(1) analog signal and digital signal

Different data must be converted into corresponding signals before transmission: analog data are generally represented by analog signals, such as a series of continuously changing electromagnetic waves (such as electromagnetic waves in radio and television) or voltage signals (such as audio voltage signals in telephone transmission); Digital data is represented by digital signals, such as a series of intermittent voltage pulses (for example, we can use a constant positive voltage to represent binary number 1 and a constant negative voltage to represent binary number 0) or optical pulses. When analog signals are represented by continuously changing electromagnetic waves, the electromagnetic waves themselves are both signal carriers and transmission media. When analog signals are represented by continuously changing signal voltages, they are generally transmitted through traditional analog signal transmission lines (such as telephone networks and cable television networks). When digital signals are expressed by intermittent voltages or optical pulses, twisted pair, cable or optical fiber media are generally needed to connect the two communication parties and transmit signals from one node to another.

(2) mutual conversion between analog signals and digital signals

Analog signals and digital signals can be converted to each other: analog signals are generally quantized into digital signals by PCM pulse code modulation, that is, different amplitudes of analog signals correspond to different binary values. For example, analog signals can be quantized into 2 8 = 256 orders of magnitude by 8-bit coding, and in practice, 24-bit or 30-bit coding is often used; Digital signals are usually converted into analog signals by phase shifting a carrier wave. Binary digital signals are used in computers, computer local area networks and metropolitan area networks. At present, both binary digital signals and analog signals converted from digital signals are actually transmitted in computer WAN. But the more promising application is digital signal.

2. Digitalization is to convert a large number of complex and changeable information into measurable numbers and data, and then use these numbers and data to establish a suitable digital model, and then convert it into a series of binary codes, and introduce them into a computer for unified processing. This is the basic process of digitalization. (a solution)

Digitization converts any continuously changing input, such as the lines or sound signals of a picture, into a series of separate units, which are represented by 0 and 1 in the computer. This conversion is usually done by an analog-to-digital converter. (second solution)

Today is an information age, and researchers pay more and more attention to the digitalization of information. As early as 1940s, Shannon proved the sampling theorem, that is, under certain conditions, a continuous function can be completely represented by a discrete sequence. In essence, sampling theorem lays an important foundation for digital technology.

The importance of digital technology can at least be reflected in the following aspects:

Digitalization is the foundation of digital computer: without digitization technology, there would be no computer today, because all the operations and functions of digital computers are completed by numbers.

Digitalization is the foundation of multimedia technology: numbers, characters, images, sounds, including virtual reality, and various information in the visual world. In fact, it can be represented by 0 and 1 through the sampling theorem, so the digitized 0 and 1 are the most basic and simple representations of all kinds of information. Therefore, computers can not only calculate, but also make sounds, make phone calls, send faxes, play videos and watch movies. This is because 0 and 1 can represent the image of this multimedia. Using 0 and 1 can also create a virtual house, so digital media can represent all kinds of media and describe the diverse real world.

Digitalization is the foundation of software technology and intelligent technology: system software, tool software and application software in software, and digital filtering, coding, encryption and decompression in signal processing technology are all based on digitalization. For example, the amount of image data is large, which can be compressed to 10 to several hundred times after digitization; The image is blurred by interference, and the image can be made clear by filtering technology. These are the results obtained after digital processing.

Digitalization is the technical foundation of the information society: Digitalization technology is also triggering a wide product revolution, and all kinds of household appliances and information processing equipment will be transformed into digitalization. Such as digital TV, digital broadcasting, digital movies, DVD, etc. Now the communication network is also developing in the direction of digitalization.

Digitalization is the technical foundation of the information society. Some people say that the economy of the information society is a digital economy, which is enough to prove the impact of digitalization on society.

3. Any file stored on the computer has its format, such as text format like. txt.doc, picture format like jpg.tif.bmp, and so on.

All compression also has a compression format. Generally, the compression format we see is rar.zip, but the main function of compression is to make a file occupy less space. For example, 30MB can be compressed to more than 20 MB.

