外文翻译----数字图像处理方法的研究(中英文)(1).pdf

The research of digital image processing technique 1Introduction Interest in digital image processing methods stems from two principal application areas improvement of pictorial information for human interpretation and processing of image data for storage transmission and representation for autonomous machine perception 1 1What Is Digital Image Processing An image may be defined as a two dimensional function f x y where x and y are spatial plane coordinates and the amplitude of f at any pair of coordinates x y is called the intensity or gray level of the image at that point When x y and digital image The field of digital image processing refers to processing digital images by means of a digital computer Note that a digital image is composed of a finite number of elements each of which has a particular location and value These elements are referred to as picture elements image elements pels and pixels Pixel is the term most widely used to denote the elements of a digital image We consider these definitions in more formal terms in Chapter2 Vision is the most advanced of our senses so it is not surprising that images play the single most important role in human perception However unlike human who are limited to the visual band of the electromagnetic EM spectrum imaging machines cover almost the entire EM spectrum ranging from gamma to radio waves They can operate on images generated by sources that human are not accustomed to associating with image These include ultrasound electron microscopy and computer generated images Thus digital image processing encompasses a wide and varied field of application There is no general agreement among authors regarding where image processing stops and other related areas such as image analysis and computer vision start Sometimes a distinction is made by defining image processing as a discipline in which both the input and output of a process are images We believe this to be a limiting and somewhat artificial boundary For example under this definition even the trivial task of computing the average intensity of an image which yields a single number would not be considered an image processing operation On the other hand there are fields such as computer vision whose ultimate goal is to use computer to emulate human vision including learning and being able to make inferences and take actions based on visual inputs This area itself is a branch of artificial intelligence AI whose objective is to emulate human intelligence This field of AI is in its earliest stages of infancy in terms of development with progress having been much slower than originallyanticipated Theareaof imageanalysis alsocalledimage understanding is in between image processing and computer vision There are no clear cut boundaries in the continuum from image processing at one end to computer vision at the other However one useful paradigm is to consider three types of computerized processes is this continuum low mid and high ever processes Low levelprocessesinvolveprimitiveoperationsuchasimage preprocessing to reduce noise contrast enhancement and image sharpening A low level process is characterized by the fact that both its input and output are images Mid level processing on images involves tasks such as segmentation partitioning an image into regions or objects description of those objects to reduce them to a form suitable for computer processing and classification recognition of individual object Amid level process is characterized by the fact that its inputs generally are images but its output is attributes extracted from those images e g edges contours and the identity of individual object Finally higher level processing involves making sense of an ensemble of recognized objects as in image analysis and at the far end of the continuum performing the