 spectral distribution. 18
5.10 Intermittent tungsten-halogen lamp slide projection 1 000 klx . 21
5.11 Computation of light stability . 21
6 Test report . 21
6.1 Introduction . 21
6.2 Dark stability tests. 23
6.3 Light stability tests . 24
Annex A (informative) Numbering system for related International Standards. 25
Annex B (informative) A method of interpolation for step wedge exposures. 27
Annex C (informative) Method for power equation d correction of reflection print materials. 28
min
Annex D (informative) Illustration of Arrhenius calculation for dark stability . 33
Annex E (informative) The importance of the starting density in the assessment of dye fading and
colour balance changes in light-stability tests. 37
Annex F (informative) Enclosure effects in light-stability tests with prints framed under glass or
plastic sheets. 39
Annex G (informative) Data treatment for the stability of light-exposed colour images. 41
Bibliography . 49

iv © ISO 2006 – All rights reserved

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 18909 was prepared by Technical Committee ISO/TC 42, Photography.
This first edition cancels and replaces ISO 10977:1993, of which it constitutes a technical revision.
Introduction
This International Standard is one of a series of standards dealing with the physical properties and stability of
imaging materials. To facilitate identification of these documents, they are assigned a number within the block
from 18900 – 18999 (see Annex A).
This International Standard is divided into two parts. The first covers the methods and procedures for
predicting the long-term, dark storage stability of colour photographic images; the second covers the methods
and procedures for measuring the colour stability of such images when exposed to light of specified intensities
and spectral distribution, at specified temperatures and relative humidities.
Today, the majority of continuous-tone photographs are made with colour photographic materials. The length
of time that such photographs are to be kept can vary from a few days to many hundreds of years and the
importance of image stability can be correspondingly small or great. Often the ultimate use of a particular
photograph may not be known at the outset. Knowledge of the useful life of colour photographs is important to
many users, especially since stability requirements often vary depending upon the application. For museums,
archives, and others responsible for the care of colour photographic materials, an understanding of the
behaviour of these materials under various storage and display conditions is essential if they are to be
preserved in good condition for long periods of time.
Organic cyan, magenta and yellow dyes that are dispersed in transparent binder layers coated on to
transparent or white opaque supports form the images of most modern colour photographs. Colour
photographic dye images typically fade during storage and display; they will usually also change in colour
balance because the three image dyes seldom fade at the same rate. In addition, a yellowish (or occasionally
other colour) stain may form and physical degradation may occur, such as embrittlement and cracking of the
support and image layers. The rate of fading and staining can vary appreciably and is governed principally by
the intrinsic stability of the colour photographic material and by the conditions under which the photograph is
stored and displayed. The quality of chemical processing is another important factor. Post-processing
treatments, such as application of lacquers, plastic laminates and retouching colours, may also affect the
stability of colour materials.
The two main factors that influence storage behaviour, or dark stability, are the temperature and relative
humidity of the air that has access to the photograph. High temperature, particularly in combination with high
relative humidity, will accelerate the chemical reactions that can lead to degradation of one or more of the
image dyes. Low-temperature, low-humidity storage, on the other hand, can greatly prolong the life of
photographic colour images. Other potential causes of image degradation are atmospheric pollutants (such as
oxidizing and reducing gases), micro-organisms and insects.
Primarily the intensity of the illumination, the duration of exposure to light, the spectral distribution of the
illumination, and the ambient environmental conditions influence the stability of colour photographs when
displayed indoors or outdoors. (However, the normally slower dark fading and staining reactions also proceed
during display periods and will contribute to the total change in image quality). Ultraviolet (UV) radiation is
particularly harmful to some types of colour photographs and can cause rapid fading as well as degradation of
plastic layers such as the pigmented polyethylene layer of resin-coated (RC) paper supports.
In practice, colour photographs are stored and displayed under varying combinations of temperature, relative
humidity and illumination, and for different lengths of time. For this reason, it is not possible to precisely
predict the useful life of a given type of photographic material unless the specific conditions of storage and
display are known in advance. Furthermore, the amount of change that is acceptable differs greatly from
viewer to viewer and is influenced by the type of scene and the tonal and colour qualities of the image.
After extensive examination of amateur and professional colour photographs that have suffered varying
degrees of fading or staining, no consensus has been achieved on how much change is acceptable for
various image quality criteria. For this reason, this International Standard does not specify acceptable end-
points for fading and changes in colour balance. Generally, however, the acceptable limits are twice as wide
vi © ISO 2006 – All rights reserved

