ISO 13655:2009

INTERNATIONAL ISO
STANDARD 13655
Second edition
2009-12-15
Graphic technology — Spectral
measurement and colorimetric
computation for graphic arts images
Technologie graphique — Mesurage spectral et calcul colorimétrique
relatifs aux images dans les arts graphiques

Reference number
©
ISO 2009
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©  ISO 2009
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ii © ISO 2009 – All rights reserved

Contents Page
Foreword .iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .2
4 Spectral measurement requirements.4
5 Colorimetric computation requirements.8
6 Measurement data reporting requirements .15
Annex A (normative) Sample backing .16
Annex B (informative) Computation of the CIE 2000 total colour difference (CIEDE2000) .20
Annex C (informative) Geometry .23
Annex D (informative) Fluorescent samples.26
Annex E (informative) Improving inter-instrument agreement.27
Annex F (informative) Certified reference materials (CRMs).29
Annex G (informative) Special cases: Use of polarization .31
Annex H (normative) Test method for UV-cut conformance .32
Annex I (informative) Procedures for widening the bandwidth.34
Bibliography.36

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 13655 was prepared by Technical Committee ISO/TC 130, Graphic technology, in collaboration with
Technical Committee ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 13655:1996), which has been technically
revised in the following parts:
Clause 4, “Spectral measurement requirements”, was revised concerning the spectral power distribution of the
measurement source, the measurement of self-luminous displays, and the backing material to be used for
reflectance measurement.
Clause 5, “Colorimetric computation requirements” was amended by inclusion of the CIE 1976 a, b colour
space (see ISO 11664-4).
Some of the previous eight annexes were combined and shortened, two new annexes were introduced, and
the Bibliography was updated.
iv © ISO 2009 – All rights reserved

Introduction
There are many choices allowed when making spectral measurements and performing colorimetric
computations. The specific choices made can result in different numerical values for the same property for the
same sample. Thus, it might not be possible to make valid comparisons unless the data being compared is all
based on the same set of measurement and computational choices. The purpose of this International
Standard is to specify a limited number of such choices for the measurement and computation of the
colorimetric characteristics of graphic arts images to allow valid and comparable data to be obtained. While
this International Standard references ISO 3664, the International Standard established for viewing conditions
in graphic arts and photography, it is not expected that measured colorimetric data will provide an absolute
correlation with visual colour appearance.
When the revision of this International Standard was started, it was observed that almost all graphic arts
specimens exhibited fluorescence. In most cases, this was due to optical brightening agents contained in the
paper substrates. In rare cases, the printing inks were fluorescent. According to the recommendations of the
1996 version of this International Standard, this would have meant that the source used for the measurements
(i.e. the spectral power distribution of the sample illumination) was required to closely match CIE illuminant
D50. Yet when this revision was started, not a single colour-measuring instrument sold for the graphic arts
market provided an illumination system that closely matched CIE illuminant D50. Instead, most instruments
used incandescent lamps for light sources. The spectral power distribution of such lamps have varying
amounts of UV content. The variation in UV content between instruments could easily amount to a colour
difference of 5 ∆b* when measuring papers with a high level of optical brightening agents. Consequently, the
measurement results for unprinted paper substrates and lighter colours differed appreciably between different
instrument models. For a thorough study of fluorescence effects, see CIE Publication 163.
It has also been observed that graphic arts viewing booths vary with respect to UV content, even those that
comply with the 1996 version of ISO 3664. The practical result is that specimens that have nearly identical
measured colorimetric properties, at times will not visually match when viewed in the viewing booth, and vice
versa. Only part of such discrepancies can be attributed to fluorescence. There can also be metameric effects
due to “non-standard” observers and to instrument wavelength errors, in addition to deviations in the
measurement source away from CIE D50. Despite these other potential influences it was deemed important to
provide measurement solutions that would minimize the systematic errors introduced by the interaction of
paper fluorescence and variations in the spectral power distribution of the sample illumination. Methods for the
correction of instrument errors and procedures for reliable visual evaluation of colour images are outside of
the scope of this International Standard.
