by Peter Bodrogi and Tran Quoc Khanh
Reviewed by Janos Schanda
Illumination, Colour and Imaging by Peter Bodrogi and Tran Quoc Khanh is an exceptionally interesting, unique piece of work whose title suggests an overview of light, color, and imaging. (The subtitle narrows the subject to visual displays.) Rather than a textbook, it is more a compendium of research results from the authors and their collaborators as performed over the past 2 decades. The descriptions of the achievements of the authors are supplemented by a review of results obtained by other researchers, rounding off the work as a comprehensive overview of two subject areas: visual displays and color rendering.
The authors begin with some fundamental research on color vision as it relates to self-luminous display technologies. Here, one finds pointers to other chapters of the book where topics such as long-term memory effects and questions of visually evoked emotions will be discussed.
Next, the authors deal with colorimetric and color-appearance-based characterization of displays. They report their own experience of monitor calibration, differences compared to sRGB, problems with channel interdependence, and similar questions. This is not a primer from which to learn basic calibration principles, but if the reader has already learned the fundamentals, the descriptions in this chapter will help provide a deeper understanding, as well as ways to avoid some pitfalls. As this section deals mainly with the experience of one of the authors and reviews his work of the past 10–15 years, some of the examples refer to technologies (power-supply overload problems with CRT monitors and visual-angle questions of early LCD monitors) that have been surpassed by new developments. In other areas, the authors offer interesting details, such as where they discuss their experiments for color-appearance studies with total immersion into a colored surrounding.
Chapter 3 deals with ergonomic issues (even if the reviewer might question its title, which proposes the "enhancement of color displays; naturally, the display cannot be enhanced, only the quality of the images produced.) Issues such as visual acuity, its background luminance dependence, the focusing ability of the observer, luminance dependence, time dependence of adaptation, etc., are discussed in the introductory part of the chapter. The authors review the principles of ergonomic color design, together with the use of color to increase legibility and conspicuity. The effect of chromaticity contrast on search performance is introduced, with the example of an experiment performed by one of the authors.
An interesting section of this discussion of ergonomic issues deals with long-term memory colors and their intercultural differences (another area in which one of the authors, together with collaborators, performed fundamental research). Memory colors are those of familiar objects as remembered by the observer; e.g., the color of a ripe banana is familiar to everybody, but if asked to point in a color atlas to the color of a banana, an individual will select a color different from that of the actual banana. This shift between the real banana color and the color reproduced from memory is an interesting and important issue when colors are selected, for example, in virtual environments. The authors provide hints as to how color quality can be increased using memory colors. Color image quality is influenced by white-point selection and local and global contrast, items dealt with further on, where age-related effects are also discussed. A thorough summary that could help orient readers with regard to the many very important questions – not addressed in other books in such a detailed form – would make this chapter even more useful.
The next chapter deals in detail with the special application of color image processing: management and image quality in the film- and TV-studio environment. The very detailed and competent treatment of the subject found here certainly is not equalled in any other books. The chapter provides an insight into the colorimetry of present-day film and TV studios and discusses the entire process, starting with an overview of camera technology and a comparison with conventional chemical film technologies, pointing out items still necessary for development. Questions of intermediate processing and final film production are reviewed and color-quality experiments described (here, also, one of the authors could refer more to his long experience and research results). Readers receive insight into colorimetric problems and the use of different color-appearance models and are guided as to how different pitfalls can be avoided. Perceptual and image-quality aspects of the different processes, among other questions of compression, are discussed, and performance and results of image-quality experiments described. One subsection deals with watermarking and another, which is particularly interesting, discusses visually evoked emotions in color motion pictures.
A description of how to provide the best pixel architecture for displays rounds off the description of display color. Topics such as target color sets, factors of optimization color gamut and large-gamut settings, white-point selection, optimum color primaries, and the possibility of optimizing subpixel architecture (color fringe artifacts) are all discussed and explained by experiments performed by the authors.
The next-to-last chapter jumps to a different subject: color rendering of light sources, which deserves a book all to itself. In this respect, the discussion is slightly out of balance compared to other sections. However, the authors have performed some very important research in this area that has not been published in book form up to now. After an introduction of the two concepts of light-source color rendering – color fidelity and color preference – the authors enumerate the well-known problems of the currently used CIE test method and provide a very short overview of the models proposed by different authors for a new color-rendering metric, but do not evaluate the advantages and disadvantages of these. Here, again, are the descriptions of the experiments of the authors to assess the properties of color quality of illuminated scenes. The strength of the chapter is that the very important research results of the authors of the book are summarized in one place. Based on these results, one can expect that both the authors and some other research groups will further develop new light-source color-quality descriptors.
