Illumination, Color and Imaging E-Book

Peter Bodrogi

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Serie: Wiley Series in Display Technology
• Sprache: Englisch

Seitenzahl: 694

Veröffentlichungsjahr: 2012

Beschreibung

This much needed, comprehensive and modern reference on display technology, illumination sources and color imaging focuses on visual effects and how reproduced images are best matched to human visual features. As such, it teaches readers how to exploit the knowledge of human color information processing to design usable, ergonomic, and pleasing displays or visual environments. The contents describe design principles and methods to optimize self-luminous visual technologies for the human user, including modern still and motion image displays, and indoor light sources. Design principles and methods are derived from the knowledge of the human visual system, with a special emphasis on color vision, color cognition, color harmony, color preference and visually evoked emotions. The expert authors include the most important and latest applications of the design principles and methods, forming a comprehensive view of human color information processing from the receptors through the retina via high-level visual perception right up to the level of cognition, preference, harmony, as well as visually evoked emotions. This book is included in the Wiley SID Series.

Leseprobe

Contents

Cover

Wiley-SID Series in Display Technology

Title Page

Copyright

Dedication

Series Editor's Foreword

Preface

About the Authors

Chapter 1: Color Vision and Self-Luminous Visual Technologies

1.1 Color Vision Features and the Optimization of Modern Self-Luminous Visual Technologies

1.2 Color Vision-Related Technological Features of Modern Self-Luminous (Nonprinting) Visual Technologies

1.3 Perceptual, Cognitive, and Emotional Features of the Visual System and the Corresponding Technological Challenge

References

Chapter 2: Colorimetric and Color Appearance-Based Characterization of Displays

2.1 Characterization Models and Visual Artifacts in General

2.2 Characterization Models and Visual Artifacts of the Different Display Technologies

2.3 Display Light Source Technologies

2.4 Color Appearance of Large Viewing Angle Displays

References

Chapter 3: Ergonomic, Memory-Based, and Preference-Based Enhancement of Color Displays

3.1 Ergonomic Guidelines for Displays

3.2 Objectives of Color Image Reproduction

3.3 Ergonomic Design of Color Displays: Optimal Use of Chromaticity Contrast

3.4 Long-Term Memory Colors, Intercultural Differences, and Their Use to Evaluate and Improve Color Image Quality

3.5 Color Image Preference for White Point, Local Contrast, Global Contrast, Hue, and Chroma

3.6 Age-Dependent Method for Preference-Based Color Image Enhancement with Color Image Descriptors

References

Chapter 4: Color Management and Image Quality Improvement for Cinema Film and TV Production

4.1 Workflow in Cinema Film and TV Production Today – Components and Systems

4.2 Components of the Cinema Production Chain

4.3 Color Gamut Differences

4.4 Exploiting the Spatial–Temporal Characteristics of Color Vision for Digital TV, Cinema, and Camera Development

4.5 Optimum Spectral Power Distributions for Cinematographic Light Sources and Their Color Rendering Properties

4.6 Visually Evoked Emotions in Color Motion Pictures

References

Chapter 5: Pixel Architectures for Displays of Three- and Multi-Color Primaries

5.1 Optimization Principles for Three- and Multi-Primary Color Displays to Obtain a Large Color Gamut

5.2 Large-Gamut Primary Colors and Their Gamut in Color Appearance Space

5.3 Optimization Principles of Subpixel Architectures for Multi-Primary Color Displays

5.4 Three- and Multi-Primary Subpixel Architectures and Color Image Rendering Methods

Acknowledgment

References

Chapter 6: Improving the Color Quality of Indoor Light Sources

6.1 Introduction to Color Rendering and Color Quality

6.2 Optimization for Indoor Light Sources to Provide a Visual Environment of High Color Rendering

6.3 Optimization of Indoor Light Sources to Provide Color Harmony in the Visual Environment

6.4 Principal Components of Light Source Color Quality

6.5 Assessment of Complex Indoor Scenes Under Different Light Sources

6.6 Effect of Interobserver Variability of Color Vision on the Color Quality of Light Sources

Acknowledgments

References

Chapter 7: Emerging Visual Technologies

7.1 Emerging Display Technologies

7.2 Emerging Technologies for Indoor Light Sources

7.3 Summary and Outlook

Acknowledgments

References

Index

Wiley-SID Series in Display Technology

Series Editor:

Anthony C. Lowe

Consultant Editor:

Michael A. Kriss

Display Systems: Design and Applications

Lindsay W. MacDonald and Anthony C. Lowe (Eds.)

