ISO 13655:2009
(Main)Graphic technology — Spectral measurement and colorimetric computation for graphic arts images
Graphic technology — Spectral measurement and colorimetric computation for graphic arts images
ISO 13655:2009 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. ISO 13655:2009 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.
Technologie graphique — Mesurage spectral et calcul colorimétrique relatifs aux images dans les arts graphiques
Grafična tehnologija - Spektrometrija in kolorimetrični izračuni za grafične upodobitve
Ta mednarodni standard vzpostavlja postopke za merjenje in kolorimetrične izračune, ki ustrezajo predmetom, ki odsevajo, oddajajo ali sami osvetljujejo, vključno s ploščatimi zasloni. Vzpostavlja tudi postopke za izračun kolorimetričnih parametrov za grafične upodobitve. Grafične upodobitve vključujejo, a niso omejene na pripravo materiala in količinsko proizvodnjo za procese proizvodnega tiskanja, ki vključujejo ofsetno litografijo, knjigotisk, fleksografijo, globoki tisk in sitotisk. Ta mednarodni standard ne obravnava spektralnih meritev za potrebe drugih načinov uporabe, kot so tisti, ki se uporabljajo med proizvodnjo materialov, npr. barve za tiskanje, papirja za tiskanje in sredstev za poskusno tiskanje.
General Information
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Buy Standard
Standards Content (Sample)
SLOVENSKI STANDARD
SIST ISO 13655:2010
01-maj-2010
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SIST ISO 13655:1997
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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
Ta slovenski standard je istoveten z: ISO 13655:2009
ICS:
17.180.20 Barve in merjenje svetlobe Colours and measurement of
light
37.100.01 *UDILþQDWHKQRORJLMDQD Graphic technology in
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SIST ISO 13655:2010 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST ISO 13655:2010
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SIST ISO 13655:2010
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 13655:2009(E)
©
ISO 2009
---------------------- Page: 3 ----------------------
SIST ISO 13655:2010
ISO 13655:2009(E)
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.
COPYRIGHT PROTECTED DOCUMENT
© ISO 2009
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 2009 – All rights reserved
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SIST ISO 13655:2010
ISO 13655:2009(E)
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
© ISO 2009 – All rights reserved iii
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SIST ISO 13655:2010
ISO 13655:2009(E)
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
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SIST ISO 13655:2010
ISO 13655:2009(E)
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.
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SIST ISO 13655:2010
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SIST ISO 13655:2010
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.
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SIST ISO 13655:2010
ISO 13655:2009(E)
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
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SIST ISO 13655:2010
ISO 13655:2009(E)
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
© ISO 2009 – All rights reserved 3
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SIST ISO 13655:2010
ISO 13655:2009(E)
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.
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SIST ISO 13655:2010
ISO 13655:2009(E)
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.
© ISO 2009 – All rights reserved 5
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SIST ISO 13655:2010
ISO 13655:2009(E)
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
2
P =
X
1
where:
P is the gloss suppression factor;
X is the value measured without the polarizing filter;
1
X is the value measured with the polarizing filter.
2
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 t
...
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 13655:2009(E)
©
ISO 2009
---------------------- Page: 1 ----------------------
ISO 13655:2009(E)
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.
COPYRIGHT PROTECTED DOCUMENT
© ISO 2009
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 2009 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 13655:2009(E)
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
© ISO 2009 – All rights reserved iii
---------------------- Page: 3 ----------------------
ISO 13655:2009(E)
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
---------------------- Page: 4 ----------------------
ISO 13655:2009(E)
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.
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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.
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ISO 13655:2009(E)
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
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ISO 13655:2009(E)
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
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ISO 13655:2009(E)
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.
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ISO 13655:2009(E)
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.
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ISO 13655:2009(E)
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
2
P =
X
1
where:
P is the gloss suppression factor;
X is the value measured without the polarizing filter;
1
X is the value measured with the polarizing filter.
2
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
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