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Society of Dyers and Colourists xv
Preface xvii
1 Generalities on Colour and Colorimetry 1
1.1 Colour 1
1.2 Colorimetry 2
References 4
Bibliography 4
2 Optics for Colour Stimulus 5
2.1 Introduction 5
2.2 Electromagnetic Waves 7
2.3 Photons 11
2.4 Radiometric and Actinometric Quantities 11
2.5 Inverse Square Law 14
2.6 Photometric Quantities 14
2.7 Retinal Illumination 16
References 16
Bibliography 16
3 Colour and Light-Matter Interaction 17
3.1 Introduction 17
3.1.1 Luminous Colours 17
3.1.2 Non?]luminous Colours 18
3.1.3 Light Phenomena and Body Appearance 18
3.2 Light Sources 19
3.3 Planckian Radiator 20
3.4 Light Regular Reflection and Refraction 21
3.4.1 Snell's Laws 22
3.4.2 Fresnel's Laws 23
3.5 Light Scattering 24
3.5.1 Lambertian Diffusion 25
3.5.2 Light Scattering on a Rough Surface 25
3.5.3 Light Scattering in an Optically Heterogeneous Medium 26
3.6 Light Absorption and Colour Synthesis 28
3.6.1 Simple Subtractive Synthesis 28
3.6.2 Complex Subtractive Synthesis 28
3.7 Fluorescence 29
3.8 Transparent Media 30
3.8.1 Internal Transmittance of a Medium 30
3.8.2 Total Transmittance and Total Reflectance 32
3.9 Turbid Media 33
3.9.1 Two?]Flux Model of Kubelka-Munk 34
3.9.2 Saunderson's Equation 36
3.9.3 Colorant Characterization and Formulation 38
3.10 Ulbricht's Integration Sphere 41
References 43
Bibliography 44
4 Perceptual Phenomenology of Light and Colour 45
4.1 Introduction 45
4.2 Perceived Colours, Categorization and Language 46
4.3 Light Dispersion and Light Mixing 47
4.3.1 Newton's Prism Experiment, Colour Wheel and Colour Attributes 48
4.3.2 Maxwell's Disk Experiment 50
4.4 Unique Hues, Colour Opponencies and Degree of Resemblance 52
4.5 Colour Similitude 55
4.6 Unrelated and Related Colours 56
4.6.1 Relative Attributes 56
4.7 Colour Interactions 57
References 65
5 Visual System 67
5.1 Introduction 67
5.2 Eye Anatomy and Optical Image Formation 68
5.3 Eye and Pre?]retina Physics 72
5.4 Anatomy of the Retina 74
5.4.1 Retina Layers 76
5.4.2 Fovea 77
5.4.3 Foveola 78
5.4.4 Extra Fovea 78
5.4.5 Macula Lutea 79
5.4.6 Rod and Cone Distribution 79
5.5 From the Retina to the Brain 80
5.5.1 Scotopic Vision 80
5.5.2 Photopic Trichromatic Vision 81
5.5.3 Rushton's Univariance Principle and Photoreceptor Activation 82
5.5.4 Horizontal Cells 83
5.5.5 Bipolar Cells 83
5.5.6 Amacrine Cells 84
5.5.7 Ganglion Cells and Visual Pathways 84
5.5.8 From the Ganglion Cells to the Visual Cortex 85
5.6 Visual System and Colorimetry 87
Bibliography 88
References 88
6 Colour?]Vision Psychophysics 91
6.1 Introduction 91
6.1.1 Psychophysics and Physiology 91
6.1.2 Visual Judgement 92
6.1.3 Modes of Colour Appearance and Viewing Situations 93
6.1.4 Colour Stimuli 95
6.1.5 Colour?]Attribute Matching 98
6.1.6 Visual Detection Threshold and Sensitivity 99
6.1.7 Scaling of Colour Attributes 100
6.2 Adaptation 103
6.2.1 Brightness Adaptation 105
6.2.2 Threshold in Dark Adaptation 106
6.3 Absolute Thresholds in Human Vision 108
6.4 Absolute Threshold and Spectral Sensitivity in Scotopic and Photopic Visions 108
6.4.1 Silent Substitution Method 109
6.5 Luminous Efficiency Function 113
6.5.1 Abney Additivity Law and Luminance 114
6.6 Light Adaptation and Sensitivity 116
6.7 Weber's and Fechner's Laws 118
6.7.1 Contrast Sensitivity 119
6.7.2 Fechner's Scaling 119