Electronic Display Measurement: Concepts, Techniques, and Instrumentation

Peter A. Keller

Reflective Liquid Crystal Displays

Shin-Tson Wu and Deng-Ke Yang

Colour Engineering: Achieving Device Independent Colour

Phil Green and Lindsay MacDonald (Eds.)

Display Interfaces: Fundamentals and Standards

Robert L. Myers

Digital Image Display: Algorithms and Implementation

Gheorghe Berbecel

Flexible Flat Panel Displays

Gregory Crawford (Ed.)

Polarization Engineering for LCD Projection

Michael G. Robinson, Jianmin Chen, and Gary D. Sharp

Fundamentals of Liquid Crystal Devices

Deng-Ke Yang and Shin-Tson Wu

Introduction to Microdisplays

David Armitage, Ian Underwood, and Shin-Tson Wu

Mobile Displays: Technology and Applications

Achintya K. Bhowmik, Zili Li, and Philip Bos (Eds.)

Photoalignment of Liquid Crystalline Materials: Physics and Applications

Vladimir G. Chigrinov, Vladimir M. Kozenkov and Hoi-Sing Kwok

Projection Displays, Second Edition

Matthew S. Brennesholtz and Edward H. Stupp

Introduction to Flat Panel Displays

Jiun-Haw Lee, David N. Liu and Shin-Tson Wu

LCD Backlights

Shunsuke Kobayashi, Shigeo Mikoshiba and Sungkyoo Lim (Eds.)

Liquid Crystal Displays: Addressing Schemes and Electro-Optical Effects, Second Edition

Ernst Lueder

Transflective Liquid Crystal Displays

Zhibing Ge and Shin-Tson Wu

Liquid Crystal Displays: Fundamental Physics and Technology

Robert H. Chen

3D Displays

Ernst Lueder

OLED Display Fundamentals and Applications

Takatoshi Tsujimura

Illumination, Color and Imaging: Evaluation and Optimization of Visual Displays

Tran Quoc Khanh and Peter Bodrogi

All books published by Wiley-VCH are carefully produced. Nevertheless, authors, editors, and publisher do not warrant the information contained in these books, including this book, to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Library of Congress Card No.: applied for

British Library Cataloguing-in-Publication Data

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

Bibliographic information published by the Deutsche Nationalbibliothek

The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.d-nb.de.

© 2012 Wiley-VCH Verlag & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

Print ISBN: 978-3-527-41040-8

ePDF ISBN:978-3-527-65075-0

ePub ISBN:978-3-527-65074-3

mobi ISBN:978-3-527-65073-6

oBook ISBN:978-3-527-65072-9

Cover Design Spieszdesign, Neu-Ulm

Typesetting Thomson Digital, Noida, India

To Prof. János Schanda, for his research and teaching in the domains of color science, colorimetry, photometry and visual technologies

Series Editor's Foreword

Display manufacturers spend a great deal of time and resource improving the visual characteristics of their display products. Such improvements encompass resolution, contrast, color gamut, viewing angle, and switching speed. Yet the manner in which displays are used is often haphazard, with too little attention being paid to the orientation of the display to sources of ambient illumination, to the ambient illuminance, or to the hue of the illuminant. How much better their visual experience would be if users or those responsible for display use within an organization had more knowledge of all these factors and applied them appropriately. How much more effectively could manufacturers and product developers use their resources if they paid greater attention to the realistic limits imposed by the human visual system and by the gamut of the majority of colors we experience in real life. Too often, marketing statements enter the realm of improbability with claims of massive color gamuts and contrast ratios achievable only under dark room conditions.

This latest book in the series is written by two respected experts in the field of display evaluation and optimization. It addresses the issues I have outlined above and a great deal more. It is a very complete book. In fact, the authors have provided such a complete description of its contents in the preface that I shall not comment further on it in detail here.

