THE MEASUREMENT OF APPEARANCE Second Edition

RICHARD S. HUNTER RICHARD W. HAROLD

Hunter Associates Laboratory, Inc.

Reston, Virginia

A WILEY-INTERSCIENCE PUBLICATION

JOHN WILEY & SONS

New York / Chichester / Brisbane / Toronto / Singapore

CONTENTS

PART ONE APPEARANCE ATTRIBUTES AND

THEIR BASES IN PHYSICS,

PSYCHOLOGY, AND PHYSIOLOGY

1 ATTRIBUTES OF THE APPEARANCE OF OBJECTS 3

Evaluating Light 4 Modes of Appearance 5 Evaluating the Appearance of Objects 7

Color Attributes 7 Color Order Systems 10

Ostwald 10 Geometric Attributes 13

DIFFUSE AND SPECULAR LIGHT DISTRIBUTIONS 13

Classification of Objects (The Sub-Modes) 16

2 LIGHT SOURCES AND ILLUMINATION 20

What Is Light? 20 Luminosity 21 Describing Light Spectrally 23

Light Sources 24 Incandescent Sources 24 Other Sources 25

Illuminants 28

3 INTERACTION OF OBJECTS WITH LIGHT 29

What Objects Do to Light 29 Ehe Optical Similarities of Different Products 33 The Relation Between Absorption and Scattering 35

CONTENTS

Physical Evaluation of Light from Objects 37 Spectrophotometric Curves 38 Goniophotometric Curves 41

4 THE HUMAN OBSERVER AND VISUAL EVALUATION OF OBJECT APPEARANCE 51

The Human Observer 51 Color Vision 51 Visual Sensitivity to Light Signals 53 The Capabilities of the Human Observer 54

Visual Evaluation of Appearance 55 Spectral Conditions 55 Geometric Conditions 55 Light Intensity 56 Summary of Conditions to Be Controlled 57

Standardized Conditions for Visual Evaluation of Color 57 Light Sources and Illuminants 57 Artificial Daylight Illuminants 61 Lighting Arrangement and Placement of Specimens 63

Standardized Conditions for Visual Evaluation of Gloss 64 General Rules for Visual Examination 66

5 PSYCHOPHYSICAL SCALES FOR APPEARANCE MEASUREMENT 68

Psychophysics and Appearance Scales 68

PART T W O T H E DEVELOPMENT OF

NUMERICAL SPECIFICATIONS

FOR APPEARANCE ATTRIBUTES

SCALES FOR GLOSS AND OTHER GEOMETRIC ATTRIBUTES 75

Gloss 75 Established Methods to Measure Gloss 82 Limitations of Instrumental Methods for Measuring Gloss 89 Surface Texture 89

CONTENTS xi

Transparent Materials 90 Opacity 90

7 THE CIE STANDARD OBSERVERS 95

Luminosity 95 Additive and Subtractive Color Mixing 96 Analyzing the Wavelength Response Characteristics

of Observers 97 Transformations 100 The Standard Observer 100

Using the Standard Observer Functions 101 Object Color Computations for X, Y, Z 103

THE WEIGHTED-ORDINATE INTEGRATION METHOD 103 THE SELECTF.n-ORDINATF. INTEGRATION METHOD 104 INSTRUMENT AUTOMATIC INTEGRATION 104

Metamerism 106 CIL Chromaticity 107

The Chromaticity Diagram 107 Adapting CIE Specifications to Object Colors 111

The Y, x, у Color Solid, Defined by the MacAdam Limits 114 The 10° 1964 CIE Supplementary Standard Observer 116 Summary of Terms 117

8 UNIFORM COLOR SCALES 119

Lightness Perception and Uniform Lightness Scales 121 The Development of Uniform Color Scales 123 Wavelength and Purity Discriminations and the Judd

