Contents
Society of Dyers and Colourists
Preface
1 Generalities on Colour and Colorimetry
1.1 Colour
1.2 Colorimetry
References
Bibliography
2 Optics for Colour Stimulus
2.1 Introduction
2.2 Electromagnetic Waves
2.3 Photons
2.4 Radiometric and Actinometric Quantities
2.5 Inverse Square Law
2.6 Photometric Quantities
2.7 Retinal Illumination
References
Bibliography
3 Colour and Light-Matter Interaction
3.1 Introduction
3.2 Light Sources
3.3 Planckian Radiator
3.4 Light Regular Reflection and Refraction
3.5 Light Scattering
3.6 Light Absorption and Colour Synthesis
3.7 Fluorescence
3.8 Transparent Media
3.9 Turbid Media
3.10 Ulbricht’s Integration Sphere
References
Bibliography
4 Perceptual Phenomenology of Light and Colour
4.1 Introduction
4.2 Perceived Colours, Categorization and Language
4.3 Light Dispersion and Light Mixing
4.4 Unique Hues, Colour Opponencies and Degree of Resemblance
4.5 Colour Similitude
4.6 Unrelated and Related Colours
4.7 Colour Interactions
References
5 Visual System
5.1 Introduction
5.2 Eye Anatomy and Optical Image Formation
5.3 Eye and Pre-retina Physics
5.4 Anatomy of the Retina
5.5 From the Retina to the Brain
5.6 Visual System and Colorimetry
Bibliography
References
6 Colour-Vision Psychophysics
6.1 Introduction
6.2 Adaptation
6.3 Absolute Thresholds in Human Vision
6.4 Absolute Threshold and Spectral Sensitivity in Scotopic and Photopic Visions
6.5 Luminous Efficiency Function
6.6 Light Adaptation and Sensitivity
6.7 Weber’s and Fechner’s Laws
6.8 Stevens’ Law
6.9 Fechner’s and Stevens’ Psychophysics
6.10 Wavelength Discrimination
6.11 Saturation Discrimination and Least Colorimetric Purity
6.12 Rushton’s Univariance Principle and Scotopic Vision
6.13 Tristimulus Space
6.14 Lightness Scales
6.15 Helmholtz-Kohlrausch Effect
6.16 Colour Opponencies and Chromatic Valence
6.17 MacAdam’s Chromatic Discrimination Ellipses
6.18 Perceived Colour Difference
6.19 Abney’s and Bezold-Brücke’s Phenomena
6.20 Chromatic Adaptation and Colour Constancy
6.21 Colour-Vision Psychophysics and Colorimetry
References
7 CIE Standard Photometry
7.1 Introduction
7.2 History of the Basic Photometric Unit
7.3 CIE 1924 Spectral Luminous Efficiency Function
7.4 CIE 1924 and CIE 1988 Standard Photometric Photopic Observers
7.5 Photometric and Radiometric Quantities
7.6 CIE 1951 Standard Scotopic Photometric Observer
7.7 CIE 2005 Photopic Photometric Observer with 10° Visual Field
7.8 CIE Fundamental Photopic Photometric Observer with 2°/10° Visual Field
References
8 Light Sources and Illuminants for Colorimetry
8.1 Introduction
8.2 Equal-Energy Illuminant
8.3 Blackbody Illuminant
8.4 CIE Daylights
8.5 CIE Indoor Daylights
8.6 CIE Standard Illuminants
8.7 CIE Light Sources: A, B and C
8.8 CIE Sources for Colorimetry
8.9 CIE Illuminants: B, C and D
8.10 Fluorescent Lamps
8.11 Gas-Discharge Lamps
8.12 Light-Emitting Diodes
References
9 CIE Standard Psychophysical Observers and Systems
9.1 Introduction
9.2 CIE 1931 Standard Colorimetric System and Observer
9.3 CIE 1964 (Supplementary) Standard Colorimetric Observer/System (10°-Standard
Colorimetric Observer)
9.4 CIE 1989 Standard Deviate Observer/System
9.5 Vos’ 1978 Modified Observer for 2° Visual Field
9.6 CIE Standard Stockman-Sharpe’s ‘Physiologically Relevant’ Fundamentals and
XYZ Reference Frame
9.7 CIE Colorimetric Specification of Primary and Secondary Light Sources
References
10 Chromaticity Diagram from Newton to the CIE 1931 Standard System
10.1 Introduction
10.2 Newton and the Centre of Gravity Rule