There are, however, some general comments I would make. Many, perhaps most of those, who have made measurements on displays they are researching will have been solely interested in the temporal and contrast characteristics of their particular display. That is all well and good; such measurements are the fundamental basis of characterizing displays. However, what this book reveals is the complexity and richness of the stages of development that follow and that, in the authors' own words, emphasize how to use the features of the human visual system to meet today's technological challenges. Those challenges include familiar elements such as the colorimetric and color appearance-based characterization and calibration of color monitors and color management in digital TV and cinema applications. However, they also include the less familiar optimization of pixel and subpixel architectures for displays of more than three primary colors, the concepts of color conspicuity, color memory, and color preference-based enhancement of color displays for visual ergonomics and pleasing image rendering. I am among those becoming familiar with visual changes that are related to the aging process, but new to me was a quantitative treatment of cultural differences. The last of the challenges the book addresses is perhaps better considered as an opportunity. It concerns the ability to optimize the spectral power distribution of modern light sources that can be used either as indoor illuminants or as display backlights.

This book contains a significant amount of previously unpublished material. A much needed and very up-to-date work, it will provide great benefit and vital guidance to an extremely wide and diverse audience that includes but is definitely not limited to those involved in the development of image capture and display devices and systems, light sources and illumination systems, and image optimization, processing, and production software.

Braishfield, United Kingdom

Anthony C. LoweSeries Editor

Preface

This book is a monograph about how to exploit the knowledge of the human color information processing system in order to design usable, ergonomic, and pleasing information displays, entertainment displays, or a high-quality visual environment. For the designer of modern self-luminous visual technologies including displays and light sources for general lighting, optimization principles derived from the human visual system are presented. This book has arisen from the need for a specialist text that brings together these principles derived from a comprehensive view of human color information processing from retinal photoreceptors to cognition, preference, harmony, and emotions arising in the visual brain with the recent amazing developments of display technology and general indoor light source technology. In this sense, this book is not a textbook on human vision, colorimetry, color science, display technology, or light source technology. Instead, the emphasis is on how to use the features of the human visual system to meet today's technological challenges including the colorimetric and color appearance-based characterization and calibration of color monitors, color management in digital TV and cinema, optimization of pixel and subpixel architectures for displays of three or more primary colors, color conspicuity, color memory, and color preference-based enhancement of color displays for visual ergonomics and pleasing image rendering, also concerning cultural and age differences, and last but not least the optimization of spectral power distributions of modern light sources used to illuminate an indoor scene or an image rendering pixel architecture as a backlight.

Concerning the intended audience of this book, researchers and engineers of display and camera development (cameras, monitors, televisions, projectors, and head-mounted displays) may be concerned, for example, lighting engineers who develop novel light sources, researchers and engineers who develop color image optimization algorithms, software developers involved in color image processing, engineers of imaging and display systems, scientists involved in color vision research, designers of human interfaces and systems, application software developers for special effects in digital cinema postproduction, designers of lighting environments, postgraduate students in these domains, and anyone implementing a color management system. The material of this monograph can also be taken as a background reading for master's degrees in color image science and for researchers and design scientists, physicists, and engineers in the field of imaging technologies and their applications as well as university students in this field. The book may also be interesting for professionals working on software development for media and entertainment, video and film production, indoor architecture, and social aspects of home media technology as well as for graphics students and web developers.

Throughout the book, the term “self-luminous visual technologies” is used in the context of imaging technologies and illuminating technologies but printing technologies are excluded. Printing technologies and conventional photography represent a huge domain of knowledge that is out of the scope of this book. The issues of outdoor light sources such as street lighting or automotive lighting address the very complex mechanisms of human visual performance in the mesopic (twilight) luminance range; hence, these issues are also out of scope. In this book, the term “imaging technologies” is intended to mean all technologies that capture, digitalize, transmit, compress, transform, or display spectral, temporal, and spectral distributions of light, while the term “illuminating technologies” refers to all light source technologies used to illuminate reflecting or translucent objects to provide a visual environment consisting of the illuminated colored objects optimal for the user. The term “illuminating technologies” also covers the design of light sources used in digital or analog projectors or in backlit display technologies.

The book is organized into seven chapters. Chapter 1 is an introduction to color vision and self-luminous visual technologies. The question is what technology and which technological component is a specific feature of color vision relevant for and why. These features include retinal photoreceptor structure, spatial and temporal contrast sensitivity, color appearance perception, color difference perception, legibility, visibility, and conspicuity of colored objects, cognitive, preferred, harmonic, and emotional color, and the interindividual variability of color vision. Specific problems, features, and optimization potentials arising from the characteristics of color vision are described that are relevant for each technology including digital film and TV, cameras, color monitors, head-mounted displays, digital signage displays and large tiled displays, microdisplays, projectors, light sources of display backlighting, and general indoor illumination. At the end, Chapter 1 contains a table summarizing the perceptual, cognitive, and emotional features of the visual system and the corresponding technological challenge with links to specific sections later in the monograph.

