Color Appearance Models

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"A clear and authoritative review of an important field in color science." --Dr. R.W.G. Hunt

This book is a comprehensive state-of-the-art reference focusing on color appearance models, innovative tools that describe and predict color under a variety of viewing conditions. Written by a leading authority, this book provides any professional or student versed in color science basics with a complete overview of the following color appearance models:

• Nayatani et al.
• Hunt
• RLAB
• ATD
• LLAB
• ZLAB
• CIECAM97s

For each model, the book examines such aspects as input data, adaptation, opponent-color dimensions, color defining features, predictable phenomena, and the pros and cons of that model. It offers essential background information on human color perception, psychophysics, and the Commission Internationale de l'...clairage (CIE) system of colorimetry that has formed the foundation for color technology since the 1930s. Also addressed are color appearance terminology, color order systems, color appearance phenomena, and an analysis of viewing conditions. The book discusses chromatic adaptation in depth, one of the most important elements of color appearance. The book also includes an overview of device-independent color imaging-the application that represents the greatest technological push for the development of color appearance models.

In all, Color Appearance Models gives you an excellent understanding of the foundation and forefront of color technology, innovative tools now available, and how these recent developments are likely to revolutionize the field.

Sample Content

Table of Contents

Preface.


Acknowledgments.


Introduction.


1. Human Color Vision.

Optics of the Eye. The Retina Revisited. Visual Signal Processing. Mechanisms of Color Vision. Spatial and Temporal Properties of Color Vision. Color-vision Deficiencies. Key Features for Color Appearance Modeling.

Psychophysics Defined. Historical Context. Hierarchy of Scales. Threshold Techniques. Matching Techniques. One-dimensional Scaling. Multidimensional Scaling. Design of Psychophysical Experiments. Importance of Psychophysics in Color Appearance Modeling.

Basic and Advanced Colorimetry. Why Is Color? Light Sources and Illuminants. Colored Materials. The Human Visual Response. Tristimulus Values and Color-matching Functions. Chromaticity Diagrams. CIE Color Spaces. Color-difference Specification. The Next Step.

Importance of Definitions. Color. Hue. Brightness and Lightness. Colorfulness and Chroma. Saturation. Unrelated and Related Colors. Definitions in Equations. Brightness-Colorfulness Versus Lightness-Chroma.

Overview and Requirements. The Munsell Book of Color. The Swedish Natural Color System. The Colorcurve System. Other Color-order Systems. Uses of Color-order Systems. Color-naming Systems.

What Are Color-appearance Phenomena? Simultaneous Contrast, Crispening, and Spreading. Bezold-Brücke Hue Shift (Hue Changes with Luminance). Abney Effect (Hue Changes with Colorimetric Purity). Helmholtz-Kohlrausch Effect (Brightness Depends on Luminance and Chromaticity). Hunt Effect (Colorfulness Increases with Luminance). Stevens Effect (Contrast Increases with Luminance). Helson-Judd Effect (Hue of Nonselective Samples). Bartleson-Breneman Equations (Image Contrast Changes with Surround). Discounting-the-Illuminant. Other Context and Structural Effects. Color Constancy?

Configuration of the Viewing Field. Colorimetric Specification of the Viewing Field. Modes of Viewing. Unrelated and Related Colors Revisited.

Light, Dark, and Chromatic Adaptation. Physiology. Sensory and Cognitive Mechanisms. Corresponding-colors Data. Models. Computational Color Constancy.

von Kries Model. Retinex Theory. Nayatani et al. Model. Guth’s Model. Fairchild’s Model.

Definition of Color Appearance Model. Construction of Color Appearance Models. CIELAB. Why Not Use Just CIELAB? What About CIELUV?

Objectives and Approach. Input Data. Adaptation Model. Opponent-color Dimensions. Brightness. Lightness. Hue. Saturation. Chroma. Colorfulness. Inverse Model. Phenomena Predicted. Why Not Use Just the Nayatani Model?

Objectives and Approach. Input Data. Adaptation Model. Opponent-color Dimensions. Hue. Saturation. Brightness. Lightness. Chroma. Colorfulness. Inverse Model. Phenomena Predicted. Why Not Use Just the Hunt Model?