for changes in overall image density as for changes in colour balance. For this reason, different criteria have
been used as examples in this International Standard for predicting changes in image density and colour
balance.
Pictorial tests can be helpful in assessing the visual changes that occur in light and dark stability tests, but are
not included in this International Standard because no single scene is representative of the wide variety of
scenes actually encountered in photography.
In dark storage at normal room temperatures, most modern colour films and papers have images that fade
and stain too slowly to allow evaluation of the dark storage stability simply by measuring changes in the
specimens over time. In such cases, too many years would be required to obtain meaningful stability data. It is
possible, however, to assess in a relatively short time the probable long-term fading and staining behaviour at
moderate or low temperatures by means of accelerated ageing tests carried out at high temperatures. The
influence of relative humidity also can be evaluated by conducting the high-temperature tests at two or more
humidity levels.
Similarly, information about the light stability of colour photographs can be obtained from accelerated light-
stability tests. These require special test units equipped with high-intensity light sources in which test strips
can be exposed for days, weeks, months or even years, to produce the desired amount of image fading (or
staining). The temperature of the specimens and their moisture content must be controlled throughout the test
period, and the types of light sources must be chosen to yield data that can be correlated satisfactorily with
those obtained under conditions of normal use.
Accelerated light stability tests for predicting the behaviour of photographic colour images under normal
display conditions may be complicated by reciprocity failure. When applied to light-induced fading and staining
of colour images, reciprocity failure refers to the failure of many dyes to fade, or to form stain. This even
applies when dyes are irradiated with high-intensity versus low-intensity light, even though the total light
exposure (intensity × time) is kept constant through appropriate adjustments in exposure duration (see [1] in
the Bibliography). The extent of dye fading and stain formation can be greater or smaller under accelerated
conditions, depending on the photochemical reactions involved in the dye degradation, the kind of dye
dispersion, the nature of the binder material, and other variables. For example, the supply of oxygen that can
diffuse from the surrounding atmosphere into a photograph's image-containing emulsion layers may be
restricted in an accelerated test (dry gelatin is an excellent oxygen barrier). This may change the rate of dye-
fading relative to that which would occur under normal display conditions. The temperature and moisture
content of the test specimen also influence the magnitude of reciprocity failure. Furthermore, light fading is
influenced by the pattern of irradiation (continuous versus intermittent) as well as by light/dark cycling rates.
For all these reasons, long-term changes in image density, colour balance and stain level can be reasonably
estimated only for conditions similar to those employed in the accelerated tests, or when good correlation has
been confirmed between accelerated tests and actual conditions of use.
In order to establish the validity of the test methods for evaluating the dark and light stability of different types
of photographic colour films and papers, the following product types were selected for the tests:
a) colour negative film with incorporated oil-soluble couplers;
b) colour negative motion picture pre-print and negative films with incorporated oil-soluble couplers;
c) colour reversal film with incorporated oil-soluble couplers;
d) colour reversal film with incorporated Fischer-type couplers;
e) colour reversal film with couplers in the developers;
f) silver dye-bleach film and prints;