But compression requires a software. Then WinRAR. This download is very simple. You will go to Baidu and enter the name of this software. Then you will see some software installation programs provided by Sky website and Huajun website. All you have to do is click in, and when you see the words like download, click in to ensure the location of your download. Download and install.

Compression method: right-click the file to be compressed, and you will see that it is added to the compressed file or to * *. Rar, and you can click a compression at will. Its icon will look like a pile of books. Then this means that this is a compressed file.

But compressed files cannot be used and viewed directly. You must decompress first.

Uncompressed format is an uncompressed file format. In terms of picture format, BPM format is uncompressed, while other formats such as JPG are compressed. Therefore, the BPM of the same picture is about 6 times that of the JPG format with the same resolution. If your JPG format file is 500K, it will be about 3-4M or larger after being converted to BPM format.

5. What is a vector image?

Vector images, also known as object-oriented images or drawing images, are mathematically defined as a series of points connected by lines. The graphic elements in a vector file are called objects. Each object is an independent entity with properties such as color, shape, outline, size and screen position. Because each object is an independent entity, it can move and change its properties many times without affecting other objects in the legend, while maintaining its original clarity and curvature. These characteristics make vector-based programs especially suitable for legend and three-dimensional modeling, because they usually require the ability to create and manipulate a single object. Vector-based drawing is independent of resolution. This means that they can be displayed on the output device at the highest resolution.

What is a bitmap image?

Compared with the vector-based drawing program mentioned above, photo editing programs such as Photoshop are used to process bitmap images. When you work with bitmap images, you can optimize small details, make major changes and enhance the effect. Bitmap images, also known as dot matrix images or drawn images, are composed of individual points called pixels (picture elements). These dots can be arranged and dyed into different patterns. When you enlarge the bitmap, you can see that countless independent squares make up the whole image. The effect of expanding bitmap size is to increase a single pixel, which makes lines and shapes appear uneven. However, if viewed from a distance, the colors and shapes of bitmap images look continuous. Because each pixel is dyed separately, by manipulating the selection area one pixel at a time, realistic effects similar to photos can be produced, such as deepening shadows and emphasizing colors. Reducing the bitmap size will also distort the original image, because it will make the whole image smaller by reducing pixels. Similarly, because bitmap images are created in the form of pixel arrays, it is impossible to operate (e.g., move) the local bitmap independently.

6. Search engine refers to a system that collects information on the Internet according to certain strategies and uses specific computer programs, organizes and processes the information, and displays the processed information to users. It is a system that provides retrieval service for users.

7.① Blog = Blog = Weblog = Weblog = Blog = Webdiary.

② Blogger = Blogger = Blogger

Blog (noun):

A blogger is someone who writes or owns (a blog or a weblog).

2. Blog or weblog refers to weblog, which is a publishing method for individuals to spread their ideas and link to knowledge sets.

Blog (verb): refers to the process of publishing articles in the virtual space of blog or Weblog.

English full name of 8.8. BBS is bulletin board system, and Chinese translation is "bulletin board system". BBS was first used to publish information such as stock prices. At that time, BBS didn't even have the function of file transfer, so it could only run on Apple computer. Early BBS, like bulletin boards on the street and on campus, only spread or obtained news through computers. It was not until personal computers began to spread, and some people tried to transfer BBS from Apple computers to personal computers, that BBS began to spread gradually. In recent years, due to the efforts of fans, the functions of BBS have been greatly expanded.

