In this review, routine radiographs with computed tomographic (CT) correlation are used to demonstrate practical applications of Mach band theory in thoracic analysis. Mach bands represent optical psychophysiologic edge-enhancement phenomena produced by means of lateral inhibition in the retina of the eye. Visualization of Mach bands depends on a set of variables that involve primarily the contour and optical density of a structure at an interface relative to that of its surround. On the basis of their appearance, the bands are defined as positive (white) or negative (black). The concept of Mach bands contributes to a greater understanding of three-dimensional structures projected onto two-dimensional routine radiographic images of the thorax. Mach bands can help differentiate normal from abnormal anatomy and thus increase the diagnostic yield from such images. Mach bands can be seen on images that use transmitted or reflective light, including CT scout images (topograms) of the thorax.