SIST ISO 15790:2010

INTERNATIONAL ISO
STANDARD 15790
First edition
2004-01-15

Graphic technology and photography —
Certified reference materials for reflection
and transmission metrology —
Documentation and procedures for use,
including determination of combined
standard uncertainty
Technologie graphique et photographie — Matériaux de référence
certifiés pour la métrologie par réflexion et transmission —
Documentation et procédures à utiliser, y compris la détermination
d'une incertitude normale combinée




Reference number
ISO 15790:2004(E)
©
ISO 2004

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ISO 15790:2004(E)
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ISO 15790:2004(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions. 1
3.2 Symbols . 4
4 General guidelines for CRM application. 4
5 Required documentation for CRMs. 5
5.1 Identification of CRM . 5
5.2 Reporting of CRM reference values . 5
5.3 Traceability . 5
5.4 Cautions for use. 5
5.5 Care and handling of CRMs . 6
5.6 Use and procedures. 6
6 Procedures related to the use of CRMs. 6
6.1 Determination of combined standard uncertainty. 6
6.2 Computation of expanded uncertainty . 9
6.3 Calibration of a measurement system . 9
7 Reporting measurement results and their uncertainty . 10
Annex A (informative) Characteristics of CRMs. 12
Annex B (informative) Example of computation of combined standard uncertainty
(with component sensitivities equally weighted) . 13
Annex C (informative) Examples of computation of combined standard uncertainty
(including weighting of component sensitivities) . 15
Bibliography . 19

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ISO 15790:2004(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 15790 was prepared by Technical Committee ISO/TC 130, Graphic technology.

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ISO 15790:2004(E)
Introduction
[1]
The International Organization for Standardization (ISO), in ISO Guide 30 , defines a certified reference
material (CRM) as a “reference material, accompanied by a certificate, one or more of whose property values
are certified by a procedure which establishes traceability to an accurate realization of the unit in which the
property values are expressed, and for which each certified value is accompanied by an uncertainty at a
stated level of confidence”. Thus, CRMs are well-characterized materials with values traceable to stated
references (see 3.1.12). They may be used to calibrate or to determine the performance characteristics of
measurement systems in order to facilitate the exchange of data and to assist in quality control. Their use will
help to assure the long-term adequacy and integrity of the measurement and quality control processes.
Densitometers, colorimeters and spectrophotometers are widely used to make measurements for quality and
process control in the graphic arts, photographic and other imaging industries. The intent of this International
Standard is to establish documentation requirements that describe characteristics of reflection and
transmission certified reference materials that may be used for verifying performance of these instruments. In
many areas (e.g. cyan, magenta, yellow colorants) there are no readily available reference materials that are
traceable to international and national standards. This International Standard can still provide guidance in
such circumstances by showing how to determine the reproducibility of the results of measurements, even in
the absence of CRMs.
Although the calibration reference materials provided with many reflection and transmission instruments used
in graphic arts and photography are not identified as CRMs, they could often meet the requirements as such.
Instrument manufacturers are encouraged to document the characteristics of their calibration materials as
CRMs where appropriate.
This International Standard describes practical procedures to determine values that represent components of
the uncertainty of measurements for the graphic arts, photography and other image-technology industries. A
computational procedure is also provided to combine these components to determine “combined standard
uncertainty” (see 3.1.3). A more rigorous and detailed approach is described in the Guide to the expression of
uncertainty in measurement.
Furthermore, general procedures are identified for the use and maintenance of these certified reference
materials. Through use of this International Standard, manufacturers of CRMs can provide consistent general-
use information for the verification of measurement-system performance described above. This International
Standard lists appropriate documentation that should accompany CRMs, including the following:
a) areas where a CRM is and is not applicable;
b) physical characteristics of CRMs for density, colour values, uniformity, etc. (see Annex A);
c) traceability of CRM values to stated reference;
d) expected lifetime of a CRM;
e) care and storage of a CRM;
f) general procedures on how to use a CRM.
Other useful documents providing guidance in metrology and the uncertainty of measurement can be found in
the Bibliography.
This International Standard provides guidance and is a resource for manufacturers and users of CRMs. Using
CRMs as part of quality assurance activities is essential for verification and calibration of measurement
systems and can increase confidence in data obtained from measurement instruments. It provides a useful
[15] [22]
tool in support of ISO 9001 registration and ISO/IEC 17025 accreditation by providing information
relevant to graphic technology, photographic and other imaging industries.
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INTERNATIONAL STANDARD ISO 15790:2004(E)

