Intercomparison of colour measurements

European Commission Directorate-General For The Information Society And Media Directorate-General For Research And Innovation

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Synthesis report
Industrial research and development

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• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
• Nombre de lectures: 30
• Langue: English
• Poids de l'ouvrage: 2 Mo

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ISSN 1018-5593
Commission of the European Communities
ber information
APPLIED METROLOGY
INTERCOMPARISON OF COLOUR MEASUREMENTS
SYNTHESIS REPORT
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Commission of the European Communities
ber information
APPLIED METROLOGY
INTERCOMPARISON OF COLOUR MEASUREMENTS
SYNTHESIS REPORT
J.F. VERRILL
Division of Quantum Metrology
National Physical Laboratory Teddington
Middlesex
UK-7W11 OLW
Contract No 3253/1/0/129/88/11/BCR - UK (30)
SYNTHESIS REPORT
A) dot Att Q ij
Directorate-General
Science, Research and Development Ì A!X EURv-P. Biblioih.
N.C.EUR 14982 E 1993
CI. Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General XIII
Telecommunications, Information Market and Exploitation of Research
L-2920 LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting on behalf
of the Commission is responsible for the use which might be made of the following information
Catalogue number: CD-NA-14982-EN-C
ECSC — EEC — EAEC, Brussels • Luxembourg, 1993 III
PARTICIPATING LABORATORIES (in alphabetical order)
Bundesanstalt fur Materialforschung und-prufung (BAM), Berlin, Germany
- Fachgruppe 5.4, Optische Materialeigenschaften und Farbmetrik (D Gundlach).
Etablissement Technique Central de l'Armement (ETCA), Arcueil, France
- Departement Physique des Surfaces (M F Mermoud and O Proffít).
Instituto de Optica "Daza De Valdes" (IO) Madrid, Spain
- G Campos Acosta, A Pons).
National Physical Laboratory (NPL), Teddington, United Kingdom
- Division of Quantum Metrology (J F Verrill, A R Hanson, Mrs J A Larkin, J O'Halloran).
The names of persons responsible for the results of this intercomparison at the respective
laboratories are given in brackets at the end of each address. In the following report the
initials of the laboratories, eg BAM will be used. ABSTRACT
Surface colour is an important aspect in consumer acceptance of almost all
manufactured goods as well as food. The industries where colour measurement is of
importance include textiles, paint, printing, paper and food processing as well as
photography, television and graphic design. In many situations there is a requirement
to match colours to a degree acceptable to the human eye which is capable of
discriminating several million different shades. In recent years judgement of the
acceptability of colour matches has largely transferred from visual observation to
measurement by instrumentation. The development of trade in coloured goods is
dependent on the uniformity of scales throughout the European Community.
This intercomparison compared scales of colour measurement of national laboratories
from France, Germany, Spain and the United Kingdom. The samples used were
ceramic colour standards produced by Ceram Research Ltd. These are known to be
stable and uniform and have been widely used throughout the world for several
years. The reference white standard against which the samples were measured was
white opal glass with a matt surface from the Community Bureau of Reference (BCR).
The opal had previously been calibrated at NPL with measurements traceable to the
PTB (Germany) absolute scales of diffuse reflectance and 45°/0° radiance factor. Sets
of fourteen ceramic colour standards together with a white reference opal were
circulated to each of the other three laboratories by NPL (United Kingdom). All
measured values are with respect to the perfect reflecting diffuser.
The report details the methods used by each laboratory and covers the three different
measurement geometries, specular excluded, specular included and 0°/45° radiance
factor, recommended by the CIE and used almost universally in industry. Expressed
in terms of CIELAB units, differences between laboratories of up to ± 1.1 units were
recorded. A factor of ten improvement is required. VII
CONTENTS
Page
INTRODUCTION
1.1 Colour and Industry 1
1.2r Primaries
1.3 The CEE System of Colour Specification
1.4 Colour Measuring Instruments
1.5 Matt and Qossy Materials 2
1.6 Relative and Absolute Measurements
1.7 Aim and Scope of the Intercomparison
MATERIALS
PRINCIPLES OF MEASUREMENT
MEASUREMENT BY PARTICIPANTS 6
4.1 BAM
4.2 ETCA 8
4.3 IO 9
4.4 NPL 10
4.5 Summary of the Measurement Systems 12
5 RESULTS
6 UNCERTAINTIES4
7 COMPARISON OF THE RESULTS 17
7.1 Spectral Data
7.2 Colour Data9
8 CONCLUSIONS 20
9 RECOMMENDATIONS1
10 REFERENCES2 Page
ANNEX 1 23
Representative Graphs of Spectral Reflectances of Ceramic Colour Standards
ANNEX2 27
Performance of the BCR Opal Glass
A21 Translucency of the Opal Glass 27
A22 Investigation of Risk of Contamination of the Matt Face of the Opal Glass 27
A23 Stability of the Opal Glass 27
DIRECTORY OF GRAPHS 29
DIRECTORY OF TABLES 32
GRAPHS R1 - R42 Rescaled differences in reflectance (one graph for each tile) 35-76
R43-R51 Rescateds ine at three wavelengths
(one complete set of tiles for each graph) 77-85
R52-R60 Rescaled fractional differences in reflectance at three
wavelengths 86-94
R61 - R69 Rescaled colour data differences, CIE XYZ 95-103
R70 - R78 dr data, CIELAB 104-112
SAMPLE TABLES
1, 43, 71 Differences in reflectance, white tile, specular excluded 113-118