iso 7724-1-1984

International Standard @$ 7724/ 1 0 a 4 4gb ,NTERNAT,ONAL ORGAN,ZAT,ON FOR STANDARDIZATION*MEX,WHAPO,,HAfl OPrAHH3AL,MR flOCTAHflAPTH3AWlM*ORGANlSATlON INTERNATIONALE DE NORMALISATION

Paints and vainishes - Colorimetry - Part 1: Principles Peintures et vernis - Colorimdtrie - Partie I: Principes

First edition - 1984-10-01

UDC 667.6 : 636.66 Ref. No. IS0 7724/l-1984 (E)

Descriptors : paints, varnishes, calorimetry.

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Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Every 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.

Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the IS0 Council. They are approved in accordance with IS0 procedures requiring at least 75 % approval by the member bodies voting.

International Standard IS0 7724/l was prepared by Technical Committee ISO/TC 35, Paints and varnishes.

0 International Organization for Standardization, 1984 0

Printed in Switzerland

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Contents

0 Introduction.. ..............................................

1 Scope and field of application .................................

2 References.. ...............................................

3 Colour co-ordinates ..........................................

3.1 Colour co-ordinates in the CIE 1964 supplementary standard calorimetric system .....................................

3.2 Colour co-ordinates in the CIE 1976 (L*u* b*) colour space ...

Page

. . . . . . 1

. . . . . . 1

. . . . . . 1

. . . . . . 1

...... 1

...... 2

4 Standardilluminants................................................. 4

5 Spectral radiometric characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

5.1 General ...............................................

5.2 Illumination and viewing conditions. .......................

...... 4

...... 5

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INTERNATIONAL STANDARD IS0 7724/l-1984 (E)

Paints and varnishes - Colorimetry - Part 1: Principles

0 Introduction

This International Standard, IS0 7724, comprises the following parts :

Part I : Principles.

Part 2 : Colour measurement.

Part 3 : Calculation of colour differences.

Parts 1, 2 and 3 of IS0 7724 describe methods for the instrumental determination of the colour co-ordinates and colour differences of paint films, as required for such purposes as

a) the objective description of colour differences between a test specimen (a test panel coated with a paint, or a specimen from a painted article) and a reference specimen;

b) determining colour deviations in the production of painted articles so that the results may be used for the control or regulation of the process;

c) the objective description of changes in colour caused by weathering and other chemical or physical influences;

d) the objective supervision of colour reference standards.

NOTE - Colour reference standards are subject to ageing, which may lead in the course of time to pronounced changes in colour. High ac- curacy calorimetry is required for the timely detection of these changes. This is of particular importance when ordering against such reference standards.

1 Scope and field of application

This part of IS0 7724 describes the calorimetric terms and fun- damental requirements necessary for determining the colour co-ordinates of paint films and related materials.

2 References

IS0 2813, Paints and varnishes - Measurement of specular gloss of non-metallic paint films at 2Q0, W and 85O.

IS0 3668, Paints and varnishes - Visual comparison of the colour of paints.

IS0 i724/2, Paints and varnishes - Calorimetry - Part 2 : Colour measurement.

IS0 772413, Paints and varnishes - Calorimetry - Part 3: Calculation of colour differences.

CIE Publication No. 15, Calorimetry, Official CIE Recommenda- tions.

CIE Publication No. 15, Supplement No. 2, Recommendations on uniform color spaces - Color difference equations - Psychometric color terms.

CIE Publication No. 38, Radiometric and photometric characteristics of materials and their measurement.

3 Colour co-ordinates

A colour is uniquely characterized for a defined observer and a defined light source by the co-ordinates of a point in a space formed by three mutually perpendicular vectors. From among the various colour co-ordinates recommended by the Commis- sion lnternationale de Ilklairage (CIE), the colour co-ordinates given in 3.1 and 3.2 are specified for calorimetric measurements on paint films in accordance with this International Standard.

3.1 Colour co-ordinates in the CIE 1964 supplementary standard calorimetric system

The colour co-ordinates in this system (see CIE Publication No. 15) are the tristimulus value Ytc and the chromaticity co- ordinates xl0 and ylo.

