ABSTRACT
This chapter deals with a key measure of image quality: contrast. (Another key measure, resolution, is discussed in Chapter 4.) Contrast refers to the extent of grayscale or color variation in an image. The chapter begins with a discussion of properties of light that are detectable by the human eye, namely wave amplitude and color, and properties that are not, particularly wave phase. Notably, many biological specimens are largely transparent and predominantly alter wave phase and thus generate very poor contrast when visualized with a standard (brightfield) light microscope. The bulk of the chapter is devoted to a discussion of methods of enhancing the contrast of transparent, phase-altering specimens using interference, spatial filtering, and/or polarization, as exemplified in darkfield, phase-contrast, polarization, and differential interference contrast (DIC) microscopy.