g) colour prints with incorporated oil-soluble couplers;
h) colour motion picture print films with incorporated oil-soluble couplers;
i) colour dye imbibition (dye transfer) prints;
j) integral colour instant print film with dye developers;
k) peel-apart colour instant print film with dye developers;
l) integral colour instant print film with dye releasers.
The results of extensive tests with these materials showed that the methods and procedures of this
International Standard can be used to obtain meaningful information about the long-term dark stability and the
light stability of colour photographs made with a specific product. They also can be used to compare the
stability of colour photographs made with different products and to access the effects of processing variations
or post-processing treatments. The accuracy of predictions made on the basis of such accelerated ageing
tests will depend greatly upon the actual storage or display conditions.
It must also be remembered that density changes induced by the test conditions and measured during and
after the tests include those in the film or paper support and in the various auxiliary layers that may be
included in a particular product. With most materials, however, the major changes occur in the dye image
layers.
Stability when stored in the dark
The tests for predicting the stability of colour photographic images in dark storage are based on an adaptation
of the Arrhenius method described by Bard et al. (see [2] and [3] in the Bibliography) and earlier references by
Arrhenius, Steiger and others (see [4], [5], and [6] in the Bibliography). Although this method is derived from
well-understood and proven theoretical precepts of chemistry, the validity of its application for predicting
changes of photographic images rests on empirical confirmation. Although many chromogenic-type colour
products yield image-fading and staining data in both accelerated and non-accelerated dark ageing tests that
are in good agreement with the Arrhenius relationship, some other types of products do not.
NOTE For example, integral-type instant colour print materials often exhibit atypical staining at elevated
temperatures; treatment of some chromogenic materials at temperatures above 80 °C and 60 % RH may cause loss of
incorporated high-boiling solvents and abnormal image degradation; and the dyes of silver dye-bleach images
deaggregate at combinations of very high temperature and high relative humidity, causing abnormal changes in colour
balance and saturation (see [7] in the Bibliography). In general, photographic materials tend to undergo dramatic changes
at relative humidities above 60 % (especially at the high temperatures employed in accelerated tests) owing to changes in
the physical properties of gelatine.
Stability when exposed to light
The methods of testing light stability in this International Standard are based on the concept that increasing
the light intensity without changing the spectral distribution of the illuminant or the ambient temperature and
relative humidity should produce a proportional increase in the photochemical reactions that occur at typical
viewing or display conditions, without introducing any undesirable side effects.
However, because of reciprocity failures that are discussed in this Introduction, this assumption does not
always apply. Thus, the accelerated light stability test methods described in this International Standard are
valid at the specified accelerated test conditions, but may not reliably predict the behaviours of a given product
in long-term display under normal conditions.
Translucent print materials, designed for viewing by either reflected or transmitted light (or a combination of
reflected and transmitted light), shall be evaluated as transparencies or as reflection prints, depending on how
they will be used. Data shall be reported for each condition of intended use.
This International Standard does not specify which of the several light stability tests is the most important for
any particular product.
viii © ISO 2006 – All rights reserved

