《Digital Image Processing》Second Edition，Rafael C. Gonzalez Richard E. Woods

10 Chapter 1 Introduction FIGURE 1.7 Examples of X-ray imaging (a)Chest X-ray. ( b)Aortic angiogram (c)Head cen(d)Circuit boards.(e) Cygnus Loop(Images courtesy of(a)and(c)DrDavid R. Pickens, Dept of Radiology Radiological Sciences, Vanderbilt University Medical Center. (b)Dr. Thomas R Gest, Division of Anatomical Sciences, University of Michi gan Medical School, (d) Mr Joseph E. Pascente, Lixi, Inc, and(e)NASA

10 Chapter 1 ■ Introduction FIGURE 1.7 Examples of X-ray imaging. (a) Chest X-ray. (b) Aortic angiogram. (c) Head CT. (d) Circuit boards. (e) Cygnus Loop. (Images courtesy of (a) and (c) Dr. David R. Pickens, Dept. of Radiology & Radiological Sciences,Vanderbilt University Medical Center, (b) Dr. Thomas R. Gest, Division of Anatomical Sciences, University of Michi￾gan Medical School, (d) Mr. Joseph E. Pascente, Lixi, Inc., and (e) NASA.) a b c d e GONZ01-001-033.II 29-08-2001 14:42 Page 10

1.3 Examples of Fields that Use Digital Image Processing 11 large vessel as the contrast medium flows up in the direction of the kidneys. which are also visible in the image. As discussed in Chapter 3, angiography is a major area of digital image processing, where image subtraction is used to en hance further the blood vessels being studied Perhaps the best known of all uses of X-rays in medical imaging is comput erized axial tomography. Due to their resolution and 3-D capabilities, CAT scans revolutionized medicine from the moment they first became available in the early 1970s. As noted in Section 1.2, each CAT image is a"slice"taken per- pendicularly through the patient. Numerous slices are generated as the patient moved in a longitudinal direction The ensemble of such images constitutes a -D rendition of the inside of the patient, with the longitudinal resolution being proportional to the number of slice images taken. Figure 1.7(c)shows a typical head CAT slice image. Techniques similar to the ones just discussed, but generally involving higher energy X-rays, are applicable in industrial processes. Figure 1.7(d) shows ar X-ray image of an electronic circuit board. Such images, representative of lit erally hundreds of industrial applications of X-rays, are used to examine circuit boards for flaws in manufacturing, such as missing components or broken traces. Industrial CAT scans are useful when the parts can be penetrated by X-rays, such as in plastic assemblies, and even large bodies, like solid-propellant rock et motors. Figure 1.7(e) shows an example of X-ray imaging in astronomy. This image is the Cygnus Loop of Fig. 1.6(c), but imaged this time in the X-ray band 1.3.3 Imaging in the Ultraviolet Band Applications of ultraviolet"light "are varied. They include lithography, indus- trial inspection, microscopy, lasers, biological imaging, and astronomical obser vations. We illustrate imaging in this band with examples from microscopy and astronomy. Ultraviolet light is used in fluorescence microscopy, one of the fastest grow ng areas of microscopy Fluorescence is a phenomenon discovered in the mid dle of the nineteenth century, when it was first observed that the mineral fluorspar fluoresces when ultraviolet light is directed upon it. The ultraviolet light itself is not visible, but when a photon of ultraviolet radiation collides with an electron in an atom of a fluorescent material, it elevates the electron to a higher energy level. Subsequently, the excited electron relaxes to a lower level and emits light in the form of a lower-energy photon in the visible(red)light re gion. The basic task of the fluorescence microscope is to use an excitation light to irradiate a prepared specimen and then to separate the much weaker radi- ating fluorescent light from the brighter excitation light. Thus, only the emission light reaches the eye or other detector. The resulting fluorescing areas shine o gainst a dark background with sufficient contrast to permit detection.The arker the background of the nonfluorescing material, the more efficient the Instrument Fluorescence microscopy is an excellent method for studying materials that can be made to fluoresce, either in their natural form(primary fluorescence)or when treated with chemicals capable of fluorescing(secondary fluorescence) Figures 1. 8(a) and(b) show results typical of the capability of fluorescence

