1.2 The Origins of Digital Image Processing 5 a series of key advances that led to computers powerful enough to be used for digital image processing. Briefly, these advances may be summarized as follows (1) the invention of the transistor by Bell Laboratories in 1948; (2) the devel- opment in the 1950s and 1960s of the high-level programming languages COBOL(Common Business-Oriented Language)and FORTRAN (Formula Translator): ( 3)the invention of the integrated circuit (IC)at Texas Instruments in 1958; (4)the development of operating systems in the early 1960s; (5)the de- velopment of the microprocessor (a single chip consisting of the central pro- cessing unit, memory, and input and output controls) by Intel in the early 1970 (6) introduction by IBM of the personal computer in 1981; and(7) progressive miniaturization of components, starting with large scale integration(LI)in the late 1970s, then very large scale integration (VLSI) in the 1980s, to the present use of ultra large scale integration(ULSI). Concurrent with these advances were developments in the areas of mass storage and display systems, both of which are fundamental requirements for digital image processing. The first computers powerful enough to carry out meaningful image pro- cessing tasks appeared in the early 1960s. The birth of what we call digital image processing today can be traced to the availability of those machines and the onset of the space program during that period. It took the combination of those two developments to bring into focus the potential of digital image processing concepts. Work on using computer techniques for improving images from a space probe began at the Jet Propulsion Laboratory(Pasadena, California)in 1964 when pictures of the moon transmitted by Ranger 7 were processed by a computer to correct various types of image distortion inherent in the on-board television camera. Figure 1. 4 shows the first image of the moon taken by Ranger 7 on July 31, 1964 at 9: 09 A.M. Eastern Daylight Time(EDT), about 17 minutes before impacting the lunar surface(the markers, called reseau marks, are used for geometric corrections, as discussed in Chapter 5). This also is the first image of the moon taken by a U.S. spacecraft. The imaging lessons learned with Ranger 7 served as the basis for improved methods used to enhance and restore images from the Surveyor missions to the moon, the Mariner series of flyby missions to Mars, the Apollo manned flights to the moon, and others. FIGURE 1. 4 The first picture of the moon by a U.S spacecraft. Ranger 7 took this July 31 1964at9:09A.M. EDT. about 17 minutes before impacting the lunar surface ( Courtesy of
1.2 ■ The Origins of Digital Image Processing 5 FIGURE 1.4 The first picture of the moon by a U.S. spacecraft. Ranger 7 took this image on July 31, 1964 at 9 : 09 A.M. EDT, about 17 minutes before impacting the lunar surface. (Courtesy of NASA.) a series of key advances that led to computers powerful enough to be used for digital image processing. Briefly, these advances may be summarized as follows: (1) the invention of the transistor by Bell Laboratories in 1948; (2) the development in the 1950s and 1960s of the high-level programming languages COBOL (Common Business-Oriented Language) and FORTRAN (Formula Translator); (3) the invention of the integrated circuit (IC) at Texas Instruments in 1958; (4) the development of operating systems in the early 1960s; (5) the development of the microprocessor (a single chip consisting of the central processing unit, memory, and input and output controls) by Intel in the early 1970s; (6) introduction by IBM of the personal computer in 1981; and (7) progressive miniaturization of components, starting with large scale integration (LI) in the late 1970s, then very large scale integration (VLSI) in the 1980s, to the present use of ultra large scale integration (ULSI). Concurrent with these advances were developments in the areas of mass storage and display systems, both of which are fundamental requirements for digital image processing. The first computers powerful enough to carry out meaningful image processing tasks appeared in the early 1960s.The birth of what we call digital image processing today can be traced to the availability of those machines and the onset of the space program during that period. It took the combination of those two developments to bring into focus the potential of digital image processing concepts. Work on using computer techniques for improving images from a space probe began at the Jet Propulsion Laboratory (Pasadena, California) in 1964 when pictures of the moon transmitted by Ranger 7 were processed by a computer to correct various types of image distortion inherent in the on-board television camera. Figure 1.4 shows the first image of the moon taken by Ranger 7 on July 31, 1964 at 9 : 09 A.M. Eastern Daylight Time (EDT), about 17 minutes before impacting the lunar surface (the markers, called reseau marks, are used for geometric corrections, as discussed in Chapter 5). This also is the first image of the moon taken by a U.S. spacecraft.The imaging lessons learned with Ranger 7 served as the basis for improved methods used to enhance and restore images from the Surveyor missions to the moon, the Mariner series of flyby missions to Mars, the Apollo manned flights to the moon, and others. GONZ01-001-033.II 29-08-2001 14:42 Page 5
