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1、第2篇课文,Part 3 Information Engineering,信 息 工 程,Unit 11 Information SecurityUnit 12 Image ProcessingUnit 13 Multimedia,Unit 11 Information Security,Where Do Security Threats Come from?Imagine you work for an organization.1 You produce goods and/or services.They have value in the marketplace,or you woul
2、d not be doing it.2 Your organization took the risks,did the research,and made the investments.You are entitled to the fruits of your labor.Unfortunately,there is always a human element eager to take advantage of the work done by you and others,yet without the customary quid pro quo:payment for serv
3、ices rendered or for product provided.3,Direct theft of products or services is a simple motivation.More complex is the theft of information for a variety of nefarious purposes:to improve a competitors position;to further a political aim;to deny you timely access to correct information that you need
4、 to survive;to give the perpetrator an ego high.,Security is entirely a people issue.It is people who cause security problems,not machines or systems.Fortunately,our high-technology tools can also serve to thwart people who would do us harm,just the way we lock our doors against intruders.That secur
5、ity is a people problem must be borne in mind as an underlying constant theme in any discussion of security.,Even well-intentioned people are a weak point.Well-meaning people write down passwords or let others use theirs.While we try to use“social engineering”internally to modify behavior so that pe
6、ople will keep security in mind,outsiders try to use the same principle of social engineering to talk users out of passwords.In a sense,they are taking advantage of our incomplete or ineffective social engineering,trying to replace it with their own.,Now we are mentally prepared to begin to think li
7、ke our adversaries.If we can put ourselves in their place,then we can do some role-playing and begin to view our security precautions not just from the inside,but from the outside.Such a dual perspective is essential to effective security management.,What Can people Do to Our Information?They can de
8、stroy:Information Executable programs Operating systems Other computing or system resources Destruction includes both logical damage(to the system involved)and/or physical damage to the equipment itself.More subtle and short of destruction,tampers can alter any of the above,presenting the appearance
9、 of legitimacy though the reality is false.4,They can steal:Information Service Hardware Software Theft includes simply taking information not belonging to them,whether acted on or not.5 It includes the unauthorized use of system resources and is exemplified by the theft of telephone service.6 Theft
10、 plainly includes removal(such as deletion of information)as well as physical transport off the premises.,They can disclose:Information to which they have no right or need Information to unauthorized personnel for other motivations How to let others use resources not intended for outside use They ca
11、n cause service disruptions or interruptions:By causing physical or logical damage to the system By improperly denying access to legitimate users.,It is important to note that motivation is not always relevant.7 Any of the above losses can be caused accidentally.Furthermore,the above can be caused a
12、s of omission(such as failing to do a backup)or commission(such as deliberately causing a malfunction).,Classifying Threat Sources A threat is first classified as originating from outside or inside the organization.From there,we proceed to more specific subcategories:,External threats include:Hacker
13、s Commercial espionage Government-sanctioned espionage Vendors Former employees Internal threats include:Disgruntled employees Unintentional losses or security breaches Hackers,The bulk of the case evidence shows that it is the internal and not the external threat that must concern us the most.Kenne
14、th Weiss,the founder and chairman of Security Dynamics,says that 78 percent of computer abuse originates with a companys own employees.Even so,instances of external interference are growing.,Notes1Imagine you work for an organization.这是一个省略了主语的祈使句，you work for 是imagine 的宾语，引导该从句的that 也被省略掉了。2They ha
15、ve value in the marketplace,or you would not be doing it.此句中的主语They指的是上一句的goods and/or services，而it是指 produce goods and/or services这件事。,3Unfortunately,there is always a human element eager to take advantage of the work done by you and others,yet without the customary quid pro quo1:payment for servic
16、es rendered or for product provided.本句中的to take advantage of是占便宜的意思。而quid pro quo 为拉丁字，意为补偿交换物。,4More subtle and short of destruction,tampers can alter any of the above,presenting the appearance of legitimacy though the reality is false.本句中的short of表示无足够的量，本句为带有现在分词短语及though 引导的让步状语从句的主从复合句。,5Theft
17、includes simply taking information not belonging to them,whether acted on or not.此句中有两个现在分词短语，第一个是taking information，它是谓语动词includes的宾语，而第二个not belonging to 是现在分词短语的否定形式，在句中充当定语，修饰先行词information。,6It includes the unauthorized use of system resources and is exemplified by the theft of telephone servic