INTERNATIONAL STANDARD ISO 18909:2006(E)

Photography — Processed photographic colour films and paper
prints — Methods for measuring image stability
1 Scope
This International Standard describes test methods for determining the long-term dark storage stability of
colour photographic images and the colour stability of such images when subjected to certain illuminants at
specified temperatures and relative humidities.
This International Standard is applicable to colour photographic images made with traditional, continuous-tone
photographic materials with images formed with dyes. These images are generated with chromogenic, silver
dye-bleach, dye transfer, and dye-diffusion-transfer instant systems. The tests have not been verified for
evaluating the stability of colour images produced with dry- and liquid-toner electrophotography, thermal dye
transfer (sometimes called dye sublimation), ink jet, pigment-gelatine systems, offset lithography, gravure and
related colour imaging systems.
This International Standard does not include test procedures for the physical stability of images, supports or
binder materials. However, it is recognized that in some instances, physical degradation such as support
embrittlement, emulsion cracking or delamination of an image layer from its support, rather than image
stability, will determine the useful life of a colour film or print material.
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 5-2:2001, Photography — Density measurements — Part 2: Geometric conditions for transmission
density
ISO 5-3:1995, Photography — Density measurements — Part 3: Spectral conditions
ISO 5-4:1995, Photography — Density measurements — Part 4: Geometric conditions for reflection density
ISO 18911-2000, Imaging materials — Processed safety photographic films — Storage practices
3 Test methods — General
3.1 Sensitometric exposure
The photographic material shall be exposed and processed in accordance with the manufacturer’s
recommendations to obtain areas (patches) of uniform density at least 5 mm × 5 mm. This International
Standard requires measuring the changes in colour densities in minimum density areas (d ) and at a density
min
of 1,0 ± 0,05 above d . These changes are to be monitored in neutral areas, i.e. where the initial red, green
min
and blue densities are approximately equal (above their respective d ), as well as in areas selectively
min
1)
exposed to produce the purest possible cyan, magenta and yellow dye scales . These shall be made with the
aid of appropriate filters (see Table 1).
The desired density may be obtained from a single precise exposure or from a continuous wedge exposure.
Alternatively, if it is more convenient (e.g. with automated densitometry), the starting densities of 1,0 above
d may be interpolated from other densities (one way to do this is described in Annex B).
min
Table 1 — Suitable filters for exposing test specimens
Filters to generate
b c
a (e.g. Kodak Wratten filters or Fuji filters )
Type of material
Cyan dye Magenta dye Yellow dye
Minus red Minus green Minus blue
Wratten 32
Reversal and direct positive
Wratten 44 Wratten 12
Fuji SP-4
Fuji SP-5 Fuji SC-50 or SC-52
or SP-12
Red Green Blue
Negative working
Wratten 29 Wratten 99 Wratten 47B
Fuji SC-62 Fuji BPN-55 Fuji BPB-42

a
If materials to be tested have unusual spectral sensitivity characteristics, consult the manufacturer for filter recommendations.
b
Kodak Filters for Scientific and Technical Uses, Kodak Publication No. B-3, Eastman Kodak Company, Rochester, New York,
USA; 1985. This information is given for the convenience of users of this International Standard and does not constitute an
endorsement by ISO of the product named. Equivalent products may be used if they can be shown to lead to the same results.
c
Fujifilm Filter “Optical," Fuji Photo Film Co., Ltd., Tokyo, Japan; 1993. This information is given for the convenience of users of
this International Standard and does not constitute an endorsement by ISO of the product named. Equivalent products may be used if
they can be shown to lead to the same results.

3.2 Processing
The sensitometrically exposed specimens shall be processed using the processing system of primary interest.
The processing chemicals and processing procedure can have a significant effect on the dark-keeping and/or
light-keeping stability of a colour photographic material. For example, a chromogenic colour negative print
paper processed in a washless or non-plumbed system with a stabilizer rinse bath instead of a water wash
probably has stability characteristics that are different from the same colour paper processed in a conventional
chemistry and a final water wash. Therefore, the specific processing chemicals and procedure shall be listed
along with the name of the colour product in any reference to the test results.
Stability data obtained from a colour material processed in certain processing chemicals shall not be applied
to the colour material processed in different chemicals, or using a different processing procedure. Likewise,
data obtained from test specimens shall not be applied to colour materials that have been subjected to post-
processing treatments (e.g. application of lacquers, plastic laminates or retouching colours) that differ from the
treatments given to the test specimens.

1) Because of optical or chemical interactions, a neutral patch or a patch with a colour composed of a mixture of two
dyes, e.g. red, green or blue, often exhibit stability effects that are different from pure cyan, magenta or yellow dye patches.

This situation is particularly likely to occur when images are subjected to light fading.
2 © ISO 2006 – All rights reserved