6 Chapter 1 Introduction n parallel with space applications, digital image processing techniques began in the late 1960s and early 1970s to be used in medical imaging, remote Earth re- sources observations, and astronomy. The invention in the early 1970s of comput erized axial tomography( CAT), also called computerized tomography(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 repeated. Tomography consists of algorithms that use the sensed data to construct an image that represents a"slice"through the ob- ject Motion of the object in a direction perpendicular to the ring of detectors pro- duces 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 discov- ered 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 active application areas of image processing today From the 1960s until the present, the field of image processing has grown vig- orously. In addition to applications in medicine and the space program, digital image processing techniques now are used in a broad range of applications. Com puter 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, medi- cine, 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 expensive 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, computer techniques routinely enhance images of ex- periments in areas such as high-energy plasmas and electron microscopy. Similar- ly successful applications of image processing concepts can be found in astronomy, biology, nuclear medicine, law enforcement, defense, and industrial applications. These examples illustrate processing results intended for human interpreta- tion. The second major area of application of digital image processing techniques mentioned at the beginning of this chapter is in solving problems dealing with machine perception. In this case, interest focuses 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 perception that routinely utilize image processing techniques are automatic character recog nition, industrial machine vision for product assembly and inspection, military recognizance, automatic processing of fingerprints, screening of X-rays and blood samples, and machine processing of aerial and satellite imagery for weather
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 tomography (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 repeated.Tomography consists of algorithms that use the sensed data to construct 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 active application areas 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, digital image processing techniques now are used in a broad range of applications. 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 expensive 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, computer techniques routinely enhance images of experiments in areas such as high-energy plasmas and electron microscopy. Similarly successful applications of image processing concepts can be found in astronomy, biology, nuclear medicine, law enforcement, defense, and industrial applications. These examples illustrate processing results intended for human interpretation.The second major area of application of digital image processing techniques mentioned at the beginning of this chapter is in solving problems dealing with machine perception. In this case, interest focuses 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 perception that routinely utilize image processing techniques are automatic character recognition, industrial machine vision for product assembly and inspection, military recognizance, automatic processing of fingerprints, screening of X-rays and blood samples, and machine processing of aerial and satellite imagery for weather GONZ01-001-033.II 29-08-2001 14:42 Page 6