cognitive function normally associated with vision Based on the preceding comments we see that a logical place of overlap between image processing and image analysis is the area of recognition of individual regions or objects in an image Thus what we call in this book digital image processing encompasses processes whose inputs and outputs are images and in addition encompasses processes that extract attributes from images up to and including the recognition of individual objects As a simple illustration to clarify these concepts consider the area of automated analysis of text The processes of acquiring an image of the area containing the text Preprocessing that images extracting segmenting the individual characters describing the characters in a form suitable for computer processing and recognizing those individual characters are in the scope of what we call digital image processing in this book Making sense of the content of the page may be viewed as being in the domain of image analysis and even computer vision depending on the level of complexity implied by the statement making cense As will become evident shortly digital image processing as we have defined it is used successfully in a broad rang of areas of exceptional social and economic value The concepts developed in the following chapters are the foundation for the methods used in those application areas 1 2The Origins of Digital Image Processing One of the first applications of digital images was in the newspaper industry when pictures were first sent by submarine cable between London and NewYork Introduction of the Bartlane cable picture transmission system in the early 1920s reduced the time required to transport a picture across the Atlantic from more than a week to less than three hours Specialized printing equipment coded pictures for cable transmission and then reconstructed them at the receiving end Figure 1 1 was transmitted in this way and reproduced on a telegraph printer fitted with typefaces simulating a halftone pattern Some of the initial problems in improving the visual quality of these early digital pictures were related to the selection of printing procedures and the distribution of intensity levels The printing method used to obtain Fig 1 1 was abandoned toward the end of 1921 in favor of a technique based on photographic reproduction made from tapes perforated at the telegraph receiving terminal Figure 1 2 shows an images obtained using this method The improvements over Fig 1 1 are evident both in tonal quality and in resolution FIGURE 1 1Adigital picture produced inFIGURE 1 2Adigital picture 1921 from a coded tape by a telegraph printermade in 1922 from a tape punched With special type faces McFarlane after the signals had crossed the Atlantic twice Some errors are Visible McFarlane The early Bartlane systems were capable of coding images in five distinct level of gray This capability was increased to 15 levels in 1929 Figure 1 3 is typical of the images that could be obtained using the 15 tone equipment During this period introduction of a system for developing a film plate via light beams that were modulated by the coded picture tape improved the reproduction process considerably Although the examples just cited involve digital images they are not considered digital image processing results in the context of our definition because computer were not involved in their creation Thus the history of digital processing is intimately tied to the development of the digital computer In fact digital images require so much storage and computational power that progress in the field of digital image processing has been dependent on the development of digital computers of supporting technologies that include data storage display and transmission The idea of a computer goes back to the invention of the abacus in Asia