3.3 Densitometry
Image density shall be measured with the spectral conditions specified for Status A densitometry
(transparencies and reflection prints) and for Status M densitometry (negatives) as described in ISO 5-3.
Transmission density, D , (90° opal; S: < 10°; s) shall be measured with an instrument complying with the
T
geometric conditions described in ISO 5-2. Reflection density, D , (40° to 50°; S: 5°; s) shall be measured as
R
described in ISO 5-4.
One of the problems encountered in densitometry is the instability of the measuring devices, especially during
the course of long-term tests. Some of the components of densitometers that can change appreciably with
age, as well as from one unit or batch to another, are the optical filters, the light sensors and the lamps. For
example, the filters in many modern densitometers will deteriorate with age and must be replaced periodically,
often within 2 y to 3 y. However, replacement filters of the same type frequently do not exactly match the
original filters in spectral transmittance characteristics. Such changes in transmittance will cause unequal
changes in the measured density values of dyes having different spectral absorption properties.
One way of dealing with such problems in a densitometer system is to keep standard reference specimens of
each test product sealed in vapour-proof containers and stored at −18 °C or lower. These specimens can be
used to check the performance of the system periodically and to derive correction factors for different products
as required (the calibration standards supplied with a densitometer are not adequate for this purpose).
3.4 Definition of density terms
d is the symbol for measured density;
D is the symbol for density corrected for d .
min
3.5 Density values to be measured
The following densities of the specimens, prepared as described in 3.1, shall be measured before and after
the treatment interval (see Figure 1):
(a) d (R) , d (G) , d (B)
min t min t min t
the red, green and blue minimum densities of specimens that have been treated for time t, where t takes on
values from 0 to the end of the test;
(b) d (R) , d (G) , d (B)
N t N t N t
the red, green and blue densities of neutral patches that initially had densities of 1,0 above d and that have
min
been treated for time t, where t takes on values from 0 to the end of the test;
(c) d (R) , d (G) , d (B)
C t M t Y t
the red, green and blue densities of cyan, magenta and yellow colour patches that initially had densities of 1,0
above d and that have been treated for time t, where t takes on values from 0 to the end of the test.
min
3.6 Method of correction of density measurements for d changes
min
3.6.1 General
The areas of minimum density of many types of colour photographs change with time during dark storage, and
generally to a lesser extent also change on prolonged exposure to light during display or projection. Such
changes most commonly take the form of density (stain) increases, usually yellowish in colour. However,
some materials, under certain conditions, may exhibit a loss in minimum density; e.g. colour negatives in dark
storage.
For the purposes of this International Standard, changes in minimum density as measured in d patches,
min
whether increases or losses, are assumed to have occurred equally at all density levels. Therefore, in order to
determine accurately the amount of dye-fading that has taken place during testing or during storage and
display, it is necessary to take into account the change in the d value (see Table 2).
min
a
Table 2 — Correction of density measurements for d changes
min
Type of material and test Correction
Transmission materials in dark and light stability tests Full d correction (for starting density of 1,0 above
min
d )
min
Reflection materials in dark and light stability tests 1/2 d correction (for starting densities of 0,7 to 1,0
min
above d )
min
Reflection materials in dark and light stability tests d correction by power equation
min
(alternative method – see Annex C)
a
No correction is made for d changes when determining colour balance changes of neutral patches.
min
Different methods of d correction are specified for transmission and reflection materials because multiple
min
internal reflections affect the d density values obtained with reflection materials, but not those of
min
transmission materials (see [8] and [9] in the Bibliography). Specifically, the multiple reflections within the
image and auxiliary layers of a reflection material cause an increase in the measured value of the stain
density, but have much less effect on the measured values of reflection densities in the range of 0,7 to 1,0
above d . It was determined empirically that one-half the change measured in the d value of reflection
min min
materials provides a reasonable approximation of the actual d contribution to measured reflection densities
min
in the range of 0,7 to 1,0 above d .
min
For translucent materials the most common method of density measurement is transmission; however, these
materials shall be measured by reflection if that is their intended use. Translucent materials with very high
initial transmission d may show a loss of d with light or dark treatment. In these cases, the use of half
min min
d correction may confound the measurements and caution must be used.
min
An alternative method for d correction using a multi-power relationship among stain, dye and measured
min
densities is described in Annex C. This method is particularly useful for the correction of measured densities
when relatively high stain levels are present and/or when measuring low-density levels below 0,7.
Two examples are described in a) and b) to help clarity the d correction procedures (illustrated in Figure 1
min
for transmission materials and Figure 2 for reflection materials).
4 © ISO 2006 – All rights reserved