The final chapter of the book discusses emerging visual technologies such as flexible displays, laser and LED displays, and projectors. Topics include the color changes observed with LED aging and dimming, and some hints are provided with regard to indoor light sources, such as accent lighting, and the influence of circadian rhythms with light.
Every chapter has its own bibliography with, in some cases, over 50 entries, and a very large number of figures, with many figures in color. Good-quality color figures should really serve to make the content of the book more understandable.
In summary, this work is unique and should be on the bookshelf of every scholar and developer of color displays. Both the overviews of the general literature, provided by real experts in the subject, and the description of their own research work, make it an important reading piece that cannot be found elsewhere.
by Robert H. Chen
Reviewed by Birendra Bahadur
As a well-established, mature, high-performance technology, liquid-crystal displays (LCDs) have become an indispensable part of our lives. It is by far the largest display technology and is used in simple devices such as watches, calculators, clocks, handheld games, and medical and retail monitors to complex applications such as mobile phones, laptops, desktops, TVs, medical imaging, digital signage, avionics, and military equipment. LCDs constitute more than 80% of the over-$100-billion display market.
The LCD journey began in the late 1960s and has undergone many interesting developments and phases during the last 45 years. InLiquid Crystal Displays: Fundamental Physics and Technology, author Robert Chen describes this journey extremely well. There are many fine books on LCDs, but this one is unique in that it not only discusses the physics, chemistry, and technology of LCDs, but throws light on historical developments as well. Numerous witty footnotes of historical and technical relevance are included, which make the reading enjoyable as well as fascinating. Another unique aspect is that the author begins with a description of fundamental physics and mathematics in order to explain the complex theory and science of LCDs in a simple way. Chen is able to link many LCD developments with earlier physics and optics work and with more than 100 years of liquid-crystal research.
The book is divided into 27 chapters and can be read at several different levels – by someone relatively unversed in the concepts of high-level physics and by professionals in the field. The first through the 11th chapters are basically introductory. Although it is advisable to read all the chapters in sequence for continuity, a college-educated physicist or electrical engineer could skip the first four chapters on double refraction, electromagnetism, light in matter, and the polarization of electromagnetic waves. The book then turns to a brief description of the history, types, physical properties, and order parameter of liquid crystals, then proceeds to the thermo-dynamics of liquid crystals and the calculus of variations.
Subsequent sections describe different theories of liquid crystals and the derivation of many display parameters. Included are discussions of the Landau–de Gennes theory and the mean field concepts leading to the Maier– Saupe theory and its extension. The author describes the static continuum theory and the splay, bend, and twist elastic constants that led to derivations of threshold voltages for the Fréedericksz transition, twisted-nematic (TN), and in-plane-switching (IPS) cells. He also covers the dynamic continuum theory (Ericksen– Leslie) and derives the switching times of LCDs.
One chapter deals with the historically important but currently obsolete topic of dynamic scattering. Later topics include liquid-crystal chemistry and mixture formulation, with emphasis on the early developments, ownership claims, and patent controversies around TN-LCDs. The author also looks at the limitations of TN displays for high-level multiplexing and the advent of super-twisted-nematic (STN) and active-matrix LCDs. One unique chapter covers the historic and cultural background of the development of notebook screens. The next chapter, which might be skipped by an engineering graduate student, covers the basics and history of transistors and ICs. The author then proceeds to a description of active-matrix and TFT fabrication, and then to gray scales, color filters, signal processing, and backlights (fluorescent as well as LEDs). The physics of compensation films for widening viewing angles and reducing image inversions are described, as are popular LCD modes for TV applications, including multi-domain vertical alignment (MVA) and IPS and their variants. Response-time issues such as slow response and flicker for TN, MVA, and IPS modes are examined, along with methods (such as overdrive schemes) used to improve them. The LCD fabrication process is very well described, and so is the global LCD business, with a discussion of the impact of the cultural, national, and business background of companies on LCD development and manufacturing. The final chapter describes new display technologies such as OLEDs, electrophoretic, PSCT, and blue phase, as well as newer applications including touch screens and 3-D.
The book is well written and very useful. The photographs and figures are informative and clear. The basic science, physics, optics, chemistry, technology, and historical developments and manufacturing of LCDs are described clearly. Numerous electro-optical effects are helpfully outlined as well. The main drawback is a lack of references for LCD researchers. The author also did not refer to many well-known early LCD books and review articles. However, as a textbook, it serves an excellent purpose. Everyone, from beginner to advanced researcher, will find Liquid Crystal Displays: Fundamental Physics and Technology rewarding as well as interesting. It should serve as an important textbook for advanced undergraduate and graduate students interested in LCDs, and I strongly recommend it to anyone interested in LCDs. •