A=24

ylo = ho c p(A) j,&) AA

A = I

x10 = x10

I YlO = 50

xl0 + vo + ZlO x10 + YlO + Go

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IS0 7724/l-1984 (E)

The chromaticity co-ordinates are formed by the tristimulus values

A= u

x10 = ho c

qdA) X,,(A) AL, =I

A=u

ZlO = klo c 6pLU Zlo(L) AA and A=I

yto

where

(p(l) denotes the colour stimulus function, which is the product of the relative spectral power distribution SA for the standard illuminant (see clause 4) and the spectral function that characterizes the reflectance of the paint film (see clause 5) ;

~tolo(l), y,,(L) and Go(A) are the colour-matching functions (see note I) used to define the CIE 1964 standard col- orimetric observer for observation fields of angular subtense larger than 4O (loo observer) (see table I);

1 and u are the respective summation limits for the short- wave and long-wave limits of the visible spectrum;

An is the width of the wavelength interval (for the choice of I and U, and AA, see IS0 772412);

klo is a normalizing factor calculated by using the equa- tion

4, = lcn/(~~sAi,o~~, *j

which causes the tristimulus value Ylofor the perfect reflecting diffuser to assume a value of 100.

In this system, the colour co-ordinates do not provide a perceptually uniform colour space (see 3.2).

NOTES

1 The coafficients$,W, j$M and Mom ware formerly termed CIE spectral tristimulus values or CIE trichromatic weighting coaf- ficiants.

2 Colour co-ordinates in the CIE 1931 standard colorimatric system are defined by analogous equations using the colour-matching functions Ffh 1, y(k) and fiA 1 of the CIE 1931 standard colorimatric observer for the 2O observation field. Colour-matching functions at 5 nm wavelength intervals are given in CIE Publication No. 15.

The loo observation field corresponds more closely with practice than the 2O observation field and is consistent with the viewing conditions recommended in IS0 3666 for the visual comparison of the colour of paints.

3.2 Colour co-ordinates in the CIE 1976 (L*u*b*) colour space

In comparison with the CIE 1964 calorimetric system (see 3.11, the colour co-ordinates in the perceptually more uniform CIE 1976 U,a*b*) colour space (see CIE Publication No. 15 Supplement No. 2) are specified for the evaluation of colour differences.

The colour co-ordinates are calculated from the following equations :

L* = 116(YlY,)3 - 16 for Y/Y, > 0608856

L+ = 903,3 ( Y/Y) for Y/Y, < 0608856

a = 500 yrX/X, - jl Y/Y)1

b* = 200 ff( Y/Y,,) - flz/z,)l

f(XlX, = (XIX,3 forX/X, > 0908856

fCXlX,l = 7,767 CXlX,) + 16/l 16 forX/X, < 0,008856

fCY/Y, = (Y/Y)3 for Y/Y, > 0908856

fC Y/Y,,) = 7,767 (Y/Y,,) + 16/116 for Y/Y, < 0,008856

fCZ/Z, = (Z/Z,)3 for Z/Z, > 0.008856

f(Z/Z,) = 7,787 (Z/Z,) + 16/116 forZ/Z, < 0.008856

X, Y, Z denote the loo tristimulus values of the paint film;

X,, Y,, Z, are the loo tristimulus values of the perfect reflecting diffuser under the chosen standard illuminant (see table 2).

NOTE - If 2O tristimulus values are used, L*, a, b* co-ordinates for the 2O observer will be obtained. The corresponding values for X,, and Z, can be calculated from the 2O chromaticity co-ordinates for the standard illuminants D 65 and A (sea CIE Publication No. 151 with Y = loo.

It is sometimes convenient to express colour not in terms of the rectangular co-ordinates L+,a*, b*, but in terms of the rectilinear lightness and the polar co-ordinates chroma and hue (see CIE Publication No. 15 Supplement No. 2).

These may be calculated from L*, a*, b to give

CIE 1976 psychometric lightness L*

CIE 1976 a b chroma qb= (a*2 + t)*2)1/2

CIE 1976 a b hue angle h& = arctan (b*la*) between O and 360

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IS0 7724/l-1984 (E)

Table 1 - Colour-matching functions for the IO observer at 5 nm wavelength intervals

1 nm

360

z 395

iii 410 415 420

425

iii

iii

z

ii 470

475

iii

iii

E 510 515 520

525

E

Ei

E

Es!! 670

575

Ei 590 595

J$#)