9. E-mail (e-mail for short, logo: @, also known as "Yi Meier"), also known as e-mail and e-mail, is a communication method that provides information exchange by electronic means. It is the most widely used service on the Internet: through the e-mail system of the network, users can get in touch with network users in any corner of the world in a very fast way (it can be sent to any destination you specify in the world in a few seconds), and the price is very low (no matter where it is sent, only the telephone and network fees need to be paid). These emails can be in many forms, such as text, images and sounds. At the same time, users can get a lot of free news and special emails to realize easy information search. This is unmatched by any traditional way. E-mail is widely used because of its simple use, rapid delivery, low cost, easy preservation and unimpeded global access, which has greatly changed people's communication methods. In addition, email can be sent in a one-to-many way, and the same email can be sent to many people at the same time. Most importantly, e-mail is a system that directly faces the information exchange between people in the whole Internet and all other network systems. Its data sender and receiver are both human beings, so it greatly meets the communication needs of a large number of people.

E-mail refers to the communication mode of transmitting letters, documents, materials and other information by electronic means. E-mail combines the characteristics of telephone communication and postal letters. It can transmit information as quickly as a telephone and make the receiver receive a written record like a letter at the receiving end. E-mail system is also called computer-based mail information system. It undertakes the whole processing process from the mail entering the system to the mail reaching the destination. E-mail can be transmitted not only through telephone network, but also through any communication network. When using the telephone network, you can also use it to transmit information during off-peak hours, which is of special value to commercial mail. An electronic system controlled by a central computer and a small computer for limited users can be regarded as a computer conference system.

10. Computer viruses are clearly defined in the Regulations on the Security Protection of Computer Information Systems in People's Republic of China (PRC). A virus refers to "a set of computer instructions or program codes compiled or inserted in a computer program that destroy computer functions or data, affect the use of the computer and can replicate itself". In general textbooks and general materials, it is defined as a set of instruction sets or program codes that are sent by an infected computer to destroy computer data and affect the normal work of the computer by taking advantage of the defects of computer software and hardware. Computer viruses first appeared in the science fiction novels of David Jerrod in 1970s, when H.A.R.L.I.E was one of them. The earliest scientific definitions appeared in1983: virus in the startup area of Dr. Fred Cohen's thesis Computer Virus Experiment and "a computer program that can inject itself (or evolve) into other programs". Macro virus and script virus have the same concept, and the transmission mechanism is similar to biological virus, which injects itself into cells. A complete Trojan horse system consists of hardware, software and specific connection parts.

(1) Hardware part: Hardware entity necessary for establishing Trojan horse connection. Control terminal: the party that remotely controls the server. Server: the party remotely controlled by the controlled terminal. Internet: the network carrier for remote control and data transmission from the control terminal to the service terminal.

(2) Software part: software program necessary for remote control. Control terminal program: the program used by the control terminal to remotely control the server. Trojan horse: A program that sneaks into a server and gains its operating rights. Trojan configurator: a program that sets port number, trigger condition, Trojan name, etc. Make it better hidden in the server.

(3) Specific connection part: the necessary elements to establish Trojan horse channel between the server and the control terminal through the Internet. IP of control terminal and IP of service terminal: the network addresses of control terminal and service terminal, and also the destination of Trojan horse for data transmission. Control port, Trojan horse port: the data portal of the control terminal and server, through which data can directly reach the control terminal program or Trojan horse program.

The word "1 1 Hacker" is translated from English hacker and refers to computer enthusiasts who specialize in studying and discovering computer and network vulnerabilities. They grow with the development of computers and networks. Hackers have a fanatical interest and persistent pursuit of computers. They are constantly learning computer and network knowledge, looking for loopholes in computers and networks, and like to challenge difficult network systems and find loopholes from them, and then propose solutions and remedial measures to administrators.

Image format: Image format is the format in which image files are stored on the memory card, usually JPEG, TIFF, RAW, etc. Because the image file shot by digital camera is very large, but the storage capacity is limited, the image is usually compressed and then stored.

JPEG image format: JPG extension, full name is Joint Photographic Experts Group. It uses a distorted image compression method to compress images in a small storage space, and its compression ratio is usually between 10: 1 ~ 40: 1. This can make the image occupy less space, so it is very suitable for the image of the web page. JPEG images mainly compress high-frequency information, but retain color information well, so they are also widely used in images that need continuous tone.

