ISO 18314-5:2022

Analytical colorimetry — Part 5: Procedure for colorimetric determination of colour differences of object colours according to equidistant colour spaces

This document specifies the procedure and test report for determining small colour differences of object colours according to equidistant colour spaces. Three suggestions for metrics for the quantitative determination of small colour differences (∆E Annexes A, B and C. These examples are related to the three colour space models: OSA-UCS modified by Oleari et al., DIN99o and CAM16-UCS (uniform colour space). This document is applicable for the assessment of pigments, dyestuff and extenders in the field of coatings, plastic and prints only that are evaluated in pairs for colour conformity, and which have small perceptible colour differences.

Analyse colorimétrique — Partie 5: Mode opératoire pour la détermination colorimétrique des différences de couleur des couleurs d'objets selon des espaces colorimétriques équidistants

General Information

• Status: Published
• Publication Date: 24-Nov-2022
• ICS: 87.060.10 - Pigments and extenders
• Technical Committee: ISO/TC 256 - Pigments, dyestuffs and extenders
• Drafting Committee: ISO/TC 256/WG 3 - General test methods for colorants and extenders
• Current Stage: 6060 - International Standard published
• Start Date: 25-Nov-2022
• Due Date: 21-Oct-2022
• Completion Date: 25-Nov-2022

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 18314-5
First edition
2022-11
Analytical colorimetry —
Part 5:
Procedure for colorimetric
determination of colour differences
of object colours according to
equidistant colour spaces
Analyse colorimétrique —
Partie 5: Mode opératoire pour la détermination colorimétrique
des différences de couleur des couleurs d'objets selon des espaces
colorimétriques équidistants
Reference number
ISO 18314-5:2022(E)
© ISO 2022

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ISO 18314-5:2022(E)
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© ISO 2022
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Published in Switzerland
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ISO 18314-5:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 S c op e . 1
2 Nor m at i ve r ef er enc e s . 1
3 Terms and definitions . 1
4 P r o c e du re .1
5 Te s t r ep or t . 2
Annex A (informative) OSA-UCS colour space modified by Oleari et al. . 3
Annex B (informative) DIN99o colour space . 6
Annex C (informative) CAM16-UCS colour space .12
Bibliography .15
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ISO 18314-5:2022(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.
This document was prepared by Technical Committee ISO/TC 256, Pigments, dyestuffs and extenders.
A list of all parts in the ISO 18314 series can be found on the ISO website.
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 18314-5:2022(E)
Introduction
The scope of ISO/TC 256 is standardization in the field of colorants, i.e. pigments, dyestuffs and
extenders. Standards on test metrics in this field is a very effective basis for the introduction and
improvement of quality management systems. The consequent use of standardized test metrics within
a company can cut down testing costs to a fraction of the original costs. Carefully written test metrics
improve the precision of the test results. Standards for pigments, dyestuffs and extenders used as raw
materials support the trade of these materials.
Several formulas had been developed in the past for the assessment of colour differences. For presenting
colours in a colour space, the CIELAB (CIE 1976 L*a*b*) colour space (adopted by ISO and published as
[1]
ISO/CIE 11664-4) and colour coordinates are the most prominent. For predicting colour differences,
the International Commission on Illumination (CIE) has standardized CIEDE2000 (adopted by ISO
[2]
and published as ISO/CIE 11664-6) . The CIEDE2000 formula is intended to be applicable within the
sample colour-difference magnitude of 0 to 5 CIELAB units. However, it does not have a new associated
analytical colour space, but is still based on CIELAB.
For the steering and adjustment of colorant production or extender production in colorants industry, a
uniform colour space (UCS) is an essential tool in addition to a colour difference formula. This requires
adjusting colorant formulations in a colour space. Both corrective actions in production and the delivery
specifications with customers are based on tolerance ellipsoids in the colour space applied. In CIE 217,
different colour difference formulas and colour space models have been analysed using actual and
reliable visual data sets. Several models gave similar performance, so no specific uniform colour space
model or Euclidian colour-difference formula can be proposed performing statistically significantly
better than CIEDE2000. However, three colour spaces stood out: OSA-UCS, DIN99o and CAM02-UCS,
in chronological order of their publications. In this document, the actual editions of these models are
standardized for the assessment of coloristic properties of pigments, dyestuff and extenders.
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INTERNATIONAL STANDARD ISO 18314-5:2022(E)
Analytical colorimetry —
Part 5:
Procedure for colorimetric determination of colour
differences of object colours according to equidistant
colour spaces
1 S cope
This document specifies the procedure and test report for determining small colour differences of
object colours according to equidistant colour spaces. Three suggestions for metrics for the quantitative
determination of small colour differences (∆E < 5) of non-luminous colours are given in Annexes A, B
and C. These examples are related to the three colour space models: OSA-UCS modified by Oleari et al.,
DIN99o and CAM16-UCS (uniform colour space).
This document is applicable for the assessment of pigments, dyestuff and extenders in the field of
coatings, plastic and prints only that are evaluated in pairs for colour conformity, and which have small
perceptible colour differences.
2 Normat ive references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
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/
4 Procedure
For determining small colour differences (∆E < 5) of object colours according to equidistant colour
spaces, one of the three procedures from Annexes A, B and C should be used. Three suggestions for
metrics for the quantitative determination of small colour differences of non-luminous colours are
given in detail in Annexes A, B and C for information. These examples are related to the three colour
1)
space models OSA-UCS modified by Oleari et al., DIN99o and CAM16-UCS. Further information on
these models can be found in References [11] to [31].
The used calculation metric for the colour difference shall be stated in the test report.
When the formulae described in Annexes A, B and C are used for large colour differences (greater than
approximately 10 CIELAB units), larger deviations between calculated colour differences and visual
evaluations are to be expected. This is due to a nonlinear relationship between small and large colour
differences. If it is intended to use the formulae in this range, it should be explicitly agreed between the
interested parties.
[19] [18] [21]
1) DIN99o was denoted DIN99b but has later been referred to as DIN99o .
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ISO 18314-5:2022(E)
5 Test report
The test report shall contain at least the following information:
a) all details necessary to identify the product tested;
b) a reference to this document, i.e. ISO 18314-5:2022;
c) the colour space model used for the determination of the colour differences;
d) the results of the test;
e) any deviations from the procedure specified;
f) any unusual features (anomalies) observed during the test;
g) the date of the test.
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ISO 18314-5:2022(E)
Annex A
(informative)