In this revision, four measurement choices are specified. Measurement condition M0 requires the source
illumination to closely match that of illuminant A; this provides consistency with existing instrumentation and
ISO 5-3. Measurement condition M1 requires the colorimetry of the specimen illumination to closely match
CIE illuminant D50. Measurement condition M2 only requires that the spectral power distribution of the
specimen illumination be provided in the wavelength range from 420 nm to at least 700 nm and have no
substantial radiation power in the wavelength range below 400 nm (often referred to as “UVCut”).
Measurement condition M3 has the same sample illumination requirements as M2 and includes a polarizing
filter in the influx and efflux portions of the optical path with their principal axes of polarization in the orthogonal
or “crossed” orientation.
The requirements of this International Standard are focused on colorimetric measurement equipment intended
for use in the graphic arts environment. Helpful information on issues such as substrate backing materials,
reporting, standardization, standard and improved colour difference metrics, fluorescence and ways to
improve the inter-instrument agreement are included. These will be useful to technical advisors of graphic arts
associations, specialized graphic arts research institutes, and practitioners with an interest in the basics of
measurement and process control.

INTERNATIONAL STANDARD ISO 13655:2009(E)

Graphic technology — Spectral measurement and colorimetric
computation for graphic arts images
1 Scope
This International Standard establishes procedures for the measurements and colorimetrical computations
appropriate to objects that reflect, transmit, or self-illuminate, including flat-panel displays. It also establishes
procedures for computation of colorimetric parameters for graphic arts images. Graphic arts includes, but is
not limited to, the preparation of material for, and volume production by, production printing processes that
include offset lithography, letterpress, flexography, gravure and screen printing.
This International Standard does not address spectral measurements appropriate to other specific application
needs, such as those used during the production of materials, e.g. printing ink, printing paper and proofing
media.
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 reference document
(including any amendments) applies.
ISO 5-2, Photography and graphic technology — Density measurements — Part 2: Geometric conditions for
transmittance density
ISO 5-4:2009, Photography and graphic technology — Density measurements — Part 4: Geometric conditions
for reflection density
ISO 3664, Graphic technology and photography — Viewing conditions
ISO 11664-1:2007, Colorimetry — Part 1: CIE standard colorimetric observers
ISO 11664-2:2007, Colorimetry — Part 2: CIE standard illuminants
ISO 11664-4:2008, Colorimetry — Part 4: CIE 1976 L*a*b* Colour space
ISO 28178, Graphic technology — Exchange format for colour and process control data using XML or ASCII
text
CIE Publication 15:2004, Colorimetry, 3rd ed.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
adopted white
spectral radiance distribution as seen by an image capture or measurement device and converted to colour
signals that are considered to be perfectly achromatic and to have an observer adaptive luminance factor of
unity, i.e. colour signals that are considered to correspond to a perfect white diffuser
[ISO 22028-1]
3.2
bandwidth
width of the spectral response function of the instrument, measured between the half-power points
3.3
calibration
set of operations that establish, under specified conditions, the relationship between values of quantities
indicated by a measuring instrument or measuring system, or values represented by a material measure or a
reference material, and the corresponding values realized by standards
[ISO/IEC Guide 99 (VIM)]
NOTE Contrary to a common usage, calibration is not the process of adjusting a measurement system such that it
produces values that are believed to be correct. Calibration permits either the assignment of values of measurands to the
indications (creating a reference table) or the decision to reset or adjust the device. Following the resetting or adjusting of
the device, a calibration needs to be verified to ensure that the new device setting(s) provide indications within the
accepted values.
3.4
CIE illuminant
illuminant defined by the International Commission on Illumination (CIE) in terms of relative spectral power
distribution
NOTE Examples are CIE illuminants A, C, and various D illuminants.
3.5
illuminant
numeric tabulation of the relative spectral distribution of the radiant (light) flux incident on the specimen
surface
NOTE The CIE defines an illuminant as “radiation with a relative spectral power distribution defined over the
wavelength range that influences object colour perception”. In everyday English the term is more widely used to mean
any kind of light falling on a body or scene. See IEC 60050-845:1987 ⎪ CIE Publication 17.4:1987 (a joint publication

between the IEC and CIE) for further information.