1.3 ■ Examples of Fields that Use Digital Image Processing 11 large vessel as the contrast medium flows up in the direction of the kidneys, which are also visible in the image. As discussed in Chapter 3, angiography is a major area of digital image processing, where image subtraction is used to en￾hance further the blood vessels being studied. Perhaps the best known of all uses of X-rays in medical imaging is comput￾erized axial tomography. Due to their resolution and 3-D capabilities, CAT scans revolutionized medicine from the moment they first became available in the early 1970s.As noted in Section 1.2, each CAT image is a “slice” taken per￾pendicularly through the patient. Numerous slices are generated as the patient is moved in a longitudinal direction.The ensemble of such images constitutes a 3-D rendition of the inside of the patient, with the longitudinal resolution being proportional to the number of slice images taken. Figure 1.7(c) shows a typical head CAT slice image. Techniques similar to the ones just discussed, but generally involving higher￾energy X-rays, are applicable in industrial processes. Figure 1.7(d) shows an X-ray image of an electronic circuit board. Such images, representative of lit￾erally hundreds of industrial applications of X-rays, are used to examine circuit boards for flaws in manufacturing, such as missing components or broken traces. Industrial CAT scans are useful when the parts can be penetrated by X-rays, such as in plastic assemblies, and even large bodies, like solid-propellant rock￾et motors. Figure 1.7(e) shows an example of X-ray imaging in astronomy.This image is the Cygnus Loop of Fig. 1.6(c), but imaged this time in the X-ray band. 1.3.3 Imaging in the Ultraviolet Band Applications of ultraviolet “light” are varied. They include lithography, indus￾trial inspection, microscopy, lasers, biological imaging, and astronomical obser￾vations.We illustrate imaging in this band with examples from microscopy and astronomy. Ultraviolet light is used in fluorescence microscopy, one of the fastest grow￾ing areas of microscopy. Fluorescence is a phenomenon discovered in the mid￾dle of the nineteenth century, when it was first observed that the mineral fluorspar fluoresces when ultraviolet light is directed upon it. The ultraviolet light itself is not visible, but when a photon of ultraviolet radiation collides with an electron in an atom of a fluorescent material, it elevates the electron to a higher energy level. Subsequently, the excited electron relaxes to a lower level and emits light in the form of a lower-energy photon in the visible (red) light re￾gion.The basic task of the fluorescence microscope is to use an excitation light to irradiate a prepared specimen and then to separate the much weaker radi￾ating fluorescent light from the brighter excitation light.Thus, only the emission light reaches the eye or other detector. The resulting fluorescing areas shine against a dark background with sufficient contrast to permit detection. The darker the background of the nonfluorescing material, the more efficient the instrument. Fluorescence microscopy is an excellent method for studying materials that can be made to fluoresce, either in their natural form (primary fluorescence) or when treated with chemicals capable of fluorescing (secondary fluorescence). Figures 1.8(a) and (b) show results typical of the capability of fluorescence GONZ01-001-033.II 29-08-2001 14:42 Page 11

Chapter 1 Introduction FIGURE 1 ultraviole (a) Normal corn. (b)Smut corn. (c)Cygnus Loop (b)Dr Michael Florida State (c)NASA) microscopy. Figure 1.8(a) shows a fluorescence microscope image of normal corn, and Fig. 1. 8(b)shows corn infected by "smut, " a disease of cereals, corn, grasses, onions, and sorghum that can be caused by any of more than 700 species of parasitic fungi. Corn smut is particularly harmful because corn is one of the principal food sources in the world. As another illustration, Fig. 1.8(c)shows the Cygnus Loop imaged in the high-energy region of the ultraviolet band. 1.3.4 Imaging in the Visible and Infrared Bands Considering that the visual band of the electromagnetic spectrum is the most familiar in all our activities, it is not surprising that imaging in this band out weighs by far all the others in terms of scope of application. The infrared band

12 Chapter 1 ■ Introduction FIGURE 1.8 Examples of ultraviolet imaging. (a) Normal corn. (b) Smut corn. (c) Cygnus Loop. (Images courtesy of (a) and (b) Dr. Michael W. Davidson, Florida State University, (c) NASA.) microscopy. Figure 1.8(a) shows a fluorescence microscope image of normal corn, and Fig. 1.8(b) shows corn infected by “smut,” a disease of cereals, corn, grasses, onions, and sorghum that can be caused by any of more than 700 species of parasitic fungi. Corn smut is particularly harmful because corn is one of the principal food sources in the world. As another illustration, Fig. 1.8(c) shows the Cygnus Loop imaged in the high-energy region of the ultraviolet band. 1.3.4 Imaging in the Visible and Infrared Bands Considering that the visual band of the electromagnetic spectrum is the most familiar in all our activities, it is not surprising that imaging in this band out￾weighs by far all the others in terms of scope of application. The infrared band a b c GONZ01-001-033.II 29-08-2001 14:42 Page 12

