SIST ISO 5631-1:2023

Paper and board — Determination of colour by diffuse reflectance — Part 1: Indoor daylight conditions (C/2°)

This document specifies a method for measuring the colour of paper and board by the diffuse reflectance method with the elimination of specular gloss.
This document is not applicable to coloured papers or boards which incorporate fluorescent dyes or pigments. It may be used to determine the colour of papers or boards which contain fluorescent whitening agents provided the UV content of the illumination on the test piece has been adjusted to conform to that in the CIE illuminant C, using a fluorescent reference standard that fulfils the requirements for international fluorescent reference standards of level 3 (IR3) as prescribed by ISO 2469 with an assigned ISO brightness value provided by an authorized laboratory, as described in ISO 2470‑1.

Papier et carton — Détermination de la couleur par réflectance diffuse — Partie 1: Conditions d’éclairage intérieur de jour (C/2°)

Le présent document spécifie une méthode pour mesurer la couleur du papier et du carton par la méthode de la réflectance diffuse avec élimination du brillant spéculaire.
Le présent document n’est pas applicable aux papiers et cartons colorés qui contiennent des colorants ou des pigments fluorescents. Il peut être utilisé pour déterminer la couleur des papiers et cartons contenant des agents d’azurage fluorescents, sous réserve que la teneur en UV de l’éclairage sur l’éprouvette ait été ajustée de manière à être conforme à celle de l’illuminant CIE C, à l’aide d’un étalon de référence fluorescent satisfaisant aux exigences applicables aux étalons de référence fluorescents internationaux de niveau 3 (IR3), comme spécifié dans l’ISO 2469, présentant un degré de blancheur ISO dont la valeur a été attribuée par un laboratoire agréé, comme décrit dans l’ISO 2470-1.

Papir, karton in lepenka - Določanje barve z razpršeno odsevnostjo - 1. del: Pogoji osvetlitve v prostoru (C/2°)

Ta dokument določa metodo za merjenje barve papirja, kartona in lepenke z metodo razpršene odsevnosti z odstranitvijo refleksijskega sijaja.
Ta dokument se ne uporablja za barvni papir, karton ali lepenko, ki vsebuje fluorescentne barve ali pigmente. Uporablja se lahko za določanje barve papirja, kartona ali lepenke, ki vsebuje fluorescentna belilna sredstva, pod pogojem, da je bila vsebnost UV-osvetlitve preskušanca prilagojena tako, da ustreza vrsti svetlobe CIE C, pri čemer je treba uporabiti referenčni standard za fluorescenco, ki izpolnjuje zahteve mednarodnih referenčnih standardov za fluorescenco 3. ravni (IR3), kot zahteva standard ISO 2469, z dodeljeno vrednostjo svetlosti ISO, ki jo je določil pooblaščeni laboratorij, kot je opisano v standardu ISO 2470-1.

General Information

• Status: Published
• Publication Date: 07-Jun-2023
• ICS: 85.060 - Paper and board
• Technical Committee: VPK - Pulp, paper, board and products
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 11-May-2023
• Due Date: 16-Jul-2023
• Completion Date: 08-Jun-2023
• Ref Project: ISO 5631-1:2022 - Paper and board — Determination of colour by diffuse reflectance — Part 1: Indoor daylight conditions (C/2°)

Relations

• Revises: SIST ISO 5631-1:2016 - Paper and board - Determination of colour by diffuse reflectance - Part 1: Indoor daylight conditions (C/2 degrees)
• Effective Date: 01-Jul-2023

Standards Content (Sample)

SLOVENSKI STANDARD
SIST ISO 5631-1:2023
01-julij-2023
Papir, karton in lepenka - Določanje barve z razpršeno odsevnostjo - 1. del: Pogoji
osvetlitve v prostoru (C/2°)
Paper and board — Determination of colour by diffuse reflectance — Part 1: Indoor
daylight conditions (C/2°)
Papier et carton — Détermination de la couleur par réflectance diffuse — Partie 1:
Conditions d’éclairage intérieur de jour (C/2°)
Ta slovenski standard je istoveten z: ISO 5631-1:2022
ICS:
85.060 Papir, karton in lepenka Paper and board
SIST ISO 5631-1:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST ISO 5631-1:2023

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SIST ISO 5631-1:2023
INTERNATIONAL ISO
STANDARD 5631-1
Third edition
2022-07
Paper and board — Determination of
colour by diffuse reflectance —
Part 1:
Indoor daylight conditions (C/2°)
Papier et carton — Détermination de la couleur par réflectance
diffuse —
Partie 1: Conditions d’éclairage intérieur de jour (C/2°)
Reference number
ISO 5631-1:2022(E)
© ISO 2022

---------------------- Page: 3 ----------------------
SIST ISO 5631-1:2023
ISO 5631-1:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
  © ISO 2022 – All rights reserved

---------------------- Page: 4 ----------------------
SIST ISO 5631-1:2023
ISO 5631-1:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Apparatus . 3
5.1 Reflectometer . 3
5.2 Reference standards . 4
5.3 Working standards . 4
6 Sampling and conditioning . 4
7 Preparation of test pieces .4
8 Procedure .5
9 Calculation . 5
9.1 CIE tristimulus values . 5
9.2 CIELAB coordinates . 5
9.3 Dispersion of the results . 6
10 Expression of results . 6
11 Precision . 6
12 Test report . 6
Annex A (normative) Spectral characteristics of reflectometers for determining tristimulus
values . 8
Bibliography .13
iii
© ISO 2022 – All rights reserved

---------------------- Page: 5 ----------------------
SIST ISO 5631-1:2023
ISO 5631-1:2022(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/
iso/foreword.html.
The committee responsible for this document is ISO/TC 6, Paper, board and pulps.
This third edition cancels and replaces the second edition (ISO 5631-1:2015), of which it constitutes a
minor revision. The changes are as follows:
— update of the CIE and joint ISO/CIE Normative and Bibliographic references to current versions.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
  © ISO 2022 – All rights reserved

---------------------- Page: 6 ----------------------
SIST ISO 5631-1:2023
ISO 5631-1:2022(E)
Introduction
The colour of an object can be uniquely characterized by means of a triplet of colour coordinates such
as the CIE tristimulus values or the CIELAB 1976 L*, a*, b* coordinates for a specified CIE illuminant and
CIE standard observer.
Apart from the optical properties of the sample, the values of such coordinates depend upon the
conditions of measurement, particularly the spectral and geometric characteristics of the instrument
used. This document should therefore be read in conjunction with ISO 2469.
This document describes the measurement and description of colour in terms of the CIE illuminant C
and the CIE 1931 (2°) standard observer. The other parts of the ISO 5631 series describe measurements
and calculations carried out in an analogous manner using either the CIE standard illuminant D65
and the CIE 1964 (10°) standard observer or the CIE illuminant D50 and the CIE 1931 (2°) standard
observer.
The choice of illuminant conditions is important when determining the colour coordinates of white
papers containing a fluorescent whitening agent. In ISO 5631-2, the UV content of the illumination is
much higher, approximating UV levels encountered in outdoor viewing conditions.
ISO 5631-3 describes the measurement and description of colour in terms of the CIE illuminant D50
and the CIE 1931 (2°) standard observer. This method is especially applicable to graphic arts situations
since these illuminant/observer conditions are used within the graphic arts industry.
v
© ISO 2022 – All rights reserved