Graphic technology and photography — Certified reference
materials for reflection and transmission metrology —
Documentation and procedures for use, including
determination of combined standard uncertainty
1 Scope
This International Standard specifies the documentation requirements for certified reference materials (CRMs),
procedures for the use of CRMs, and procedures for the computation and reporting of the combined standard
uncertainty of reflectance and transmittance measurement systems used in graphic arts, photographic and
other imaging industries.
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.
Guide to the expression of uncertainty in measurement, published jointly by BIPM/IEC/IFCC/ISO/IUPAC/
IUPAP/OIML, 1995
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1.1
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
[2]
[adapted from International vocabulary of basic and general terms in metrology]
NOTE Contrary to a common misconception, 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 is normally repeated to ensure that the new device setting(s) provide indications
within the accepted ranges.
3.1.2
certified reference material
CRM
reference material, accompanied by a certificate, one or more of whose property values are certified by a
procedure which establishes traceability to an accurate realization of the unit in which the property values are
expressed, and for which each certified value is accompanied by an uncertainty at a stated level of confidence
[1]
[ISO Guide 30]
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ISO 15790:2004(E)
3.1.3
combined standard uncertainty
u
c
standard uncertainty of the result of a measurement when that result is obtained from the values of a number
of other quantities, equal to the positive square root of a sum of terms, the terms being the variances or
covariances of these other quantities weighted according to how the measurement result varies with changes
in these quantities
[Guide to the expression of uncertainty in measurement]
3.1.4
coverage factor
k
numerical factor used as a multiplier of the combined standard uncertainty in order to obtain an expanded
uncertainty
[Guide to the expression of uncertainty in measurement]
3.1.5
CRM reference value
value of the certified property of a CRM, reported in the documentation supplied with it
3.1.6
expanded uncertainty
U
quantity defining an interval about the result of a measurement that may be expected to encompass a large
fraction of the distribution of values that could reasonably be attributed to the measurand
[Guide to the expression of uncertainty in measurement]
NOTE Expanded uncertainty is the product of the combined standard uncertainty, u , and the chosen coverage
c
factor, k.
3.1.7
experimental standard deviation
s
quantity characterizing the dispersion of the results for a series of n measurements of the same measurand
and given by the following formula:
n
2
()xx−
i
∑
i=1
s=
n −1
where
n is the number of measurements;
x is the arithmetic mean of the n results considered;
x is the result of the i th measurement.
i
[2]
[adapted from International vocabulary of basic and general terms in metrology]
[7]
NOTE According to ISO 3534-1:1993 , 2.34, the standard deviation is the positive square root of the variance.
3.1.8
manufacturer's calibration reference material
physical device or material, certified or non-certified, supplied by the instrument manufacturer, which may be
used to calibrate a specific instrument
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ISO 15790:2004(E)
3.1.9
measurand
particular quantity subject to measurement
[2]
[International vocabulary of basic and general terms in metrology]
EXAMPLES Density, lightness, transmittance, and reflectance factor.
3.1.10
reference material
material or substance one or more of whose property values are sufficiently homogeneous and well
established to be used for the calibration of an apparatus, for the assessment of a measurement method, or
for assigning values to materials
[1]
[ISO Guide 30]
3.1.11
reproducibility
〈results of measurements〉ҏ closeness of the agreement between the results of measurements of the same
measurand carried out under changed conditions of measurement
[2]
[adapted from International vocabulary of basic and general terms in metrology]
NOTE Reproducibility is distinct from repeatability. Repeatability is the closeness of the agreement between the
results of successive measurements of the same measurand carried out under the same conditions, e.g. using a single
instrument, by the same observer, in the same location and in a short period of time.
3.1.12
traceability
property of the result of a measurement or the value of a standard whereby it can be related to stated
references, usually national or international standards, through an unbroken chain of comparisons, all having
stated uncertainties
[2]
[adapted from International vocabulary of basic and general terms in metrology]
3.1.13
uncertainty of measurement
parameter, associated with the result of a measurement, that characterizes the dispersion of the values that
could reasonably be attributed to the measurand
[2]
[adapted from International vocabulary of basic and general terms in metrology]
NOTE 1 For the purposes of this International Standard, each component of the uncertainty is assumed to have a
normal distribution. The concepts and rules for cases where this assumption may not be valid are considered in the Guide
to the expression of uncertainty in measurement.
NOTE 2 The result of a measurement is only an approximation or estimate of the value of the measurand and thus is
complete only when accompanied by a statement of the uncertainty of that estimate (see 3.1.3 and 6.1.7).
3.1.14
uncertainty of CRM
U
CRM
measurement uncertainty that is attributed to the reported value of a CRM in the certificate supplied with it,
often expressed as an expanded uncertainty with a coverage factor
3.1.15
variance
a measure of dispersion, which is the sum of the squared deviations of observations from their average
divided by one less than the number of observations
[7]
[adapted from ISO 3534-1:1993]
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ISO 15790:2004(E)
3.2 Symbols
b maximum value of the known correction
max
D reflection density
R
k coverage factor
s experimental standard deviation
S influx spectrum based on CIE illuminant A
A
T status T red response
R
U expanded uncertainty
u combined standard uncertainty
c
u uncertainty of reproducibility of results of measurements
r
U uncertainty of CRM reference values
CRM
U maximum expanded uncertainty
max
Y(t) measurand function
4 General guidelines for CRM application
CRMs may be used for several purposes:
 to verify the accuracy of a measurement device or system;
 to verify measurement system performance on a routine basis;
 to estimate the uncertainty of reported measurements;
 to improve agreement between/among independently calibrated measurement systems and to determine
correlation.
The manufacturer's calibration reference material normally includes properties and values that are designed to
work with a specific instrument and for a specific application. A manufacturer's calibration reference material is