6.8 Stevens' Law 119
6.8.1 Brightness Scaling and Stevens' Law 119
6.9 Fechner's and Stevens' Psychophysics 121
6.10 Wavelength Discrimination 121
6.11 Saturation Discrimination and Least Colorimetric Purity 123
6.12 Rushton's Univariance Principle and Scotopic Vision 124
6.13 Tristimulus Space 125
6.13.1 Rushton's Univariance Principle and Grassmann's Laws in Photopic Vision 126
6.13.2 Metamerism 130
6.13.3 Chromaticity 131
6.13.4 Reference Frames in Tristimulus Space 132
6.13.5 Measurement of the Colour-Matching Functions in the RGB Reference Frame 134
6.13.6 Luminance and Exner-Schrödinger's 'Helligkeit' Equation 139
6.13.7 Dichromats and Fundamental Reference Frame 141
6.13.8 Newton's Centre?]of?]Gravity Rule and Chromaticity?]Diagram Properties 145
6.14 Lightness Scales 149
6.15 Helmholtz-Kohlrausch Effect 150
6.16 Colour Opponencies and Chromatic Valence 153
6.17 MacAdam's Chromatic Discrimination Ellipses 155
6.18 Perceived Colour Difference 156
6.19 Abney's and Bezold-Brücke's Phenomena 161
6.20 Chromatic Adaptation and Colour Constancy 164
6.20.1 Asymmetric Colour Matching 165
6.20.2 Empirical Data 166
6.20.3 Von Kries's Coefficient Law 166
6.20.4 Retinex 168
6.21 Colour?]Vision Psychophysics and Colorimetry 170
References 171
7 CIE Standard Photometry 177
7.1 Introduction 177
7.2 History of the Basic Photometric Unit 180
7.3 CIE 1924 Spectral Luminous Efficiency Function 180
7.4 CIE 1924 and CIE 1988 Standard Photometric Photopic Observers 181
7.5 Photometric and Radiometric Quantities 182
7.6 CIE 1951 Standard Scotopic Photometric Observer 185
7.7 CIE 2005 Photopic Photometric Observer with 10° Visual Field 185
7.8 CIE Fundamental Photopic Photometric Observer with 2°/10° Visual Field 185
7.8.1 Photopic Spectral Luminous Efficiency Functions for the 2° Fundamental Observer 186
7.8.2 Photopic Spectral Luminous Efficiency Functions for the 10° Fundamental Observer 186
References 186
8 Light Sources and Illuminants for Colorimetry 189
8.1 Introduction 189
8.2 Equal?]Energy Illuminant 190
8.3 Blackbody Illuminant 191
8.4 CIE Daylights 193
8.5 CIE Indoor Daylights 195
8.6 CIE Standard Illuminants 196
8.7 CIE Light Sources: A, B and C 197
8.8 CIE Sources for Colorimetry 198
8.9 CIE Illuminants: B, C and D 199
8.10 Fluorescent Lamps 199
8.10.1 Typical Fluorescent Lamps 199
8.10.2 New Set of Fluorescent Lamps 200
8.11 Gas?]Discharge Lamps 204
8.12 Light?]Emitting Diodes 205
References 208
9 CIE Standard Psychophysical Observers and Systems 209
9.1 Introduction 209
9.2 CIE 1931 Standard Colorimetric System and Observer 210
9.2.1 CIE 1931 RGB Reference Frame and WDW Chromaticity?]Coordinates Normalization 211
9.2.2 CIE 1931 XYZ Reference Frame 214
9.3 CIE 1964 (Supplementary) Standard Colorimetric Observer/System (10°?]Standard Colorimetric Observer) 218
9.4 CIE 1989 Standard Deviate Observer/System 221
9.5 Vos' 1978 Modified Observer for 2° Visual Field 221
9.5.1 Smith-Pokorny's Cone Fundamentals 223
9.5.2 Vos' 1978 2° Fundamental Observer Data and MacLeod-Boynton's Chromaticity Diagram 223
9.6 CIE Standard Stockman?]Sharpe's 'Physiologically Relevant' Fundamentals and XYZ Reference Frame 224
9.6.1 XFYFZF and XF,10YF,10ZF,10 Reference Frames 226
9.6.2 MacLeod-Boynton's Tristimulus Space and Chromaticity Diagram 229
9.7 CIE Colorimetric Specification of Primary and Secondary Light Sources 232
References 234