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SIST ISO 5631-1:2023

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SIST ISO 5631-1:2023
INTERNATIONAL STANDARD ISO 5631-1:2022(E)
Paper and board — Determination of colour by diffuse
reflectance —
Part 1:
Indoor daylight conditions (C/2°)
1 Scope
This document specifies a method for measuring the colour of paper and board by the diffuse reflectance
method with the elimination of specular gloss.
This document is not applicable to coloured papers or boards which incorporate fluorescent dyes
or pigments. It may be used to determine the colour of papers or boards which contain fluorescent
whitening agents provided the UV content of the illumination on the test piece has been adjusted
to conform to that in the CIE illuminant C, using a fluorescent reference standard that fulfils the
requirements for international fluorescent reference standards of level 3 (IR3) as prescribed by
ISO 2469 with an assigned ISO brightness value provided by an authorized laboratory, as described in
ISO 2470-1.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 186, Paper and board — Sampling to determine average quality
ISO 2469, Paper, board and pulps — Measurement of diffuse radiance factor (diffuse reflectance factor)
ISO 2470-1, Paper, board and pulps — Measurement of diffuse blue reflectance factor — Part 1: Indoor
daylight conditions (ISO brightness)
ASTM E308, Standard Practice for Computing the Colors of Objects by Using the CIE System
CIE Publication 015:2018, Colorimetry, 4th ed.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
1
© ISO 2022 – All rights reserved

---------------------- Page: 9 ----------------------
SIST ISO 5631-1:2023
ISO 5631-1:2022(E)
3.1
radiance factor
β
ratio of the radiance of a surface element of a body in the direction delimited by a given cone, with
its apex at the surface element, to that of the perfect reflecting diffuser under the same conditions of
illumination
Note 1 to entry: For fluorescent (luminescent) materials, the total radiance factor, β, is the sum of two portions,
the reflected radiance factor, β , and the luminescent radiance factor, β , so that β = β + β .
R L R L
For non-fluorescent materials, the reflected radiance factor, β , is numerically equal to the reflectance factor, R.
R
3.2
intrinsic radiance factor
β
∞
radiance factor (3.1) of a layer or pad of material thick enough to be opaque, such that increasing the
thickness of the pad by doubling the number of sheets results in no change in the measured radiance
factor
Note 1 to entry: The intrinsic radiance factor is often expressed as a percentage.
3.3
reflectance factor
R
ratio of the radiation reflected by a surface element of a body in the direction delimited by a given cone,
with its apex at the surface element to that of the perfect reflecting diffuser under the same conditions
of illumination
Note 1 to entry: The ratio is often expressed as a percentage.
Note 2 to entry: The reflectance factor is influenced by the backing if the body is translucent.
3.4
intrinsic reflectance factor
R
∞
reflectance factor (3.3) of a layer or pad of material thick enough to be opaque, such that increasing the
thickness of the pad by doubling the number of sheets results in no change in the measured reflectance
factor
Note 1 to entry: The reflectance factor of a non-opaque sheet is dependent on the background and is not a
material property.
3.5
tristimulus values
X, Y, Z
amount of the three reference colour stimuli, in a given chromatic system, required to match the colour
of stimulus considered
Note 1 to entry: In this document, the CIE illuminant C and the CIE 1931 (2°) standard observer are used to
define the trichromatic system.
Note 2 to entry: No subscript is applied to conform to the CIE convention that tristimulus values have no subscript
when the CIE 1931 (2°) standard observer is used [the subscript 10 is applied for tristimulus values that are
obtained using the CIE 1964 (10°) standard observer].
2
  © ISO 2022 – All rights reserved

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SIST ISO 5631-1:2023
ISO 5631-1:2022(E)
3.6
CIELAB colour space
three-dimensional, approximately uniform colour space, produced by plotting, in rectangular
coordinates L*, a*, b*, quantities defined by the formulae given in Clause 9
Note 1 to entry: The quantity, L*, is a measure of the lightness of the test piece, where L* = 0 corresponds to black
and L* = 100 is defined by the perfect reflecting diffuser. Visually, the quantities a* and b* represent respectively
the red-green and yellow-blue axes in colour space, such that
   +a* is a measure of the degree of redness of the test piece,
   −a* is a measure of the degree of greenness of the test piece,
   +b* is a measure of the degree of yellowness of the test piece, and
   −b* is a measure of the degree of blueness of the test piece.
If both a* and b* are equal to zero, the test piece is achromatic.
4 Principle
The light reflected from a sample under specified conditions is analysed either by a tristimulus-filter
colorimeter or by an abridged spectrophotometer, and the colour coordinates are then calculated for
C/2° conditions.
5 Apparatus
5.1 Reflectometer
5.1.1 Reflectometer, having the geometric, spectral and photometric characteristics described in
ISO 2469, and calibrated in accordance with the provisions of ISO 2469.
If materials containing fluorescent whitening agents are to be measured, the reflectometer shall be
equipped with a radiation source having an adequate UV content control, adjusted to a UV condition
corresponding to the C illuminant by the use of a reference standard, as described in ISO 2470-1.
5.1.2 In the case of a filter reflectometer, a set of filters that, in conjunction with the optical
characteristics of the basic instrument, give overall responses equivalent to the CIE tristimulus
values X, Y and Z of the CIE 1931 standard colorimetric system of the test piece evaluated for the CIE
illuminant C.
In the case of a filter reflectometer, the radiation falling upon the test piece shall have a UV content
corresponding to that of the CIE illuminant C.
5.1.3 In the case of an abridged spectrophotometer, the instrument shall have a function that permits
calculation of the CIE tristimulus values X, Y and Z of the CIE 1931 standard colorimetric system of the
test piece evaluated for the CIE illuminant C using the weighting functions given in Annex A where the
Tables A.1 and A.2 are used for instruments without bandpass correction and Tables A.3 and A.4 are
used for instruments with ban
...

INTERNATIONAL ISO
STANDARD 5631-1
Third edition
2022-07
Paper and board — Determination of
colour by diffuse reflectance —
Part 1:
Indoor daylight conditions (C/2°)
Papier et carton — Détermination de la couleur par réflectance
diffuse —
Partie 1: Conditions d’éclairage intérieur de jour (C/2°)
Reference number
ISO 5631-1:2022(E)
© ISO 2022

---------------------- Page: 1 ----------------------
ISO 5631-1:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
  © ISO 2022 – All rights reserved

---------------------- Page: 2 ----------------------
ISO 5631-1:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Apparatus . 3
5.1 Reflectometer . 3
5.2 Reference standards . 4
5.3 Working standards . 4
6 Sampling and conditioning . 4
7 Preparation of test pieces .4
8 Procedure .5
9 Calculation . 5
9.1 CIE tristimulus values . 5
9.2 CIELAB coordinates . 5
9.3 Dispersion of the results . 6
10 Expression of results . 6
11 Precision . 6
12 Test report . 6
Annex A (normative) Spectral characteristics of reflectometers for determining tristimulus
values . 8
Bibliography .13
iii
© ISO 2022 – All rights reserved

---------------------- Page: 3 ----------------------
ISO 5631-1:2022(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/
iso/foreword.html.
The committee responsible for this document is ISO/TC 6, Paper, board and pulps.
This third edition cancels and replaces the second edition (ISO 5631-1:2015), of which it constitutes a
minor revision. The changes are as follows:
— update of the CIE and joint ISO/CIE Normative and Bibliographic references to current versions.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
  © ISO 2022 – All rights reserved

---------------------- Page: 4 ----------------------
ISO 5631-1:2022(E)
Introduction
The colour of an object can be uniquely characterized by means of a triplet of colour coordinates such
as the CIE tristimulus values or the CIELAB 1976 L*, a*, b* coordinates for a specified CIE illuminant and
CIE standard observer.
Apart from the optical properties of the sample, the values of such coordinates depend upon the
conditions of measurement, particularly the spectral and geometric characteristics of the instrument
used. This document should therefore be read in conjunction with ISO 2469.
This document describes the measurement and description of colour in terms of the CIE illuminant C
and the CIE 1931 (2°) standard observer. The other parts of the ISO 5631 series describe measurements
and calculations carried out in an analogous manner using either the CIE standard illuminant D65
and the CIE 1964 (10°) standard observer or the CIE illuminant D50 and the CIE 1931 (2°) standard
observer.
The choice of illuminant conditions is important when determining the colour coordinates of white
papers containing a fluorescent whitening agent. In ISO 5631-2, the UV content of the illumination is
much higher, approximating UV levels encountered in outdoor viewing conditions.
ISO 5631-3 describes the measurement and description of colour in terms of the CIE illuminant D50
and the CIE 1931 (2°) standard observer. This method is especially applicable to graphic arts situations
since these illuminant/observer conditions are used within the graphic arts industry.
v
© ISO 2022 – All rights reserved

