6 Chapter 1 ■ Introduction
In parallel with space applications, digital image processing techniques
began in the late 1960s and early 1970s to be used in medical imaging, remote
Earth resources observations, and astronomy. The invention in the early 1970s
of computerized axial tomography (CAT), also called computerized tomogra-
phy (CT) for short, is one of the most important events in the application of
image processing in medical diagnosis. Computerized axial tomography is a
process in which a ring of detectors encircles an object (or patient) and an
X-ray source, concentric with the detector ring, rotates about the object. The
X-rays pass through the object and are collected at the opposite end by the
corresponding detectors in the ring.As the source rotates, this procedure is re-
peated. Tomography consists of algorithms that use the sensed data to con-
struct an image that represents a “slice” through the object. Motion of the
object in a direction perpendicular to the ring of detectors produces a set of
such slices, which constitute a three-dimensional (3-D) rendition of the inside
of the object. Tomography was invented independently by Sir Godfrey
N. Hounsfield and Professor Allan M. Cormack, who shared the 1979 Nobel
Prize in Medicine for their invention. It is interesting to note that X-rays were
discovered in 1895 by Wilhelm Conrad Roentgen, for which he received the
1901 Nobel Prize for Physics. These two inventions, nearly 100 years apart, led
to some of the most important applications of image processing today.
From the 1960s until the present, the field of image processing has grown
vigorously. In addition to applications in medicine and the space program, dig-
ital image processing techniques now are used in a broad range of applica-
tions. Computer procedures are used to enhance the contrast or code the
intensity levels into color for easier interpretation of X-rays and other images
used in industry, medicine, and the biological sciences. Geographers use the
same or similar techniques to study pollution patterns from aerial and satellite
imagery. Image enhancement and restoration procedures are used to process
degraded images of unrecoverable objects or experimental results too expen-
sive to duplicate. In archeology, image processing methods have successfully
restored blurred pictures that were the only available records of rare artifacts
lost or damaged after being photographed. In physics and related fields, com-
puter techniques routinely enhance images of experiments in areas such as
high-energy plasmas and electron microscopy. Similarly successful applica-
tions of image processing concepts can be found in astronomy, biology, nuclear
medicine, law enforcement, defense, and industry.
These examples illustrate processing results intended for human interpreta-
tion. The second major area of application of digital image processing tech-
niques mentioned at the beginning of this chapter is in solving problems dealing
with machine perception. In this case, interest is on procedures for extracting
from an image information in a form suitable for computer processing. Often,
this information bears little resemblance to visual features that humans use in
interpreting the content of an image. Examples of the type of information used
in machine perception are statistical moments, Fourier transform coefficients,
and multidimensional distance measures.Typical problems in machine percep-
tion that routinely utilize image processing techniques are automatic character
recognition, industrial machine vision for product assembly and inspection,