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CH APT E R 1

Geometric Camera Models

There are many types of imaging devices, from animal eyes to video cameras and
radio telescopes, and they may or may not be equipped with lenses. For example,
the first models of the camera obscura (literally, dark chamber) invented in the
sixteenth century did not have lenses, but instead used a pinhole to focus light rays
onto a wall or translucent plate and demonstrate the laws of perspective discovered
a century earlier by Brunelleschi. Pinholes were replaced by more and more sophis-
ticated lenses as early as 1550, and the modern photographic or digital camera is
essentially a camera obscura capable of recording the amount of light striking every
small area of its backplane (Figure 1.1).

FIGURE 1.1: Image formation on the backplate of a photographic camera. Figure from
US NAVY MANUAL OF BASIC OPTICS AND OPTICAL INSTRUMENTS, prepared
by the Bureau of Naval Personnel, reprinted by Dover Publications, Inc. (1969).

The imaging surface of a camera is in general a rectangle, but the shape of
the human retina is much closer to a spherical surface, and panoramic cameras may
be equipped with cylindrical retinas. Imaging sensors have other characteristics.
They may record a spatially discrete picture (like our eyes with their rods and
cones, 35mm cameras with their grain, and digital cameras with their rectangular
picture elements, or pixels), or a continuous one (in the case of old-fashioned TV
tubes, for example). The signal that an imaging sensor records at a point on its
retina may itself be discrete or continuous, and it may consist of a single number
(as for a black-and-white camera), a few values (e.g., the RGB intensities for a
color camera or the responses of the three types of cones for the human eye),
many numbers (e.g., the responses of hyperspectral sensors), or even a continuous
function of wavelength (which is essentially the case for spectrometers). Chapter 2

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