Chapter 2 deals with the colorimetric and color appearance-based characterization of displays starting with a general description of display characterization models such as tone curve models, phosphor matrices, sRGB, and other characterization models. The additivity or independence of the monitor's color channels is an important criterion for an efficient characterization model. Multidimensional phosphor matrices and other methods are presented to reduce the colorimetric error arising from color channel interdependence. Methods are presented to test and ensure the spatial uniformity of the display to achieve accurate colors in every point. Also, the color predicted at a specific point should not depend on the color of other positions on the screen according to the important criterion of spatial independence. Methods to predict spatial interdependence are also described and the concept of viewing direction uniformity is presented that is especially important for liquid crystal displays. A paragraph is devoted to the miscellaneous visual artifacts, that is, the visually disturbing patterns arising from the imperfectness of display technology. The effect of the viewing environment including viewing conditions, viewing modes, and ambient light is described to be able to apply CIELAB, CIELUV, and CIECAM02 to a self-luminous display. Specific characterization models are described for the specific display technologies. Different projector light sources and backlighting light sources including LEDs are compared with relevance to the use of color filters, their white points, local dimming, and high dynamic range imaging. Finally, Chapter 2 also deals with the color appearance difference between small and large color stimuli, the so-called color size effect, and its mathematical modeling. Specifically, the color appearance of large color stimuli (e.g., 60–100° on a PDP) is different from small to medium size colors (i.e., below 20°). This effect is accounted for by an extension of CIELAB for the specific viewing condition of large self-luminous displays.

Chapter 3 deals with the ergonomic, memory-based, and preference-based enhancement of color displays. Ergonomic guidelines of visual displays and the objectives of color image reproduction are summarized. The principles of ergonomic color design are described for color displays to support effective work with the user interface appearing on the display based on the relationship among legibility, conspicuity, and visual search. A method of optimal use of chromaticity contrast to optimize search performance is presented together with the issues of chromaticity contrast preference and luminance contrast preference for young and elderly display users. In Chapter 3, long-term memory colors of familiar objects are located in color space and their intercultural differences are pointed out. A method to obtain a color image preference data set and a preference-based color image enhancement method are presented containing color image transforms that influence color image preference including the preferred white point, local contrast, global contrast, hue, and chroma.

Chapter 4 deals with the issues of color management and image quality improvement for cinema film and TV production. The components and systems of color management workflows in today's cinema film and TV production are described together with the components of the cinema production chain. An overview of camera technology and postproduction systems is given and the applicability of CIELAB and CIEDE2000 color difference formulas under the viewing conditions of TV and cinema production is dealt with. It is described how to apply the CIECAM02 color appearance model in the digital image processing system for motion picture films. Color gamut differences among cinema motion picture digital cameras, HDTV CRT monitors, film projectors, and DLP projectors are pointed out. It is shown how to exploit the spatial–temporal characteristics of color vision for digital TV, cinema, and camera development including how to optimize the resolution of digital motion picture cameras and how to compress motion pictures without impairing their perceived image quality. Methods of image quality evaluation and an image quality experiment are described. The important issue of watermarking algorithms for the protection of digital motion picture films is dealt with in detail. This is one of the most typical applications of human visual principles to advance display technology described in this book. The next issue of Chapter 4 concerns the optimum spectral power distributions for cinematographic light sources to optimize their color image rendering properties. Finally, the interesting question of visually evoked emotions in color motion pictures is dealt with. The question is how the technological parameters of video sequences influence or strengthen those parts of human emotions that are evoked by the visual appearance of the movie.

Chapter 5 deals with the different pixel architectures for self-luminous displays with three or more primary colors. To optimize the color gamut of the display, several factors are considered including the target colors to be covered by the optimized color gamut, color quantization, the number of primary colors, the white point, the issues of virtual primaries and technological constraints, and also the visually acceptable luminance ratio between a primary color and the white point. Several sets of optimum primary colors are presented together with the shape of their optimum color gamuts in color appearance space. In Chapter 5, a set of principles derived from human spatial color vision are also described to optimize the subpixel architectures of modern displays with three to seven primary colors including the requirements of minimal color fringe error, good modulation transfer function, isotropy, good luminance resolution, high aperture ratio, and large color gamut. Examples of actual subpixel architectures and color image rendering methods are also shown.