3.6
opacity of substrate
measure of the property that describes the ability of a specimen to hide a surface behind and in contact with it
NOTE The numerical value of opacity as used in this International Standard is 100 times the ratio of the luminous
reflectance factor of the substrate over black backing (as defined in A.2) to the luminous reflectance factor over white
backing (as defined in A.3). This is different from the measurement of opacity used by the paper manufacturing industry
and defined in ISO 2471.
3.7
opaque substrate
substrate whose opacity, measured according to A.3, is 0,99 or greater
2 © ISO 2009 – All rights reserved

3.8
transparent substrate
clear material having minimal absorption or scattering of transmitted visible light
EXAMPLE Clear packaging film.
3.9
reflectance factor
ratio of the radiant or luminous flux reflected in the directions delimited by the given cone to that reflected in
the same directions by a perfect reflecting diffuser identically irradiated or illuminated
[IEC 60050-845:1987 ⎪ CIE Publication 17.4:1987]
NOTE 1 The industry commonly uses the term reflectance rather than reflectance factor.
NOTE 2 It is important to specify the geometry that establishes the given conditions of measurement. See Annex C.
3.10
specimen backing
material placed behind and in contact with the specimen during measurement
NOTE For this International Standard this can be either white or black.
3.11
spectroradiometer
instrument for measuring radiometric quantities in narrow wavelength intervals over a given spectral region
[IEC 60050-845:1987 ⎪ CIE Publication 17.4:1987]
3.12
telespectroradiometer
spectroradiometer that uses an optical relay component to allow measurements to be made at a distance from
the specimen
3.13
transmittance
〈for incident radiation of a given spectral composition, polarization, and geometrical distribution〉 ratio of the
transmitted radiant or luminous flux to the incident flux in the given conditions
[IEC 60050-845:1987 ⎪ CIE Publication 17.4:1987]
NOTE It is important to specify the geometry that establishes the given conditions of measurement. See Annex C.
3.14
transmittance factor
ratio of flux transmitted by a specimen in a given optical system to the flux transmitted when the specimen is
removed from the sampling aperture
NOTE For example, this is the case when radiation penetrating a slide situated in a projector and reaching a screen
is compared to the radiation when the slide is removed from a projector and only an empty slide mount is in the projector.
3.15
polarizing filter
filter that converts randomly polarized light into linearly polarized light while absorbing all radiation with
wavelengths less than 400 nm
4 Spectral measurement requirements
4.1 Instrument standardization and adjustment
The measurement device or system shall be verified (standardized and possibly adjusted) in accordance with
its manufacturer's instructions. See also Annexes E and F.
NOTE 1 ISO 15790 defines the use of a certified reference material (CRM) to check calibration of a measurement
system. It also provides additional information relating to the use of CRMs, the determination of combined standard
uncertainty and data reporting.
NOTE 2 Where multiple instruments are used for measurement, there can be differences in the resulting data due to
the individual characteristics of the instruments and variations in measurement conditions. Annexes E and F provide
information on the improvement of inter-instrument agreement and the use of certified reference materials.
4.2 Reflectance factor measurement
4.2.1 Wavelength range, wavelength interval and bandwidth
The data should be measured from 360 nm to 780 nm and shall be measured from 400 nm to 700 nm,
inclusive. Data should be measured at 10 nm intervals with a spectral response function that is triangular with
a 10 nm bandwidth at the half-power point. Where data is measured at other intervals and bandwidths, which
shall not exceed 20 nm (interval and bandwidth), estimated data shall be reported at 10 nm intervals, and the
data shall be adjusted to simulate measurement data obtained with a triangular spectral response function
with a 10 nm bandwidth.
4.2.2 Illumination requirements and measurement conditions
4.2.2.1 Measurement condition M0
Historically, many spectrophotometers used in the graphic arts have used an incandescent lamp with a
relative spectral power distribution that is close to CIE standard illuminant A, as defined in ISO 11664-2. In
addition, this illuminant has historically been required for the measuring of density. M0 is provided to allow the
identification of data measured using existing instrumentation or instrumentation optimized for photographic
density measurements (see ISO 5-3).
The relative spectral power distribution of the flux incident on the specimen surface should conform to CIE
illuminant A (corresponding to a correlated colour temperature of 2 856 K). In practical instruments, the
relative spectral power distribution of the flux incident on the specimen surface should conform to a correlated
colour temperature of 2 856 K ± 100 K.
