EXCERPT
This book provides guidance on maintaining image quality in the selection and operation of electronic displays. The book is intended for anyone who must perform critical information extraction tasks using electronically displayed continuous-tone imagery, particularly in medical and military applications. It is also of value to managers and operations and maintenance personnel associated with such tasks, as well as supporting procurement personnel. The book is written at multiple levels such that a variety of users can find the information needed to perform their jobs. At a minimum, the individual user can determine how to select and evaluate a viewing system. For those readers interested in proceeding further, the rationale for recommendations is provided, using both image examples and results of empirical studies. Five of the chapters cover the fundamentals of display operation, the human visual system, and image quality measurement. Measurement procedures are provided for those readers who have access to measurement instrumentation, and alternatives are provided for those without such access. A CD is included that contains a wide range of test targets.
The book begins with an overview and examples demonstrating the importance
of maintaining image quality in the display process. The display chain is defined and briefly reviewed. A road map for readers with differing needs is provided. Chapter 2 introduces light and color measures and measurement. Chapter 3 provides a brief overview of electronic display operation. Both CRT and flat-panel display technologies are covered, although the emphasis is on CRT technology. The operation of common display controls is demonstrated with graphs and image examples.
Chapters 4 and 5 discuss physical and perceptual display quality measures. Physical measures include measures of resolution, contrast, and noise, both spatial and temporal. Perceptual measures are rating scales and performance measures used to rate the absolute or relative perceived quality of a display. Chapter 6 provides information on the performance of the human visual system. A brief description of the physiology of the eye is followed by a discussion of visual system capabilities— spatial, contrast, and color. The effects of individual differences are also described (including aging effects). The chapter ends with a review of visual performance models, with emphasis on the Barten model used as the basis for the NEMA/DICOM display calibration process. Subsequent chapters draw on the literature using these measures to illustrate the effects of display quality parameters.
The next three chapters of the book (7–9) provide guidance in display selection, covering luminance and spectral measures, resolution measures, and temporal/spatial measures. Each section begins with a listing of the recommended performance
parameters and criteria values for both monochrome and color displays. The parameters are defined, the selection criteria are provided, and the measurement procedures are described at both the perceptual and physical levels. Sources of performance information and their interpretation are discussed. Results of studies on key quality measures are provided where available. These studies are drawn from both the surveillance/reconnaissance and medical literature. Numerous figures are provided showing both measurement definitions and image examples to illustrate the effect of the key quality measures. Many of the desired performance measures are not routinely provided by vendors and require sophisticated equipment for measurement. Equipment and measurement procedures are defined for organizations that have either the capability of acquiring and operating such equipment or of specifying measurement performance requirements to vendors. For individuals or organizations without such capabilities, simplified procedures and tools are provided. Many of the tools are perceptual.
The operating environment is a critical factor in maintaining image quality. Recommended procedures are provided in Chapter 10 with emphasis on the control of room lighting. Chapter 10 also covers monitor selection, setup, and maintenance. Monitor luminance compensation techniques to account for the performance of the human visual system and procedures for generating the necessary look-up table are described. Monitor performance degrades with age, so the effects of the aging process are explained. Procedures for periodic quality assessment are defined.
Since software manipulation of an image is an important part of the image chain, Chapter 11 covers pixel processing operations including tonal, color, spatial filtering, and geometric manipulation. The proper sequence of operations is defined and alternative methods of processing discussed. A final chapter provides guidance on hard-copy capture and presentation. Digitizer properties are described, and guidance on digitizer selection and operation is provided. The process of transferring displayed soft-copy images to presentation media such as prints and transparencies is discussed. Printer calibration and look-up table generation procedures are defined to best emulate the originally displayed image on the presentation media. A brief section on electronic projection displays is also included.