1.3 Examples of Fields that Use Digital Image Processing 7 prediction and environmental assessment. The continuing decline in the ratio of computer price to performance and the expansion of networking and commu- nication bandwidth via the world wide web and the internet have created un precedented opportunities for continued growth of digital image processing Some of these application areas are illustrated in the following section 1.3 Examples of Fields that Use Digital Image Processing Today, there is almost no area of technical endeavor that is not impacted in some way by digital image processing. We can cover only a few of these appli cations in the context and space of the current discussion. However, limited as it is, the material presented in this section will leave no doubt in the reader's mind regarding the breadth and importance of digital image processing. W show in this section numerous areas of application, each of which routinely uti- lizes the digital image processing techniques developed in the following chap- ters. Many of the images shown in this section are used later in one or more of the examples given in the book. All images shown are digital The areas of application of digital image processing are so varied that some form of organization is desirable in attempting to capture the breadth of this field. One of the simplest ways to develop a basic understanding of the extent of image processing applications is to categorize images according to their source (e.g, visual, X-ray, and so on). The principal energy source for images in use today is the electromagnetic energy spectrum. Other important sources of energy in- clude acoustic, ultrasonic, and electronic (in the form of electron beams used in electron microscopy ). Synthetic images, used for modeling and visualization, are generated by computer. In this section we discuss briefly how images are gener- ated in these various categories and the areas in which they are applied. Meth ods for converting images into digital form are discussed in the next chapter. Images based on radiation from the EM spectrum are the most familiar, es pecially images in the X-ray and visual bands of the spectrum Electromagnet ic waves can be conceptualized as propagating sinusoidal waves of varying wavelengths, or they can be thought of as a stream of massless particles, each traveling in a wavelike pattern and moving at the speed of light. Each masses particle contains a certain amount(or bundle)of energy. Each bundle of ener gy is called a photon. If spectral bands are grouped according to energy per photon, we obtain the spectrum shown in Fig. 1. 5, ranging from gamma rays (highest energy) at one end to radio waves(lowest energy) at the other. The bands are shown shaded to convey the fact that bands of the EM spectrum are not distinct but rather transition smoothly from one to the other Energy of one photon(electron volts) 1010510410310210110-110-110-210-310-410-510-610-710-8109 FIGURE 1.5 The electromagnetic spectru nged according to energy per photon
1.3 ■ Examples of Fields that Use Digital Image Processing 7 prediction and environmental assessment.The continuing decline in the ratio of computer price to performance and the expansion of networking and communication bandwidth via the World Wide Web and the Internet have created unprecedented opportunities for continued growth of digital image processing. Some of these application areas are illustrated in the following section. Examples of Fields that Use Digital Image Processing Today, there is almost no area of technical endeavor that is not impacted in some way by digital image processing. We can cover only a few of these applications in the context and space of the current discussion. However, limited as it is, the material presented in this section will leave no doubt in the reader’s mind regarding the breadth and importance of digital image processing. We show in this section numerous areas of application, each of which routinely utilizes the digital image processing techniques developed in the following chapters. Many of the images shown in this section are used later in one or more of the examples given in the book. All images shown are digital. The areas of application of digital image processing are so varied that some form of organization is desirable in attempting to capture the breadth of this field. One of the simplest ways to develop a basic understanding of the extent of image processing applications is to categorize images according to their source (e.g., visual, X-ray, and so on).The principal energy source for images in use today is the electromagnetic energy spectrum. Other important sources of energy include acoustic, ultrasonic, and electronic (in the form of electron beams used in electron microscopy). Synthetic images, used for modeling and visualization, are generated by computer. In this section we discuss briefly how images are generated in these various categories and the areas in which they are applied. Methods for converting images into digital form are discussed in the next chapter. Images based on radiation from the EM spectrum are the most familiar, especially images in the X-ray and visual bands of the spectrum. Electromagnetic waves can be conceptualized as propagating sinusoidal waves of varying wavelengths, or they can be thought of as a stream of massless particles, each traveling in a wavelike pattern and moving at the speed of light. Each massless particle contains a certain amount (or bundle) of energy. Each bundle of energy is called a photon. If spectral bands are grouped according to energy per photon, we obtain the spectrum shown in Fig. 1.5, ranging from gamma rays (highest energy) at one end to radio waves (lowest energy) at the other. The bands are shown shaded to convey the fact that bands of the EM spectrum are not distinct but rather transition smoothly from one to the other. 