TIFF image format: the extension is TIF, and the full name is marked image file format. It is a lossless compression format (the highest compression ratio can only be 2 ~ 3 times), which can keep the color and level of the original image, but it takes up a lot of space. For example, a 2-megapixel image occupies almost 6MB of storage capacity, so TIFF is usually used for more professional purposes, such as book publishing and posters, and is rarely used on the Internet.

GIF image format: the extension is GIF. In the process of compression, the pixel data of the image will not be lost, but the color of the image will be lost. GIF format can only store 256 colors at most, so it is usually used to display simple graphics and fonts. Some digital cameras have a shooting mode called text mode, which can be stored in GIF format.

FPX image format: the extension is FPX. It is an image format with multiple resolutions, that is, the image is stored in a series of different resolutions. The advantage of this format is that the image quality can still be maintained when it is enlarged. In addition, when the FPX image is modified, only the modified part will be processed, and the whole image will not be processed at the same time, thus reducing the burden on the processor and reducing the image processing time.

RAW image format: the extension is RAW. RAW is a lossless compression format, and its data is an original file that has not been processed by the camera, so its size is slightly smaller than TIFF format. Therefore, when uploading to the computer, it must be directly imported into TIFF format with Twain interface of image software before processing.

Vector animation format: SWF(Shockwave Format) file format is a vector animation format in two-dimensional animation software Flash, which is mainly used for animation publishing on web pages. At present, it has become the de facto standard of network animation. SWF files have the extension. Sovereign wealth fund.

The animated images in this format can express rich multimedia forms with a relatively small volume. In terms of image transmission, you don't have to wait for all files to be downloaded before you can watch them. You can watch them while downloading them, which is especially suitable for network transmission.

be harmless

It is a sound file format developed by Microsoft, which conforms to the specification of PIFFRESOURCE exchange file format, and is used to save the audio information resources of WINDOWS platform, and is supported by WINDOWS platform and its application programs. “*。 WAV "format supports many compression algorithms such as MSADPCM and CCITT A LAW, and supports many audio bits, sampling frequencies and channels. Like CD format, the sampling frequency of standard WAV file is 44. 1K, the rate is 88K/ s, and the quantization bit is 16. Look, the quality of audio files in WAV format is almost the same as that in CD format. But the disadvantage is that the size is too "huge".

MP3 format was born in Germany in 1980s. The so-called MP3 also refers to the audio part of the MPEG standard, that is, the MPEG audio layer. According to the difference of compression quality and coding processing, it is divided into three layers, which correspond to three kinds of sound files: * .mp1* .mp2/* .mp3. It should be noted that the compression of MPEG audio files is lossy compression. MPEG3-3 audio coding has a high compression ratio of10:12:1,while basically keeping the low audio part undistorted, but sacrificing the high audio part from 12KHz to 16KHz in the sound file. Music files with the same length are stored in * * .mp3 format, generally only * *110. WAV file, and the sound quality is not as good as CD format or wav format Because it has small files and good sound quality; So at the beginning of its appearance, no other audio format can match it, thus providing good conditions for the development of * * .mp3 format. Until now, this format is still all the rage, and its position as the mainstream audio format is hard to shake. But the copyright problem of MP3 music has not been solved, because MP3 has no copyright protection technology, which means anyone can use it clearly.

There are many sampling frequencies for MP3 compressed music. The sampling frequency of 64Kbps or lower can save space, and the standard of 320Kbps can also achieve extremely high sound quality. We use the MP3 encoder of Fraunhofer IIS Mpeg Lyaer3 (the best encoder at present) to encode a 3-minute song at 128Kbps, and get a 2.82MB MP3 file. The default CBR (fixed sampling frequency) technology can sample a song at a fixed frequency, while VBR (variable sampling frequency) can increase the sampling frequency to obtain higher sound quality when the music is "busy", but the generated MP3 file may not be played on some players. We set the level of VBR to be basically the same as the previous CBR file, and the generated VBR MP3 file is 2.9MB.

