Table of Contents

Series Page

Title Page

Copyright

Prologue

About the Authors

Series Preface

Preface

To the First Edition

To the Second Edition

To the Third Edition

To the Fourth Edition

Acknowledgements

For the First Edition

For the Second Edition

For the Third Edition

For the Fourth Edition

Chapter 1: Colour Vision

1.1 Introduction

1.2 The Spectrum

1.3 Construction of the Eye

1.4 The Retinal Receptors

1.5 Spectral Sensitivities of the Retinal Receptors

1.6 Visual Signal Transmission

1.7 Basic Perceptual Attributes of Colour

1.8 Colour Constancy

1.9 Relative Perceptual Attributes of Colours

1.10 Defective Colour Vision

1.11 Colour Pseudo-Stereopsis

References

General References

Chapter 2: Spectral Weighting Functions

2.1 Introduction

2.2 Scotopic Spectral Luminous Efficiency

2.3 Photopic Spectral Luminous Efficiency

2.4 Colour-Matching Functions

2.5 Transformation From R, G, B to X, Y, Z

2.6 CIE Colour-Matching Functions

2.7 Metamerism

2.8 Spectral Luminous Efficiency Functions for Photopic Vision

References

General References

Chapter 3: Relations Between Colour Stimuli

3.1 Introduction

3.2 The Y Tristimulus Value

3.3 Chromaticity

3.4 Dominant Wavelength and Excitation Purity

3.5 Colour Mixtures on Chromaticity Diagrams

3.6 Uniform Chromaticity Diagrams

3.7 CIE 1976 Hue-Angle and Saturation

3.8 CIE 1976 Lightness, L*

3.9 Uniform Colour Spaces

3.10 CIE 1976 Colour Difference Formulae

3.11 CMC, CIE94, and CIEDE2000 Color Difference Formulae

3.12 An Alternative Form of the CIEDE2000 Colour-Difference Equation

3.13 Summary of Measures and Their Perceptual Correlates

3.14 Allowing for Chromatic Adaptation

3.15 The Evaluation of Whiteness

3.16 Colorimetric Purity

3.17 Identifying Stimuli of Equal Brightness

3.18 CIEDE2000 Worked Example

References

General References

Chapter 4: Light Sources

4.1 Introduction

4.2 Methods of Producing Light

4.3 Gas Discharges

4.4 Sodium Lamps

4.5 Mercury Lamps

4.6 Fluorescent Lamps

4.7 Xenon Lamps

4.8 Incandescent Light Sources

4.9 Tungsten Lamps

4.10 Tungsten Halogen Lamps

4.11 Light Emitting Diodes

4.12 Daylight

4.13 Standard Illuminants and Sources

4.14 CIE Standard Illuminant A

4.15 CIE Illuminants B and C

4.16 CIE Sources

4.17 CIE Illuminants D

4.18 CIE Indoor Daylight

4.19 Comparison of Commonly used Sources

References

General References

Chapter 5: Obtaining Spectral Data and Tristimulus Values

5.1 Introduction

5.2 Radiometry and Photometry

5.3 Spectroradiometry

5.4 Tele-Spectroradiometry

5.5 Spectroradiometry of Self-Luminous Colours

5.6 Spectrophotometry of Non-Self-Luminous Colours

5.7 Reference Whites and Working Standards

5.8 Geometries of Illumination and Viewing

5.9 CIE Geometries of Illumination and Measurement

5.10 Spectroradiometers and Spectrophotometers

5.11 Choice of Illuminant

5.12 Calculation of Tristimulus Values from Spectral Data

5.13 Colorimeters using Filtered Photo-Detectors

References

General References

Chapter 6: Metamerism and Colour Constancy

6.1 Introduction

6.2 The Cause of Metamerism

6.3 The Definition of Metamerism

6.4 Examples of Metamerism in Practice

6.5 Degree of Metamerism

6.6 Index of Metamerism for Change of Illuminant

6.7 Index of Metamerism for Change of Observer

6.8 Index of Metamerism for Change of Field Size

6.9 Colour Matches and Geometry of Illumination and Measurement

6.10 Correcting for Inequalities of Tristimulus Values