Because the specification of correlated colour temperature does not define UV, the UV content is not
controlled under M0, and it is therefore recommended that M1 be used when there is the need to interchange
data on sheets that exhibit fluorescence. When instruments meeting M1 are not available and relative data is
sufficient for process control or other data exchange applications, M0 instruments of like manufacturer and
model provide a viable alternative.
4.2.2.2 Measurement condition M1
To minimize the variations in measurement results between instruments due to fluorescence (by optical
brighteners in the substrate and/or fluorescence of the printing and/or proofing colorants), the spectral power
distribution of the light flux incident on the specimen surface for the measurement should match CIE illuminant
D50.
NOTE 1 Because ISO 3664 also specifies the use of D50, this will improve the consistency between measurement
results made under condition M1 and visual assessment in viewing booths that meet the requirements of ISO 3664.
NOTE 2 For material testing as defined in ISO 5631-3, the UV-content of the illumination on the test piece has been
adjusted to conform to that of CIE illuminant C. Therefore measurements conforming to ISO 5631-3 might not be
compatible with measurements conforming to this International Standard.
4 © ISO 2009 – All rights reserved

There are two methods to achieve conformance to condition M1.
1) The spectral power distribution of the measurement source at the sample plane should match CIE
illuminant D50. It shall conform to the UV range metamerism index specified for viewing condition P1
of ISO 3664. This method is to be used when both luminescent colorants and optical brighteners are
of concern.
2) A spectral match of the spectral power distribution of the measurement source in the range from
400 nm to 700 nm at the sample plane is not required if a compensation method is used with a
controlled adjustment of the radiant power in the UV spectral region below 400 nm. This can be done
by active adjustment of the relative power in this range with respect to a calibrated standard for D50.
This compensation aims only to correct the effects of fluorescence of optical brighteners in the
substrate. The spectral power distribution in the range from 400 nm to 700 nm shall be continuous.
The instrument manufacturer should supply a representative spectral power distribution of the measurement
source at the sample plane with the instrument documentation.
It should be noted that for the proper evaluation of materials with optical brightening agents, it is important that
the ratio of the power in the region between 300 nm and 400 nm and the power in the region between 400 nm
to 500 nm be very similar to the ratio of D50 between these same regions.
The conformance of M1 measurement condition shall be judged indirectly by measuring a set of certified
reference materials (CRMs) (see Annex F) that includes a specimen material with a high concentration of
optical brighteners where the difference in CIE b* measured with and without UV energy incident on the
specimen material is greater than 3. Where the indicated values, including the combined uncertainty, are
within the specified tolerances of the CRM, the instrument can be considered to be in conformance with this
International Standard.
NOTE 3 Annex D provides information on fluorescence and techniques to test for its presence.
NOTE 4 In cases where a printing ink fluoresces and accurate colorimetric data is required, measurement condition M1
is the only choice. However, in many situations, instruments meeting M1 are not available and relative data is sufficient for
process control or other data exchange applications. In such situations, comparison of data from instruments of like
manufacturer and model provides a viable alternative.
4.2.2.3 Measurement condition M2
To exclude variations in measurement results between instruments due to fluorescence of optical brightening
agents in the substrate surface, the spectral power distribution of the measurement source at the sample
plane shall only contain substantial radiation power in the wavelength range above 400 nm. This may be
accomplished through appropriate design of the source or through the addition of a filter between the source
and the specimen.
The visible fluorescence of optical brightener agents in paper is typically excited in the UV range from 300 nm
up to 410 nm. In order to eliminate completely any fluorescence excitation of optical brighteners, the optimum
cut-off wavelength for the UV component would be 420 nm. However, it is desirable also to measure
reflectance factors at 400 nm and 410 nm. Therefore, for each instrument type, the optimum trade-off has to
be found between a sufficient suppression of residual fluorescent excitation and a reasonable signal-to-noise
ratio of the measurement signal.
NOTE 1 For common spectrophotometers with a tungsten light source, a typical UV-cut filter will have the following
transmittance characteristics:
⎯ greater than 0,85 in the visible range above 420 nm;
⎯ less than 0,50 at 410 nm;
⎯ less than 0,10 at 400 nm;
⎯ less than 0,01 at 395 nm.