---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 5631-1:2022(E)
Paper and board — Determination of colour by diffuse
reflectance —
Part 1:
Indoor daylight conditions (C/2°)
1 Scope
This document specifies a method for measuring the colour of paper and board by the diffuse reflectance
method with the elimination of specular gloss.
This document is not applicable to coloured papers or boards which incorporate fluorescent dyes
or pigments. It may be used to determine the colour of papers or boards which contain fluorescent
whitening agents provided the UV content of the illumination on the test piece has been adjusted
to conform to that in the CIE illuminant C, using a fluorescent reference standard that fulfils the
requirements for international fluorescent reference standards of level 3 (IR3) as prescribed by
ISO 2469 with an assigned ISO brightness value provided by an authorized laboratory, as described in
ISO 2470-1.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 186, Paper and board — Sampling to determine average quality
ISO 2469, Paper, board and pulps — Measurement of diffuse radiance factor (diffuse reflectance factor)
ISO 2470-1, Paper, board and pulps — Measurement of diffuse blue reflectance factor — Part 1: Indoor
daylight conditions (ISO brightness)
ASTM E308, Standard Practice for Computing the Colors of Objects by Using the CIE System
CIE Publication 015:2018, Colorimetry, 4th ed.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
1
© ISO 2022 – All rights reserved

---------------------- Page: 6 ----------------------
ISO 5631-1:2022(E)
3.1
radiance factor
β
ratio of the radiance of a surface element of a body in the direction delimited by a given cone, with
its apex at the surface element, to that of the perfect reflecting diffuser under the same conditions of
illumination
Note 1 to entry: For fluorescent (luminescent) materials, the total radiance factor, β, is the sum of two portions,
the reflected radiance factor, β , and the luminescent radiance factor, β , so that β = β + β .
R L R L
For non-fluorescent materials, the reflected radiance factor, β , is numerically equal to the reflectance factor, R.
R
3.2
intrinsic radiance factor
β
∞
radiance factor (3.1) of a layer or pad of material thick enough to be opaque, such that increasing the
thickness of the pad by doubling the number of sheets results in no change in the measured radiance
factor
Note 1 to entry: The intrinsic radiance factor is often expressed as a percentage.
3.3
reflectance factor
R
ratio of the radiation reflected by a surface element of a body in the direction delimited by a given cone,
with its apex at the surface element to that of the perfect reflecting diffuser under the same conditions
of illumination
Note 1 to entry: The ratio is often expressed as a percentage.
Note 2 to entry: The reflectance factor is influenced by the backing if the body is translucent.
3.4
intrinsic reflectance factor
R
∞
reflectance factor (3.3) of a layer or pad of material thick enough to be opaque, such that increasing the
thickness of the pad by doubling the number of sheets results in no change in the measured reflectance
factor
Note 1 to entry: The reflectance factor of a non-opaque sheet is dependent on the background and is not a
material property.
3.5
tristimulus values
X, Y, Z
amount of the three reference colour stimuli, in a given chromatic system, required to match the colour
of stimulus considered
Note 1 to entry: In this document, the CIE illuminant C and the CIE 1931 (2°) standard observer are used to
define the trichromatic system.
Note 2 to entry: No subscript is applied to conform to the CIE convention that tristimulus values have no subscript
when the CIE 1931 (2°) standard observer is used [the subscript 10 is applied for tristimulus values that are
obtained using the CIE 1964 (10°) standard observer].
2
  © ISO 2022 – All rights reserved

---------------------- Page: 7 ----------------------
ISO 5631-1:2022(E)
3.6
CIELAB colour space
three-dimensional, approximately uniform colour space, produced by plotting, in rectangular
coordinates L*, a*, b*, quantities defined by the formulae given in Clause 9
Note 1 to entry: The quantity, L*, is a measure of the lightness of the test piece, where L* = 0 corresponds to black
and L* = 100 is defined by the perfect reflecting diffuser. Visually, the quantities a* and b* represent respectively
the red-green and yellow-blue axes in colour space, such that
   +a* is a measure of the degree of redness of the test piece,
   −a* is a measure of the degree of greenness of the test piece,
   +b* is a measure of the degree of yellowness of the test piece, and
   −b* is a measure of the degree of blueness of the test piece.
If both a* and b* are equal to zero, the test piece is achromatic.
4 Principle
The light reflected from a sample under specified conditions is analysed either by a tristimulus-filter
colorimeter or by an abridged spectrophotometer, and the colour coordinates are then calculated for
C/2° conditions.
5 Apparatus
5.1 Reflectometer
5.1.1 Reflectometer, having the geometric, spectral and photometric characteristics described in
ISO 2469, and calibrated in accordance with the provisions of ISO 2469.
If materials containing fluorescent whitening agents are to be measured, the reflectometer shall be
equipped with a radiation source having an adequate UV content control, adjusted to a UV condition
corresponding to the C illuminant by the use of a reference standard, as described in ISO 2470-1.
5.1.2 In the case of a filter reflectometer, a set of filters that, in conjunction with the optical
characteristics of the basic instrument, give overall responses equivalent to the CIE tristimulus
values X, Y and Z of the CIE 1931 standard colorimetric system of the test piece evaluated for the CIE
illuminant C.
In the case of a filter reflectometer, the radiation falling upon the test piece shall have a UV content
corresponding to that of the CIE illuminant C.
5.1.3 In the case of an abridged spectrophotometer, the instrument shall have a function that permits
calculation of the CIE tristimulus values X, Y and Z of the CIE 1931 standard colorimetric system of the
test piece evaluated for the CIE illuminant C using the weighting functions given in Annex A where the
Tables A.1 and A.2 are used for instruments without bandpass correction and Tables A.3 and A.4 are
used for instruments with bandpass correction.
In the case of an abridged spectrophotometer, the instrument shall have an adjustable filter with a
cut-off wavelength of 395 nm or some other equivalent system, and this filter shall be adjusted or the
system shall be calibrated with the help of the fluorescent reference standard (5.2.2), so that the UV
content of the illumination falling upon the sample corresponds to that of the CIE illuminant C.
3
© ISO 2022 – All rights reserved

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...

NORME ISO
INTERNATIONALE 5631-1
Troisième édition
2022-07
Papier et carton — Détermination de
la couleur par réflectance diffuse —
Partie 1:
Conditions d’éclairage intérieur de
jour (C/2°)
Paper and board — Determination of colour by diffuse reflectance —
Part 1: Indoor daylight conditions (C/2°)
Numéro de référence
ISO 5631-1:2022(F)
© ISO 2022

