数字图像处理3rd - Chapter 1 - 3

Struggle

 

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 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 your 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.
 

1.3 使用数字图像处理的实例

今天，几乎没有一个技术领域不受数字图像处理的影响。在当前讨论的背景和空间下，我们只能涵盖其中的一些应用。然而，尽管有限，本节介绍的资料将使你对数字图像处理的广度和重要性深信不疑。我们在本节中展示了许多应用领域，其中每一个领域都利用了以下各章中开发的数字图像处理技术。本节所展示的许多图像在后面的例子中都会用到。所有显示的图像都是数字的。


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.

数字图像处理的应用领域是如此之多，以至于在试图捕捉这个领域的广度时，需要好好组织一下。对图像处理的应用范围有一个最简单的了解，就是根据图像的来源（如视觉、X射线等）对其进行分类。今天使用的图像的主要能量来源是电磁能谱。其他重要的能量来源包括声学、超声波和电子（以电子显微镜中使用的电子束的形式）。用于建模和可视化的合成图像是由计算机生成的。在本节中，我们将简要讨论这些不同类别的图像是如何产生的，以及它们的应用领域。将图像转换为数字形式的方法将在下一章讨论。

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.

基于电磁波谱的辐射的图像是最熟悉的，特别是光谱中的X射线和视觉波段的图像。电磁波可以理解为传播中的不同波长的正弦波，也可以被认为是无质量粒子的流，每个粒子都以波浪式的模式移动，并以光速移动。每个无质量的粒子都包含一定量（或束）的能量。每束能量被称为一个光子。如果根据每个光子的能量对光谱带进行分组，我们会得到图1.5所示的光谱，从一端的伽马射线（最高能量）到另一端的无线电波（最低能量）。

Gamma 射线 / X 射线 / 紫外线 / 可见光 / 红外线 / 微波 / 无线电波
FIGURE 1.5 The electromagnetic spectrum arranged according to energy per photon.
图1.5 根据每个光子的能量排列的电磁波谱。

电子伏特（electron volt），符号为eV，是能量的单位。代表一个电子（所带电量为1.6×10-19C的负电荷）经过1伏特的电位差加速后所获得的动能。
电子伏特与能量单位焦耳（J）的换算关系是1 eV = 1.602176565×10^-19 J

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.
这些波段由一段阴影表示，以表达电磁波谱的波段不是截然不同的，而是从一个平滑过渡到另一个的事实。

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 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.

1.3.1 伽马射线成像
基于伽马射线的成像的主要用途包括核医学和天文观测。在核医学中，其方法是给病人注射一种放射性同位素，这种同位素在衰变的过程中会释放出伽马射线。图像由伽马射线探测器收集的发射产生。图1.6(a)显示了通过使用伽马射线成像获得的完整骨扫描图像。这种图像可用于定位骨病变的部位，如感染或肿瘤。图1.6(b)显示了另一种主要的核成像方式，即正电子发射断层扫描（PET）。其原理与第1.2节中简要提到的X射线断层摄影相同。 然而，不是使用外部的X射线能量源，而是给病人提供一种放射性同位素，它在衰变时发射正电子。当一个正电子遇到一个电子时，两者都被湮灭，并放出两个伽马射线。这些射线被检测到，并利用断层扫描的基本原理形成断层图像。图1.6(b)所示的图像是构成病人三维立体图的序列的一个样本。该图像显示了大脑中的一个肿瘤和肺部的一个肿瘤，很容易看到白色的小肿块。

  

FIGURE 1.6 Examples of gamma-ray imaging.
(a)Bone scan.  (b)PET image.
图1.6 伽马射线成像的例子。
(a)骨扫描。 (b)PET图像。

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 an image of the Cygnus Loop in the gamma-ray band. Unlike the two examples 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.

天鹅座的一颗恒星在大约1.5万年前爆炸了，产生了一个过热的静止气体云（被称为天鹅星云），发出了一系列壮观的色彩。图1.6(c)显示了天鹅座星云在伽马射线波段的图像。与图1.6(a)和(b)中的两个例子不同，这个图像是利用被成像物体的自然辐射获得的。最后，图1.6(d)显示了来自核反应堆阀门的伽马辐射图像。在图像的左下方可以看到一个强辐射的区域。

  

FIGURE 1.6 Examples of gamma-ray imaging.
(c)Cygnus Loop.   (d)Gamma radiation(bright spot) from a reactor valve.
图1.6 伽马射线成像的例子。
(c)天鹅座星云。  (d)来自反应堆阀门的伽马辐射（亮点）。


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.
图片来源说明。


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 X-rays is controlled by a  voltage applied across the anode, and 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 more detail in Chapters 2 and 4.