Key
X log of exposure
Y transmission density
1 before testing
2 after testing
Figure 1 — Illustration of the blue transmission density of a neutral patch of
a transparency-type colour material (as defined by equations in 3.6.2)
a) A colour transparency material tested for dark stability had a neutral patch with a starting blue density
D (B) of 1,0 since:
N o
d (B) = 1,1
N o
d (B) = 0,1, and therefore
min o
D (B) = [d (B) − d (B) ] = 1,1 − 0,1 = 1,0
N o N o min o
After incubation for time t, the blue density D (B) was 0,72 because the measured density values had
N t
changed as follows:
d (B) = 0,90
N t
d (B) = 0,18, and therefore
min t
D (B) = [d (B) − d (B) ] = 0,90 − 0,18 = 0,72
N t N t min t
Hence, the blue density of the neutral patch decreased by 0,28, whereas that of the minimum density patch
increased (due to formation of yellowish stain) by 0,08. If the d value had increased less, or even
min
decreased (as can occur with colour negative films, for example), the value of d (B) would have changed by
N t
a different, commensurate amount. However, by subtracting the d density from the density of the neutral
min
patch, both before and after incubation, the actual change in density of the neutral patch is determined.
Similar procedures are employed to correct the cyan, magenta and yellow patches for d changes.
min
Key
X log of exposure
Y refection density
1 before testing
2 after testing
Figure 2 — Illustration of the blue reflection density of a neutral patch of
a reflection-type colour material (as defined by equations in 3.6.3)
b) A colour reflection print material tested for dark stability had a neutral patch with a starting blue density
D (B) of 1,0 since:
N o
d (B) = 1,1
N o
d (B) = 0,1, and therefore
min o
D (B) = [d (B) − d (B) ] = 1,1 − 0,1 = 1,0
N o N o min o
After incubation for time t, the blue density D (B) was 0,76 because the measured density values had
N t
changed as follows:
d (B) = 0,90
N t
d (B) = 0,18, and therefore
min t
D (B) = d (B) − d (B) + ½ [d (B) − d (B) ] = 0,90 − 0,18 + ½ (0,18 − 0,10) = 0,72 + 0,04 = 0,76
N t N t min t min t min o
Hence, the blue density of the neutral patch decreased by 0,24, whereas that of the minimum density patch
increased (due to formation of yellowish stain) by 0,08. However, this increase in the measured d value
min
was due in part to the effects of multiple internal reflections, as explained in 3.5. Therefore, a correction was
made equal to + ½ the measured change of 0,08. Such a correction of + ½ d change would also have to be
min
made if the d value had decreased rather than increased. Similar procedures are employed to correct the
min
cyan, magenta and yellow patches for d changes.
min
6 © ISO 2006 – All rights reserved