Appropriate suppression of the UV portion of the spectral power distribution of the flux at the sample plane
shall be verified using the test procedure of Annex H.
For measurement condition M2, the source is not explicitly specified. However, it shall be continuous in the
wavelength range from 420 nm to at least 700 nm. The radiative power in each wavelength interval shall be
sufficiently high, in order to enable precise calibration and repeatable measurement results according to the
instrument specifications.
NOTE 2 The utility of M2 data can be determined by first considering whether the substrate of the samples to be
measured contains any optical brightening agents. If it does not, measurement conditions M0, M1 and M2 will ideally
produce the same results. In this case, the primary differences will be due to specific differences in instruments.
NOTE 3 Annex D provides information on fluorescence and techniques to test for its presence.
4.2.2.4 Measurement condition M3
For use in the special cases detailed in informative Annex G, an instrument may be equipped with a polarizing
filter in order to suppress the influence of first-surface reflection on the colour co-ordinates. An instrument
fitted with a polarizing filter shall also meet the requirements of 4.2.2.3. Using the test method of ISO 5-
4:2009, Annex D, as modified below, the gloss suppression factors shall be determined for CIE X, CIE Y,
CIE Z; none of which shall be lower than 50.
When using the test method of ISO 5-4 to evaluate an instrument providing colour co-ordinates, substitute
“measured value reaches a maximum” for “reflection density reaches a minimum”. The equation becomes:
X
P =
X
where:
P is the gloss suppression factor;
X is the value measured without the polarizing filter;
X is the value measured with the polarizing filter.
The gloss suppression factor is computed in a similar manner for CIE Y and CIE Z.
NOTE For directional and uniplanar measurement geometries, which are not specified by this International Standard,
the polarization vectors of the illumination and measurement channels need to be either parallel or perpendicular to the
plane of incidence of the test object.
4.2.3 Sample backing material
The specimen shall be backed by either a black or a white material that conforms to A.2 or A.3, respectively.
Where samples being measured by reflection are transparent, the backing used shall be white and the
method shown in A.5 may be used to correct such measurements to an absolute reference.
NOTE For guidance concerning which sample backing material to use, refer to application standards such as those
from the ISO 12647 series of process control standards.
4.2.4 Measurement geometry
The measurement geometry shall be (45°:0°) or (0°:45°), annular or circular; see Annex C. It shall also
conform to the geometric conditions defined in ISO 5-4 and shall meet the requirement that the realized
boundary of the larger of the illuminator region and the receiver region shall be outside the boundary of the
smaller by at least 0,5 mm, as specified for small sampling apertures. While being measured the sample shall
lie on a flat surface. The instrument base and the sample surface shall lie in the same plane.
NOTE 1 For angles and nomenclature for geometries, see C.1.1.
6 © ISO 2009 – All rights reserved

NOTE 2 The use of (45°:0°) or (0°:45°) geometry will not always adequately address variations in all surface
characteristics. Other instrumentation might be used to detect specific characteristics such as “bronzing”.
NOTE 3 Annex C provides further information on minimum sampling aperture size.
4.2.5 Data reporting
Reflectance factor shall be reported to the nearest 0,001 relative to a perfect reflecting diffuser having a
reflectance factor of 1,000 at all wavelengths. This data shall be reported as either reflectance factor or
percent reflectance factor (i.e. reflectance factor multiplied by 100). For non-opaque sample substrate
materials, the CIEXYZ data for the unprinted substrate material shall be reported for both black and white
backing, so that a white/black conversion, as described in Annex A, can be carried out whenever necessary.
See also Clause 6.
4.3 Transmittance factor measurement
4.3.1 Wavelength range, wavelength interval and bandwidth
The data should be measured from 360 nm to 780 nm and shall be measured from 400 nm to 700 nm,
inclusive. Data should be measured at 10 nm intervals where the spectral response function is triangular with
a 10 nm bandwidth at the half-power point. Where data is measured at other intervals and bandwidths, data
shall be computed that estimates the values that would have been obtained from measurements made at
10 nm intervals with a triangular spectral response function with a 10 nm bandwidth at the half-power point.
Measurement data shall not be collected at intervals greater than 20 nm.
