The purpose of photometry and colorimetry is to measure quantitatively the radiation and the derived quantities that determine what is seen by a human observer, a camera, or some other image recording device. The goal of this chapter is to lay a foundation so that the reader will understand what is required to record an image accurately, that is, so that accurate information can be obtained from the recorded data. While the accurate information is often used to present a display of the image, it may also be used to derive information about objects in the scene that is used for computer vision or target tracking. Of course, the accurate display of an image is impossible without accurate data. However, to produce an accurate display requires much more. It requires accurate information about the display device and the intent of the observer, who will be judging the image.

Because densitometry is closely associated with quantitative imaging, it is discussed in this chapter. The fundamental difference of densitometry from photometry and colorimetry is that densitometry is concerned with the measurement of physical quantities of display media. The density of a colorant on paper or dyes on film can be related to the appearance of the image that is produced using these means. The relationship is usually approximate. However, since it is so commonly used in the printing and film industries, it is appropriate to discuss its uses here.