10.3 Material Colours and Impalpable Colours in the Eighteenth Century
10.4 Physiological Intuitions and the Centre of Gravity Rule–Young, Grassmann,
Helmholtz, Maxwell and Schrödinger
10.5 Conclusion
References
11 CIE Standard Psychometric Systems
11.1 Introduction to Psychometric Systems in Colour Vision
11.2 CIE Lightness L*
11.3 Psychometric Chromaticity Diagrams and Related Colour Spaces
11.4 Colour Difference Specification
11.5 Conclusion
References
12 Instruments and Colorimetric Computation
12.1 Introduction
12.2 Reflection and Transmission Optical-Modulation
12.3 Spectroradiometric and Spectrophotometric Measurements
12.4 Colorimetric Calculations
12.5 Uncertainty in Colorimetric Measurements
12.6 Physical Standards for Colour-Instrument Calibration
References
13 Basic Instrumentation for Radiometry, Photometry and Colorimetry
13.1 Introduction
13.2 Lighting Cabinet
13.3 Visual Comparison Colorimeter
13.4 Instruments with Power Spectral Weighting Measurement
13.5 Instruments for Measurements with Spectral Analysis
13.6 Glossmeter
13.7 Imaging Instruments
References
14 Colour-Order Systems and Atlases
14.1 Introduction
14.2 Colour Solid, Optimal Colours and Full Colours
14.3 Ostwald’s Colour-Order System and Atlas
14.4 Munsell’s Colour-Order System and Atlas
14.5 DIN 6264’s Colour-Order System and Atlas
14.6 OSA-UCS’s Colour-Order System and Atlas
14.7 NCS’s Colour-Order System and Atlas
References
15 Additive Colour Synthesis in Images
15.1 Introduction
15.2 Video Colour Image
15.3 Principles of Halftone Printing
15.4 Towards the Colorimetry of Appearance
References
16 Software
16.1 Introduction to the Software
16.2 Monitor
16.3 Colour-Vision Tests
16.4 Visual Contrast Phenomena
16.5 Colour Atlases
16.6 CIE 1976 CIELUV and CIELAB Systems
16.7 Cone Activation and Tristimulus
16.8 CIE Colorimetry
16.9 Black Body and Daylight Spectra and Other CIE Illuminant Spectra
16.10 Additive Colour Synthesis
16.11 Subtractive Colorant Mixing
16.12 Spectral Data View and Download – Illuminant-Observer Weights
16.13 Save File Opening
List of Illustrations
Chapter 2
Figure 2.1 (a) Plane electromagnetic waves represented in space at fixed time and (b) in the time in a fixed point in space. This graphical representation shows the wavelength and the frequency in space and time, respectively. (c) The third graph from the top represents a wave with ‘circular polarization’; here only the electric field is represented and the magnetic field is orthogonal to the electric field. The electric field and magnetic field are mutually perpendicular and together orthogonal to the propagation direction.
Figure 2.2 Complete spectrum of electromagnetic radiation characterized by wavelength and frequency. The part of the spectrum related to visible light is expanded and a hue name is associated to each wavelength range. The colours printed here are only representative and approximate for many reasons, which will become clear on reading the book. For completeness, the non-spectral hues (purple and magenta hues) are added, which are specified by the complementary wavelengths (Section 4.3). ‘c’ before the wavelength numbers in the extra-spectral region means ‘complementary of’. Figure 2.3 Section of the ocular bulb and geometrical aspects of the radiation in relation with the definition of radiance. In this case, the apparent surface is shown. Figure 2.4 Section of the ocular bulb and geometrical aspects of the radiation in relation with the definition of radiance. In this case, the solid angles and the distances of the observed objects is considered.