10 Chromaticity Diagram from Newton to the CIE 1931 Standard System 237
10.1 Introduction 237
10.2 Newton and the Centre of Gravity Rule 237
10.3 Material Colours and Impalpable Colours in the Eighteenth Century 243
10.4 Physiological Intuitions and the Centre of Gravity Rule - Young, Grassmann, Helmholtz, Maxwell and Schrödinger 245
10.5 Conclusion 251
References 251
11 CIE Standard Psychometric Systems 253
11.1 Introduction to Psychometric Systems in Colour Vision 253
11.2 CIE Lightness L* 254
11.3 Psychometric Chromaticity Diagrams and Related Colour Spaces 255
11.3.1 CIE 1960 (u, v) UCS Psychometric Chromaticity Diagram 255
11.3.2 CIE 1964 (U*, V*, W*) Uniform Colour Space - CIEUVW Colour Space 257
11.3.3 CIE 1976 (u', v') UCS Psychometric Chromaticity Diagram 257
11.3.4 CIE 1976 (L*, u*, v*) Colour Space - CIELUV Colour Space 259
11.3.5 CIE 1976 (L*, a*, b*) Colour Space - CIELAB Colour Space 261
11.4 Colour Difference Specification 264
11.4.1 Colour Difference Data 264
11.4.2 CIE 1976 Colour?]Difference Formulae 265
11.4.3 CMC(l : c) Colour?]Difference Formula 266
11.4.4 CIE 1994 Colour?]Difference Formula 267
11.4.5 CIEDE2000 Total Colour?]Difference Formula 268
11.4.6 Small Colour Differences in OSA?]UCS Space 270
11.4.7 Metamerism Indices 270
11.4.8 Daylight?]Simulator Evaluation and 'Special Metamerism Index: Change in Illuminant' 273
11.5 Conclusion 276
References 276
12 Instruments and Colorimetric Computation 279
12.1 Introduction 279
12.2 Reflection and Transmission Optical?]Modulation 282
12.2.1 Absolute Quantities of Optical?]Modulation 282
12.2.2 Relative Quantities of Optical?]Modulation 283
12.3 Spectroradiometric and Spectrophotometric Measurements 296
12.3.1 Introduction to the Spectrometer 296
12.3.2 Instrumental Convolution 303
12.3.3 Deconvolution 308
12.4 Colorimetric Calculations 309
12.4.1 CIE Colour Specification 309
12.4.2 Relative Colour Specification 310
12.4.3 Deconvolution 312
12.4.4 Interpolation 313
12.4.5 Extrapolation 315
12.5 Uncertainty in Colorimetric Measurements 315
12.5.1 Laws of Propagation of Uncertainty 317
12.5.2 Uncertainty Computation 318
12.6 Physical Standards for Colour?]Instrument Calibration 320
References 322
13 Basic Instrumentation for Radiometry, Photometry and Colorimetry 325
13.1 Introduction 325
13.2 Lighting Cabinet 327
13.3 Visual Comparison Colorimeter 329
13.4 Instruments with Power Spectral Weighting Measurement 330
13.4.1 Photometric Instruments 330
13.4.2 Colorimetric Instruments 332
13.5 Instruments for Measurements with Spectral Analysis 336
13.5.1 Spectroradiometer 336
13.5.2 Spectrophotometer 337
13.5.3 Multiangle Spectrophotometers 337
13.5.4 Fibre?]Optic?]Reflectance Spectroscopy (FORS) 338
13.6 Glossmeter 341
13.7 Imaging Instruments 343
13.7.1 Imaging Photometer 343
13.7.2 Colorimetric Camera 344
13.7.3 Multispectral and Hyperspectral Camera 344
References 346
14 Colour?]Order Systems and Atlases 349
14.1 Introduction 349
14.2 Colour Solid, Optimal Colours and Full Colours 351
14.2.1 MacAdam's Limit 354
14.3 Ostwald's Colour?]Order System and Atlas 354
14.3.1 Ostwald's Hue Circle with Temperate Scale 355
14.3.2 Ostwald's Semichrome 356
14.3.3 Ostwald's Blackness, Whiteness and Purity 357
14.3.4 Ostwald's Atlas 358
14.4 Munsell's Colour?]Order System and Atlas 360
14.4.1 Munsell's Instruments 362
14.4.2 Chromatic Tuning Fork 362
