Effective Color Displays is an excellent book. It is well written, scholarly, and packed with information in a readily accessible and useful form... In the past few years there have been several books which have attempted the same mission. Effective Color Displays is the best of this genre.”
— Louis Silverstein, Color Research and Application.

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Table of contents


Electronic displays are ubiquitous as the interface between people and computers. They are used to present information in the form of text, numbers and graphics. Over the last five years, computer systems have grown considerably in sophistication and one of the main areas of change has been the increasing use of color on visual display units. The standard IBM personal computer can now display 256,000 colors and a Sun workstation can display 16.8 million. Hence, hardware is no longer a limiting factor in the decision to use color on a visual display and users perceive its absence as old-fashioned. As a consequence, computer interfaces that fail to use color may not be endorsed by users.

Color can be a most effective way of conveying information and it has important uses in tasks where identification, coding and response times are important. Moreover, there is no question that in most contexts users prefer color to monochrome displays: color interfaces sell and succeed. But when color is used inappropriately it can be very counter productive and few software designers have much experience with the use of color. The aim of this book is to synthesize our current knowledge in the area and specify guidelines so that programmers, engineers and psychologists can use color effectively.

This book has been written for managers, human factors engineers, computer scientists and anyone else involved in the design process. A small amount of experience with computers and the use of visual displays is assumed but no knowledge of color science, psychology or physiology. The book can be used as a reference text or as the basis of a course on color displays, for example in degree courses in Computer Science, Ergonomics, Electronic Engineering or Psychology.

The author's strategy has been to introduce tutorial material where this is necessary to grasp fundamental principles and to understand the limitations of both the display device and the perceptual system. Technical terms are defined in a glossary; and in order to place each chapter squarely within the context of color display use, each is preceded by an overview. Also provided at the end of each chapter is a summary of guidelines for the design of color displays drawn from the arguments in the text. This structure is intended to provide the student with the necessary information to begin display design without burdening him or her with excessive and unnecessary information. Ancillary sections at the end of each chapter provide annotated bibliographies that are intended to guide the student towards those areas that he or she may wish to explore in greater depth.

In order that the book may be understood by non-specialists, the first two chapters contain introductory material. Chapter 1 considers the design of color displays: this includes a discussion of how such displays work and how they may be effectively controlled by microcomputer. This includes reviews of all the major display technologies, and cathode-ray displays in particular. Frame buffer systems are covered in some depth. The concepts introduced in this chapter are required in succeeding chapters where readers may use the information to evaluate their own color display.

Chapter 2 presents a model of color vision that considers each stage in the perceptual process from eye to brain. This chapter also considers color deficiency: it describes the incidence of color deficiency, the common color confusions and the probable causes. It also describes how to test for color deficiency. Finally, the chapter considers the relevance of color vision and color deficiency to the design of color displays. It shows that an understanding of color vision puts designers and engineers in a better position to use color properly on color displays.

Chapter 3 describes methods of color specification. Although the number of applications that use color are many and varied, it is generally the case that color is used on visual displays for one of four reasons. First, color may be used on displays to represent color qua color, that is for realism. This includes applications such as computer-aided design, where products are "built" and may be shown to customers as an example of the finished version; or for example in the printing industry, where precise color specification and color judgements must be made. This is the substance of Chapter 3. This chapter describes eight color spaces, including the internationally agreed standards, and provides the information required to transform to them from computer RGB color specifications. Students frequently find these transformations needlessly difficult; to simplify the procedure as much as possible a simple introduction to matrix algebra is provided in one appendix, and another appendix lists a set of computer functions (written in 'C') that carry out these transformations.

Chapter 4 considers the other three reasons why color is used on displays: for formatting, coding and aesthetic purposes. For aesthetic purposes, what matters is simply that the final display looks appealing. To achieve this, the rules of color harmony are reviewed. But color may also be used for coding or formatting purposes: for example, this would be the case in applications where it was important to segregate or group different types of visual information, or to signify meaning by use of color. Methods for achieving this are reviewed in this chapter, and the final section shows how the model of color vision can be used to answer specific design problems.

Finally, Chapter 5 presents practical suggestions for ways in which the designer may assess a display system that uses color. This chapter supplies readers with the necessary information required to evaluate the display system, the working environment of the user, the system hardware and the software. This chapter is complemented by an appendix that synthesizes the environmental guidelines into a simple checklist.

Color displays in the work environment will soon become as commonplace as the microcomputer. This book provides the reader with the necessary intellectual tools to make their introduction effective.