6.11 Terms Used in Connection with Metamerism

6.12 Colour Inconstancy

6.13 Chromatic Adaptation Transforms

6.14 The Von Kries Transform

6.15 The CAT02 Transform

6.16 A Colour Inconstancy Index

6.17 Worked examples

References

Chapter 7: Colour Rendering by Light Sources

7.1 Introduction

7.2 The Meaning of Colour Rendering

7.3 CIE Colour Rendering Indices

7.4 Spectral Band Methods

7.5 Other Methods for Assessing the Colour Rendering of Light Sources

7.6 Comparison of Commonly used Sources

References

General References

Chapter 8: Colour Order Systems

8.1 Introduction

8.2 Variables

8.3 Optimal Colours

8.4 The Munsell System

8.5 The Munsell Book of Color

8.6 Unique Hues and Colour Opponency

8.7 The Natural Colour System (NCS)

8.8 Natural Colour System Atlas

8.9 The DIN System

8.10 The Coloroid System

8.11 The Optical Society of America (OSA) System

8.12 The Hunter Lab System

8.13 The Tintometer

8.14 The Pantone System

8.15 The Ral System

8.16 Advantages of Colour Order Systems

8.17 Disadvantages of Colour Order Systems

References

General References

Chapter 9: Precision and Accuracy in Colorimetry

9.1 Introduction

9.2 Sample Preparation

9.3 Thermochromism

9.4 Geometry of Illumination and Measurement

9.5 Reference White Calibration

9.6 Polarisation

9.7 Wavelength Calibration

9.8 Stray Light

9.9 Zero Level and Linearity

9.10 Use of Secondary Standards

9.11 Bandwidth

9.12 Correcting for Errors in the Spectral Data

9.13 Calculations

9.14 Precautions to be Taken in Practice

References

Chapter 10: Fluorescent Colours

10.1 Introduction

10.2 Terminology

10.3 Use of Double Monochromators

10.4 Illumination with White Light

10.5 Correcting for Differences Between an Actual and the Desired Source

10.6 Two-Monochromator Method

10.7 Two-Mode Method

10.8 Filter-Reduction Method

10.9 Luminescence-Weakening Method

10.10 Practical Considerations

References

Chapter 11: RGB Colorimetry

11.1 Introduction

11.2 Choice and Specification of Matching Stimuli

11.3 Choice of Units

11.4 Chromaticity Diagrams Using r and g

11.5 Colour-Matching Functions in RGB Systems

11.6 Derivation of XYZ from RGB Tristimulus Values

11.7 Using Television and Computer Displays

References

General References

Chapter 12: Colorimetry with Digital Cameras

12.1 Introduction

12.2 Camera Characterisation

12.3 Metamerism

12.4 Characterisation Methods

12.5 Practical Considerations in Digital Camera Characterisation

12.6 Practical Example

12.7 Discussion

References

General References

Chapter 13: Colorant Mixtures

13.1 Introduction

13.2 Non-Diffusing Colorants in a Transmitting Layer

13.3 Non-Diffusing Colorants in a Layer in Optical Contact with a Diffusing Surface

13.4 Layers Containing Colorants which Diffuse and Absorb Light

13.5 The use of Multi-Spectral Analysis to Reduce Metamerism in Art Restoration

References

General References

Chapter 14: Factors Affecting the Appearance of Coloured Objects

14.1 Introduction

14.2 Measuring Optical Properties

14.3 Colour

14.4 Gloss

14.5 Translucency

14.6 Surface Texture

14.7 Conclusions

References

Chapter 15: The CIE Colour Appearance Model CIECAM02

15.1 Introduction

15.2 Visual Areas in the Observing Field

15.3 Chromatic Adaptation in CIECAM02

15.4 Spectral Sensitivities of the Cones in CIECAM02

15.5 Cone Dynamic Response Functions in CIECAM02

15.6 Luminance Adaptation in CIECAM02

15.7 Criteria for Achromacy and for Constant Hue in CIECAM02