Series of Scales 125 Judd Uniform Chromaticity Scale Triangle 126 MacAdam u,v Diagram 128 breckenridge and Schaub: RUCS 129 Hunter Alpha-Beta Diagram and L ' ,a ' ,ß ' Color Solid 131 The CIE 1964 U*V*W* and CIE 1976 L*u*v* Systems 133 CIE 1976 L*u*v* (CIELUV) Color Space 135

Munsell Based Scales 135 Adams: Chromatic Value and Chromatic Valence 136 Adams-Nickerson and Modified Adams-Nicker son Scales 139 Hunter Rd, a, b and L, a, b Scales 141

CONTENTS

Glasser Cube Root 142 CIE 1976 L* a* b* 143 CIE 1976 L* a* b* (CIELAB) Color Space 145 CIE 1976 Correlates of Perceived Lightness, Chroma,

and Hue 146 Scale-Expansion Coefficients for L, a, and /; Type

Opponent-Colors Scales 148 MacAdam-Base Scales—The MacAdam-Friele Group 153

MacAdam (P,Q,S) and the EMC Metric 154 Other Uniform Color Scales 155 Intercomparison of Color Scales 156 Interconversion Among Color Scales 158 Selection of Color Scales 158

SCALES FOR THE MEASUREMENT OF COLOR DIFFERENCE 162

Concept of Color Difference 163 The Historical Development of Methods of

Color-Difference Measurement 164 Munsell System Color-Difference Scales 167 Adams-Nickerson Series 169 Judd-Hunter Systems 170 MacAdam Systems 175 CIE 1976 Recommendations 177 The JPC79 and CMC(/:c) Colour-Difference Formulas 180 Interrelationships of Color Difference Scales 183 Factors Affecting Visual Color Difference Evaluations 185 Variables Affecting Visual and Instrumental Estimates

of Color Difference 186 Selection of Methods of Color Difference Measurement 189

Levels of Color Difference Discrimination 189 Nonsymmetry of Color Tolerances 191 Necessity for High Precision 191

Metamerism Indexes 193

SPECIAL SCALES FOR WHITE COLORS 195

The Optics of White Materials 195 Measurement Scales for Whites 199

Luminous Reflectance Factor Y or Lightness L 201

CONTENTS xi i i

Blue Reflectance Factor В 203 Yellowness Index YI 205 Whiteness Index Wl 206

Graphic Techniques 208

11 OTHER SCALES FOR COLOR IDENTIFICATION 209

Single-Number Golor Scales for Specific Products 209 Single-Number Scales for Yellowness of Amber-Colored

Liquids and Resins 210 Scales Used to Measure Color Quality of

Specific Food Products 214 Color Identification by Subtractive Color Mixture 218

Lovibond Color System and Tintometer 218 Densitometry and the Subtractive-Mixture Color Solid 220

Color Identification by Additive Color Mixture 224 Visual Additive Colorimeters 226 Disk Colorimetry 226

Collections of Colored Chips for Identification of Colors of Surfaces; Color-Order Systems 227

Munsell Color System 227 ISCC-NBS System of Color Names 231 Oslwald Color System 231 The DIN Color System 233 The Natural Colour System 234 The Ridgway Color Standards and Color Nomenclature 236 Maen and Raul Dictionary 237

PART THREE INSTRI;MENTS FOR THE MEASUREMENT OK APPEARANCE

12 INSTRUMENT CLASSIFICATION AND COMPONENTS 241

Instrument Types 242 Spectral and Geometric Factors of Instrument Design 243 Light Sources 246

Incandescent Light Sources 246 Fluorescent Lamps 249

CONTENTS

Xenon Arc Lamps 249 Lasers 249

Geometrie Design—Illuminating and Viewing Beams of Light 250

Directions of Light Beams 250 Spatial Dimensions of Light Beams 254 Vignetting 256 Parallel- and Converging-Beam Configurations 257 The Specimen and Its Window 257 Equal Weighting of all Permitted Light Rays 258 Interchange of Directions of Illumination and View 258 Precision of One- and Two-Beam Configurations 259