18、e.此句中的it指的是theft。7It is important to note that motivation is not always relevant.本句中，it 是形式上的主语，真正的主语是that 引导的一个主语从句，此处的motivation 是指破坏（或作案）的动机。,Grammar Review（一）定语从句1That security is a people problem(that)must be borne in mind as an underlying constant theme in any discussion of security.,（二）宾语从句1K
19、enneth Weiss，the founder and chairman of Security Dynamics,says that 78 percent of computer abuse originates with a companys own employees.,（三）强调句型1It is people who cause security problems,not machines or systems.,（四）短语1More complex is the theft of information for a variety of nefarious purposes:to
20、improve a competitors position;to further a political aim;to deny you timely access to correct information that you need to survive;to give the perpetrator an ego high.2In a sense,they are taking advantage of our incomplete or ineffective social engineering,trying to replace it with their own.3Now w
21、e are mentally prepared to begin to think like our adversaries.,（五）多重复合句1Fortunately,our high-technology tools can also serve to thwart people who would do us harm,just the way we lock our doors against intruders.2While we try to use“social engineering”internally to modify behavior so that people wi
22、ll keep security in mind,outsiders try to use the same principle of social engineering to talk users out of passwords.,3The bulk of the case evidence shows that it is the internal and not the external threat that must concern us the most.4If we can put ourselves in their place,then we can do some ro
23、le-playing and begin to view our security precautions not just from the inside,but from the outside.,Unit 12 Image Processing,1Representation of Images Images can have either digital or analog representation.In the digital representation of gray-level images,the image is presented as a two dimension
24、al array of numbers.Each number represents the intensity or gray level of the image at that relative position.If each gray level is represented as 8 bits(1 byte),then the gray levels are allowed 28 or 256 possible values.These levels are usually assigned integer values ranging from 0 to 255,with 0 r
25、epresenting the darkest intensity level and 255 the brightest intensity level.,Each element in the matrix is called a picture element,which is usually referred to as PEL or pixel.In a color image,the representation is similar,except at each location of the matrix the number represents three primary
26、colors:red,green and blue.For a 24-bit color representation per pixel,the number is divided into three 8-bit segments.Each segment represents the intensity of one of the color primaries.,To understand how a digital image is formed consider the illustration shown in Fig.12.1.1 In this figure an imagi
27、nary grid is placed on the image.The size of the openings in the grid determines the size of the pixel.,The pixels gray level is evaluated by the average light intensity at each opening of the grid.The finer the grid size,the higher the resolution.In the new field of advanced television technology t
28、he purpose is to provide the viewer with double the amount of resolution of present-day standards,thus providing a higher-quality image.,Fig.12.1 Representation of a gray-level digital image.,In the analog world,images are usually presented as horizontal raster lines(Fig.12.2).Each line is basically
29、 an analog signal carrying the continuous variations of light intensities along a horizontal line in the original scene.Images on television sets are displayed through raster scanning.Although the term“analog”is used in describing raster-scanned images,the image is analog only along the horizontal d
30、irection.,It is discrete along the vertical direction,and should be considered as a hybrid signal.Television sets designed to receive signals encoded in the U.S.NTSC.2 standard display approximately 525 lines.,The field of advanced television technology endeavors to provide us with double the amount
31、 of lines for a better resolution in large-screen television sets.A set having a screen greater than 28 inches is considered a large-screen set.Note that a TV set displays the same number of lines whether it is a 5-inch set or 50-inch projection television set.For larger sets the human eye is able t
32、o discriminate the raster lines from a normal viewing distance,which is about 10 feet.,Fig.12.2 Representation of an analog image.,2Image Data Compression Image compression is the art/science of efficiently coding digital images to reduce the number of bits required in representing an image.The purp
33、ose of doing so is to reduce the storage and transmission costs while maintaining good quality.4 To appreciate the need for image compression,we consider the amount of storage required and the transmission time using a 9600-baud(bit/s)modem for the following images.,A 512512 pixel,8-bit-per-pixel,gr