15.8 Effects of Luminance Adaptation in CIECAM02

15.9 Criteria for Unique Hues in CIECAM02

15.10 Redness-Greenness, a, and Yellowness-Blueness, b, in CIECAM02

15.11 Hue Angle, h, in CIECAM02

15.12 Eccentricity Factor, e, in CIECAM02

15.13 Hue Quadrature, H, and Hue Composition, Hc, in CIECAM02

15.14 The Achromatic Response, A, in CIECAM02

15.15 Correlate of Lightness, J, in CIECAM02

15.16 Correlate of Brightness, Q, in CIECAM02

15.17 Correlate of Chroma, C, in CIECAM02

15.18 Correlate of Colourfulness, M, in CIECAM02

15.19 Correlate of Saturation, s, in CIECAM02

15.20 Comparison of CIECAM02 with the Natural Colour System

15.21 Testing Model CIECAM02

15.22 Filtration of Projected Slides and CIECAM02

15.23 Comparison of CIECAM02 with CIECAM97s

15.24 Uniform Colour Space Based on CIECAM02

15.25 Some Problems with CIECAM02

15.26 Steps for Using the CIECAM02 Model

15.27 Steps for Using the CIECAM02 Model in Reverse Mode

15.28 Worked Example for the Model CIECAM02

References

Chapter 16: Models of Colour Appearance for Stimuli of Different Sizes

16.1 Introduction

16.2 Stimuli of Different Sizes

16.3 Room Colours

16.4 A Model for Predicting Room Colours

16.5 Steps in Using the Model for Predicting Room Colours

References

Chapter 17: Model of Colour Appearance for Unrelated Colours in Photopic and Mesopic Illuminances

17.1 Introduction

17.2 A Model for Predicting Unrelated Colours

17.3 Input Data Required for the Model

17.4 Steps in Using the Model for Unrelated Colours

17.5 Worked Example in the Model for Predicting Unrelated Colours

References

Appendices

Appendix 1: Radiometric and Photometric Terms and Units

A1.1 Introduction

A1.2 Physical Detectors

A1.3 Photometric Units and Terms

A1.4 Radiant and Quantum Units and Terms

A1.5 Radiation Sources

A1.6 Terms for Measures of Reflection and Transmission

A1.7 Other Spectral Luminous Efficiency Functions

A1.8 Mesopic Photometry

Reference

Appendix 2: Spectral Luminous Efficiency Functions

Appendix 3: CIE Colour-Matching Functions

Appendix 4: CIE Spectral Chromaticity Co-Ordinates

Appendix 5: Relative Spectral Power Distributions of Illuminants

A5.1 Introduction

A5.2 Cie Illuminants

A5.3 Representative Fluorescent Lamps

A5.4 Planckian Radiators

A5.5 Gas Discharge Lamps

A5.6 Method of Calculating D Illuminant Distributions

Appendix 6: Colorimetric Formulae

A6.1 Chromaticity Relationships

A6.2 CIELUV, CIELAB, and U*V*W* Relationships

Appendix 7: Calculation of the CIE Colour Rendering Indices

A7.1 Spectral Radiance Factors of Test Colours

A7.2 Worked Example of the CIE Colour Rendering Indices

Appendix 8

Appendix 9: Glossary of Terms

Reference

Index

Wiley-IS&T Series in Imaging Science and Technology

Series Editor:

Michael A. Kriss

Consultant Editor:

Lindsay W. MacDonald

Reproduction of Colour (6th Edition)

R. W. G. Hunt

Colour Appearance Models (2nd Edition)

Mark D. Fairchild

Colorimetry: Fundamentals and Applications

Noburu Ohta and Alan R. Robertson

Color Constancy

Marc Ebner

Color Gamut Mapping

Ján MoroviC

Panoramic Imaging: Sensor-Line Cameras and Laser Range-Finders

Fay Huang, Reinhard Klette and Karsten Scheibe

Digital Color Management (2nd Edition)

Edward J. Giorgianni and Thomas E. Madden

The JPEG 2000 Suite

Peter Schelkens, Athanassios Skodras and Touradj Ebrahimi (Eds.)

Color Management: Understanding and Using ICC Profiles

Phil Green (Ed.)

Fourier Methods in Imaging

Roger L. Easton, Jr.