Spectral Design—Wavelength Selection Devices and Photodetectors 259

Wavelength-Selection Devices 260 NARROW- AND BROADBAND WAVELENGTH SELECTION 263

FILTER COMBINATIONS 264

Light Detectors 264 HUMAN EYE 264

Photodetectors 265 PHOTOEMLSSIVF. DETECTORS 265

PHOTOVOLTAIC CELLS 266

PHOTOCONDUCTIVE CELLS 268

Electrical Measurement Devices 270 Measuring Systems for Signal Analysis 270 Data Display Devices 271

INSTRUMENTS FOR THE GEOMETRIC ATTRIBUTES OF OBJECT APPEARANCE 273

Cioniophotometers 273 Historical Background 275 Goniophotometer Design 275 Uses of Goniophotometers 276

Diffuse Reflection Meters 276 Historical Background 276 Reflectometer Design 278 Uses of Diffuse Reflection Meters 279

DENSITOMETERS (REFLECTION AND TRANSMISSION) 280

Specular Gloss and Reflection Meters 281 Historical Background 281 Glossmeter Design 282 Use of Specular Glossmeters 283

Direction-Contrast Meters for Contrast Gloss, Distinctness-of-Image Gloss, and Reflection Haze 284

Lustermeter for Measurement of Contrast Gloss 285 üistinctness-oj-Reflected-1 mage and Reflection-Haze Meters 285

Instruments for Transmission Measurements 287 Haze Meters 287 Clarity Meters, Turbidimeters, Transmission Opacimeters 287

INSTRUMENTS FOR THE CHROMATIC ATTRIBUTES OF OBJECT APPEARANCE 290

Spectrophotometers 290 Design Features of Spectrophotometers 292

WAVELENGTH ISOLATION AND IDENTIFICATION 292

SPECIMEN ILLUMINATION AND VIEWING 293

Use of the Spectrophotometry: Output 296 CONVERSION OF SPECTRAL CURVES TO TRISTIMULUS

X, Y, Z VALUES 296

COLOR FORMULATION BY SPECTROPHOTOMETRY

AND COMPUTER 296

Tristimulus Instruments—Reflectometers and Colorimeters 296 Historical Background 297 Tristimulus Colorimeters 297

DESIGN OF COLORIMETERS 299

LIGHT SOURCES 299

LIGHT RECEIVERS—THE PHOTODE I ECTORS 301

INSTRUMENT READOUTS 301

USES OF TRISTIMULUS INSTRUMENTS 302

STANDARDS, STANDARDIZATION, AND MEASUREMENT TECHNIQUES 303

Accuracy and Precision 303 Ideal or Perfect Standards References 304 Primary Standards 305

CONTENTS

Secondary Standards 306 Standards Materials 309 Care of Standards 314 Measurement Techniques 315

16 SPECIMEN SELECTION, PREPARATION, AND PRESENTATION 316

Objectives in Specimen Preparation 318 Effects of Preparation on Specimen Properties 319 Requirements for Specimen Preparation Depending upon

Type of Measurement to Be Made 320 Techniques for Handling Specimens of Different Forms 321 Benefits of the Specimen Averaging Technique 330

17 APPLICATIONS OF APPEARANCE MEASUREMENTS 334

Importance of Product Appearance 334 Products and Industries Where Appearance

Analyses Are Used 336 Uses of Measurements of Appearance Attributes 338

Identification 339 Tests for Conformity to Specifications 339

INCOMING RAW MATERIAL TESTING 339

MATERIALS IN PROCESS OF BEING MANUFACTURED 341

FINISHED MATERIAL READY FOR DELIVERY 341

Grading for Quality 343 Shade Sorting 344 Guiding or Adjusting Formulation of Product Color 348 Assessment of Product Performance in Service 354 Measurement of Nonappearance Variables 355

l e s t Methods for Appearance Analysis and Measurement 355

APPENDIX 361

BIBLIOGRAPHY/AUTHOR INDEX 381

GLOSSARY/SUBJECT INDEX 391