0,0002 0,0007 0,0024 0,0072

O,oooO 0.0001

8:E

0,0191

igz 0:1406 0,2045

O,W20 0,0045

EE 0:0214

0.2647 0,0295 0,3147 0,0387 0,3577 0,0496 0.3637 0,0621 0,3867 0,0747

0,3707 0.3430 0,3023 0,2541 0.1956

i%z 0:1282 0,1526 0,1652

0.1323

Ez 0:0162 0.0051

0,2199 1,0302 0,2536 0.7721 0,2977 0,5701 0,3391 0,4153 0.= 0.3024

0,0038 0,4608 0.0154 0.5314 0,0375 66067 0,0714 0,6857 0,1177 0.7618

0.1730 0,= 0.3042 0,3768 0,4516

Ei 0:7052 0,7936 0,6767

0,9918 0,9991 0,9973 0,9924 0,9556

0,9512 1,0142 1,0743 1,1185 1,1343

0.9152

iEi!E 0:7774 0,7204

0.0007 0,0029 0.0105 0,0323

~~

EEi 0:9725

1,2625

Ez 1:9673 2;0273

I,9948 1,9007 1,7454 13549 1,3176

0,2185 0,1592 0,112O 0,= 0.0607

0.0431 0,0305

E% o:w79

8:K

Ezi 0:OWO

x:Ei

Kz 0:WOO

L nm

600 605

610 615 620

625

ii

E

E

El

670

675

iii

E

E 710 715 720

725

730 735

740 745

750 5;

765 770

z

qo(A)

11240 1.0991

1,- 0,9507 0,8563

0,7549 0,6475 0,5351 O/l316 0.3437

0.2663 0,2043

0,1526 0.1122

0,0813

0,057s

0,0409 0.0266

0,0199 0,0138

Ei 0:0046 0,0031 0,0022

0.0015

0,OOlO 0,0007

O,ooo5 0.-

O.ooo3 0,0002 0,OOol 0.0001 0,OOol

;E

Yid4

Of6583 0,=

:%i 0:3961

~:~

:Ei 0:1402

0,1076 0.0812

0,0603 0.0441

0,0318

0,0226

0,0159 0.0111

O,W77 0,0054

0.0037 0,0026 0.0018 0,0012 O,ooo8

Ez

0:WO3

O,ooo2 0,OoOl

0,am 0,OoOl O,oooO

::E

8:EE

q&i

O,oooO O,oooO

xi 0:OOOO

O,oooO O,oooO

EE 0:OOOO

O,oooO

~~

8:E

O,oooO

8:Ei

i:E

X:E

iEz 0:WOO

O,oooO

i:E

8:E

O,oooO

i%i 0:OWO 0.~

O,oooO O.oooO

Table 2 - 10 tristimulus values for the perfect reflecting diffuser for stardard illuminants D 55 and A

I Tristimulus I Standard illuminant value D0S 1 A I XII 94,81 111.14 Y" lW,W lW,W &I 107,34 35,20



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IS0 7724/l-1984 (El

4 Standard illuminants specified for the calorimetric determination of a special metamerism index (see clause 5 of IS0 7724/2).

The CIE standard illuminant D 65 which corresponds to natural daylight at a correlated colour temperature of about 6 500 K (see CIE Publication No. 15). should be specified for colour measurements in accordance with this International Standard.

Numerical values for the relative spectral power distribution S, of standard illuminants D 65 and A are given in table 3.

NOTE - Thestandard illuminant C corresoondstonaturaldavlightata 5 Spectral radiometric characteristics - correlated colourtemperature of6 744 K. Its spectral distribution does not approach that of natural daylight so closely as that of standard illuminant D 65, especially in the ultraviolet region.

5.1 General

The standard illuminant A, which represents the light of a tungsten lamp and corresponds in its spectral distribution to a perfect black body at a temperature of 2 656 K, should be

Of the various possible spectral radiometric characteristics that describe the reflecting properties of materials (see CIE Publica- tion No. 361, the three characteristics defined in 5.1 .l to 5.1.3 are used in this part of IS0 7724 for paint film calorimetry.

Table 3 - Relative spectral power distribution SAof standard illuminants D 65 and A at 5 nm wavelength intervals

zi 410 415 420

425

ii! 440 446

E 480 486 470

475

z

iii

E 510 515 520

525 630 535

E

550 555

E 570

575 580 585

E

sA,DlS sA, A

WO 52,3

Fig

g.@J 10.90 1269 13,35

2: 91:5 92.5 93,4

14,71 16,15 1766 19,29 21,00

2; 95:8

104,9 110,9

22,79 24.67 2664 28.70 30.85

117.0 a~ 117.4 35,41 117,8 37,81 116.3 w= 114.9 42,87

115.4 115,9 112,4 108,8 109,l

2% 51:cM 53,91 =m

109,4 108.6 107,8 106,3 104.8

2: 88:06 69,25 72,50

106.2 107.7 106,o 104,4 104,2

104,o 102.0 100.0 98.2 96,3

2: 92:2

75,79 79,13 82,52 86,95 89,41

92,91 =AJ

100,OO 10356 107,18

11060 11444 118.08 121,73 12539

1 nm SA, Ds6 %, A FE 610 615 620

8W 893 :z 8717

129,04 132.70 136.35 13999 143,62

625 85,5 147.23 630 83,3 150.84 635 83,5 154,42 640 83,7 15798 645 81,9 161,52

656 655

Ei 670

80,O 16593 W1 168.51 802 171.96 81,2 17538 823 178.77

675

ii!