Objectives and Approach. Input Data. Adaptation Model. Opponent-color Dimensions. Lightness. Hue. Chroma. Saturation. Inverse Model. Phenomena Predicted. Why Not Use Just the RLAB Model?

Overview. ATD Model. LLAB Model.

Overview. Qualitative Tests. Corresponding-colors Data. Magnitude-estimation Experiments. Direct Model Tests. CIE Activities. A Pictorial Review of Color Appearance Models.

Color Rendering. Color Differences. Indices of Metamerism. A General System of Colorimetry?

The Problem. Levels of Color Reproduction. General Solution. Device Calibration and Characterization. The Need for Color Appearance Models. Definition of Viewing Conditions. Viewing-conditions-independent Color Space. Gamut Mapping. Color Preferences. Inverse Process. Example System. ICC Implementation.

Will There Be One Color Appearance Model? Other Color Appearance Models. Ongoing Research to Test Models. Ongoing Model Development. What to Do Now.

Historical Development, Objectives, and Approach. Bradford-Hunt 96S (Simple) Model. Bradford-Hunt 96C (Comprehensive) Model. The CIE TC1-34 Model, CIECAM97s. The ZLAB Color Appearance Model. Outlook.

Preface

The law of proportion according to which the several colors are formed, even if a man knew, he would be foolish in telling, for he could not give any necessary reason, nor indeed any tolerable or probable explanation of them.

-Plato

Despite Plato's warning, this book is about one of the major unresolved issues in the field of color science, the efforts that have been made toward its resolution, and the techniques that can be used to address current technological problems. That issue is the prediction of the color appearance experienced by an observer when viewing stimuli in natural, complex settings. Useful solutions to this problem have impacts in a number of industries, such as lighting, materials, and imaging.

In lighting, color appearance models can be used to predict the color-rendering properties of various light sources, thereby allowing specification of quality rather than just efficiency. In materials fields (coatings, plastics, textiles, and so on), color appearance models can be used to specify tolerances across a wider variety of viewing conditions than is currently possible. The imaging industries have produced the biggest demand for accurate and practical color appearance models. The rapid growth in color-imaging technology, particularly the desktop publishing market, has led to the emergence of color-management systems. It is widely acknowledged that such systems require color appearance models to allow images originating in one medium and viewed in a particular environment to be acceptably reproduced in a second medium and viewed under different conditions.

While the need for color appearance models is recognized, their development has been at the forefront of color science and confined to the discourse of academic journals and conferences. This book brings the fundamental issues and current solutions in the area of color appearance modeling together in a single place for those needing to solve practical problems.

Everyone knows what color is, but the accurate description and specification of colors is quite another story. In 1931, the Commission Internationale de l'...clairage (CIE) recommended a system for color measurement that established the basis for modern colorimetry. That system allowed the specification of color matches through CIE XYZ tristimulus values. However, it was immediately recognized that more advanced techniques were required. The CIE recommended the CIELAB and CIELUV color spaces in 1976 to enable uniform international practice for the measurement of color differences and the establishment of color tolerances.

While the CIE system of colorimetry has been applied successfully for nearly 70 years, it is limited to the comparison of stimuli that are identical in every spatial and temporal respect and viewed under matched viewing conditions. CIE XYZ values describe whether two stimuli match. CIELAB values can be used to describe the perceived differences between stimuli in a single set of viewing conditions. Color appearance models extend the current CIE systems to allow the description of what color stimuli look like under a variety of viewing conditions. The application of such models opens up a world of possibilities for the accurate specification, control, and reproduction of color.

Understanding color-appearance phenomena and developing models to predict them have been the topics of a great deal of research-particularly in the last 10 to 15 years. Color appearance remains a topic of much active research that is often being driven by technological requirements. Despite the fact that the CIE is not yet able to recommend a single color appearance model as the best that is available for all applications, many specialists need to implement some form of a model to solve their research, development, and engineering needs.

One application area is the development of color-management systems based on the ICC profile format that is being developed by the International Color Consortium and incorporated into essentially all modern computer operating systems. However, implementation of color management using ICC profiles requires the application of color appearance models with no specific instructions on how to do so. And unfortunately, the fundamental concepts, phenomena, and models of color appearance are not recorded in a single source. Currently, anyone interested in the field must search out the primary references across a century of scientific journals and conference proceedings. This is due to the large amount of active research in the area.