OSA-UCS colour space modified by Oleari et al.
A.1 Description of the modified OSA-UCS colour space
The OSA-UCS colour space was first published in 1947 by the Optical Society of America (OSA) and
further developed in the subsequent years. The model is based on the characterization of colours
using approximately 500 lattice points in a regular rhombohedral shape in an Euclidian space. This
can be illustrated by a cube with each of the eight corners being cut symmetrically. The CIE 10°
standard observer and the D65 standard illuminant was used. This colour space is based on the three
perpendicular coordinates lightness: L , Jaune J (the yellow/blue axis) and Green G (the green/red
OSA
axis).
For OSA-UCS lightness, L , the value of 0 corresponds to a 30 % reflective neutral background.
OSA
Assuming nearly zero values for G, positive values of J indicate yellowish or brownish colours, and
negative values of J blue colours.
Assuming nearly zero values for J, positive values of G indicate greens and negative values of G purple
colours.
In this document, Oleari’s concept of a logarithmic compression in chroma and lightness leading to ΔE
E
is applied, using the new coordinates J, and G. Further details are described in A.2 and the References
[12] to [17].
For the transformation from the X , Y , Z coordinates or the x , y , z -chromaticity coordinates,
10 10 10 10 10 10
respectively to the OSA-UCS system proposed by Oleari, the following and Formulae (A.1) to (A.5) are
applied:
Let (Y , x , y ) and (L , J, G) be the colour specification in two spaces. The unit of distance in the
10 10 10 OSA
OSA-UCS space is approximately 10 just noticeable difference, assuming that this space conforms to
Euclidean metrics.
The lightness is defined as in the original OSA-UCS formula [Formula (A.1)]:
2 1
 13/  13/ 
+− −
LY=−59,,0 042()Y 30 14,4 (A.1)
 
OSA {}0
0
 
3
  
2
with
2 2
YY=+4,,493 44xy303 44−−,,276 01xy 374 42x − ,5664 31y + ,.810 3
( )
01010 10 10 10 10 10
The lightness L has no simple analytical conversion from the OSA-UCS space to the tristimulus space.
OSA
The coordinates J and G, which correspond to the empirical j and g of the OSA-UCS system, are obtained
by a sequence of linear transformations and a logarithmic compression – see Formula (A.2) and
Formula (A.3):
A 0,,659 70 449 20− ,108 9 X
 
   
10
 
   
B = −0,,305 31 212 60,092 7 Y , (A.2)
    10 
   
 
C −−0,,037 40 479 50,557 9 Z
    10 
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ISO 18314-5:2022(E)
  AB/ 
ln
  
S 0 AB/
J −sincααos
      
J nn
 
=
   
 
 
G 0 S sincββ− os
      BC/ 
G
 
ln
 
 
BC/
  
nn
AB/
  
ln
 
 
20(,573 57L + ,)089 20
01, 7992 0,983 7
   0,936 6
OSA  
 
= (A.3)
  
