The study of imaging now embraces many major areas of modern technology, especially the several disciplines within electrical engineering, and will be both the stimulus for and the recipient of, new advances in information science, computer science, environmental science, device and materials science, and just plain high-speed computing. It can be confidently recommended as a fertile subject area for students entering upon a career in engineering.
—R. N. Bracewell 
This chapter introduces the radiation field as a relationship between luminous objects and optical detectors. Visibility and the modulation of visibility using optical elements are the most important concepts of the chapter. Visibility is a relationship between points in a space. Two points are visible to each other if light radiated from one illuminates the other. In three dimensions, visibility is a six-dimensional relationship between each pair of points. The concept of visibility in the present chapter anticipates the impulse response function in Chapter 3, the point spread function in Chapter 4, and coherence response kernels in Chapter 6.
We consider systems consisting of objects, object spaces, radiation fields, optical elements, and detectors, as illustrated in Fig. 2.1. The goal of the system is to estimate object parameters from the detector state. Most commonly, the object ...