While searching for and keeping track of primary references is fine for those doing research on color appearance models, it should not be necessary for every scientist, engineer, and software developer interested in the field. So the goal of this book is to provide, in a single source, an overview of color appearance and details of many of the most widely used models. The general approach has been to provide an overview of the fundamentals of color measurement and the phenomena that necessitate the development of color appearance models. This eases the transition into the formulation of the various models and their applications that appear later in the book. This approach has proven quite useful in various university courses, short courses, and seminars in which the full range of material must be presented in a limited time.

Following is a preview of each chapter:

• Chapters 1 through 3 review the fundamental concepts of human color vision, psychophysics, and the CIE system of colorimetry that are prerequisites to an understanding of the development and implementation of color appearance models.
• Chapters 4 through 7 present the fundamental definitions, descriptions, and phenomena of color appearance. They review the historical literature that has led to modern research and development of color appearance models.
• Chapters 8 and 9 concentrate on one of the most important component mechanisms of color appearance: chromatic adaptation. The models of chromatic adaptation described in Chapter 9 are the foundation of the color appearance models described in later chapters.
• Chapter 10 presents the definition of color appearance models and outlines their construction using the CIELAB color space as an example.
• Chapters 11 through 13 provide detailed descriptions of the Nayatani et al., Hunt, and RLAB color appearance models, along with the advantages and disadvantages of each.
• Chapter 14 reviews the ATD and LLAB appearance models that are of increasing interest for some applications.
• Chapters 15 and 16 describe tests of the various models through a variety of visual experiments and colorimetric applications of the models.
• Chapter 17 presents an overview of device-independent color imaging, the application that has provided the greatest technological push for the development of color appearance models.
• Chapter 18 includes thoughts on the future directions for color appearance modeling research and application.
• The appendix provides a snapshot of the status of the CIE color appearance models being developed for further testing by CIE TC1-34 as this book goes to press.

The field of color appearance modeling is still in its infancy and likely to continue developing in the near future. However, Chapters 1 through 10 of this book provide overviews of fundamental concepts, phenomena, and techniques that will change little, if at all, in the coming years. Thus these chapters should serve as a steady reference. The later chapters describe models, tests, and applications that will be subject to evolutionary changes as research progresses. However, they do provide a useful snapshot of the current state of affairs and provide a basis from which it should be much easier to keep track of future developments. To assist readers in this task, a World Wide Web page has been set up that lists important developments and publications since the publication of this book (see http://www.awl.com/cseng/ and/or http:// www.cis.rit.edu/people/faculty/ fairchild). A spreadsheet with example calculations can also be found there.

'Yes,' I answered her last night;
'No,' this morning sir, I say,
Colours seen by candle-light
Will not look the same by day.

-Elizabeth Barrett Browning

Acknowledgments

A project like this book is never really completed by a single person. I particularly thank my family for the undying support that encouraged its completion. The research and learning that led to it are directly attributable to my students. Much of the research would not have been completed without their tireless work, and I would not have learned about color appearance models were it not for their keen desire to learn more about them from me. I am deeply indebted to all of my students and friends-those who did research with me, those who worked at various times in the Munsell Color Science Laboratory, and those who participated in my university and short courses at all levels. There is no way to list all of them without making an omission, so I will take the easy way out and thank them as a group.

I also am indebted to those who reviewed various chapters while this book was being prepared and who provided useful insights, suggestions, and criticisms. These reviewers include Paula J. Alessi, Edwin Breneman, Ken Davidson, Ron Gentile, Robert W. G. Hunt, Lindsay MacDonald, Mike Pointer, Michael Stokes, Jeffrey Wang, Eric Zeise, and Valerie Zelenty.

Thanks also to all of the industrial and government sponsors of our research and education in the Munsell Color Science Laboratory at R.I.T. In particular, thanks to Thor Olson of Management Graphics for the donation of the Opal image recorder and the loan of the 120-camera back used to output the color images included in this book. Last, but not least, I thank Colleen Desimone for her excellent work as the Munsell Color Science Laboratory secretary, which makes life at the office much easier.

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