1.3 Examples of Fields that Use Digital Image Processing 13 often is used in conjunction with visual imaging, so we have grouped the visi ble and infrared bands in this section for the purpose of illustration We consider in the following discussion applications in light microscopy, astronomy, remote sensing, industry, and law enforcement. Figure 1.9 shows several examples of images obtained with a light microscope The examples range from pharmaceuticals and microinspection to materials haracterization. Even in just microscopy, the application areas are too numer- ous to detail here. It is not difficult to conceptualize the types of processes one might apply to these images, ranging from enhancement to measurements. a b c d f FIGURE 1.9 Examples of light images. (a) Taxol(anticancer agent), magnified 250×.(b) Cholesterol-40×. ocessor-60X.(d)Nickel oxide thin film-600 X(e)Surface of audio CD-1 Organic superconductor-450X(Images cour- tesy of Dr Michael W Davids State University

1.3 ■ Examples of Fields that Use Digital Image Processing 13 FIGURE 1.9 Examples of light microscopy images. (a) Taxol (anticancer agent), magnified 250µ. (b) Cholesterol—40µ. (c) Microprocessor—60µ. (d) Nickel oxide thin film—600 µ. (e) Surface of audio CD—1750µ. (f) Organic superconductor—450µ. (Images cour￾tesy of Dr. Michael W. Davidson, Florida State University.) often is used in conjunction with visual imaging, so we have grouped the visi￾ble and infrared bands in this section for the purpose of illustration.We consider in the following discussion applications in light microscopy, astronomy, remote sensing, industry, and law enforcement. Figure 1.9 shows several examples of images obtained with a light microscope. The examples range from pharmaceuticals and microinspection to materials characterization. Even in just microscopy, the application areas are too numer￾ous to detail here. It is not difficult to conceptualize the types of processes one might apply to these images, ranging from enhancement to measurements. a b c d e f GONZ01-001-033.II 29-08-2001 14:42 Page 13

14 Chapter 1Introduction TABLE 1.1 Band no Thematic bands Wavelength(um) Characteristics and Uses in NASAs Visible blue 0.45-0.52 Maximum water LANDSAT penetration satellite Visible green 0.52-0.60 Good for measuring plant Ⅴ isible red 0.63-0.69 Vegetation discrimination Near infrared 0.76-0. Biomass and shoreline 5 Middle infrared 1.55-1.75 Moisture content of soil geta Thermal infrared 104-12.5 Soil moisture: thermal mapping 7 Middle infrared 2.08-2.35 Mineral mapping Another major area of visual processing is remote sensing, which usually includes several bands in the visual and infrared regions of the spectrum Table 1.1 shows the so-called thematic bands in nasas landsat satel lite. The primary function of LANDSAT is to obtain and transmit images of the Earth from space, for purposes of monitoring environmental conditions on the planet. The bands are expressed in terms of wavelength, with 1 um being equal to 10 m(we discuss the wavelength regions of the electromag netic spectrum in more detail in Chapter 2). Note the characteristics and uses of each band In order to develop a basic appreciation for the power of this type of multi spectral imaging, consider Fig 1.10, which shows one image for each of the spec FIGURE 1.10 LANDSAT satellite images of the Washington, D. C area. The numbers refer to the thematic bands in Table 1.1.(Images courtesy of NASA

14 Chapter 1 ■ Introduction FIGURE 1.10 LANDSAT satellite images of the Washington, D.C. area. The numbers refer to the thematic bands in Table 1.1. (Images courtesy of NASA.) TABLE 1.1 Thematic bands in NASA’s LANDSAT satellite. Band No. Name Wavelength (m) Characteristics and Uses 1 Visible blue 0.45–0.52 Maximum water penetration 2 Visible green 0.52–0.60 Good for measuring plant vigor 3 Visible red 0.63–0.69 Vegetation discrimination 4 Near infrared 0.76–0.90 Biomass and shoreline mapping 5 Middle infrared 1.55–1.75 Moisture content of soil and vegetation 6 Thermal infrared 10.4–12.5 Soil moisture; thermal mapping 7 Middle infrared 2.08–2.35 Mineral mapping Another major area of visual processing is remote sensing, which usually includes several bands in the visual and infrared regions of the spectrum. Table 1.1 shows the so-called thematic bands in NASA’s LANDSAT satel￾lite. The primary function of LANDSAT is to obtain and transmit images of the Earth from space, for purposes of monitoring environmental conditions on the planet. The bands are expressed in terms of wavelength, with 1 m being equal to 10–6 m (we discuss the wavelength regions of the electromag￾netic spectrum in more detail in Chapter 2). Note the characteristics and uses of each band. In order to develop a basic appreciation for the power of this type of multi￾spectral imaging, consider Fig. 1.10, which shows one image for each of the spec- 123 4567 GONZ01-001-033.II 29-08-2001 14:42 Page 14