Chapter 6 deals with the optimization of color quality for indoor light sources of general lighting. The issues of color rendering and color quality are introduced including the psychological dimensions of color quality and their metrics such as the metrics used to quantify color fidelity. Visual color fidelity experiments are also described together with a set of color rendering prediction methods to be used for both conventional light sources and solid-state light sources such as LED lamps. Visual color harmony experiments, mathematical methods to predict the color harmony of different color combinations, and computational methods of color harmony rendering represent an interesting special case of color quality evaluation completed by several other factors of color quality such as perceived brightness, visual clarity, color discrimination capability, and color preference. Chapter 6 also shows the result of a principal component analysis of the latter factors followed by a description of a so-called “acceptability” experiment that deals with realistic colored test objects illuminated by different light sources of different color rendering properties of various color distributions. Finally, the effect of interobserver variability on the color quality of light sources is discussed.

Chapter 7 deals with today's emerging visual technologies including flexible displays, lasers, and LED displays with LED lifetime considerations. Color gamut extension algorithms for multi-primary displays are also described together with the temperature dependence of their color gamut by the example of a four-primary color sequential (RGCB) model LED display consisting of colored chip LEDs. Red and cyan colored chip LEDs were replaced by red and cyan phosphor-converted LEDs and the model computation was repeated. Chapter 7 also deals with the emerging technologies for indoor light sources including tunable LED lamps for accent lighting and a possible co-optimization of LED spectral power distributions for brightness and circadian rhythm. Additional issues addressed in Chapter 7 include the accentuation of different aspects of color quality, the use of new phosphor blends, and the implications of color constancy for light source design. Finally, a summary of the whole book and an outlook for future research is given.

This book contains material from various sources including the authors' articles previously published in Color Research and Application, Displays, the German journal Licht, the Journal of Electronic Imaging, Proceedings of AIC, CGIV, and CIE conferences, the German journal FKT (TV and Cinema Technology), and the authors' lecture qualification theses. This material has been organized and is now presented in a consistent and more readable way because the material has been reviewed very thoroughly and then reformulated. The authors' original ideas have been reconsidered, refined, and further explained to include several new insights from the lighting engineer's point of view, also in the view of numerous recent literature items including patent publications. Complex interdependences across the material have been pointed out. Thus, this book provides a more detailed, more comprehensive, more thorough, and more systematic treatment of the subject than the original articles. In addition to this, the book contains numerous new ideas and a lot of new material published in the sections of this monograph for the first time. To obtain this latter material, we gratefully acknowledge the help from the coworkers of the Laboratory of Lighting Technology of the Technische Universität Darmstadt, especially Mr. Marvin Böll, Mr. Stefan Brückner, Ms. Nathalie Krause, Mr. Wjatscheslaw Pepler, and Mr. Quang Vinh Trinh, in no particular order. The authors would like to thank the colleagues and the diploma students of the company Arnold & Richter (Munich, Germany) for the cooperation during the development of the film scanner, film recorder, and the digital cinema camera with all related research and development aspects, especially Mr. Franz Kraus, Dr. Johannes Steurer, Dr. Achim Oehler, Dr. Peter Geissler, Mr. Michael Koppetz, Mr. Joachim Holzinger, Mr. Harald Brendel, Mr. Christian Bueckstuemmer, Ms. Doreen Wunderlich, Mr. Alexander Vollstaedt, Dr. Sebastian Kunkel, Mr. Ole Gonschorek, Mr. Andreas Kraushaar, Mr. Constantin Seiler, Ms. Christina Hacker, and Mr. Nils Haferkemper.

P. BodrogiT.Q. Khanh

About the Authors

PeterBodrogi is a senior research fellow at the Laboratory of Lighting Technology of the Technische Universität Darmstadt in Darmstadt, Germany. He graduated in Physics from the Loránd Eötvös University of Budapest, Hungary. He obtained his PhD degree in Information Technology from the University of Pannonia in Hungary. He has co-authored numerous scientific publications and invented patents about color vision and self-luminant display technology. He has received several scientific awards including a Research Fellowship of the Alexander von Humboldt Foundation, Germany, and the Walsh-Weston Award, Great Britain. He has been member of several Technical Committees of the International Commission of Illumination (CIE).