Measuring Colour (4th Edition)

R.W.G. Hunt and M.R. Pointer

Published in association with the Society for Imaging Science and Technology

This edition first published 2011

© 2011, John Wiley & Sons, Ltd

Previous Editions:

1st Edition ISBN 0 7458 01250 0, Ellis Horwood, Chichester, 1987

2nd Edition ISBN 0 13 567686 X, Ellis Horwood, Chichester, 1991

3rd Edition ISBN 0 86343 387 1, Fountain Press, Kingston-upon-Thames, 1998

Registered office

John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, United Kingdom

For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com.

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All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher.

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Library of Congress Cataloging-in-Publication Data

Hunt, R.W.G. (Robert William Gainer), 1923-

Measuring colour / R.W.G. Hunt, M.R. Pointer.– 4th ed.

p. cm.– (The Wiley-IS&T series in imaging science and technology)

Includes bibliographical references and index.

ISBN 978-1-119-97537-3 (hardback)

1. Colorimetry. I. Pointer, Michael, Ph. D. II. Title.

QC495.H84 2011

535.6028′7– dc23

2011018730

A catalogue record for this book is available from the British Library.

Print ISBN: 978-1-119-97537-3

ePDF ISBN: 978-1-119-97573-1

oBook ISBN: 978-1-119-97559-5

ePub ISBN: 978-1-119-97840-4

Mobi ISBN: 978-1-119-97841-1

Prologue

This is the story of Mister Chrome

who started out to paint his home.

The paint ran out when half way through

so to the store he quickly flew

to buy some more of matching hue,

a delicate shade of egg-shell blue.

But when he tried this latest batch,

he found it simply didn't match.

No wonder he was in a fix,

for of the colours we can mix,

the major shades and those between,

ten million different can be seen.

You foolish man, said Missis Chrome,

you should have taken from the home

a sample of the colour done;

you can't remember every one.

Taking care that she had got

a sample from the early pot,

she went and bought her husband more

of better colour from the store.

Before she paid, she checked the shade,

and found a perfect match it made.

In triumph now she took it home,

and gave it straight to Mister Chrome.

He put it on without delay,

and found the colour now okay.

But, after dark, in tungsten light,

they found the colour still not right.

So to the store they both went now,

with samples clear, and asked them how

a paint that matched in daylight bright

could fail to match in tungsten light.

The man's reply to their complaint

was that the pigments in the paint

had been exchanged, since they had bought,

for others of a different sort.

To solve the problem on their wall,

he gave them paint to do it all

from just one batch of constant shade,

and then at last success was made.

To compensate them for their trouble,

the store sent to them curtains double.

They hung them up with great delight;

they matched in tungsten and daylight.

A neighbour then did make a call

and fixed his eye upon the wall;

the paint, he said was all one colour,

but clearly saw the curtains duller!

Though colours strange at times appear,

the moral of this tale is clear:

to understand just what we see,

object, light, and eye, all three,

must colour all our thinking through

of chromic problems, old or new!

About the Authors

Dr Robert W. G. Hunt received his Ph.D and DSc from the University of London. He was a research scientist at the Kodak Research Laboratories, where he worked on factors affecting the quality of colour images, and devices for making reflection prints from both negative and positive images on film; he was finally Assistant Director of Research. Since 1982 he has worked as an independent colour consultant, and has taken a leading role in the development of colour appearance models. He has written over 100 papers on colour vision, colour reproduction, and colour measurement, and his other book, The Reproduction of Colour, is now in its sixth edition. He has been awarded the Newton Medal of the Colour Group (Great Britain) (1974), the Progress Medal of the Royal Photographic Society (1984), the Judd-AIC Medal of the International Colour Association (1987), the Gold Medal of the Institute of Printing (1989), the Johann Gutenberg Prize of the Society for Information Display (2002), the Godlove Award of the Inter-Society Color Council, U.S.A (2007), and Honorary Fellowship of the Society of Dyers and Colourists (2009). In 2009 he was appointed an Officer of the British Empire (OBE) for ‘services to the field of colour science and to young people through Crusaders’.