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ISO 5631-1:2022(F)
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© ISO 2022
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ISO 5631-1:2022(F)
Sommaire Page
Avant-propos .iv
Introduction .v
1 Domaine d’application . 1
2 Références normatives .1
3 Termes et définitions . 1
4 Principe. 3
5 Appareillage . 3
6 Échantillonnage et conditionnement . 4
7 Préparation des éprouvettes . 4
8 Mode opératoire . 5
9 Calcul . 5
9.1 Composantes trichromatiques CIE . 5
9.2 Coordonnées CIELAB . 5
9.3 Dispersion des résultats . 6
10 Expression des résultats . 6
11 Fidélité . 6
12 Rapport d’essai . 6
Annexe A (normative) Caractéristiques spectrales des réflectomètres pour déterminer
les composantes trichromatiques .8
Bibliographie .14
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ISO 5631-1:2022(F)
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes
nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est
en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude
a le droit de faire partie du comité technique créé à cet effet. Les organisations internationales,
gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.
L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui
concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents
critères d’approbation requis pour les différents types de documents ISO. Le présent document a été
rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir www.
iso.org/directives).
L’attention est attirée sur le fait que certains des éléments du présent document peuvent faire l’objet de
droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable
de ne pas avoir identifié de tels droits de propriété et averti de leur existence. Les détails concernant
les références aux droits de propriété intellectuelle ou autres droits analogues identifiés lors de
l’élaboration du document sont indiqués dans l’Introduction et/ou dans la liste des déclarations de
brevets reçues par l’ISO (voir www.iso.org/brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données
pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un
engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion
de l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles
techniques au commerce (OTC), voir le lien suivant: www.iso.org/iso/fr/avant-propos.html.
Le comité chargé de l’élaboration du présent document est l’ISO/TC 6, Papiers, cartons et pâtes.
Cette troisième édition annule et remplace la deuxième édition (ISO 5631-1:2015), dont elle constitue
une révision mineure. Les modifications sont les suivantes:
— mise à jour des références normatives et bibliographie de la CIE et communes ISO/CIE selon les
versions actuelles.
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes
se trouve à l’adresse www.iso.org/fr/members.html.
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ISO 5631-1:2022(F)
Introduction
La couleur d’un objet peut être caractérisée de manière unique au moyen d’un triplet de coordonnées
colorimétriques telles que les composantes trichromatiques CIE ou les coordonnées L*, a*, b*
CIELAB 1976, pour un illuminant CIE et un observateur normalisé CIE spécifiés.
Outre les propriétés optiques de l’échantillon, les valeurs de ces coordonnées dépendent des conditions
de mesurage, notamment des caractéristiques spectrales et géométriques de l’appareil utilisé. Il
convient donc de lire le présent document conjointement avec l’ISO 2469.
Le présent document détaille le mesurage et la description de la couleur avec l’illuminant CIE C et
l’observateur normalisé CIE 1931 (2°). Les autres parties de la série ISO 5631 décrivent les mesurages
et les calculs effectués de manière analogue en utilisant soit l’illuminant normalisé CIE D65 et
l’observateur normalisé CIE 1964 (10°), soit l’illuminant CIE D50 et l’observateur normalisé CIE 1931
(2°).
Le choix des conditions relatives à l’illuminant est important lorsqu’il s’agit de déterminer les
coordonnées colorimétriques de papiers blancs contenant un agent d’azurage fluorescent. Dans
l’ISO 5631-2, la teneur en UV de l’éclairage est très supérieure, avoisinant les niveaux d’UV rencontrés
dans des conditions d’observation en extérieur.
L’ISO 5631-3 détaille le mesurage et la description de la couleur avec l’illuminant CIE D50 et l’observateur
normalisé CIE 1931 (2°). Cette méthode convient particulièrement bien au domaine des arts graphiques,
car elle correspond aux conditions d’illuminant et d’observateur utilisées dans ce secteur.
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NORME INTERNATIONALE ISO 5631-1:2022(F)
Papier et carton — Détermination de la couleur par
réflectance diffuse —
Partie 1:
Conditions d’éclairage intérieur de jour (C/2°)
1 Domaine d’application
Le présent document spécifie une méthode pour mesurer la couleur du papier et du carton par la
méthode de la réflectance diffuse avec élimination du brillant spéculaire.
Le présent document n’est pas applicable aux papiers et cartons colorés qui contiennent des colorants
ou des pigments fluorescents. Il peut être utilisé pour déterminer la couleur des papiers et cartons
contenant des agents d’azurage fluorescents, sous réserve que la teneur en UV de l’éclairage sur
l’éprouvette ait été ajustée de manière à être conforme à celle de l’illuminant CIE C, à l’aide d’un étalon
de référence fluorescent satisfaisant aux exigences applicables aux étalons de référence fluorescents
internationaux de niveau 3 (IR3), comme spécifié dans l’ISO 2469, présentant un degré de blancheur
ISO dont la valeur a été attribuée par un laboratoire agréé, comme décrit dans l’ISO 2470-1.
2 Références normatives
Les documents de référence suivants sont indispensables pour l’application du présent document. Pour
les références datées, seule l’édition citée s’applique. Pour les références non datées, la dernière édition
du document de référence s’applique (y compris les éventuels amendements).
ISO 186, Papier et carton — Échantillonnage pour déterminer la qualité moyenne
ISO 2469, Papier, carton et pâtes — Mesurage du facteur de luminance énergétique diffuse (facteur de
réflectance diffuse)
ISO 2470-1, Papier, carton et pâtes — Mesurage du facteur de réflectance diffuse dans le bleu — Partie 1:
Conditions d'éclairage intérieur de jour (degré de blancheur ISO)
ASTM E308, Standard Practice for Computing the Colors of Objects by Using the CIE System
CIE Publication 015:2018, Colorimetry, 4th ed.
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions suivants s’appliquent.
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp
— IEC Electropedia: disponible à l’adresse https:// www .electropedia .org/
1
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ISO 5631-1:2022(F)
3.1
facteur de luminance énergétique
β
rapport de la luminance énergétique d’un élément de surface d’un corps dans la direction délimitée par
un cône donné dont le sommet se trouve au niveau de l’élément de surface, à la luminance énergétique
du diffuseur parfait par réflexion, dans les mêmes conditions d’éclairage
Note 1 à l'article: Pour les matériaux fluorescents (luminescents), le facteur de luminance énergétique totale, β,
est la somme de deux grandeurs, le facteur de luminance énergétique par réflexion, β , et le facteur de luminance
R
énergétique par luminescence, β , de sorte que β = β + β .
L R L
Pour les matériaux non fluorescents, le facteur de luminance énergétique par réflexion, β , est numériquement
R
égal au facteur de réflectance, R.
3.2
facteur de luminance énergétique intrinsèque
β
∞
facteur de luminance énergétique (3.1) d’une couche ou d’une liasse de matériau suffisamment épaisse
pour être opaque, de sorte que l’augmentation de l’épaisseur de la liasse par doublement du nombre de
feuilles la constituant n’engendre aucune modification du facteur de luminance énergétique mesuré
Note 1 à l'article: Le facteur de luminance énergétique intrinsèque est souvent exprimé sous forme de
pourcentage.
3.3
facteur de réflectance
R
rapport du rayonnement réfléchi par un élément de surface d’un corps dans la direction délimitée par
un cône donné dont le sommet se trouve au niveau de l’élément de surface, au rayonnement réfléchi par
le diffuseur parfait par réflexion, dans les mêmes conditions d’éclairage
Note 1 à l'article: Ce rapport est souvent exprimé sous forme de pourcentage.
Note 2 à l'article: Le fond a une incidence sur le facteur de réflectance si le corps est translucide.
3.4
facteur de réflectance intrinsèque
R
∞
facteur de réflectance (3.3) d’une couche ou d’une liasse de matériau suffisamment épaisse pour être
opaque, de sorte que l’augmentation de l’épaisseur de la liasse par doublement du nombre de feuilles la
constituant n’engendre aucune modification du facteur de réflectance mesuré
Note 1 à l'article: Le facteur de réflectance d’une feuille non opaque dépend du fond et n’est pas une propriété du
matériau.
3.5
composantes trichromatiques
X, Y, Z
quantité des trois stimuli de couleur normalisés, dans un système chromatique donné, nécessaire pour
correspondre à la couleur du stimulus considéré
Note 1 à l'article: Dans le présent document, l’illuminant CIE C et l’observateur normalisé CIE 1931 (2°) sont
utilisés pour définir le système trichromatique.
Note 2 à l'article: Aucun indice n’est utilisé pour respecter la convention CIE selon laquelle les composantes
trichromatiques ne comportent pas d’indice lorsque l’on utilise l’observateur normalisé CIE 1931 (2°) [l’indice 10
est utilisé pour les composantes trichromatiques obtenues lorsque l’on utilise l’observateur normalisé CIE 1964
(10°)].
2
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ISO 5631-1:2022(F)
3.6
espace chromatique CIELAB
espace chromatique à trois dimensions approximativement uniforme, obtenu en portant en coordonnées
rectangulaires les grandeurs L*, a*, b* définies par les formules données dans l’Article 9
Note 1 à l'article: La grandeur L* est une mesure de la clarté de l’éprouvette, où L* = 0 correspond au noir et
L* = 100 est définie comme étant le diffuseur parfait par réflexion. Visuellement, les grandeurs a* et b*
représentent respectivement les axes rouge-vert et jaune-bleu de l’espace chromatique, de sorte que:
   +a* est une mesure de la composante rouge de l’éprouvette;
   −a* est une mesure de la composante verte de l’éprouvette;
   +b* est une mesure de la composante jaune de l’éprouvette; et
   −b* est une mesure de la composante bleue de l’éprouvette.
Si a* et b* sont toutes les deux égales à zéro, l’éprouvette est achromatique.
4 Principe
La lumière réfléchie par un échantillon dans des conditions spécifiées est analysée soit au moyen d’un
colorimètre à filtre trichromatique, soit à l’aide d’un spectrophotomètre continu, et les coordonnées
colorimétriques sont calculées pour les conditions C/2°.
5 Appareillage
5.1 Réflectomètre
5.1.1 Réflectomètre, ayant les caractéristiques géométriques, spectrales et photométriques décrites
dans l’ISO 2469 et étalonné conformément aux dispositions de l’ISO 2469.
Si des matériaux contenant des agents d’azurage fluorescents doivent être mesurés, le réflectomètre
doit être équipé d’une source de rayonnement avec un contrôle adéquat de la teneur en UV, réglée à
un niveau correspondant à l’illuminant C au moyen d’un étalon de référence, comme décrit dans
l’ISO 2470-1.
5.1.2 En cas d’utilisation d’un réflectomètre à filtre, l'instrument doit avoir un ensemble de filtres
qui donne, conjointement aux caractéristiques optiques de l’appareil de base, des réponses globales
équivalentes aux composantes trichromatiques CIE X, Y et Z du système colorimétrique normalisé
CIE 1931 de l’éprouvette évaluée pour l’illuminant CIE C.
Dans le cas d’un réflectomètre à filtre, le rayonnement tombant sur l’éprouvette doit avoir une teneur
en UV correspondant à celle de l’illuminant CIE C.
5.1.3 En cas d’utilisation d’un spectrophotomètre continu, l'instrument doit avoir une fonction qui
permet de calculer les composantes trichromatiques CIE X, Y et Z du système colorimétrique normalisé
CIE 1931 de l’éprouvette évaluée pour l’illuminant CIE C, en utilisant les fonctions de pondération
indiquées en Annexe A, les Tableaux A.1 et A.2 étant utilisés pour les appareils sans correction de la
bande passante et les Tableaux A.3 et A.4 pour les appareils avec correction de la bande passante.
Dans le cas d’un spectrophotomètre continu, l’appareil doit être équipé d’un filtre réglable avec une
longueur d’onde de coupure de 395 nm ou d’un système équivalent; ce filtre doit être réglé ou le système
doit être étalonné à l’aide de l’étalon de référence fluorescent (5.2.2), de sorte que la teneur en UV du
rayonnement tombant sur l’échantillon corresponde à celle de l’illuminant CIE C.
3
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ISO 5631-1:2022(F)
5.2 Étalons de référence
Les étalons de référence servent à l’étalonnage de l’appareil et des étalons de travail, et sont utilisés
de manière suffisamment fréquente pour garantir un étalonnage et un réglage du rayonnement UV
satisfaisants.
5.2.1 Étalon de référence non fluorescent, pour l’étalonnage photométrique, provenant d’un
laboratoire agréé conformément aux dispositions de l’ISO 2469.
5.2.2 Étalon de référence fluorescent, destiné au réglage de la teneur en UV du rayonnement
incident tombant sur l’échantillon, présentant un degré de blancheur ISO dont la valeur a été attribuée
par un laboratoire agréé, comme spécifié dans l’ISO 2470-1.
5
...