Where measurement data is collected at intervals of less than 10 nm, it may be widened using the method of
Annex I.
4.3.2 Measurement geometry
Measurement geometry shall be normal:diffuse (0:d) or diffuse:normal (d:0). It shall conform to the geometric
conditions defined in ISO 5-2.
NOTE For more information, see C.2.
4.3.3 Resolution and data reporting
Transmittance factor shall be reported to the nearest 0,000 1 relative to a perfect transmitting diffuser having a
transmittance factor of 1,000 0 at all wavelengths. This data may be reported as either a decimal value or as a
percentage. The fact that an opal geometry was used shall also be reported. See also Clause 6.
4.4 Self-luminous displays (spectral radiance) measurement
4.4.1 Wavelength range, wavelength interval and bandwidth
Data should be measured at intervals of 5 nm or less with a triangular spectral response function and a
half-power point bandwidth equal to the measurement interval. Data shall be measured at 10 nm intervals
where the spectral response function is triangular with a 10 nm bandwidth at the half-power point.
NOTE CIE recommends (CIE Publication DS 014-3) that the standard method of calculating tristimulus values
(CIE X, CIE Y and CIE Z) use 1 nm intervals. However, that same document also notes that, in some cases, the standard
method cannot be used because the colour stimulus function or relative colour stimulus function is not available over the
full range of 360 nm to 830 nm in 1 nm intervals. If it is demonstrated that the resulting errors are insignificant for the
purpose of the user, tristimulus values can be calculated by numerical summation from 380 nm to 780 nm at wavelength
intervals, delta lambda, equal to 5 nm using colour matching functions x (lambda), y (lambda), z (lambda) defined in
ISO 11664-1.
4.4.2 Measurement geometry
4.4.2.1 General
The spectral data may be measured either with a spectroradiometer in contact with the display surface, or a
telespectroradiometer placed at a typical viewer position. The measurements shall be carried out in the
direction of the normal to the display surface. The area measured for each sample shall have a diameter of no
less than 4 mm and shall contain at least 150 pixels.
For measurements made with a spectroradiometer or telespectroradiometer, the angular width of the sensing
cone, i.e. the angle region over which the efflux is sensed by the receiver, shall not be more than a half angle
of 5° and should not be more than a half angle of 2,5°.
4.4.2.2 Viewer position
These measurements will be specific to the viewing conditions. Generally, the ambient illumination should
conform to ISO 3664. However, when the ambient illumination to be used in practice is known, it may be
desirable to perform the measurements with this illumination. The illuminance level and chromaticity of the
ambient illumination, as measured at the display faceplate, should be reported. Care should be taken to
minimize reflection of the ambient illumination from the display faceplate towards the measurement device.
Specular reflections should be avoided.
4.4.2.3 Contact
These measurements should be performed with the display in the dark. This can be achieved by covering the
display and measurement device or by darkening the room. Care should be taken to ensure that only radiation
from the sample area is measured.
NOTE Contact measurements are used to characterize the display only; they are independent of the ambient
illumination. If contact measurements are performed but viewer position measurements are desired, it is necessary to add
the veiling glare that would be observed by the viewer to obtain measurements equivalent to those obtained from the
viewer position.
4.4.3 Polarization
The measurement shall be independent of polarization effects when the following test is performed: Rotate the
instrument around the normal on the display surface. The resulting data points in the CIE xy chromaticity
coordinates shall fit into a circle of 0,002 radius. The deviation of luminance of each measurement shall be
less than 1 % from the average luminance.
4.4.4 Resolution and data reporting
The measured efflux from the display surface with the small angular sensing cone corresponds to the spectral
radiance. The radiance values of the spectrum shall be reported in units of W/(m /sr/nm) at equally spaced
wavelength intervals of 1 nm, 5 nm or 10 nm over the defined wavelength range. Values derived from the
radiance spectrum according to 5.2, such as CIE X, CIE Y and CIE Z or CIE x, CIE y and CIE L, may be
reported. The luminance CIE L shall be reported in cd/m . See also Clause 6.
The uncertainty of the instrument shall be defined for the measurement of chromaticity coordinates of a typical
monitor white in accordance with ISO 3664 (short-term repeatability, 75 cd/m , D65). The uncertainty of the
CIE xy chromaticity coordinates under these conditions shall be within the radius of < 0,002. The deviation of
luminance of each measurement shall be less than 1 % from the average luminance. See also Clause 6.