02−+(,0 764 09L ,)252 1 0,,948 20− 317 5  
BC/
    
OSA
ln
  
09, 880 7
  
S and S are suitable normalization-scale factors and α and β are the angles between the reference
G J
axes of the main chromatic opponent functions and the directions of parallel lines with constants g and
[11]
j, respectively . A , B and C are the values of A, B and C according to Formula (A.3) for the neutral
n n n
standard illuminant D65.
The analytical reversibility of this transformation is straightforward, excluding the conversion of L .
OSA
The chroma and hue angles are obtained in OSA-UCS space from J and G coordinates as in CIELAB from
a* and b* according to Formulae (A.4) and (A.5):
22
CJ=+G (A.4)
OSA
J
 
h =arctan (A.5)
OSA  
−G
 
NOTE h is expressed in degrees (°).
OSA
A.2 Determination of colour differences according to OSA-UCS colour space
modified by Oleari et al.
[12]
From colour space proposed by Oleari et al. (see A.1), the colour-difference formula ΔE was
GP
introduced. Next, based on a logarithmic compression of the OSA-UCS coordinates in the colour space
modified by Oleari et al., new coordinates L , J , G were proposed, defining a new colour space with
E E E
[13]
an Euclidean colour-difference formula named ΔE . The ΔE and ΔE colour-difference formulas
E GP E
were tested by CIE/TC 1-55 in CIE 217, together with CIEDE2000, DIN99o and other colour-difference
formulas.
Based on the original coordinates OSA-chroma C and L , the definitions of this formula and of
OSA OSA
the OSA-UCS space with chroma and lightness log compressed are recalled by Formula (A.6) to
Formula (A.10):
2 2 2
ΔΔEL=( )+()ΔΔGJ+( ) , (A.6)
EE E E
   
1 b
L
L = ln 1+ ()10L (A.7)
 
E  OSA 
b a
 L   L 
with  a =2,890 ,  b =0,015 ,
L L
GC=c− os h ,
()
EE
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ISO 18314-5:2022(E)
JC=sin h , (A.8)
()
EE
with
J
 
h =−arctan ,
 
G
 
 1   b 
C
C = ln 11+ 0C (A.9)
()
E    OSA 
b a
C C
   
with  a =1,256 ,  b =0,050 ,
C C
22
CG=+J. (A.10)
OSA
Greater insight into this concept and the introduction or derivation of the colour coordinates, as well as
the formulae, can be obtained from References [14] to [17].
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ISO 18314-5:2022(E)
Annex B
(informative)

DIN99o colour space
B.1 Description of the DIN99o colour space
B.1.1 General
The DIN99o formula was the result of the adjustment of the parameters of the well-established
CIELAB colour space. The goal was to fit the results of the colour differences according to CIEDE2000
but keeping the properties of a colour space. Vectors are no longer of significance in the CIEDE2000
formula, therefore, there is no colour space based on the CIEDE2000 formula.
B.1.2 Determination of coordinates L , a , b , C , h of the DIN99o formula
99o 99o 99o 99o 99o
The starting point for the determination of the colour coordinates L , a , b , C , h of the
99o 99o 99o 99o 99o
DIN99o formula is the determination of the colour coordinates L*, a*, b* according to ISO/CIE 11664-4.
The colour coordinates L , a , b , C , h are determined according to Formulae (B.1) to
99o 99o 99o 99o 99o
Formula (B.15) [for calculation examples see B.2]:

DIN 99o lightness:   L = 303,67 ln (1,0 + 0,0039 L*)/k (B.1)
99o E
Auxiliary variable for
redness:   e = a* cos 26° + b* sin 26° (B.2)
o
Auxiliary variable for
yellowness:    f = −0,83 a* sin 26° + 0,83 b* cos 26° (B.3)
o
Auxiliary variable for
2 2 0,5
chroma:    G = (e + f ) (B.4)
o o o
Auxiliary variable for hue
angle:    h = arctan ( f /e )   for e > 0 and f ≥ 0 (B.5)
eofo o o o o

(in radians)   h = π/2   for e = 0 and f > 0 (B.6)
eofo o o

       h = π + arctan ( f /e )   for e < 0 (B.7)
eofo o o o

       h = 3π/2   for e = 0 and f < 0 (B.8)
eofo o o

       h = 2π + arctan ( f /e )   for e > 0 and f < 0 (B.9)
eofo o o o o

       h = 0   for e = 0 and f = 0 (B.10)
eofo o o
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ISO 18314-5:2022(E)

DIN 99o variable:
DIN 99o hue angle
in degrees:    h = (h 180°/π )+ 26°   for h < 334° π/180° (B.11)
99o eofo eofo

   h = [(h − 2π)180°/π ]+ 26°   for h ≥ 334° π/180° (B.12)
99o eofo eofo

DIN 99o chroma:   C = [ln (1 + 0,075 G )]/(0,043 5 k k ) (B.13)
99o o CH E

DIN 99o green-redness:   a = C cos (h π/180°) (B.14)
99o 99o 99o

DIN 99o blue-yellowness:   b = C sin (h π/180°) (B.15)
...