1.3 10–9 10–8 10–7 10–6 10–5 10 106 105 104 103 102 101 10–1 10–1 10–2 10–3 –4 Energy of one photon (electron volts) Gamma rays X-rays Ultraviolet Visible Infrared Microwaves Radio waves FIGURE 1.5 The electromagnetic spectrum arranged according to energy per photon. GONZ01-001-033.II 29-08-2001 14:42 Page 7
Chapter 1 Introduction 1.3.1 Gamma-Ray Imaging Major uses of imaging based on gamma rays include nuclear medicine and as- tronomical observations. In nuclear medicine, the approach is to inject a pa tient with a radioactive isotope that emits gamma rays as it decays. Images are produced from the emissions collected by gamma ray detectors. Figure 1.6(a) shows an image of a complete bone scan obtained by using gamma-ray imag- ing. Images of this sort are used to locate sites of bone pathology, such as in- fections or tumors. Figure 1.6(b) shows another major modality of nuclear imaging called positron emission tomography(PET). The principle is the same a b FIGURE 1.6 imaging(a) Bone scan.(b)PET image.(c)Cygnus Loop.(d)Gamma radiation(brigl spot)from a reactor valve (Images courtesy of(a)GE Medical Systems, (b)Dr Michael E. Casey, CTI PET Systems, (c) NASA (d) Professors Zhong he and David K. wehe Michigan
8 Chapter 1 ■ Introduction FIGURE 1.6 Examples of gamma-ray imaging. (a) Bone scan. (b) PET image. (c) Cygnus Loop. (d) Gamma radiation (bright spot) from a reactor valve. (Images courtesy of (a) G.E. Medical Systems, (b) Dr. Michael E. Casey, CTI PET Systems, (c) NASA, (d) Professors Zhong He and David K. Wehe, University of Michigan.) 1.3.1 Gamma-Ray Imaging Major uses of imaging based on gamma rays include nuclear medicine and astronomical observations. In nuclear medicine, the approach is to inject a patient with a radioactive isotope that emits gamma rays as it decays. Images are produced from the emissions collected by gamma ray detectors. Figure 1.6(a) shows an image of a complete bone scan obtained by using gamma-ray imaging. Images of this sort are used to locate sites of bone pathology, such as infections or tumors. Figure 1.6(b) shows another major modality of nuclear imaging called positron emission tomography (PET).The principle is the same a b c d GONZ01-001-033.II 29-08-2001 14:42 Page 8
1.3 Examples of Fields that Use Digital Image Processing 9 as with X-ray tomography, mentioned briefly in Section 1. 2. However, instead of using an external source of X-ray energy, the patient is given a radioactive iso- tope that emits positrons as it decays. When a positron meets an electron, both are annihilated and two gamma rays are given off. These are detected and a to- mographic image is created using the basic principles of tomography. The image shown in Fig. 1.6(b)is one sample of a sequence that constitutes a 3-D rendi tion of the patient. This image shows a tumor in the brain and one in the lung, easily visible as small white masses. A star in the constellation of Cygnus exploded about 15,000 years ago, gen erating a superheated stationary gas cloud(known as the Cygnus Loop)that glows in a spectacular array of colors. Figure 1. 6(c)shows the Cygnus Loop im aged in the gamma-ray band. Unlike the two examples shown in Figs. 1.6(a) and(b), this image was obtained using the natural radiation of the object being imaged. Finally, Fig. 1.6(d) shows an image of gamma radiation from a valve in a nuclear reactor. An area of strong radiation is seen in the lower, left side of the image 1.3.2 X-ray Imaging X-rays are among the oldest sources of EM radiation used for imaging. The best known use of X-rays is medical diagnostics, but they also are used exten sively in industry and other areas, like astronomy. X-rays for medical and in dustrial imaging are generated using an X-ray tube, which is a vacuum tube with a cathode and anode. The cathode is heated causing free electrons to be released. These electrons flow at high speed to the positively charged anode When the electrons strike a nucleus, energy is released in the form of X-ray ra diation. The energy(penetrating power)of the X-rays is controlled by a volt- age applied across the anode, and the number of X-rays is controlled by a curren applied to the filament in the cathode. Figure 1.7(a)shows a familiar chest X-ray generated simply by placing the patient between an X-ray source and a film sensitive to X-ray