5 Colorimetric computation requirements
5.1 Calculation of tristimulus values for reflective and transmissive samples
To provide consistency with graphic arts viewing conditions, defined in ISO 3664, calculated tristimulus values
shall be based on CIE illuminant D50 and the CIE 1931 standard colorimetric observer (often referred to as
8 © ISO 2009 – All rights reserved

the 2 ° standard observer), as defined in ISO 11664-1. Computation shall be at 10 nm intervals. Factors
representing the product of CIE illuminant D50 and the 2 ° standard observer data, to be used for weighting
spectral reflectance and transmittance data, shall be those given in Table 1 for 10 nm intervals, as taken, with
permission, from ASTM E 308:2006.
NOTE 1 The 2 ° standard observer is preferred over the 10 ° standard observer, because it more closely matches the
conditions under which image detail in printed material is being viewed.
NOTE 2 The weights given in Table 1 are based on triangular bandpass characteristics as referred to in 4.3.1.
NOTE 3 Adding the values of the weights from 360 nm to 780 nm in Table 1 does not give a sum equal to the values
for X , Y and Z . This is because the writers of ASTM E 308:2006 computed X , Y and Z to greater precision than given
n n n n n n
by the summation of the table values. The check sums in Table 1 are provided for use in data transcription validation.
The computation of the CIE X, CIE Y and CIE Z values for reflective specimen data shall be as follows:
XR=×()λλW ( ) (1)
X
∑
λ = 360
YR=×()λλW ( ) (2)
∑ Y
λ = 360
ZR=×()λλW () (3)
Z
∑
λ = 360
where
λ is the wavelength, in nanometres (nm);
R(λ) is the reflectance factor at wavelength λ;
W (λ) is the weighting factor at wavelength λ for CIE X;
X
W (λ) is the weighting factor at wavelength λ for CIE Y;
Y
W (λ) is the weighting factor at wavelength λ for CIE Z.
Z
The computation of the CIE X, CIE Y and CIE Z values for transmission sample data shall be as follows:
XT=×()λλW () (4)
∑ X
λ = 360
YT=×()λλW ( ) (5)
∑ Y
λ = 360
ZT=×()λλW ( ) (6)
∑ Z
λ = 360
where
λ is the wavelength, in nanometres (nm);
T(λ) is the transmittance factor at wavelength λ;
W (λ) is the weighting factor at wavelength λ for CIE X;
X
W (λ) is the weighting factor at wavelength λ for CIE Y;
Y
W (λ) is the weighting factor at wavelength λ for CIE Z.
Z
If the measured spectral data begin at a wavelength greater than 360 nm, then all the weighting values in
Table 1 for wavelengths less than the first measured wavelength shall be summed and added to the weighting
value for the first wavelength measured. If the last measured spectral data point is at a wavelength less than
780 nm, then all the weighting values in Table 1 for wavelengths greater than the last measured wavelength
shall be summed and added to the weighting value for the last measured wavelength.
NOTE 4 This procedure is consistent with ASTM E 308:2006.
EXAMPLE Reflectance data are provided from 400 nm to 700 nm at 10 nm bandwidth and interval. First, sum the
weights contained in Table 1 from 360 nm to 390 nm and from 710 nm to 780 nm for W (λ), W (λ), and W (λ) individually
X Y Z
and add them to the values for 400 nm and 700 nm, respectively. Enter the spectral and weight data into a spreadsheet or
similar program and carry out the wavelength-wise multiplications. The results of that summation are the values for CIE X;
for CIE Y, for CIE Z.