14.4.3 Munsell's Value and Grey Scale 364
14.4.4 Munsell's Hue 365
14.4.5 Munsell's Value in Coloured Scales 367
14.4.6 Colour Sphere and Munsell's Colour Specification 367
14.4.7 Munsell's Chroma 369
14.4.8 Colour Tree 369
14.4.9 Munsell's System and CIE Chromaticity Specification 369
14.4.10 Helmholtz-Kohlrausch's Effect and Abney's Hue Shift Phenomenon in the Munsell Atlas 371
14.4.11 Munsell's Colour Atlas 371
14.5 DIN 6264's Colour?]Order System and Atlas 372
14.6 OSA?]UCS's Colour?]Order System and Atlas 374
14.6.1 OSA?]UCS's Lightness 376
14.6.2 OSA?]UCS's (g, j) Coordinates 377
14.6.3 OSA?]UCS's Colour Difference Formula 379
14.6.4 OSA?]UCS's Metrics 379
14.7 NCS's Colour?]Order System and Atlas 380
14.7.1 NCS's Axioms 381
14.7.2 NCS's Hue, Chromaticness and Nuance 382
14.7.3 Production of the NCS System and Visual Situation 384
14.7.4 Psychophysics and Psychometrics for NCS 384
14.7.5 Luminance Factor and NCS's Whiteness Scale 385
14.7.6 NCS's Atlas 387
References 387
15 Additive Colour Synthesis in Images 391
15.1 Introduction 391
15.2 Video Colour Image 392
15.2.1 RGB Colorimetry 395
15.2.2 Video Signal and ¿ Correction 397
15.2.3 Tristimulus Space and YIQ Reference Frame 401
15.2.4 sRGB System 404
15.2.5 Prints in the sRGB System 406
15.2.6 Camera, Photo?]Site and Pixel 406
15.2.7 Spectral Sensitivities of Digital Cameras 409
15.3 Principles of Halftone Printing 412
15.4 Towards the Colorimetry of Appearance 419
References 420
16 Software (Software developed by Gabriele Simone) 423
16.1 Introduction to the Software 423
16.1.1 Software Installation 423
16.1.2 Data Files 425
16.2 Monitor 429
16.2.1 Monitor Setup 429
16.2.2 Visual Evaluation of Gamma (¿) 430
16.3 Colour?]Vision Tests 432
16.4 Visual Contrast Phenomena 440
16.4.1 Simultaneous Brightness Contrast and Crispening 440
16.4.2 Simultaneous Brightness Contrast in Colour Scales 441
16.4.3 Brightness and Chromatic Contrast 442
16.4.4 After Image 442
16.5 Colour Atlases 443
16.5.1 Ostwald's Atlas 444
16.5.2 Munsell's Atlas 444
16.5.3 DIN's Atlas 444
16.5.4 OSA?]UCS' Atlas 446
16.5.5 NCS' Atlas 447
16.6 CIE 1976 CIELUV and CIELAB Systems 448
16.7 Cone Activation and Tristimulus 450
16.8 CIE Colorimetry 451
16.8.1 CIE Colour Specification 452
16.8.2 CIE Systems 456
16.8.3 Chromaticity Diagrams 459
16.8.4 Fundamental Observers 462
16.8.5 Dominant Wavelength and Purity 463
16.8.6 Tristimulus Space Transformations 463
16.8.7 Colour?]Difference Formulae ¿E 464
16.8.8 CIE 1974 Colour Rendering Index Ra 465
16.9 Black Body and Daylight Spectra and Other CIE Illuminant Spectra 470
16.10 Additive Colour Synthesis 471
16.10.1 RGB Monitor, Additive Colour Mixture 472
16.10.2 Halftone CMY Printing 472
16.11 Subtractive Colorant Mixing 474
16.11.1 Two Pigment Mixture 475
16.11.2 Four Pigment Mixture 475
16.12 Spectral Data View and Download - Illuminant-Observer Weights 478
16.13 Save File Opening 478
References 480
Index 481
The Commission Internationale de l'Éclairage (CIE) is the official institution devoted to worldwide cooperation and the exchange of information on all matters relating to the science and art of light and lighting, colour and vision, photobiology and image technology.
CIE publications are the main reference for this book.1-3 This book is about colorimetry and has the definitions of colour and colorimetry as its starting point.