ISO/WD nnn-n
Style Definition: RefNorm
ISO/TC 6
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0.71 cm, Don't add space between paragraphs of the same
Date: 2021-09-28
style
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ISO/FDIS 5631-120211:2022(E)
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Committee identification: ISO/TC 6WG 3
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Secretariat: SCC
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Paper and board — Determination of colour by diffuse reflectance — Part 1: Indoor Style Definition: bib_medline: Font: Cambria
Style Definition: Base_Text: Tab stops: 0.7 cm, Left + 1.4
daylight conditions (C/2°)
cm, Left + 2.1 cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2
cm, Left + 4.9 cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7
Papier et carton — Détermination de la couleur par réflectance diffuse — Partie 1:
cm, Left
Conditions d'éclairage intérieur de jour (C/2°)
Style Definition: Body Text_Center
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Left + 1.72 cm, Left + 2.3 cm, Left + 2.87 cm, Left + 3.45
cm, Left + 4.02 cm, Left + 4.6 cm, Left + 5.17 cm, Left +
5.74 cm, Left
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Hanging: 1.43 cm, Space After: 12 pt
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ISO/FDIS 5631-1:20212022(E) Formatted: Font: Cambria, French (Switzerland)
Formatted: Left
© ISO 2021
Formatted: Font: Cambria, French (Switzerland)
Formatted: Section start: New page
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no
part of this publication may be reproduced or utilized otherwise in any form or by any means,
electronic or mechanical, including photocopying, or posting on the internet or an intranet, without
prior written permission. Permission can be requested from either ISO at the address below or ISO’s
member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 20212022 – All rights reserved