Tran Quoc Khanh is University Professor and Head of the Laboratory of Lighting Technology at the Technische Universität Darmstadt in Darmstadt, Germany. He graduated in Optical Technologies, obtained his PhD degree in Lighting Engineering, and his degree of lecture qualification (habilitation) for his thesis in Colorimetry and Colour Image Processing from the Technische Universität Ilmenau, Germany. He has gathered industrial experience as a project manager by ARRI Cine Technik in Munich, Germany. He has been the organizer of the well-known series of international symposia for automotive lighting (ISAL) in Darmstadt, Germany, and is a member of several Technical Committees of the International Commission of Illumination (CIE).

Chapter 1

Color Vision and Self-Luminous Visual Technologies

Color vision is a complicated phenomenon triggered by visible radiation from the observer's environment imaged by the eye on the retina and interpreted by the human visual brain [1]. A visual display device constitutes an interface between a supplier of electronic information (e.g., a television channel or a computer) and the human observer (e.g., a person watching TV or a computer user) receiving the information stream converted into light. The characteristics of the human component of this interface (i.e., the features of the human visual system such as visual acuity, dynamic luminance range, temporal sensitivity, color vision, visual cognition, color preference, color harmony, and visually evoked emotions) cannot be changed as they are determined by biological evolution.

Therefore, to obtain an attractive and usable interface, the hardware and software features of the display device (e.g., size, resolution, luminance, contrast, color gamut, frame rate, image stability, and built-in image processing algorithms) should be optimized to fit the capabilities of human vision and visual cognition. Accordingly, in this chapter, the most relevant characteristics of human vision – especially those of color vision – are introduced with special respect to today's different display technologies.

The other aim of this chapter is to present a basic overview of some essential concepts of colorimetry [2] and color science [3–5]. Colorimetry and color science provide a set of numerical scales for the different dimensions of color perception (so-called correlates for, for example, the perceived lightness or saturation of a color stimulus). These numerical correlates can be computed from the result of physical light measurement such as the spatial and spectral light power distributions of the display. Using these numerical correlates, the display can be evaluated and optimized systematically by measuring the spectral and spatial power distributions of their radiation – without cumbersome and time-consuming direct visual evaluations.

1.1 Color Vision Features and the Optimization of Modern Self-Luminous Visual Technologies

This section summarizes the most important features of color vision for the evaluation and optimization of self-luminous color displays including the photoreceptor structure of the retina, the spatial and temporal contrast sensitivity of the human visual system, color appearance and color difference perception, the components of visual performance and ergonomics (legibility, visibility, and conspicuity of colored objects), and certain features arising at a later stage of human visual information processing such as cognitive, preferred, harmonic, and emotional color phenomena. The important issue of interindividual variability of color vision will also be dealt with in this section.

1.1.1 From Photoreceptor Structure to Colorimetry

Human color vision is trichromatic [1]. This feature has its origin in the retinal photoreceptor structure consisting of three types of photoreceptors that are active at daytime light intensity levels: the L-, M-, and S-cones. Rods constitute a further type of retinal photoreceptors but as they are responsible for nighttime vision and partially for twilight viewing conditions, they are out of the scope of this book. Displays should ensure a high enough general luminance level (e.g., higher than 50–100 cd/m2, depending on the chromaticity of the stimulus) for the three types of cones to operate in an optimum state for the best possible perception of colors. Generally, above a luminance of about 100 cd/m2, rods produce no signal for further neural processing and it is possible to predict the matching and the appearance of colors from the cone signals only.

L-, M-, and S-cones constitute a characteristic retinal cone mosaic. The central (rod-free) part of the cone mosaic can be seen Figure 1.1.

Figure 1.1 The cone mosaic of the rod-free inner fovea, that is, the central part of the retina subtending about 1°, that is, about 300 µm. Red dots: long-wavelength sensitive cone photoreceptors (L-cones). Green dots: middle-wavelength sensitive cones (M-cones). Blue dots: short-wavelength sensitive cones (S-cones).

Source: Figure 1.1 from Sharpe, L.T., Stockman, A., Jägle, H., and Nathans, J. (1999) Opsin genes, cone photopigments, color vision and color blindness, in Ref. [1], pp. 3–51. Reproduced with permission from Cambridge University Press.

As can be seen from , the inner area of the central part (subtending a visual angle of about 0.3° or 100 µm) is free of S-cones resulting in the so-called small-field tritanopia, that is, the insensitivity to bluish light for very small central viewing fields. There are on average 1.5 times as many L-cones as M-cones in this region of the retina [1]. L- and M-cones represent 93% of all cones, while S-cones represent the rest (7%).