In non-specialist language, the word 'colour' is ambiguous, because it is used to describe the quality of the objects, self-luminous and non-luminous, and to describe a quality of the viewing experience. These meanings of the same word 'colour' are different but they are not disjoint, because the first one is the stimulation of the visual experience and the other the visual experience itself. Between these two meanings there is a correspondence and colorimetry quantitatively describes this correspondence.
The colour of self-luminous and non-luminous objects is associated with a physical quantity, which is properly called colour stimulus and is measurable because it is external to the body of the observer:
"Colour stimulus - visible radiation entering the eye and producing a sensation of colour, either chromatic or achromatic."1
The definition of colour as an effect of the colour stimulus is given by the Optical Society of America (OSA) in the 1952 report:
"Color consists of the characteristics of light other than spatial and temporal inhomogeneities; light being the aspect of radiant energy of which a human being is aware through the visual sensations which arise from the stimulation of the retina of the eye."4
Among the many definitions of colour, the most comprehensive, albeit in its brevity, is given by the American Society for Testing and Materials (ASTM),5 which with the definitions opens highly technical discussions, which are clarified later in the book:
The 'perceived colour' is defined using the names of the colours. This means that the names of the colours represent fundamental concepts, which are not definable in other words. The perceived colour is incommunicable. Humans evoke the perceived colour in the interlocutors with conventional words - red, yellow, green, blue, black, grey, white, so on -.
Discussion - perceived colour depends greatly on the spectral power distribution of the colour stimulus, but also on the size, shape, structure, and surround of the stimulus area, the state of adaptation of the observer's visual system, and the observer's experience with similar observations."5
Robert W. Hunt6,7 distinguishes between:
"Psychophysical colour terms - terms denoting objective measures of physical variables that are evaluated so as to relate to the magnitudes of important attributes of light and colour. These measures identify stimuli that produce equal responses in a visual process in specified viewing conditions."
and
"Psychometric colour terms - terms denoting objective measures of physical variables that are evaluated so as to relate to differences between magnitudes of important attributes of light and colour and such that equal scale intervals represent approximately equal perceived differences in the attribute considered. These measures identify pairs of stimuli that produce equally perceptible differences in response in a visual process in specified viewing conditions."6
Psychophysical colour terms regard Psychophysical colorimetry and psychometric colour terms regard Psychometric colorimetry. Both definitions of psychophysical and psychometric colour refer to colour stimuli, whose measurement and processing are same as those in the human visual system. The human visual system is a tool that measures the colour stimulus, as a camera, (psychophysics) and processes the signals produced quantifying the colour attributes according to a perceptive scale (psychometrics).
Psychophysical colorimetry is limited to the measurement of colour stimuli, attributing the same specification to different colour stimuli which induce equal colour sensations. This is exactly what happens in a photographic camera.
The human eye, unlike the camera, has a sensor - the retina - that has not the same optical properties in all its parts. The central part, for acute vision, is different from the surrounding parts, for which, according to a simplified diagram, there are two different colorimetries. In 1931 the CIE defined a colorimetry for acute vision - observer with a visual field of 2° described in Section 9.2 - and in 1964 a colorimetry for non-acute vision - observer with the field of view of 10° described in Section 9.3 -.
Table 1.1 Scheme of the colour specification according to historical steps, stages of vision, visual fields and referred to the CIE standard systems.
i
e
l
CIELAB system (L*10, a*10, b*10)
The distinctions between psychophysical and psychometric colorimetries, and between the 2° and 10° visual fields, have led to four different colorimetries, as summarized in Table 1.1.
Over time, the study of colour-vision has led to improving the standard observers by adding new cases within the schema of Table 1.1, that is, Vos and fundamental observers described in Sections 9.5 and 9.6. These improvements are considered so small that the industries and laboratories continue to use the standard CIE 1931 and CIE 1964.
This distinction among different colorimetries corresponds to a distinction among the historical phases of colorimetry7:
A first phase concerned with 'which colours match' and is termed psychophysical in strict sense (Chapter 9) and also classical colorimetry or tristimulus colorimetry.
A second phase concerned with 'whether colour differences are equal' and is termed psychometric (Chapter 11).
A third phase concerned with 'what colours look like' and is termed "colour appearance:
The third phase of colour-appearance colorimetry is in rapid progress and is a subject of debate; therefore, it is not considered in this book.
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