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ISO/FDIS 5631-1:20212022(E) Formatted: Font: Cambria, French (Switzerland)
Formatted: Font: Cambria, French (Switzerland)
Formatted: Font: Cambria, French (Switzerland)
Contents Page
Foreword . iv
Introduction . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Apparatus . 3
5.1 Reflectometer . 3
5.2 Reference standards . 3
5.3 Working standards . 4
6 Sampling and conditioning . 4
7 Preparation of test pieces . 4
8 Procedure . 4
9 Calculation . 5
9.1 CIE tristimulus values . 5
9.2 CIELAB coordinates . 5
9.3 Dispersion of the results . 6
10 Expression of results . 6
11 Precision . 6
12 Test report . 6
Annex A (normative) Spectral characteristics of reflectometers for determining tristimulus
values . 8
A.1 Filter reflectometers . 8
A.2 Abridged spectrophotometers. 8
A.2.1 General . 8
A.2.2 Procedure for using data without bandpass correction . 8
A.2.3 Procedure for using data with bandpass correction . 9
Bibliography . 14
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ISO/FDIS 5631-1:20212022(E) Formatted: Font: Cambria, French (Switzerland)
Formatted: Left
Formatted: Font: Cambria, French (Switzerland)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national Formatted: English (United States)
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. Formatted: English (United States)
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the Formatted: English (United States)
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives www.iso.org/directives). Formatted: English (United States)
Formatted: English (United States)
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patentswww.iso.org/patents). Formatted: English (United States)
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement. Formatted: English (United States)
For an explanation onof the voluntary nature of standards, the meaning of ISO specific terms and Formatted: English (United States)
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT)), see the following Formatted: English (United States)
URL: Foreword - Supplementary informationwww.iso.org/iso/foreword.html.
Formatted: English (United States)
Formatted: English (United States)
The committee responsible for this document is ISO/TC 6, Paper, board and pulps.
Formatted: English (United States)
Formatted: Font color: Auto
This third edition cancels and replaces the second edition (ISO 5631-1:2015). A minor revision has been
carried out to update the CIE and joint ISO/CIE Normative and Bibliographic references to current Formatted: English (United States)
versions and to correct a few spelling errors.), of which it constitutes a minor revision. The changes are
Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers
as follows:
Formatted: English (United States)
ISO 5631 consists of the following parts, under the general title Paper and board — Determination of
colour by diffuse reflectance:
— Part 1: Indoor daylight conditions (C/2°)
— Part 2: Outdoor daylight conditions (D65/10°)
— Part 3: Indoor illumination conditions (D50/2°)
— update of the CIE and joint ISO/CIE Normative and Bibliographic references to current
versions.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/FDIS 5631-1:20212022(E) Formatted: Font: Cambria, French (Switzerland)
Formatted: Font: Cambria, French (Switzerland)
Formatted: Font: Cambria, French (Switzerland)
Introduction
The colour of an object can be uniquely characterized by means of a triplet of colour coordinates such as
the CIE tristimulus values or the CIELAB 1976 L*, a*, b* coordinates for a specified CIE illuminant and
CIE standard observer.
Apart from the optical properties of the sample, the values of such coordinates depend upon the
conditions of measurement, particularly the spectral and geometric characteristics of the instrument
used. This part of ISO 5631docuement should therefore be read in conjunction with ISO 2469.
This part of ISO 5631document describes the measurement and description of colour in terms of the
CIE illuminant C and the CIE 1931 (2°) standard observer. The other parts of this International
Standardthe ISO 5631 series describe measurements and calculations carried out in an analogous
manner using either the CIE standard illuminant D65 and the CIE 1964 (10°) standard observer or the
CIE illuminant D50 and the CIE 1931 (2°) standard observer.
The choice of illuminant conditions is important when determining the colour coordinates of white
papers containing a fluorescent whitening agent. In ISO 5631-2, the UV content of the illumination is
much higher, approximating UV levels encountered in outdoor viewing conditions.
ISO 5631-3 describes the measurement and description of colour in terms of the CIE illuminant D50 and
the CIE 1931 (2°) standard observer. This method is especially applicable to graphic arts situations
since these illuminant/observer conditions are used within the graphic arts industry.
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Formatted: Font: Cambria, French (Switzerland)
ISO/FDIS 5631-1
INTERNATIONAL STANDARD
Formatted: Font: Cambria, French (Switzerland)
:2022(E)
Formatted: Font: Cambria
:2021
Formatted: Left, Line spacing: Exactly 11 pt
Formatted: Space Before: 6 pt, After: 6 pt, Line spacing:
Exactly 11 pt
Paper and board — Determination of colour by diffuse
reflectance — Part 1: Indoor daylight conditions
1 Scope
This part of ISO 5631document specifies a method for measuring the colour of paper and board by the
diffuse reflectance method with the elimination of specular gloss.
This part of ISO 5631document is not applicable to coloured papers or boards which incorporate
fluorescent dyes or pigments. It may be used to determine the colour of papers or boards which contain
fluorescent whitening agents provided the UV content of the illumination on the test piece has been
adjusted to conform to that in the CIE illuminant C, using a fluorescent reference standard that fulfils
the requirements for international fluorescent reference standards of level 3 (IR3) as prescribed by
ISO 2469 with an assigned ISO brightness value (C/2°) provided by an authorized laboratory, as
described in ISO 2470-1.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
ISO 186, Paper and board — Sampling to determine average quality
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
ISO 2469, Paper, board and pulps — Measurement of diffuse radiance factor (diffuse reflectance factor)
ISO 2470-1, Paper, board and pulps — Measurement of diffuse blue reflectance factor — Part 1: Indoor
daylight conditions (ISO brightness)
ASTM E308, Standard Practice for Computing the Colors of Objects by Using the CIE System Formatted: Default Paragraph Font
CIE Publication 015:2018, Colorimetry, 4th ed. Formatted: bib_book
Formatted: bib_year
Formatted: bib_publisher
3 Terms and definitions
Formatted: bib_publisher, Font: Not Italic
Formatted: Font: Not Italic
For the purposes of this document, the following terms and definitions apply.
Formatted: bib_editionno
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
Formatted: bib_editionno, Not Superscript/ Subscript
— ISO Online browsing platform: available at https://www.iso.org/obp
Formatted: bib_editionno
Formatted: Adjust space between Latin and Asian text,
— IEC Electropedia: available at https://www.electropedia.org/
Adjust space between Asian text and numbers
3.1
radiance factor
β Formatted: Font: Bold
© ISO 20212022 – All rights reserved 1

---------------------- Page: 6 ----------------------
ISO/FDIS 5631-1:20212022(E) Formatted: Font: Cambria, French (Switzerland)
Formatted: Left
ratio of the radiance of a surface element of a body in the direction delimited by a given cone, with its
Formatted: Font: Cambria, French (Switzerland)
apex at the surface element, to that of the perfect reflecting diffuser under the same conditions of
illumination
Note 1 to entry: For fluorescent (luminescent) materials, the total radiance factor, β, is the sum of two portions, Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
the reflected radiance factor, β , and the luminescent radiance factor, β , so that β = β + β .
R L R L
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
For non-fluorescent materials, the reflected radiance factor, β , is numerically equal to the reflectance factor, R. Formatted: Font: Italic
R
3.2
intrinsic radiance factor
β∞ Formatted: Font: Bold
radiance factor (3.1) of a layer or pad of material thick enough to be opaque, such that increasing the
Formatted: Font: Italic
thickness of the pad by doubling the number of sheets results in no change in the measured radiance
factor
Note 1 to entry: The intrinsic radiance factor is often expressed as a percentage.
Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
3.3
reflectance factor
R Formatted: Font: Bold
ratio of the radiation reflected by a surface element of a body in the direction delimited by a given cone,
with its apex at the surface element to that of the perfect reflecting diffuser under the same conditions
of illumination
Note 1 to entry: The ratio is often expressed as a percentage. Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
Note 2 to entry: The reflectance factor is influenced by the backing if the body is translucent.
3.4
intrinsic reflectance factor
R Formatted: Font: Bold
∞
reflectance factor (3.3) of a layer or pad of material thick enough to be opaque, such that increasing the
Formatted: Font: Italic
thickness of the pad by doubling the number of sheets results in no change in the measured reflectance
factor
Note 1 to entry: The reflectance factor of a non-opaque sheet is dependent on the background and is not a
Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
material property.
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
3.5
tristimulus values
X, Y, Z Formatted: Font: Bold
amount of the three reference colour stimuli, in a given chromatic system, required to match the
stimulus considered
Note 1 to entry: In this part of ISO 5631document, the CIE illuminant C and the CIE 1931 (2°) standard observer
Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
are used to define the trichromatic system.
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
Note 2 to entry: No subscript is applied to conform to the CIE convention that tristimulus values have no
subscript when the CIE 1931 (2°) standard observer is used [the subscript 10 is applied for tristimulus values that
are obtained using the CIE 1964 (10°) standard observer].
3.6
CIELAB colour space
three-dimensional, approximately uniform colour space, produced by plotting, in rectangular
coordinates L*, a*, b*, quantities defined by the formulae given in Clause 9
2 © ISO 20212022 – All rights reserved

