1.2 The Origins of Digital Image Processing

1.2 数字图像处理的起源

One of the first applications of digital images was in the newspaper industry, when pictures were first sent by submarine cable between London and New York. 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.

数字图像的最早应用之一是在报业中，当时图片首次通过海底电缆在伦敦和纽约之间发送。20世纪20年代初引进的Bartlane电缆图片传输系统将横跨大西洋的图片传输时间从一个多星期缩短到不到三个小时。专门的印刷设备为电缆传输的图片进行编码，然后在接收端进行重组。图1.1就是以这种方式传输的，并在装有模拟半色调图案的字体的电报打印机上进行重印。

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 image obtained using this method. The improvements over Fig. 1.1 are evident, both in tonal quality and in resolution.

在改善这些早期数字图片的视觉质量方面，最初的一些问题与印刷工艺的选择和亮度值的分布有关。用于获得图1.1的印刷方法在1921年底被放弃，转而采用一种新的摄影图像复制的技术，在电报接收终端使用打孔磁带。图1.2显示了使用这种方法获得的图像。与图1.1相比，无论是色调质量还是分辨率，都有明显的改进。

FIGURE 1.1 A digital picture produced in 1921 from a coded tape by a telegraph printer with special type faces. (McFarlane.)  

图1.1 1921年，由一台带有特殊字体的电报打印机根据编码纸带制作的数字图片。

FIGURE 1.2 A digital picture made in 1922 from a tape punched after the signals had crossed the Atlantic twice. (McFarlane.)

图1.2 1922年用信号两次穿越大西洋后的穿孔纸带制作的数字图片。

The early Bartlane systems were capable of coding images in five distinct levels of gray. This capability was increased to 15 levels in 1929. Figure 1.3 is typical of the type of 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.

早期的Bartlane系统能够对图像进行五种不同灰度的编码。这种能力在1929年增加到15级。图1.3是使用15级色调设备可以获得的典型图像类型。在这一时期，引入了一个通过光束显影的系统，该光束由图像的编码纸带调制，极大地改善了复制过程。

FIGURE 1.3 Unretouched cable picture of Generals Pershing and Foch, transmitted in 1929 from London to New York by 15-tone equipment. (McFarlane.)

图1.3 未经修饰的Pershing和Foch将军的电报照片，1929年通过15色调设备从伦敦传送到纽约。

Although the examples just cited involve digital images, they are not considered digital image processing results in the context of our definition because computers were not involved in their creation. Thus, the history of digital image 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 and of supporting technologies that include data storage, display, and transmission.

尽管刚才引用的例子涉及数字图像，但在我们的定义中，它们不被认为是数字图像处理结果，因为计算机没有参与它们的创造。因此，数字图像处理的历史是与数字计算机的发展紧密相连的。事实上，数字图像需要大量的存储和计算能力，所以数字图像处理领域的进展一直依赖于数字计算机和包括数据存储、显示和传输在内的支持技术的发展。

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 a 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. These two ideas are the foundation of a central processing unit (CPU), which is at the heart of computers today. Starting with von Neumann, there were 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 at 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.

计算机的概念可以追溯到5000多年前小亚细亚的算盘发明。最近，在过去的两个世纪中，有一些发展是我们今天所说的计算机的基础。然而，我们所说的现代数字计算机的基础只能追溯到20世纪40年代，由约翰-冯-诺伊曼提出的两个关键概念。(1）储存程序和数据的存储器，以及2）条件性分支。这两个概念是中央处理器（CPU）的基础，是今天计算机的核心。从冯-诺依曼开始，有一系列的关键进展，导致计算机强大到足以用于数字图像处理。简而言之，这些进展可以总结为以下几点。(1）1948年贝尔实验室发明了晶体管；（2）20世纪50年代和60年代开发了高级编程语言COBOL（Common Business-Oriented Language）和FORTRAN（Formula Translator）；（3）1958年德州仪器公司发明了集成电路（IC）；（4）60年代初开发了操作系统。(5) 英特尔公司在70年代初开发了微处理器（由中央处理单元、存储器和输入输出控制组成的单一芯片）；(6) IBM公司在1981年推出了个人电脑；以及 (7) 组件的逐步小型化，从70年代末的大规模集成(LI)开始，然后是80年代的超大规模集成（VLSI），到现在的超大规模集成（ULSI）。与这些进展同时进行的还有大容量存储和显示系统领域的发展，这两个领域都是数字图像处理的基本要求。

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 to 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 2). 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.