Dr Michael R. Pointer received his Ph.D from Imperial College, London, working with David Wright. He then worked in the Research Division of Kodak Limited on fundamental issues of colour science applied to the photographic system. After periods at the University of Westminster and the National Physical Laboratory, he is now a Visiting Professor at the University of Leeds, as well as working as a consultant scientist. In 1997, he received the Fenton Medal, The Royal Photographic Society's award for services to the Society. In 2004, he received a Silver Medal from the Society of Dyers and Colourists for ‘contributions to colour science’. He has authored over 100 scientific papers, is a Fellow of The Royal Photographic Society and the Institute of Physics, Secretary of CIE Division 1 Vision & Colour, and UK Associate Editor of the journal, Color Research & Application.

Series Preface

Imagine Alice in Wonderland saying this: ‘I wonder if I've changed colour in the night? Let me think. Was I the same hue when I got up this morning? I almost think I can remember feeling a little less saturated. But if I'm not the same x-y value, the next question is ‘What Lab value in the world am I?’ Ah, that's the great puzzle!’

The fourth edition of Measuring Colour by Dr Robert W.G. Hunt and Dr Michael R. Pointer is the eleventh book in the Wiley-IS&T Series in Imaging Science and Technology. This excellent text, while not solving the complex puzzle of colour, provides readers with the means to solve their colour puzzle.

The 17-chapter book starts with the basic concepts of colour vision then covers the methodology of converting a spectrum to CIE values (XYZ or Lab) so one can match colours and detect metamers. Visual models are then used to indicate how colour changes under different viewing conditions and to explain why surface characteristics influence the perception of a given spectrum. The details of using digital cameras to measure colour are an important addition in the fourth edition, as the authors recognise that the CCD and CMOS sensors in digital cameras, together with colour filter arrays and digital signal processing, present a new opportunity to measure spatial variation in colour.

Human beings are very sensitive to colour changes or differences and find it difficult to decide, from a set of colours, for example on a paint palette, which one is wanted. People have a strong sense of memory of preference for the colour of green grass, blue skies or pink sunsets. They notice when a photographic image (from a film or digital camera) of a red tablecloth comes out wrong or when the sweater that was bought in a shopping mall under tungsten (fluorescent) light looks different in daylight.

Neural scientists can use Functional Magnetic Resonance Imaging to locate where in the brain the perceptions of the colours of the visible spectrum are located. Colour scientists know that each colour has an exact spectral power distribution which can be measured to a high degree of accuracy. Why, then, is colour such a puzzle?

What Alice did not know when she fell down the rabbit hole was that the human visual system can play a lot of tricks on how we perceive colour. The perception of colour depends not just on its native spectrum but also on the spectra of the direct illumination, the ambient illumination and the near and far surround colours. Geometrical patterns can cause local colour changes as seen by the observer, as can adaptation to a uniform colour field. So how can the puzzle called colour be solved when there are so many variables and boundary conditions?

The Mock Turtle might have said: ‘What is the use of studying all that colour stuff, if you can't measure it as you go on? It's by far the most confusing thing I ever heard!’

But then, he was not privy to the fourth edition of Measuring Colour which provides a welcome and major contribution to the continuing understanding of the puzzle that is colour.

MICHAEL A. KRISS

Formerly of the Eastman Kodak Research

Laboratories and the University of Rochester, USA

Preface

To the First Edition

This book is intended to provide the reader with the basic facts needed to measure colour. It is a book about principles, rather then a guide to instruments. With the continual advances in technology, instruments are being improved all the time, so that any description of particular colorimeters, spectroradiometers, or spectrophotometers is likely to become out of date very quickly. For such information, manufacturers' catalogues are a better source of information than books. But the principles of measuring colour are not subject to rapid change, and are therefore appropriate for treatment in the more permanent format offered by books.

Recommendations about the precise way in which the basic principles of colour measurement should be applied have for over 50 years been the province of the International Commission on Illumination (CIE). The second edition of its publication No. 15, Colorimetry, includes several new practices, and it is therefore timely to restate the basic principles of colorimetry together with these latest international recommendations on their application; this is the aim of Measuring Colour.

Colour is, of course, primarily a sensation experienced by the individual. For this reason, the material has been set in the context of the colour vision properties of the human observer: the first chapter is a review of our current knowledge of colour vision; and the last chapter provides a description of a model of colour vision that can be used to extend colour measurement, beyond the territory covered by the CIE at present, to the field of colour appearance.