---------------------- Page: 7 ----------------------
ISO/FDIS 5631-1:20212022(E) Formatted: Font: Cambria, French (Switzerland)
Formatted: Font: Cambria, French (Switzerland)
Note 1 to entry: The quantity, L*, is a measure of the lightness of the test piece, where L* = 0 corresponds to
Formatted: Font: Cambria, French (Switzerland)
black and L* = 100 is defined by the perfect reflecting diffuser. Visually, the quantities a* and b* represent
Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
respectively the red-green and yellow-blue axes in colour space, such that
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
   +a* is a measure of the degree of redness of the test piece,
   −a* is a measure of the degree of greenness of the test piece,
   +b* is a measure of the degree of yellowness of the test piece, and
   −b* is a measure of the degree of blueness of the test piece.
If both a* and b* are equal to zero, the test piece is achromatic.
4 Principle
The light reflected from a sample under specified conditions is analysed either by a tristimulus-filter
colorimeter or by an abridged spectrophotometer, and the colour coordinates are then calculated for
C/2° conditions.
5 Apparatus
5.1 Reflectometer
5.1.1 Reflectometer, having the geometric, spectral and photometric characteristics described in Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
ISO 2469, and calibrated in accordance with the provisions of ISO 2469.
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
If materials containing fluorescent whitening agents are to be measured, the reflectometer shall be
equipped with a radiation source having an adequate UV content control, adjusted to a UV condition
corresponding to the C illuminant by the use of a reference standard, as described in ISO 2470-1.
5.1.2 In the case of a filter reflectometer, a set of filters that, in conjunction with the optical Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
characteristics of the basic instrument, give overall responses equivalent to the CIE tristimulus values X,
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
Y and Z of the CIE 1931 standard colorimetric system of the test piece evaluated for the CIE
illuminant C.
In the case of a filter reflectometer, the radiation falling upon the test piece shall have a UV content
corresponding to that of the CIE illuminant C.
5.1.3 In the case of an abridged spectrophotometer, a function that permits calculation of the CIE Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
tristimulus values X, Y and Z of the CIE 1931 standard colorimetric system of the test piece evaluated for
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
the CIE illuminant C using the weighting functions given in Annex A where the Tables A.1 and A.2 are
used for instruments without bandpass correction and Tables A.3 and A.4 are used for instruments
with bandpass correction.
In the case of an abridged spectrophotometer, the instrument shall have an adjustable filter with a cut-
off wavelength of 395 nm or some other equivalent system, and this filter shall be adjusted or the
system shall be calibrated with the help of the fluorescent reference standard (5.2.2), so that the UV
content of the illumination falling upon the sample corresponds to that of the CIE illuminant C.
5.2 Reference standards Formatted: Don't adjust space between Latin and Asian text,
Don't adjust space between Asian text and numbers, Tab
stops: 0.71 cm, Left
Reference standards are for calibration of the instrument and the working standards and used
Formatted: Body Text
frequently enough to ensure satisfactory calibration and UV adjustment.
5.2.1 Non-fluorescent reference standard, for photometric calibration, issued by an authorized Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
laboratory in accordance with the provisions of ISO 2469.
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
© ISO 20212022 – All rights reserved 3

---------------------- Page: 8 ----------------------
ISO/FDIS 5631-1:20212022(E) Formatted: Font: Cambria, French (Switzerland)
Formatted: Left
5.2.2 Fluorescent reference standard, for use in adjusting the UV content of the radiation incident
Formatted: Font: Cambria, French (Switzerland)
upon the sample, having an ISO brightness value assigned by an authorized laboratory, as prescribed in
ISO 2470-1.

5.45.3 Working standards
Formatted: Don't adjust space between Latin and Asian text,
Don't adjust space between Asian text and numbers, Tab
stops: 0.71 cm, Left
Working standards are calibrated frequently enough to ensure that satisfactory calibration is
Formatted: Body Text
maintained.
5.3.1 Two plates of flat opal glass, made of ceramic or other suitable material, cleaned and Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
calibrated as described in ISO 2469.
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
NOTE In some instruments, the function of the primary working standard can be taken over by a built-in
internal standard.
5.3.2 A stable plastic or other tablet, incorporating a fluorescent whitening agent.
5.4 Black cavity, having a reflectance factor which does not differ from its nominal value by more than
0,2 % at all wavelengths. The black cavity should be stored upside down in a dust-free environment or
with a protective cover.
NOTE 1 The reflectance level of the black cavity can be checked by reference to the instrument manufacturer.
NOTE 2 The nominal value is given by the manufacturer.
6 Sampling and conditioning
If the tests are being made to evaluate a lot of paper or board, the sample shall be selected in
accordance with ISO 186. If the tests are made on another type of sample, make sure that the test pieces
taken are representative of the sample received.
Conditioning according to ISO 187 is recommended but not required, but preconditioning with elevated
temperatures should not be applied since it might change the optical properties.
7 Preparation of test pieces
Avoiding watermarks, dirt and obvious defects, cut rectangular test pieces approximately
75 mm × 150 mm. Assemble at least 10 test pieces in a pad with their top sides uppermost; the number
should be such that doubling the number of test pieces does not alter the radiance factor. Protect the
pad by placing an additional sheet of paper or board on both the top and bottom of the pad. Avoid
contamination and unnecessary exposure to light or heat.
Mark the top test piece in one corner to identify the sample and its top side, or to distinguish between
the two sides.
If the top side can be distinguished from the wire side, it shall be uppermost; if not, as may be the case
for papers manufactured on twin-wire machines, ensure that the same side of the sheet is uppermost.
8 Procedure
8.1 Ensure that calibration has been performed as described in ISO 2470-1 according to the instrument Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
manufacturer's instructions.
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
4 © ISO 20212022 – All rights reserved

---------------------- Page: 9 ----------------------
ISO/FDIS 5631-1:20212022(E) Formatted: Font: Cambria, French (Switzerland)
Formatted: Font: Cambria, French (Switzerland)
8.2 Remove the protective sheets from the top and the bottom of the test piece pad. Without touching
Formatted: Font: Cambria, French (Switzerland)
the test area, use the procedure appropriate to the instrument to obtain the three CIE tristimulus values
of the first test piece (or CIELAB values if the instrument is designed to report directly in this colour
space). Read and record the tristimulus values to the nearest 0,01 unit.
8.3 Move the uppermost test piece to the bottom of the pad and determine the values for succeeding
test pieces until at least 10 test pieces have been evaluated. If required, repeat the procedure for the
other side of the test pieces.
9 Calculation
9.1 CIE tristimulus values
If the instrument has a bandpass of 5 nm or narrower, calculate the CIE tristimulus values in accordance
with CIE Publication 015:2018. In all other cases, calculate the tristimulus values using the appropriate
weighting functions given in ASTM E308. If the instrument does not provide the CIE tristimulus values
directly, obtain them by calculation using the tables provided in Annex A.
9.2 CIELAB coordinates
Calculate the CIELAB coordinates from the tristimulus values X, Y, Z, by means of the following
formulae:Formula (1)
1/3 1/3
Formatted: Tab stops: 0.7 cm, Left + 1.4 cm, Left + 2.1
L*=−116 Y Y 16 L*=−116 Y Y 16
( ) ( ) (1)
n n
cm, Left + 2.8 cm, Left + 3.5 cm, Left + 4.2 cm, Left + 4.9
cm, Left + 5.6 cm, Left + 6.3 cm, Left + 7 cm, Left
1/3 1/3 1/3 1/3

a*=−500 X X Y Y a*=−500 X X Y Y (2)
( ) ( ) ( ) ( )
nn nn


1/3 1/3 1/3 1/3

b*=−200 Y Y Z Z b*=−200 Y Y Z Z (3)
( ) ( ) ( ) ( )
nn nn


Formatted: Font: Not Italic
where X , Y , Z are the tristimulus values of the perfect reflecting diffuser under C/2° conditions.
n n n
Formatted: Font: Not Italic
These are given as the “white point” values in Annex A.
Formatted: Font: Not Italic
3
Alternative equations shall, however, be used if any of the ratios X/X , Y/Y , Z/Z ≤ (24/116) are
n n n
Formatted: cite_app
satisfied as follows.
Formatted: Font: Not Italic
3 1/3
Formatted: Font: Not Italic
a) If (X/X ) ≤ (24/116) , replace the term (X/X ) in Formula (2) by the expression
n n
Formatted: Font: Not Italic
(841/108) (X/X ) + 16/116.
n
Fo
...

FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 5631-1
ISO/TC 6
Paper and board — Determination of
Secretariat: SCC
colour by diffuse reflectance —
Voting begins on:
2022-04-06
Part 1:
Voting terminates on:
Indoor daylight conditions (C/2
2022-06-01
degrees)
Papier et carton — Détermination de la couleur par réflectance
diffuse —
Partie 1: conditions d’éclairage intérieur de jour (C/2 degrées)
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 5631-1:2022(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2022

---------------------- Page: 1 ----------------------
ISO/FDIS 5631-1:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
  © ISO 2022 – All rights reserved

---------------------- Page: 2 ----------------------
ISO/FDIS 5631-1:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 3
5 Apparatus . 3
5.1 Reflectometer . 3
5.2 Reference standards . 4
5.3 Working standards . 4
6 Sampling and conditioning . 4
7 Preparation of test pieces .4
8 Procedure .5
9 Calculation . 5
9.1 CIE tristimulus values . 5
9.2 CIELAB coordinates . 5
9.3 Dispersion of the results . 6
10 Expression of results . 6
11 Precision . 6
12 Test report . 6
Annex A (normative) Spectral characteristics of reflectometers for determining tristimulus
values . 8
Bibliography .13
iii
© ISO 2022 – All rights reserved

---------------------- Page: 3 ----------------------
ISO/FDIS 5631-1:2022(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
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. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 6, Paper, board and pulps.
This third edition cancels and replaces the second edition (ISO 5631-1:2015), of which it constitutes a
minor revision. The changes are as follows:
— update of the CIE and joint ISO/CIE Normative and Bibliographic references to current versions.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
  © ISO 2022 – All rights reserved

---------------------- Page: 4 ----------------------
ISO/FDIS 5631-1:2022(E)
Introduction
The colour of an object can be uniquely characterized by means of a triplet of colour coordinates such
as the CIE tristimulus values or the CIELAB 1976 L*, a*, b* coordinates for a specified CIE illuminant and
CIE standard observer.
Apart from the optical properties of the sample, the values of such coordinates depend upon the
conditions of measurement, particularly the spectral and geometric characteristics of the instrument
used. This docuement should therefore be read in conjunction with ISO 2469.
This document describes the measurement and description of colour in terms of the CIE illuminant C
and the CIE 1931 (2°) standard observer. The other parts of the ISO 5631 series describe measurements
and calculations carried out in an analogous manner using either the CIE standard illuminant D65
and the CIE 1964 (10°) standard observer or the CIE illuminant D50 and the CIE 1931 (2°) standard
observer.
The choice of illuminant conditions is important when determining the colour coordinates of white
papers containing a fluorescent whitening agent. In ISO 5631-2, the UV content of the illumination is
much higher, approximating UV levels encountered in outdoor viewing conditions.
ISO 5631-3 describes the measurement and description of colour in terms of the CIE illuminant D50
and the CIE 1931 (2°) standard observer. This method is especially applicable to graphic arts situations
since these illuminant/observer conditions are used within the graphic arts industry.
v
© ISO 2022 – All rights reserved

---------------------- Page: 5 ----------------------
FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 5631-1:2022(E)
Paper and board — Determination of colour by diffuse
reflectance —
Part 1:
Indoor daylight conditions (C/2 degrees)
1 Scope
This document specifies a method for measuring the colour of paper and board by the diffuse reflectance
method with the elimination of specular gloss.
This document is not applicable to coloured papers or boards which incorporate fluorescent dyes
or pigments. It may be used to determine the colour of papers or boards which contain fluorescent
whitening agents provided the UV content of the illumination on the test piece has been adjusted
to conform to that in the CIE illuminant C, using a fluorescent reference standard that fulfils the
requirements for international fluorescent reference standards of level 3 (IR3) as prescribed by
ISO 2469 with an assigned ISO brightness value (C/2°) provided by an authorized laboratory, as
described in ISO 2470-1.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 186, Paper and board — Sampling to determine average quality
ISO 2469, Paper, board and pulps — Measurement of diffuse radiance factor (diffuse reflectance factor)
ISO 2470-1, Paper, board and pulps — Measurement of diffuse blue reflectance factor — Part 1: Indoor
daylight conditions (ISO brightness)
ASTM E308, Standard Practice for Computing the Colors of Objects by Using the CIE System
CIE Publication 015:2018, Colorimetry, 4th ed.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
1
© ISO 2022 – All rights reserved

---------------------- Page: 6 ----------------------
ISO/FDIS 5631-1:2022(E)
3.1
radiance factor
β
ratio of the radiance of a surface element of a body in the direction delimited by a given cone, with
its apex at the surface element, to that of the perfect reflecting diffuser under the same conditions of
illumination
Note 1 to entry: For fluorescent (luminescent) materials, the total radiance factor, β, is the sum of two portions,
the reflected radiance factor, β , and the luminescent radiance factor, β , so that β = β + β .
R L R L
For non-fluorescent materials, the reflected radiance factor, β , is numerically equal to the reflectance factor, R.
R
3.2
intrinsic radiance factor
β
∞
radiance factor (3.1) of a layer or pad of material thick enough to be opaque, such that increasing the
thickness of the pad by doubling the number of sheets results in no change in the measured radiance
factor
Note 1 to entry: The intrinsic radiance factor is often expressed as a percentage.
3.3
reflectance factor
R
ratio of the radiation reflected by a surface element of a body in the direction delimited by a given cone,
with its apex at the surface element to that of the perfect reflecting diffuser under the same conditions
of illumination
Note 1 to entry: The ratio is often expressed as a percentage.
Note 2 to entry: The reflectance factor is influenced by the backing if the body is translucent.
3.4
intrinsic reflectance factor
R
∞
reflectance factor (3.3) of a layer or pad of material thick enough to be opaque, such that increasing the
thickness of the pad by doubling the number of sheets results in no change in the measured reflectance
factor
Note 1 to entry: The reflectance factor of a non-opaque sheet is dependent on the background and is not a
material property.
3.5
tristimulus values
X, Y, Z
amount of the three reference colour stimuli, in a given chromatic system, required to match the
stimulus considered
Note 1 to entry: In this document, the CIE illuminant C and the CIE 1931 (2°) standard observer are used to
define the trichromatic system.
Note 2 to entry: No subscript is applied to conform to the CIE convention that tristimulus values have no subscript
when the CIE 1931 (2°) standard observer is used [the subscript 10 is applied for tristimulus values that are
obtained using the CIE 1964 (10°) standard observer].
2
  © ISO 2022 – All rights reserved

---------------------- Page: 7 ----------------------
ISO/FDIS 5631-1:2022(E)
3.6
CIELAB colour space
three-dimensional, approximately uniform colour space, produced by plotting, in rectangular
coordinates L*, a*, b*, quantities defined by the formulae given in Clause 9
Note 1 to entry: The quantity, L*, is a measure of the lightness of the test piece, where L* = 0 corresponds to black
and L* = 100 is defined by the perfect reflecting diffuser. Visually, the quantities a* and b* represent respectively
the red-green and yellow-blue axes in colour space, such that
   +a* is a measure of the degree of redness of the test piece,
   −a* is a measure of the degree of greenness of the test piece,
   +b* is a measure of the degree of yellowness of the test piece, and
   −b* is a measure of the degree of blueness of the test piece.
If both a* and b* are equal to zero, the test piece is achromatic.
4 Principle
The light reflected from a sample under specified conditions is analysed either by a tristimulus-filter
colorimeter or by an abridged spectrophotometer, and the colour coordinates are then calculated for
C/2° conditions.
5 Apparatus
5.1 Reflectometer
5.1.1 Reflectometer, having the geometric, spectral and photometric characteristics described in
ISO 2469, and calibrated in accordance with the provisions of ISO 2469.
If materials containing fluorescent whitening agents are to be measured, the reflectometer shall be
equipped with a radiation source having an adequate UV content control, adjusted to a UV condition
corresponding to the C illuminant by the use of a reference standard, as described in ISO 2470-1.
5.1.2 In the case of a filter reflectometer, a set of filters that, in conjunction with the optical
characteristics of the basic instrument, give overall responses equivalent to the CIE tristimulus
values X, Y and Z of the CIE 1931 standard colorimetric system of the test piece evaluated for the CIE
illuminant C.
In the case of a filter reflectometer, the radiation falling upon the test piece shall have a UV content
corresponding to that of the CIE illuminant C.
5.1.3 In the case of an abridged spectrophotometer, a function that permits calculation of the CIE
tristimulus values X, Y and Z of the CIE 1931 standard colorimetric system of the test piece evaluated
for the CIE illuminant C using the weighting functions given in Annex A where the Tables A.1 and A.2
are used for instruments without bandpass correction and Tables A.3 and A.4 are used for instruments
with bandpass correction.
In the case of an abridged spectrophotometer, the instrument shall have an adjustable filter with a
cut-off wavelength of 395 nm or some other equivalent system, and this filter shal
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