Table 1 — Spectral weights, W(λ), for illuminant D50 and the 2° observer for calculating tristimulus
from data at 10 nm intervals
Spectral weights
Wavelength
(nm)
a a a
W (λ) W (λ) W (λ)
X Y Z
360 0,000 0,000 0,001
370 0,001 0,000 0,005
380 0,003 0,000 0,013
390 0,012 0,000 0,057
400 0,060 0,002 0,285
410 0,234 0,006 1,113
420 0,775 0,023 3,723
430 1,610 0,066 7,862
440 2,453 0,162 12,309
450 2,777 0,313 14,647
460 2,500 0,514 14,346
470 1,717 0,798 11,299
480 0,861 1,239 7,309
490 0,283 1,839 4,128
500 0,040 2,948 2,466
510 0,088 4,632 1,447
520 0,593 6,587 0,736
530 1,590 8,308 0,401
540 2,799 9,197 0,196
550 4,207 9,650 0,085
560 5,657 9,471 0,037
570 7,132 8,902 0,020
580 8,540 8,112 0,015
590 9,255 6,829 0,010
10 © ISO 2009 – All rights reserved

Table 1 (continued)
Spectral weights
Wavelength
(nm)
a a a
W (λ) W (λ) W (λ)
X Y Z
600 9,835 5,838 0,007
610 9,469 4,753 0,004
620 8,009 3,573 0,002
630 5,926 2,443 0,001
640 4,171 1,629 0,000
650 2,609 0,984 0,000
660 1,541 0,570 0,000
670 0,855 0,313 0,000
680 0,434 0,158 0,000
690 0,194 0,070 0,000
700 0,097 0,035 0,000
710 0,050 0,018 0,000
720 0,022 0,008 0,000
730 0,012 0,004 0,000
740 0,006 0,002 0,000
750 0,002 0,001 0,000
760 0,001 0,000 0,000
770 0,001 0,000 0,000
780 0,000 0,000 0,000
Check sums 96,421 99,997 82,524
White point X = 96,422 Y = 100,000 Z = 82,521
n n n
a
The values of these weighting functions are extracted, with permission, from Table 5.9 of ASTM E 308:2006.
5.2 Calculation of tristimulus values for self-luminous displays
The tristimulus values are obtained by discrete summation of the following products:
Xk=∆S ()λλx( )λ (7)
∑ n
λ=360
Yk=∆S ()λλy() λ (8)
∑ n
λ=360
Zk=∆S ()λλz()λ (9)
∑ n
λ=360
where
λ is the wavelength, in nanometres (nm);
S (λ) is the measured spectral power distribution, in W/(m /sr/nm);
n
xy()λλ, () and z()λ are the colour matching functions of the CIE 1931 standard colorimetric observer
(see CIE Publication 15:2004);
∆λ is the wavelength sampling interval, corresponding to the instrument or the
adjusted bandwidth;
k is a conversion factor from watts to lumens and its value is 683 lm/W.
If the bandwidth and wavelength interval of the available data is 1 nm, the pertinent colour matching function
of ISO 11664-1 with data at 1 nm intervals shall be used for insertion into Equations (7) to (9).
Where the available data is at a bandwidth and wavelength interval other than 1 nm or 5 nm, values of the
radiance spectrum for 5 nm intervals shall be calculated from the measurement values using one of the
following steps.
⎯ If the available data is at a bandwidth and wavelength interval greater than 1 nm but less than 5 nm,
values of the radiance spectrum at 5 nm intervals shall be calculated from the measurement values using
the method of Annex I.
⎯ If the available data is at a bandwidth and wavelength interval greater than 5 nm but less than or equal to
10 nm, data interpolation shall be performed to provide values of the radiance spectrum at 5 nm intervals
using one of the interpolation procedures of CIE Publication 15:2004.
Relative values X , Y and Z shall be obtained as follows:
r r r
X = 100X/Y (10)
r w
Y = 100Y/Y (11)
r w
Z = 100Z/Y (12)
r w
where
X , Y and Z are the values relative to the adopted white;
r r r
Y is the Y value of the adopted white.
w
NOTE X , Y and Z are the values of the measured area relative to the adopted white. In many cases, the adopted
r r r
white will be selected to be the display white point; however, in some cases, it will be selected to be lower or higher in
luminance. For example, if a display is used for soft proofing, the display white point might be set to match the paper white,
in which case the adopted white CIE Y value will be higher than that of the display white point. In the case of a high
dynamic range display, the adopted white CIE Y value might be selected to be much lower than that of the display white
point, to allow above white colours to be reproduced on the display.
From the CIE 1931 tristimulus values, the chromaticity co-ordinates x, y and the CIE 1976 u', v' uniform
chromaticity co-ordinates shall be calculated using
...