To the Second Edition

The second edition contains all the material of the first edition, together with four new chapters. Two of these chapters provide entirely new material: one is on light sources and the other is on precision and accuracy in colorimetry. The other two new chapters provide expanded treatments of metamerism and of the colorimetry of fluorescent materials. Extensive revisions have been made to the chapter on the model of colour vision, so as to present it in its latest version. Finally, minor revisions have been made to the rest of the book to improve the treatment in various respects.

To the Third Edition

The following changes have been made to this third edition. The chapter on metamerism has been expanded to include a discussion of corresponding colours, colour constancy and a description of a colour inconstancy index. The material in Chapter 11 of the second edition, entitled ‘Miscellaneous topics’, has been included at the end of Chapter 3. Chapter 11 now provides a discussion of the way in which the colours of colorant mixtures can be evaluated. Chapter 12 has been updated to provide the colour appearance model adopted internationally, designated CIECAM97s. Two new Appendices have been added: Appendix 7 provides illuminant-observer weights for band-pass corrected data, and Appendix 8 provides illuminant-observer weights for band-pass uncorrected data. In addition, various minor changes have been made to update the text.

To the Fourth Edition

For this fourth edition Dr Michael R. Pointer has become a joint author. Much of the book is concerned with CIE procedures, and, as current secretary of CIE Division 1 Colour and Vision, Dr Pointer has enabled the important features of the latest CIE publications to be covered; he has also provided new chapters on ‘Factors affecting the appearance of coloured objects’ and ‘Colorimetry with digital cameras’. The first of these chapters covers the important topics of gloss, translucency and texture, which were not previously included; the second of these chapters covers the technology that enables colorimetry to be carried out on objects with complicated shapes or patterns, and which has been developed since publication of the third edition. The important topic of colour rendering by light sources now has its own chapter, and this includes descriptions of alternatives to the current CIE Colour Rendering Index. Additions to the Appendices include the recent CIE procedure for mesopic photometry, and the spectral reflectance factors for the Munsell colours used in the CIE Colour Rendering Index. For the current state of CIE publications see www.CIE.co.at. As with previous editions, various minor changes have been made to update the text. An important change in this fourth edition is the availability of colour printing on every page; this has made it possible to improve the clarity of many figures, and to position colour reproductions at their appropriate positions in the text, instead of being grouped into a section of colour plates. Since the publication of the third edition in 1998, the measurement of colour has become increasingly important in many areas, including science, medicine and manufacturing, and this fourth edition provides a more up-to-date and comprehensive treatment of this fascinating subject.

Acknowledgements

For the First Edition

I am most grateful to Dr M. R. Pointer of Kodak Limited for kindly making many helpful comments on the text, for providing some of the numerical data, and for help with the proof reading. My grateful thanks for help are also due to Dr A. Hård in connection with the section on the NCS, to Dr H. Terstiege with that on the DIN system, and to Dr A. Nemcsics with that on the Coloroid system. For permission to reproduce figures, my thanks are due to the Institute of Physics for Figure 3.5; to John Wiley and Sons for Figures 7.5, 7.12, 7.19 and 8.1; to Dr A. Hård for Figure 7.12; to Dr H. Terstiege for Figure 7.19; and to Academic Press for Figures 9.1, 9.2 and 9.3. I would also like to thank Dr J. Schanda for kindly supplying me with copies of recent CIE documents.

With regard to the colour plates, my thanks are due to the following for kindly supplying the originals: Dr A.A. Clarke and Dr M.R. Luo, of Loughborough University of Technology, for Plates 2 and 3; Dr A. Hård for Plate 5; Dr H. Terstiege for Plate 8; and Mr R. Ingalls for Plates 1, 6, and 7. I would also like to thank the Munsell Corporation for permission to reproduce Plate 4.

I am also most grateful to Mr A.J. Johnson, and some of his colleagues, of Crosfield Electronics Limited, for kindly supplying the separations for the colour illustrations.

Finally my grateful thanks are due to my wife for editorial assistance and for help with the proof reading.