34、ay-level image requires 2097,152 bits for storage and 3.64 minutes for transmission.An RGB color image of the same resolution as the previous case would require 6 million bits of storage and 11 minutes of transmission time.,A 2436 mm(35 mm)negative photograph scanned at 12 m,which amounts to 3000200
35、0 pixels,assuming 8 bits per pixel,requires 48 million bits of storage and 83 minutes for transmission.5 A color negative would require three times that much in storage and transmission.6 Obviously,the storage or transmission of a few images would pose a problem.,There are plenty of other examples t
36、hat would easily justify image compression,and therefore great attention has been directed to this topic.An RGB color image of the same resolution as the previous case would require 6 million bits of storage and 11 minutes of transmission time.,A 2436 mm(35 mm)negative photograph scanned at 12 m,whi
37、ch amounts to 30002000 pixels,assuming 8 bits per pixel,requires 48 million bits of storage and 83 minutes for transmission.5 A color negative would require three times that much in storage and transmission.6 Obviously,the storage or transmission of a few images would pose a problem.,There are plent
38、y of other examples that would easily justify image compression,and therefore great attention has been directed to this topic.Facsimile transmission of graphic documents over telephone lines,archival storage,medical image data compression,and broadcast television are some of the many potential appli
39、cations for image data compression.The advancement in microelectronics and the evolution of many commercial applications led to the development of standards and hardware for real-time image compression.7,Image compression is achieved by exploiting redundancies in the image.These redundancies could b
40、e either spatial,spectral,or temporal redundancy.Spectral redundancy is due to correlation between different color planes.Temporal redundancy is due to the correlation of different frames in a sequence of images such as in videoconferencing applications or in broadcast images.,Notes1To understand ho
41、w a digital image is formed(let us)consider the illustratin shown in Fig.12.1.本句主句为祈使句，即 let us(to)consider，其中 let us已被省略，在let us后面的不定式动词可以略去to，所以谓语动词 consider 直接用原形。To understand 是不定式动词充当目的状语，其中how引导的从句是understand 的宾语。全句应译为：为了理解图像是如何形成的，让我们来考虑图12.1所示的描述。,2NTSC是National Television Standard Committee
42、 的缩写，意为美国国家电视标准委员会。,3Note that a TV set displays the same number of lines whether it is a 5-inch set or 50-inch projection television set.本句为祈使句，谓语动词是note，that引导的是它的宾语从句，连词 whether引导的是一个条件状语从句。全句含义见参考译文。,4The purpose of doing so is to reduce the storage and transmission costs while maintaining good
43、quality.本句中 of doing so是介词短语作定语，修饰purpose。maintaining good quality 是分词短语，在句中当状语。,5A 2436 mm(35mm)negative photograph scanned at 12 m,which amounts to 3,0002,000 pixels,assuming 8 bits per pixel,requires 48 million bits of storage and 83 minutes for transmission.本句中a 2436 mm(35 mm)是主句中的主语，scanned at
44、12 m 是过去分词短语作后置定语修饰photograph。而which 引导的是一个非限定性定语从句，补充说明它前面的扫描效果。assuming 8 bits 是插入的现在分词短语作状语，说明 amounts to 3,0002,000 pixels 的前提条件。requires 才是主句的谓语动词。全句含义见参考译文。,6A color negative would require three times that much in storage and transmission.本句中的 that much 指上一句的30002000 pixels。7The advancement in
45、 microelectronics and the evolution of many commercial applications led to the development of standards and hardware for real-time image compression.本句是一个简单句，The advancement and the evolution是句中的并列主语。,Grammar Review1.定语从句（1）Each element in the matrix is called a picture element,which is usually refe
46、rred to as PEL or pixel.（2）For larger sets the human eye is able to discriminate the raster lines from a normal viewing distance,which is about 10 feet.（3）A 2436 mm(35 mm)negative photograph scanned at 12 m,which amounts to 3,0002,000 pixels,assuming 8 bits per pixel,requires 48 million bits of stor
47、age and 83 minutes for transmission.,2状语从句（1）Although the term“analog”is used in describing raster-scanned images,the image is analog only along the horizontal direction.（2）If each gray level is represented as 8 bits(1 byte),then the gray levels are allowed 28 or 256 possible values.,3介词短语（1）These l
48、evels are usually assigned integer values ranging from 0 to 255,with 0 representing the darkest intensity level and 255 the brightest intensity level.此句中的ranging from 0 to 255是分词短语在句中作定语，修饰integer values，with 0 representing是介词短语，在句中也作定语，修饰integer values。,（2）For a 24-bit color representation per pixe
49、l,the number is divided into three 8-bit segments.句中的For a 24-bit 是介词短语作状语，说明主句谓语动词的执行条件。（3）The field of advanced television technology endeavors to provide us with double the amount of lines for a better resolution in large-screen television sets.本句中的with double 是介词短语作状语，表示provide us的方式。,（4）Image c
50、ompression is achieved by exploiting redundancies in the image.本句中的 by exploiting是介词短语作方式状语。（5）Spectral redundancy is due to correlation between different color planes.本句中的due to 是介词短语作表语。（6）Temporal redundancy is due to the correlation of different frames in a sequence of images such as in videocon