Chapter 1: The Display System

This chapter describes the technology used to produce images on color displays. The first section is concerned with the cathode ray display. The screen of a cathode ray tube (crt) is made up of a number of discrete picture elements or pixels. In the limiting case, each pixel of a color display screen consists of three phosphors each driven by separate electron guns. Ideally, activation of one of these guns causes a single class of phosphor to luminesce.

In raster displays, the digitized picture is initially written in a specialized area of computer memory known as the frame buffer. This is dealt with in the second section of this chapter. The frame buffer contains three values (one for each electron gun) with each value monotonically related to the luminance of each pixel. These values may be used to directly alter the voltage of the electron guns in the display, and hence the color of each pixel. Look-up tables may be interposed between the frame buffer and the electron guns for compensation purposes (such as gamma correction).

Cathode-ray displays are generally bulky, and the crt/frame buffer system may introduce unwanted elements into the final image. Hence, the cathode-ray display is far from an ideal system, and alternative, non-crt-based display technologies are available that avoid some of these problems. The final section reviews some of the competing technologies.

Chapter 2: The Visual System

This chapter describes how we see color. In the first section, a model of color vision is described based on psychophysical and physiological measurements. The model has three broad stages. The first stage is trichromatic since it is based on the quantum catches in three types of cone photoreceptor. These three classes of cone have broad and overlapping spectral sensitivities but may be loosely referred to as long- wave sensitive (L), medium-wave sensitive (M) and short-wave sensitive (S). Each class is effectively color blind: it is unable to distinguish a change in chromaticity from a change in luminance (or, loosely, brightness). To extract chromatic information from these signals, the outputs of the different classes of cone must be compared. This occurs at a second, 'opponent', stage of color processing. Two classes of opponent pathway have been isolated: one that differences the output of M and L cones; and a second that differences the output of S cones with some combination of M and L cones. Luminance information is multiplexed with the chromatic information carried in the M and L opponent pathway. In the third stage of color vision the two chromatic signals and the luminance signal are transformed to produce the world of color.

The second section of the chapter considers color deficiency. It describes the incidence of color deficiency, the common color confusions and the probable causes. It also describes how to test for color deficiency.

Chapter 3: Specifying Colors On Color Displays

This Chapter describes methods of color specification. Any color in the world can be defined by just three numbers. These three numbers form a three-dimensional 'color space' within which colors may be specified, allowing accurate exchange of color information. Computer displays use the electronic RGB color space, in which a color is defined by the relative proportions of the red, green and blue display primaries required to produce it. This type of color space has two major disadvantages: first, because different displays have different display primaries, accurate color specification is not possible; and second, it is psychologically non-intuitive because people do not think of a color in terms of the relative proportions of red, green and blue light. Alternative color spaces are available that allow color to be accurately specified and that are more psychologically intuitive. This chapter describes eight alternative color spaces and provides the information required to transform to them from RGB color specifications.

Chapter 4: Coding, Formatting And Design

This chapter is concerned with the use of color to code, format and design visual displays. Its aim is to identify rules and guidelines for appropriate color use. The chapter first notes some general considerations, such as for what color is and is not suitable. Next the use of color is considered in three areas of system design: formatting, coding and aesthetics.

When correctly used, the benefits of color are unrivalled. It can be used to format displays by grouping and highlighting different information, such as items on a form. It can be used to color code, by identifying categories and by showing trends and relationships in information. It can be used for aesthetic purposes: users prefer color screens to monochrome screens, and the use of color can encourage system uptake. However, when incorrectly used, color has the potential to make a system unusable.

Chapter 5: Calibration And Evaluation

The scope of this chapter is using ergonomic principles to optimize the performance of users of color workstations. Its objective is to give readers the necessary information to begin 'hands on' evaluation of color workstations. A 'workstation' is a generic term comprising the visual display terminal, the human-computer interface and the environment within which these are used. Hence, it is convenient to consider the user as interacting with four broad environments: (i) The hardware environment, mainly the image quality of the display itself; (ii) The software environment, mainly the human-computer interface; (iii) The user's immediate, or 'micro' environment, such as seating and desk space; (iv) The user's extended, or 'macro', environment, such as lighting and noise.

The first two areas have been considered in detail in earlier chapters. Consequently, in this chapter, the treatment of the hardware environment is restricted to calibration methods for color displays; and the treatment of the software environment is restricted to an outline of user-centered design. The final two sections are broadly concerned with environmental ergonomics.

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