For the Second Edition

I am very grateful for help that has kindly been given to me by experts on the subject matter of the new material in this second edition. Dr F.W. Billmeyer has made many suggestions for improving the new chapters on metamerism, on precision and accuracy in colorimetry, and on the colorimetry of fluorescent materials. Miss M.B. Halstead, Mr D.O. Wharmby and Dr M.G. Abeywickrama have helped with the new chapter on light sources. Dr R.F. Berns has helped with the section on correcting for errors in spectral data, and Dr W.H. Venable with the section on the computation of tristimulus values. I am indebted to Mr J.K.C. Kempster for the data on which Figure 6.2 is based. Once again, I am most grateful to Dr M.R. Pointer for general comments, for help with computations, and for proof reading, and to my wife for editorial help and for proof reading.

For the Third Edition

I am most grateful to Dr M. R. Pointer for kindly suggesting that publication of this third edition be assisted by The Tintometer Limited, a company which has been continuously involved with colour measurement for over a hundred years; in this connection Miss Nicola Pointer's word-processing help is much appreciated. As with the earlier editions, Dr Pointer has also provided much expert help by means of general comments, and proof reading, for which I am most grateful. The tables given in Appendices 7 and 8 were originally published by the American Society for Testing Materials in their Standard ASTM E 308 - 95, Standard Practice for Computing the Colours of Objects by Using the CIE System; their permission to reproduce these tables is acknowledged with thanks. For preparing the final text in such a helpful way, I am very grateful to Mr Dennis Shearman of Priory Publications, who also performed the same task for my other book The Reproduction of Colour. Finally my best thanks are due to my wife for editorial help and for proof reading.

For the Fourth Edition

We are grateful to Janos Schanda for help with Chapter 7, to Jan and Peter Morovic for help with Chapter 12, and to Ronnier Luo and Changjun Li with Chapter 15. References to Munsell® in this publication are used with permission from X-Rite Inc. References to NCS in this publication are used with permission from NCS Color AB.

For preparing the final text in such a helpful way, we are very grateful to the Wiley staff at Chichester, who also performed the same task for Dr Hunt's The Reproduction of Colour.

Chapter 1

Colour Vision

1.1 Introduction

Ten million! That is the number of different colours that we can distinguish, according to one reliable estimate (Judd and Wyszecki, 1975). It is, therefore, no wonder that we cannot remember colours well enough to identify a particular shade. People are thus well advised to take samples of their clothing colours with them when purchasing accessories that are intended to match. They are also usually well aware that it is not enough to examine the colour match in just one type of light in a shop, but to see it in daylight as well as in artificial light. Finally, a second opinion about the match, expressed by a friend or a shop assistant, is often wisely sought.

The above activity involves the three basic components of colour: sources of light, objects illuminated by them and observers. Colour, therefore, involves not only material sciences, such as physics and chemistry, but also biological sciences, such as physiology and psychology; and, in its applications, colour involves various applied sciences, such as architecture, dyeing, paint technology, and illuminating engineering. Measuring colour is, therefore, a subject that has to be broadly based and widely applied.

Without observers possessing the faculty of sight, there would be no colour. Hence it is appropriate to start by considering the nature of the colour vision provided by the human eye and brain. Before doing this, however, a brief description must be given of the way in which it is necessary to characterise the nature of the light which stimulates the visual system.

1.2 The Spectrum

It is fair to say that understanding colour finds its foundations in the famous experiments performed by Isaac Newton in 1666. Before this date, opinions on the nature of colours and the relationships between them were most vague and of very little scientific use, but, after Newton's work became known, a way was open for progress based on experimental facts.

The historic experiments were performed in Trinity College, Cambridge, when Newton made a small hole, a third of an inch in diameter, in the shutter of an otherwise entirely dark room; through this hole, the direct rays of the sun could shine and form an image of the sun's disc on the opposite wall of the room, like a pin-hole camera. Then, taking a prism of glass, and placing it close to the hole, he observed that the light was spread out fan-wise into what he was the first to call a : a strip of light, in this case about ten inches long, and coloured red, orange, yellow, green, blue, indigo, and violet, along its length. The natural conclusion, which Newton was quick to draw, was that white light was not the simple homogeneous entity which it was natural to expect it to be, but was composed of a mixture of all the colours of the spectrum.

Lesen Sie weiter in der vollständigen Ausgabe!

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Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!