Figure 2.5 Equal surface elements A1 and A2, located, respectively, at a distance r1 and r2 from a point source, underlying solid angles Ω1 and Ω2, which are inversely proportional to the square of the distance. Since the radiant intensity is uniform within these solid angles, the flow across the elements of the surface A1 and A2 is proportional to the subtended solid angles and therefore varies with the distance r in the same way to the change of the solid angle, that is, inversely proportional to the square of the distance r.
Chapter 3
Figure 3.1 Absolute spectral distribution of radiant power on the blackbody described by the Planck formula (3.1) at different absolute temperatures. Figure 3.2 Two media are characterized by two different refractive indices n2 > n1. A ray refracted, passing from a medium with a lower refractive index to a medium with a higher refractive index, and a reflected ray are represented. Figure 3.3 Two media are characterized by two difference refractive indices n1 > n2. Reflection, refraction and critical angle are represented.
Figure 3.4 Fresnel’s reflectances, ρ (black line) and ρ// (red line), represented as a function of the incidence angle ϑi. Figure (a) regards the case without a critical angle and figure (b) the case with a critical angle. The reflectance ρ// assumes the zero value at the Brewster angle, for which the reflected radiation can only be fully polarized with the electric field perpendicular to the incidence plane.
Figure 3.5 Sketch of the path of a ray of light in interaction with a body: (A) regular or specular reflection, refraction and regular transmission according to Snell’s laws on a smooth surface (Section 3.4); (B) diffuse reflection and diffuse transmission on a rough surface (Section 3.6); (C) internal diffusion due to optical heterogeneity; inside the body there may also be absorption and fluorescence (Section 3.5). Figure 3.6 Scattering indicatrix in the case of Rayleigh and Mie scattering. Figure 3.7 Luminescence spectrum (red line) and absorption band (black line): the band of luminescence is independent of the monochromatic exciting radiation, provided that it belongs to the same absorption band. The absorption band is obtained as the envelope of the excitation lines.
Figure 3.8 (a) Internal Transmittance of three filters made with the same dye but with different thicknesses. (b) Internal optical densities of the three filters. (c) Logarithm of the internal optical densities, which reveals its modification in correspondence to the change of the thickness. The shape is invariant, independent of the concentration and thickness, as a characteristic property of the dye.
Figure 3.9 Deviation of the actual behaviour (red line) from Beer’s law (black line). Figure 3.10 Multiple reflections and refractions at the surfaces of a layer of material with refractive index different from that of the external medium, which contribute to the reflectance and the transmittance of the surface (the angle of incidence, which in reality is close to zero, is designed different from zero for a better graphical representation of the phenomenon). Figure 3.11 Fluxes within a paint layer of thickness X crossing the elementary layer ds according to the model of Kubelka-Munk. Figure 3.12 Reflectances of a mixture of two pigments, one white and one green, according to mixing ratios with increasing step equal to 10% (the top curve represents the 100% white pigment, the bottom curve 100% green pigment) and computed by the mixing law of Kubelka-Munk corrected by Saunderson. It is observed that greatest variations in reflectance are at the extreme steps, 0–10% and 90–100%. This reveals that the formulation for a mixture of pigments, in which one pigment enters the mixture with a percentage lower than 10%, is difficult to make, because a very small percentage change involves an appreciable variation of reflectance.
Figure 3.13 Chromaticity of colours obtained by mixing different pigments in varying ratios with the white pigment (Section 6.13). It is observed that in the process of subtractive synthesis implemented with mixtures of pigments, the chromaticity moves away from its straight line of additive colour mixing (Section 6.13.8). Such behaviour is calculated with the Kubelka-Munk model.
Figure 3.14 Integrating sphere of radius r, on the inner surface of which are considered in perspective view the elements of the surface dS and dA with a mutual distance equal to (2 r cosϑ), where dS receives light from dA. The point C is the centre of the sphere.