Standard Colorimetry

Colour is a sensation and as such it is a subjective and incommunicable quantity. Colour measurement is possible because we can create a correspondence between colour sensations and the light radiations that stimulate them. This correspondence concerns the physics of light radiation, the physiology of the visual process and the psychology of vision.

Historically, in parallel to standard colorimetry, systems for colour ordering have been developed that allow colour specifications in a very practical and concrete way, based on the direct vision of material colour samples arranged in colour atlases. Colour-ordering systems are sources of knowledge of colour vision, which integrate standard colorimetry.

Standard Colorimetry: Definitions, Algorithms and Software:

• Describes physiology and psychophysics useful to understand colorimetry
• Considers all the photometric and colorimetric systems standardized by CIE (XYZ, CIELAB, CIELUV, LMS)
• Presents colorimetric instrumentation in order to guide the reader toward colorimetric practice
• Discusses colorimetric computation to understand the meaning of numerical colour specification
• Considers colorimetry in colour syntheses and in imaging colour reproduction
• Includes ready-to-use, freely-available software, “Colorimetric eXercise”, which has multiple toolboxes dedicated to
  • displaying CIE systems, atlases, any colour and its whole numerical specification
  • colour-vision phenomena and tests

Standard Colorimetry: Definitions, Algorithms and Software is an accessible and valuable resource for students, lecturers, researchers and laboratory technicians in colour science and image technology.

Standard Colorimetry: Definitions, Algorithms and Software is published in partnership with the Society of Dyers and Colourists (SDC). Find out more at www.wiley.com/go/sdc

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 γ 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 (γ) 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 ΔE 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

Professor Claudio Oleari received a doctorate in physics from Padua University in 1969. His scientific activity after 1986 is dedicated to Vision Science and Colorimetry. He is visiting professor at Granada University and is a member of the Italian Society of Optics and Photonics. Oleari is the author of more than 100 papers, generally signed as the single author, and he is editor and co-author of the only Italian text book on colorimetry and color science, "Misurare il colore". Oleari is now Associate Professor of Physics at the University of Parma where he teaches coliometry, biophysics, physical optics, physics and applied physics at graduate and postgraduate levels.

Gabriele Simone received his BiT in 2005 and his MSIT in 2007 both at University of Milan-Department of Information Technology, Italy. He is currently pursuing a PhD in Color Imaging. He is a member of the Norwegian Colour and Visual Computing Laboratory at Gjøvik University College and his main research topic is contrast measure, image difference metrics, and tone mapping algorithms in HDR images. Today is working as Application Development Engineer at STMicroelectronics APG-M&RF Division-Infotainment BU.