E

80,3 182,12 78,3 18543 740 18670 69,7 191,93 70,7 195,12

700 71,6 198,26 705 73,0 201.36 710 74,3 204,41 715 68.0 207,41 720 61.6 210,36

725 65,7 213.27 730 a9 216,12 735 72,5 218.92 740 75,l 221.67 745 69,3 224.36

750 636 227,00 755 55,0 229.59 760 46,4 232.12 765 56.6 234.59 770 333 237,Ol

775 61 239,37 760 63.4 24166

L



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IS0 7724/l-1994 (E)

5.1 .l spectral reflectance factor R (1) : The ratio of the radiant flux reflected in the directions within a given cone to that reflected in the same directions by a perfect reflecting diffuser identically irradiated in the observed wavelength interval.

NOTE - In contrast to the recommendations of the CIE (see CIE Publication No. 15), this part of IS0 7724 specifies the spectral reflectance factor instead of the spectral radiance factor. The instruments commercially available are not suitable for accurate measurement of the spectral radiance factor because of systematic errors caused by the divergence of the reflected light beams.

5.1.2 spectral reflectance p(A): The ratio of the reflected radiant flux to the incident flux in the observed wavelength interval.

5.1.3 spectral diffuse reflectance e(d) (1) : The ratio of the reflected radiant flux to the incident flux in the observed wavelength interval measured with the specularly reflected light (gloss) excluded.

5.2 illumination and viewing conditions

The various modes for measuring the reflected radiation to be specified for colour measurements in accordance with this In- ternational Standard are listed in table 4.

In the directional illumination and viewing beams the angle between the beam axis and any ray shall not exceed 5O.

The diffuse illumination and viewing takes place in an integrating sphere with an internal coating chosen such that the light is diffused by the wall of the sphere uniformly and non- selectively with respect to wavelength. The total area of the sample port of the integrating sphere shall not exceed 10 % of the total internal reflecting sphere area.

Specularly reflected light can be partly suppressed for the illumination and viewing conditions 8/d and d/8 by means of a gloss trap. The results of the measurements are dependent on the size, the position, and the structure of the gloss trap.

It has proved practical to use only gloss traps which exclude at least 95 % of the light reflected by a highly polished black glass plate. These traps should be tested using a primary standard with a refractive index of between 150 and 155 as specified in IS0 2913 for the measurement of specular gloss. The quotient of the spectral reflectances of the higly polished black glass plate measured with and without gloss trap shall fulfil the con- dition

@(d)8/d(a)

@8ld(a) < 0,05 for any wavelength.

Table 4 - Spectral radiometric characteristics for calorimetry of paint films

Spectral radiometric characteristics

Symbol

Measurement conditions

Illumination Viewing Designation (Abbreviation)

Spectral reflectance

factor

Spectral reflectance

Spectral diffuse

reflectance

&5/O(A)

R0/45(1)

Rd18(A)

Rtd) d/8(l)

@B/d(l)

e(d) B/d(l)

directional 450 iT 50

directional* 00 zk 100

diffuse, integrating

sphere


sphere with

gloss trap

directional** 8O zk 2O

directional 8O 1 2

directional 00 f 100

directional 450 + 50

directional** 8 +_ 2O

directional* 8= I 2O


sphere


sphere with

gloss trap

45O/normal (45/O)

normal/45O (O/45)

diffuse/8O (d/81

diffuse/8O (d/8)

specular reflection excluded

8/diffuse (8/d)

8Ofdiffuse (8/d)

specular reflection excluded

* The possibility of interreflections between a high gloss specimen and the illuminating optics should be considered.

** This is contrary to the recommendations of the CIE (see CIE Publication No. 15) which permits the illumination or the viewing normal to the specimen (measurement conditions O/d and d/O). The illumination or observation angle with a small defined deviation from zero as specified in this part of IS0 7724 prevents interreflections between the specimen and the illuminating or viewing optics when measuring high gloss specimens.



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iso 7724-1-1984

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