a CRM if it provides the documentation conforming to 5.1 to 5.3 of this International Standard.
A CRM that is not the instrument manufacturer's calibration reference material should not arbitrarily be used
for physically readjusting the instrument. The user of a CRM should first contact the instrument manufacturer
regarding the use of a specific CRM for that purpose.
A CRM is usually designed to verify some but not all attributes of a measurement system. It is, therefore,
important to understand and follow closely the application information provided with a CRM.
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ISO 15790:2004(E)
5 Required documentation for CRMs
5.1 Identification of CRM
The following information shall be supplied with a CRM:
 manufacturer's name;
 product identification;
 serial number;
 certification date;
 expiration date or useful life.
This information shall be affixed to a CRM or uniquely associated with it.
5.2 Reporting of CRM reference values
The reference values of CRMs shall be properly identified and reported, with either the combined standard
uncertainty u (see Example 1), or the expanded uncertainties U and coverage factor k (see Example 2).
c
[5]
EXAMPLE 1 D (45; S : 0; T′ ) = 1,25 with u = 0,01; notation for densities according to ISO 5-3
R A R c
where
D is reflection density;
R
S is the influx spectrum based on CIE standard illuminant A;
A
T′ is the status T′ red spectral response.
R
EXAMPLE 2 D (45; S : 0; T′ ) = 1,25 ± 0,02 = 1,25 ± U [u = 0,01, (k = 2)]
R A R c
where the variables are the same as for Example 1.
Alternatively, the reference values of CRMs may be expressed in some other form such as a table; however,
the certificate accompanying a CRM shall clearly show either the combined standard uncertainty or the
expanded uncertainty and the coverage factor.
5.3 Traceability
A statement of traceability shall be provided with CRM reference values. A detailed description of this
traceability shall be available upon request.
Information about the instrumentation and procedures used to determine CRM reference values shall also be
supplied.
5.4 Cautions for use
The manufacturer of a CRM shall provide documentation for those characteristics of a CRM that can affect the
stability of the values measured on a CRM. See Annex A for a sample list of characteristics.
The use of CRMs having characteristics that differ from those of materials whose properties are to be
measured may yield erroneous measurement results. Consideration should be given to these characteristics
when selecting and using a CRM in order that unintended effects are minimized. Documentation should be
provided regarding any properties that can adversely affect instrument calibration.
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ISO 15790:2004(E)
If the spectral characteristics or other properties of a CRM have a noticeable influence on the measurement
by the user, they should be provided by the manufacturer. A good example is the property of some colour
reference materials to shift colour with temperature. Here, the requirements for temperature control should be
stated.
5.5 Care and handling of CRMs
The manufacturer shall provide information regarding pertinent lifetime limitations of a CRM (e.g. physical
deformities, change in surface characteristics, colour change).
Information shall include the following, when applicable:
 process for verification and recertification;
 recommended temperature, humidity and light exposure for storage and use;
 handling precautions and recommendations;
 cleaning procedures.
Documentation accompanying a CRM shall include any manufacturer's recommendations for replacement or
recertification interval, assuming no significant contamination, damage or other alteration has occurred to a
CRM during its use.
In cases where known use conditions are documented as potential causes for change, CRM reference values
should be verified through measurement auditing or surveillance.
5.6 Use and procedures
The manufacturer should provide guidelines and examples for the use of a CRM. If there is a possibility that
improper use can affect the measurement results, a detailed description of the recommended procedures
shall be given (e.g. instrument positioning relative to a CRM, appropriate instrument geometry, aperture size
range).
6 Procedures related to the use of CRMs
6.1 Determination of combined standard uncertainty
6.1.1 General
The principle components of the computation of the combined standard uncertainty are discussed in 6.1.2 to
6.1.6. The actual computation, Equation (4), is given in 6.1.7.
The scope of Guide to the expression of uncertainty in measurement “establishes the general rules for
evaluating and expressing uncertainty in measurement that can be followed at various levels of accuracy and
in many fields — from the shop floor to fundamental research”. While this guide should be considered the
ultimate document in this area, it is generally not being implemented within the graphic arts or photographic
industries. This may be for a number of reasons including ignorance of the document's existence, lack of
understanding, and/or impression that implementation is far too rigorous or unnecessary.
For application of the provisions of this International Standard, it is assumed that the input variables are
independent of each other, that they have a normal distribution and that their standard deviations are each
much smaller than the absolute magnitude of the corresponding input variable. While these assumptions do
not always hold, they provide a reasonable basis for the practical use of a CRM. For cases where these
assumptions may not be valid, such as for colour difference and chroma, users should follow the concepts
and rules presented in the Guide to the expression of uncertainty in measurement.
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ISO 15790:2004(E)
Modelling the measurement process is derived from a knowledge of the measurand. This is not measured
directly, but is modelled from a number of other quantities through the following functional relationship f :
y = f (x , x , . x , . x ) (1)
1 2 i n
where
y is the value of the output quantity;
f is the functional relationship between input and output results;
x is the measurement result for the ith input variable.
i
If some of the x are significantly correlated, these correlations must be taken into account. For example, when
i
CIELAB co-ordinates are calculated from spectral values, errors are generated at each sample wavelength.
Although the errors at each wavelength are uncorrelated, the act of calculating the derived functions X, Y, Z
produces a correlation among the errors of X, Y, Z. In cases such as this, the procedures presented in Guide
to the expression of uncertainty in measurement, 1995, 5.2, shall be used. See 6.1.2 for a discussion of
sensitivity coefficients assuming independent and normally distributed input variables.
6.1.2 Sensitivity coefficients assuming independent and normally distributed input variables
The combined standard uncertainty u ( y) of a measurement result y that depends on a number of independent
c
and normally distributed input variables x is calculated from Equation (2):
i
22 22
    