NOTE The gradient of the two curves of Figure 2 was deliberately lowered in order to provide a clearer view of the
density relations defined in the equation.
3.6.2 Transmission density corrected for d
min
a) D (R) = d (R) − d (R)
N t N t min t
b) D (G) = d (G) − d (G)
N t N t min t
c) D (B) = d (B) − d (B)
N t N t min t
d) D (R) = d (R) − d (R)
C t C t min t
e) D (G) = d (G) − d (G)
M t M t min t
f) D (B) = d (B) − d (B)
Y t Y t min t
3.6.3 Reflection density corrected for d
min
a) D (R) = d (R) − d (R) +1/2 [d (R) − d (R) ]
N t N t min t min t min o
b) D (G) = d (G) − d (G) +1/2 [d (G) − d (G) ]
N t N t min t min t min o
c) D (B) = d (B) − d (B) +1/2 [d (B) − d (B) ]
N t N t min t min t min o
d) D (R) = d (R) − d (R) +1/2[d (R) − d (R) ]
C t C t min t min t min o
e) D (G) = d (G) − d (G) +1/2 [d (G) − d (G) ]
M t M t min t min t min o
f) D (B) = d (B) − d (B) +1/2 [d (B) − d (B) ]
Y t Y t min t min t min o
NOTE The d correction for reflection density is identical to that for transmission density, except that it includes a
min
back correction equal to one half the d gain.
min
3.6.4 Colour balance in a neutral density patch
These are calculated as the percent of the average density.
dd(R) − (G)
NNtt
a) d (R−=G) ×100 %
N t
0,5[dd(R) + (G)]
NNtt
dd(R) − (B)
N tN t
b) d (R B−=) × 100 %
N t
0,5[dd(R) + (B) ]
NNtt
dd(G) − (B)
NNtt
c) d (G−=B)  × 100 %
N t
0,5[dd(G) + (B) ]
NNtt
3.6.5 d changes
min
a) d (R) − d (R)
min t min o
b) d (G) − d (G)
min t min o
d (B) − d (B)
c) min t min o
3.6.6 d colour balance
min
a) d (R − G) = d (R) − d (G)
min t min t min t
b) d (R − B) = d (R) − d (B)
min t min t min t
c) d (G − B) = d (G) − d (B)
min t min t min t
3.7 Computation of image-life parameters
From the measured density values, five image-life parameters can be computed (see Figure 1 for
transmission materials and Figure 2 for reflection materials). These image-life parameters and illustrative end-
points are listed in Table 3.
Table 3 — Image-life parameters for which times shall be reported
Illustrative end-points for positive Illustrative end-
Parameters colour transparencies and points for colour
reflection colour images negative materials
Change in neutral patches of D (R), D (G), and D (B)
N N N
30 % 15
(d corrected)
min
Change in colour patches of D (R), D (G), and D (B)
C M Y
30 % 15
(d corrected)
min
Change in colour balance of neutral patch: % D (R − G), %
N
15 % 15
D (R − B), and % D (G − B) (not d corrected)
N N min
Change in d (R), d (G), and d (B) in the d patch 0,10 % 0,05
min min min min
Change in colour balance: d (R − G), d (R − B) and
min min
0,06 % 0,05
d (G − B) in the d patch
min min
NOTE The image-life parameters listed are the critical characteristics that have practical significance for the visual degradation of
colour images; however, the numerical end-points given here are only illustrative. Each user of this International Standard shall select
end-points for the listed parameters, which, in that user's judgement, are appropriate for the specific product and intended application.
Selected end-points may be different for light and dark stability tests.

8 © ISO 2006 – All rights reserved

3.8 Effects of dye fading and stain formation on the printing quality of colour negative
images
The printing quality of colour negative images is mainly governed by three factors:
⎯ the colour printing densities of its image dyes;
⎯ the overall contrast and the contrast balance of these images;
⎯ the colour printing density of the masking dyes and the stain.
Any change in these properties, whether due to dye fading, changes in dye morphology or discolouration of
residual substances, has a greatly amplified effect on the final image because most colour print materials
have high inherent contrast. The most damaging change tends to be contrast balance distortions brought
about by differential fading of the three image dyes. These manifest themselves as shifts in colour balance
from highlights to shadows that are especially noticeable in a scale of neutrals; e.g. a shift from magenta to
green due to light-fading of the negative’s magenta image dye, or from yellow to blue (colour negatives) or
cyan to red (recent generations of colour negatives) due to dark-fading of the yellow or cyan dye. Generally,
the acceptable deviation from essentially equal contrast values of all three dye images varies from 0,10 to
0,15, depending on the scene content, on the inherent contrast values of the negative and associated positive
material, and on the conditions under which the print image is viewed. For instance, the tolerance of colour
shifts is much smaller with reflection prints viewed in normal surround conditions than with projected images
viewed in a dark room.
The second most consequential change is that caused by an increase in stain (discolouration of residual
colour couplers and/or residual processing chemicals, etc.) and/or fading of masking dyes. This is so because
the combined colour density of the stain and masking dyes governs the colour and density of low-density
image areas and non-image areas of the negative and, thereby, its printing filter balance. They also affect the
colour balance in high-density image areas. Changes in the d colour balance of colour negatives of more
min
than 0,05 result in appreciable changes in the colour balance of prints unless compensating adjustments are
made in the ra
...