TABLE OF CONTENTS Properties of human vision are central to image system engineering. They determine how many bits are necessary to represent luminance (or tristimulus) levels, and how many pixels need to be provided per degree of picture angle. This chapter introduces the intensity discrimination and spatial properties of vision.
The human retina has four types of photoreceptor cells that respond to incident radiation with different spectral response curves. A retina has about 100 million rod cells, and about 5 million cone cells (of three types).
Rods are effective only at extremely low light levels. Since there is only one type of rod cell, what is loosely called night vision cannot discern colors.
The cone cells are sensitive to longwave, mediumwave, and shortwave light- roughly, light in the red, green, and blue portions of the spectrum. Because there are just three types of color photoreceptors, three numerical components are necessary and sufficient to describe a color: Color vision is inherently trichromatic. To arrange for three components to mimic color vision, suitable spectral sensitivity functions must be used; this topic will be discussed in The CIE system of colorimetry, on page 211.
| Note | Boynton, Robert M., Human Color Vision (New York: Holt, Rinehart and Winston, 1979). |
| Note | Wandell, Brian A., Foundations of Vision (Sunderland, Mass.: Sinauer Associates, 1995). |
Vision operates over a remarkable range of luminance levels about eight orders of magnitude (decades) sketched in Figure 19.1. For about four decades at the low...