MIDI: composer's favorite

People who often play music should often hear the word MIDI (Musical Instrument Digital Interface), which allows digital synthesizers to exchange data with other devices. The MID file format is inherited from MIDI. MID file is not recorded sound, but a set of instructions that record sound information and then tell the sound card how to reproduce music. This MIDI file only needs about 5 ~ 1 0kb of music per minute. Nowadays, MID files are mainly used for original musical instruments, amateur performances of pop songs, game tracks and e-cards. *. * effect. Mid file playback depends entirely on the grade of sound card. * the biggest use. Mid format belongs to the field of computer typesetting. *.MID files can be written in composition software, or the music played by an external sequencer can be input into the computer through the MIDI port of the sound card to make *. Intermediate file.

WMA (Windows Media Audio) format is a heavyweight player from Microsoft. Its background is tough, and its sound quality is better than MP3 format and far better than RA format. Like the VQF format developed by Yamaha Company in Japan, it aims to achieve a higher compression ratio than MP3 by reducing data traffic but maintaining sound quality. Generally, the compression ratio of WMA can reach about 1: 18. Another advantage of WMA is that content providers can add copyright protection through DRM (Digital Rights Management) schemes such as Windows Media Rights Manager 7. This built-in copyright protection technology can limit the playing time and times, even the playing machine. This is good news for music companies that have been overwhelmed by piracy. In addition, WMA also supports audio streaming technology, which is suitable for play online on the Internet. As the pioneer of Microsoft's online music, it can be said that it is advanced in technology and powerful, and it is not more convenient to install a player like MP3. The seamless combination of windows operating system and Windows Media Player allows you to play WMA music directly as long as you install Windows operating system. The new version of Windows Media Player7.0 adds the function of directly converting CD into WMA sound format. In the newly produced operating system Windows XP, WMA is the default encoding format. Everyone knows what happened to Netscape, and now the "wolf" is coming again. WMA is a format that can adjust the sound quality during recording. The same format, good sound quality can be comparable to CD, high compression rate can be used for network playback. Although it is not very popular on the Internet now, with the large-scale promotion of Microsoft, it has been recognized and strongly supported by more and more websites. In the field of online music, it is almost equal to * * .mp3, and it is also carving up the world laid by Real in terms of online playing. Therefore, almost all audio formats feel the pressure of WMA format.

At present, the most common formats supported by MP3 are MP3 and WMA. Because MP3 is lossy compression, the emphasis is on the sampling rate, which is generally 44. 1KHZ. There is also a bit rate, that is, data stream, which is generally 8-320KBPS. When encoding MP3, let's see if it supports variable bit rate (VBR). Most MP3 players now support it, which can reduce the effective file size. WMA is an audio format promoted by Microsoft, which is relatively smaller than MP3.

APE format

New generation lossless audio format. APE is actually a lossless compressed audio format. Huge WAV audio files can be "slimmed down" by the software Monkey Audio and compressed into APE. Sometimes it is used for network audio file transmission, because the compressed APE file capacity is less than half of the WAV source file, which can save transmission time. More importantly, the WAV file obtained after decompression and restoration of monkey's audio can be exactly the same as the source file before compression. Therefore, APE is called "lossless audio compression format" and Monkey's audio is called "lossless audio compression software".

FLAC format

Very mature lossless compression format, word of mouth is not under APE! FLAC is the abbreviation of FreeLosslessAudioCodec. The source code of this format is completely open and compatible with almost all operating system platforms. Its coding algorithm is quite mature and has passed the rigorous test. It is said that it can play normally even if the file point is damaged (I have never tried it). This format is not only a mature Windows production program, but also supported by many third-party software. In addition, this format is the only lossless format supported by hardware. Rio's hard disk walkman Karma, sword dance car stereo MusicKeg and PhatBox's digital player can all support FLAC format.