energy. The intensity of the X-rays is modified by absorption as they pass through the patient, and the resulting energy falling on the film de- velops it, much in the same way that light develops photographic film. In digi- tal radiography, digital images are obtained by one of two methods: (1)by digitizing X-ray films; or(2)by having the X-rays that pass through the patient fall directly onto devices(such as a phosphor screen) that convert X-rays to light. The light signal in turn is captured by a light-sensitive digitizing system. We discuss digitization in detail in Chapter 2. Angiography is another major application in an area called contrast- enhancement radiography. This procedure is used to obtain images(called angiograms)of blood vessels. A catheter(a small, flexible, hollow tube) is in serted, for example, into an artery or vein in the groin. The catheter is thread ed into the blood vessel and guided to the area to be studied. When the catheter reaches the site under investigation, an X-ray contrast medium is injected through the catheter. This enhances contrast of the blood vessels and enables the radiologist to see any irregularities or blockages. Figure 1.7(b)shows an ex ample of an aortic angiogram. The catheter can be seen being inserted into the large blood vessel on the lower left of the picture. Note the high contrast of the
1.3 ■ Examples of Fields that Use Digital Image Processing 9 as with X-ray tomography, mentioned briefly in Section 1.2. However, instead of using an external source of X-ray energy, the patient is given a radioactive isotope that emits positrons as it decays. When a positron meets an electron, both are annihilated and two gamma rays are given off.These are detected and a tomographic image is created using the basic principles of tomography.The image shown in Fig. 1.6(b) is one sample of a sequence that constitutes a 3-D rendition of the patient. This image shows a tumor in the brain and one in the lung, easily visible as small white masses. A star in the constellation of Cygnus exploded about 15,000 years ago, generating a superheated stationary gas cloud (known as the Cygnus Loop) that glows in a spectacular array of colors. Figure 1.6(c) shows the Cygnus Loop imaged in the gamma-ray band. Unlike the two examples shown in Figs. 1.6(a) and (b), this image was obtained using the natural radiation of the object being imaged. Finally, Fig. 1.6(d) shows an image of gamma radiation from a valve in a nuclear reactor. An area of strong radiation is seen in the lower, left side of the image. 1.3.2 X-ray Imaging X-rays are among the oldest sources of EM radiation used for imaging. The best known use of X-rays is medical diagnostics, but they also are used extensively in industry and other areas, like astronomy. X-rays for medical and industrial imaging are generated using an X-ray tube, which is a vacuum tube with a cathode and anode. The cathode is heated, causing free electrons to be released. These electrons flow at high speed to the positively charged anode. When the electrons strike a nucleus, energy is released in the form of X-ray radiation. The energy (penetrating power) of the X-rays is controlled by a voltage applied across the anode, and the number of X-rays is controlled by a current applied to the filament in the cathode. Figure 1.7(a) shows a familiar chest X-ray generated simply by placing the patient between an X-ray source and a film sensitive to X-ray energy.The intensity of the X-rays is modified by absorption as they pass through the patient, and the resulting energy falling on the film develops it, much in the same way that light develops photographic film. In digital radiography, digital images are obtained by one of two methods: (1) by digitizing X-ray films; or (2) by having the X-rays that pass through the patient fall directly onto devices (such as a phosphor screen) that convert X-rays to light.The light signal in turn is captured by a light-sensitive digitizing system.We discuss digitization in detail in Chapter 2. Angiography is another major application in an area called contrastenhancement radiography. This procedure is used to obtain images (called angiograms) of blood vessels. A catheter (a small, flexible, hollow tube) is inserted, for example, into an artery or vein in the groin. The catheter is threaded into the blood vessel and guided to the area to be studied.When the catheter reaches the site under investigation, an X-ray contrast medium is injected through the catheter. This enhances contrast of the blood vessels and enables the radiologist to see any irregularities or blockages. Figure 1.7(b) shows an example of an aortic angiogram.The catheter can be seen being inserted into the large blood vessel on the lower left of the picture. Note the high contrast of the GONZ01-001-033.II 29-08-2001 14:42 Page 9