Perspective Projection - Transformations and Projections in Computer Graphics - page 126

Such double cameras are available commercially and can also be homemade. Fig-
ure 3.47 shows one made in 1998 by Andreas Petersik [Petersik 05] from two Nikon
cameras. Yet another solution is to construct a camera with a sliding lens. The lens is
shifted to the left and a picture is taken. The lens is then shifted to the right and an-
other picture is taken. If film is used, the two pictures are taken on two adjacent frames
of the roll of film. In a digital camera of this type, the CCD sensor slides with the
lens and both pictures are captured by the same sensor and stored in different memory
areas.
Figure 3.47: A Homemade Double Nikon Camera (Courtesy of Andreas Petersik).
Note . When a pair of stereo pictures is taken, a flash should be avoided because it
normally casts shadows. The subject being photographed is shifted in the two pictures
because the camera has moved, but any shadows cast on a wall behind the subject are
shifted twice because the camera has moved and because the light from the flash is
coming from a different direction. Thus, shadows would be placed incorrectly in the
two pictures and would interfere with the correct visualization of the brain.
Our range of expression is small, so that a smile in genuine pleasure photographs
indistinguishably from a grimace of pain; they are the same unless we know their
history and their nature.
—C.P.Snow, Strangers and Brothers (George Passant) (1948)
Exercise 3.31: The two pictures of a stereo pair differ by a horizontal shift, which
suggests the following idea. Instead of taking two pictures, take just one, copy it, shift
the copy horizontally, and use it as the second picture. What's wrong with this method?