1.3.2 X-射线成像
X射线是用于成像的最古老的电磁辐射源之一。X射线最著名的用途是医疗诊断，但它们也被广泛地用于工业和其他领域，如天文学。 用于医疗和工业成像的X射线是用X射线管产生的，它是一个有阴极和阳极的真空管。阴极被加热，导致自由电子被释放。这些电子高速地流向带正电的阳极。当电子撞击原子核时，能量以X射线辐射的形式释放出来。X射线的能量（穿透力）由施加在阳极上的电压和施加在阴极灯丝上的电流来控制。图1.7(a)显示了一个熟悉的胸部X射线，它是通过将病人放在X射线源和对X射线能量敏感的胶片之间产生的。当X射线通过病人时，其强度被吸收而改变，由此产生的能量落在胶片上使其显影，这与光照胶片的显影方式很相似。在数字放射学中，数字图像是通过两种方法之一获得的。(1)将X射线胶片转换为数字格式；或(2)通过让穿过病人的X射线直接落在将X射线转换为光的设备（如荧光屏）上。而光信号又被一个光敏的数字化系统所捕获。我们在第2章和第4章中更详细地讨论了数字化问题。

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 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 tube. 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 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 2, angiography is a major area of digital image processing, where image subtraction is used to enhance further the blood vessels being studied.

血管造影是另一个被称为对比度增强放射学的领域的主要应用。该程序用于获得血管的图像（称为血管造影）。例如，将一根导管（一根小的、灵活的、空心的管子）插入腹股沟的动脉或静脉中。导管被穿入血管并被引导到要研究的区域。当导管到达被检查的部位时，X-射线造影剂通过导管被注入。这增强了血管的对比度，使放射科医生能够看到任何不规则或堵塞的情况。图1.7(b)是一个主动脉血管造影的例子。可以看到导管被插入图片左下方的大血管中。注意大血管的高对比度，因为对比剂沿着肾脏的方向向上流动，这在图片中也是可见的。正如第二章所讨论的，血管造影是数字图像处理的一个主要领域，图像减法被用来进一步增强血管研究。

  

FIGURE 1.7 Examples of X-ray imaging. 
(a) Chest X-ray.
(b) Aortic angiogram. 
(c) Head CT.
(d) Circuit boards. 
(e) Cygnus Loop. 

图1.7 X射线成像的例子。
(a) 胸部X光。
(b) 主动脉血管造影。
(c) 头部CT。
(d) 电路板。
(e) 天鹅座星云。

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 Michigan Medical School; 
(d) Mr. Joseph E. Pascente, Lixi, Inc.; 
and (e) NASA.
图像来源说明。

Another important use of X-rays in medical imaging is computerized axial tomography (CAT). 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 perpendicularly 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 body, with the longitudinal resolution being proportional to the number of slice images taken. Figure 1.7(c) shows a typical head CAT slice image.

X射线在医学成像中的另一个重要用途是计算机化轴向断层扫描（CAT）。由于其分辨率和3-D能力，CAT扫描从1970年代初首次出现时就彻底改变了医学。如第1.2节所述，每张CAT图像是一个垂直于病人的 "切片"。当病人沿纵向移动时，会产生许多切片。这些图像的组合构成了身体内部的三维渲染，纵向分辨率与所拍摄的切片图像数量成正比。图1.7(c)是一个典型的头部CAT切片图像。

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 literally 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 rocket 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.

与刚才讨论的技术类似，但通常涉及更高能量的X射线，适用于工业加工。图1.7(d)显示了一个电子线路板的X射线图像。这样的图像，在X射线的数百种工业应用中具有代表性，被用来检查电路板在制造过程中的缺陷，如缺失的元件或断裂的线路。当部件可以被X射线穿透时，工业CAT扫描是很有用的，如塑料组件，甚至是大的身体，如固体推进剂火箭发动机。图1.7（e）显示了天文学中X射线成像的一个例子。这张图片是图1.6(c)的天鹅座星云图，但这次是以X射线波段成像的。


参考：
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