∂∂ff ∂f ∂f
2
(y)= u (x ) ++ ux( ) . ux( ) + . . . ux( ) (2)
u
    
c 12 in
∂∂xx ∂x ∂x
12 in
    
where
u ( y) is the combined standard uncertainty of the measurement result y;
c
u(x ) is the standard uncertainty of the input variable x ;
i i
∂f
is the value of the partial derivative of the function f with respect to x for the value x .
i i
∂
x
i
∂f
The factors appearing in Equation (2) are sometimes called the sensitivity coefficients because they
∂
x
i
reflect the influence of the individual uncertainties on the combined uncertainty. See also Annex B.
6.1.3 Sensitivity coefficients where the process is not functionally known
The sensitivity coefficients can also be determined experimentally if the function f is not known.
EXAMPLE 1 If it has been determined that the colour measurement of certain calibration plaques is influenced by
temperature variation, the effect of a temperature change of 1 °C on the measured colour co-ordinate can be determined
and this will be considered as the sensitivity coefficient.
A general unknown process P which is a function of several test variables x , x , . x , . x , can be expressed
1 2 i n
just as the function above for the function f. The process can then be expressed, even if unknown, as
P(x , x , . x , . x ). The sensitivity coefficient relative to any variable x can be determined experimentally by
1 2 i n i
making an incremental change of magnitude ε in that x .
i

P , , ., +−ε)(, x P , , .x ., x)
(x
xx xx
P nin
∂ i
12 1 2
≈ (3)
∂x ε
i
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ISO 15790:2004(E)
The result may then be used to replace the pertinent partial derivative in Equation (2). To obtain the product
within the brackets of Equation (2), each experimentally determined sensitivity coefficient is multiplied by the
standard uncertainty of the pertinent variable, expressed in units of the variable.
EXAMPLE 2 The sensitivity coefficient for temperature in Example 1 is multiplied by the standard uncertainty of the
temperature expressed in degrees Celsius.
Equation (3) can more conveniently be used to calculate the sensitivity coefficient if the functional relationship
is known but very complex. A small change of one input variable from a typical value while leaving the other
input variables unchanged allows the computation of the sensitivity coefficient for that variable.
6.1.4 Sensitivity coefficients assuming correlated and normally distributed input variables
Equation (2) is valid only if the input values x are independent or uncorrelated. If some of the x are
i i
significantly correlated, these co
...