Minor more than 5000 years ago More recently there were developments in the past two centuries that are the foundation of what we call computer today However the basis for what we call a modern digital computer dates back to only the 1940s with the introduction by John von Neumann of two key concepts 1 a memory to hold a stored program and data and 2 conditional branching There two ideas are the foundation of a central processing unit CPU which is at the heart of computer today Starting with von Neumann there were a series of advances that led to computers powerful enough to be used for digital image processing Briefly these advances may be summarized as follow 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 system 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 Inter in the early 1970s 6 introduction by IBM of the personal computer in 1981 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 Figure 1 3 In 1929 from London to Cenerale Pershing that New York delivers with 15 level tone equipments through cable with Foch do not the photograph by decoration Concurrent with these advances were development 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 apace 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 Figure1 4shows 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 mark 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 mission to Mars theApollo manned flights to the moon and others In parallel with space application 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 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 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 09A M EDT about 17 minutes before Impacting the lunar surface Courtesy of NASA 中文翻译 数字图像处理方法的研究 1 绪论 数字图像处理方法的研究源于两个主要应用领域 其一是为了便于人们分析 而对图像信息进行改进 其二是为了使机器自动理解而对图像数据进行存储 传 输及显示 1 1 数字图像处理的概念 一幅图像可定义为一个二维函数 f x y 这里 x 和 y 是空间坐标 而在任 何一对空间坐标 f x y 上的幅值 f 称为该点图像的强度或灰度 当 x y 和幅 值 f 为有限的 离散的数值时 称该点是由有限的元素组成的 没一个元素都有 一个特定的位置和幅值 这些元素称为图像元素 画面元素或象素 象素是广泛 用于表示数字图像元素的词汇 在第二章 将用更正式的术语研究这些定义 视觉是人类最高级的感知器官 所以 毫无疑问图像在人类感知中扮演着最 重要的角色 然而 人类感知只限于电磁波谱的视觉波段 成像机器则可覆盖几 乎全部电磁波谱 从伽马射线到无线电波 它们可以对非人类习惯的那些图像源 进行加工 这些图像源包括超声波 电子显微镜及计算机产生的图像 因此 数 字图像处理涉及各种各样的应用领域 图像处理涉及的范畴或其他相关领域 例如 图像分析和计算机视觉 的界定 在初创人之间并没有一致的看法 有时用处理的输人和输出内容都是图像这一特 点来界定图像处理的范围 我们认为这一定义仅是人为界定和限制 例如 在这 个定义下 甚至最普通的计算一幅图像灰度平均值的工作都不能算做是图像处 理 另一方面 有些领域 如计算机视觉 研究的最高目标是用计算机去模拟人类 视觉 包括理解和推理并根据视觉输人采取行动等 这一领域本身是人工智能的 分支 其目的是模仿人类智能 人工智能领域处在其发展过程中的初期阶段 它 的发展比预期的要慢得多 图像分析 也称为图像理解 领域则处在图像处理和计 算机视觉两个学科之间 从图像处理到计算机视觉这个连续的统一体内并没有明确的界线 然而 在 这个连续的统一体中可以考虑三种典型的计算处理 即低级 中级和高级处理 来区分其中的各个学科 低级处理涉及初级操作 如降低噪声的图像预处理 对 比度增强和图像尖锐化 低级处理是以输人 输出都是图像为特点的处理 中级 处理涉及分割 把图像分为不同区域或目标物 以及缩减对目标物的描述 以使 其更适合计算机处理及对不同日标的分类 识别 中级图像处理是以输人为图 像 但输出是从这些图像中提取的特征 如边缘 轮廓及不同物体的标识等 为特 点的 最后 高级处理涉及在图像分析中被识别物体的总体理解 以及执行与视 觉相关的识别函数 处在连续统一体边缘 等 根据上述讨论 我们看到 图像处理和图像分析两个领域合乎逻辑的重叠区 域是图像中特定区域或物体的识别这一领域 这样 在本书中 我们界定数字图 像处理包括输人和输出均是图像的处理 同时也包括从图像中提取特征及识别特 定物体的处理 举一个简单的文本自动分析方面的例子来具体说明这一概念 在 自动分析文本时首先获取一幅包含文本的图像 对该图像进行预处理 提取 分 割 字符 然后以适合计算机处理的形式描述这些字符 最后识别这些字符 而 所有这些操作都在本书界定的数字图像处理的范围内 理解一页的内容可能要根 据理解的复杂度从图像分析或计算机视觉领域考虑问题 这样 本书定义的数字 图像处理的概念将在有特殊社会和经济价值的领域内通用 在以下各章展开的概 念是那些应用领域所用方法的基础 1 2 数字图像处理的起源 数字图像处理最早的应用之一是在报纸业 当时 图像第一次通过海底电缆 从伦敦传往纽约 早在 20 世纪 20 年代曾引入 Btutlane 电缆图片传输系统 把 横跨大西洋传送一幅图片所需的时间从一个多星期减少到 3 个小时 为了用电缆 传输图片 首先要进行编码 然后在接收端用特殊的打印设备重构该图片 图 1 1 就是用这种方法传送并利用电报打印机通过字符模拟中间色调还原出来的图像 这些早期数字图像视觉质量的改进工作 涉及到打印过程的选择和亮度等级 的分布等问题 用于得到图 1 1 的打印方法到 1921 年底就被彻底淘汰了 转而 支持一种基于光学还原的技术 该技术在电报接收端用穿孔纸带打出图片 图 1 2 就是用这种方法得到的图像 对比图 1 1 它在色调质量和分辨率方面的改 进都很明显 图 1 11421 年由电报打印机采用特殊字图 1 21922 年在信号两次穿越大西洋后 符在编码纸带中产生的数字图像从穿孔纸带得到的数字图像 可以 McFalsne 看出某些差错 McFalsne 早期的 Bartlane 系统可以用 5 个灰度等级对图像编码 到 1929 年已增加到 15 个等级 图 1 3 所示的这种典型类型的图像就是用 15 级色调设备得到的 在 这一时期 由于引入了一种用编码图像纸带去调制光束而使底片感光的系统 明 显地改善了复原过程 刚才引用的数字图像的例子并没有考虑数字图像处理的结果 这主要是因为 没有涉及到计算机 因此 数字图像处理的历史与数字计算机的发展密切相关 事实上 数字图像要求非常大的存储和计算能力 因此数字图像处理领域的发展 必须依靠数字计算机及数据存储 显示和传输等相关技术的发展 计算机的概念