第一台强大到足以执行有意义的图像处理任务的计算机出现在60年代早期。我们今天所说的数字图像处理的诞生可以追溯到这些机器的可用性和那一时期的太空计划的开始。这两个发展的结合使数字图像处理概念的潜力成为焦点。1964年，喷气推进实验室（加利福尼亚州帕萨迪纳）开始使用计算机技术改进来自空间探测器的图像，当时由游侠7号传送的月球照片被计算机处理，以纠正机载电视摄像机固有的各种类型的图像失真。图1.4显示了游侠7号在1964年7月31日东部夏令时间（EDT）上午9:09拍摄的第一张月球图像，大约在撞击月球表面之前的17分钟（上面的十字标记，称为reseau标记，用于几何校正，在第二章中讨论）。这也是美国航天器拍摄的第一张月球图像。游侠7号的成像经验是改进方法的基础，这些方法被用来增强和恢复测月者任务、水手号系列飞越火星任务、阿波罗载人登月飞行以及其他任务的图像。

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.)

图1.4 美国航天器拍摄的第一张月球照片。游侠7号于1964年7月31日美国东部时间上午9:09拍摄了这张照片，在撞击月球表面前约17分钟。(美国宇航局提供)。

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 important applications of image processing today.

在空间应用的同时，数字图像处理技术在60年代末和70年代初开始用于医学成像、远程地球资源观测和天文学。20世纪70年代初发明的计算机化轴向断层扫描（CAT），也被称为计算机化断层扫描（CT），是图像处理在医学诊断中应用的最重要事件之一。计算机轴向断层扫描是一个过程，在这个过程中，一圈探测器环绕着一个物体（或病人），一个与探测器圈同心的X射线源围绕该物体旋转。X射线穿过物体并在另一端被环中相应的探测器收集。随着源的旋转，这个过程被重复。断层扫描包括使用传感数据来构建代表物体 "切片 "的图像的算法。物体在垂直于检测器环的方向上的运动产生一组这样的切片，构成物体内部的三维（3-D）渲染。断层扫描是由Godfrey N. Hounsfield爵士和Allan M. Cormack教授独立发明的，他们因其发明分享了1979年诺贝尔医学奖。值得注意的是，X射线是由威廉-康拉德-伦琴在1895年发现的，他因此获得了1901年诺贝尔物理学奖。这两项发明相隔近100年，导致了今天图像处理的一些最重要的应用。

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 industry.

从20世纪60年代到现在，图像处理领域一直在蓬勃发展。除了在医学和太空计划中的应用外，数字图像处理技术现在被广泛地应用于各种领域。计算机程序被用来增强 图像的对比度或将光强值编码为颜色以便更好的解读，这些图像包括X射线图片和其他在工业、医学和生物科学中使用图片。地理学家使用相同或类似的技术来研究航空和卫星图像的污染模式。图像增强和修复程序被用来处理不好的图像，尤其是不可复原的物体的图像，和成本太高而不易重复的实验结果的图像。在考古学中，图像处理方法已经成功地恢复了模糊的图片，这些罕见文物在被拍摄后即遭丢失或损坏，而图片是唯一的可用记录。在物理学和相关领域，计算机技术经常增强高能等离子体和电子显微镜等领域的实验图像。在天文学、生物学、核医学、执法、国防和工业领域也可以找到类似的图像处理概念的成功应用。

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 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 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 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.

这些例子说明了图像处理结果是为了便于人的理解。本章开头提到的数字图像处理技术的第二个主要应用领域是解决有关机器感知的问题。在这种情况下，人们关注的是从图像中提取适合计算机处理的信息的程序。通常情况下，这些信息与人类在解释图像内容时使用的视觉特征没有什么相似之处。机器感知中使用的信息类型的例子是统计矩、傅里叶变换系数和多维距离测量。机器感知中经常利用图像处理技术的典型问题是自动字符识别、用于产品装配和检查的工业机器视觉、军事识别、指纹的自动处理、X-射线和血液样本的筛选，以及用于天气预测和环境评估的航空和卫星图像的机器处理。计算机价格不断下降，性能不断提高，以及通过万维网和互联网的网络和通信带宽的扩大，为数字图像处理的持续增长创造了前所未有的机会。后面章节会说明其中的一些应用领域。

注释：

Punched tape

What is perforated tape used for? 

Perforated paper tapes were one of the first media storing low quantities of digital information. These tapes were used widely to import and export data to/from early computer, to store teletype messages or to store EPROM programmer source.

穿孔纸带的用途是什么？

穿孔纸带是最早的储存低数量数字信息的媒体之一。这些磁带被广泛用于向/从早期计算机导入和导出数据，存储电传信息或存储EPROM编程器源。