AVI is the abbreviation of audio-video interleaving. I don't think I need to explain this. This old video format released by Microsoft from WIN3. 1 era has served us for several years. If you don't know anything about it, I don't think you should look down. The advantages of this thing are nothing more than good compatibility, convenient call and good picture quality, but I think the disadvantages are also well known: large size! Because of this, we can now see the birth of MPEG 1 and the introduction of MPEG-4.

MPEG is the abbreviation of moving picture expert group, including MPEG- 1, MPEG-2 and MPEG-4 (note that there is no MPEG-3, and only MPEG Layeur 3 is familiar with MP3). MPEG- 1 is considered to be the most widely used, because it is widely used in the production of VCD and the network application of downloading some video clips. It can be said that 99% of VCDs are compressed in MPEG- 1 format. (Note that VCD2.0 does not mean that VCD is MPEG-2 compressed. Using the compression algorithm of MPEG- 1, a movie with a length of 120 minutes (excluding video files) can be compressed to the size of 1.2 GB or so. MPEG-2 is applied to the production (compression) of DVD, and also has considerable application in some HDTV (High Definition Television Broadcasting) and some demanding video editing processes. Using MPEG-2 compression algorithm to compress a movie (without video files) with a length of 120 minutes can be compressed to a size of 4 to 8 GB (of course, its performance indicators such as image quality are incomparable to MPEG- 1). MPEG-4 is a new compression algorithm. By using the ASF format of this algorithm, a movie (unwatched file) with a length of 120 minutes can be compressed into a video stream of about 300M, which can be watched online. Other DIVX formats can also be compressed to about 600M, but the picture quality is much better than ASF.

The so-called RMVB format is an upgrade and extension of RM film format of streaming media. VB is VBR, which is the abbreviation of variable bit rate. When we play a movie in RM format, we can see the words 225Kbps in the lower left corner of the player, which is the code rate. Still images and moving images have different requirements for compression sampling rate. If the bit rate is always fixed, it will waste the film quality.

RMVB, on the other hand, broke the original RM format of average compressed sampling, and set a maximum sampling rate which is generally twice the average sampling rate on the basis of ensuring the average compression ratio. High bit rate is used for complex dynamic pictures (such as singing and dancing, speeding, war, etc.). ), but the static picture is flexibly converted to a lower sampling rate, and the code rate resources are reasonably used, so that RMVB can minimize the size of the film at the expense of a small part of the film quality that you can't perceive, and finally has a nearly perfect audio-visual effect close to DVD quality, as shown in figure 1, which is the saint of Hades in RMVB format. It can be said that size and clarity are "both fish and bear's paw", and its development prospect should not be underestimated.

Compared with DVDrip, the advantages of RMVB are self-evident. First of all, under the premise of ensuring the overall audio-visual effect of the film, the size of RMVB is only about 300~450MB (calculated by a 90-minute standard film), while DVDrip needs more than 700MB; Secondly, the subtitles of RMVB are embedded subtitles, unlike DVDrip, which needs to install plug-in software to debug subtitles, and sometimes garbled codes appear; More importantly, the audio and video playback of RMVB only needs to install a decoder once, and there is no need to debug images or sound effects in the future. However, DVDrip decodes a lot of video and audio, and improper settings will also cause problems such as unsynchronization of audio and video and loss of sound in the picture.

RM format: the audio and video compression specification formulated by Real Networks Company is called Real.

Media, users can use RealPlayer or RealOne.

The player plays the network audio and video resources that meet the technical specifications of RealMedia. RealMedia can set different compression ratios according to different network transmission rates, thus realizing real-time transmission and playback of image data on low-rate networks. Another feature of this format is that users use RealPlayer or RealOne.

Player Player can realize play online without downloading audio and video content. In addition, RM, as the mainstream network video format at present, can also make use of its reality.

The server server converts videos in other formats into RM videos, which are sent by Real.

The server server is responsible for publishing and playing. RM and ASF formats can be said to have their own advantages. Generally, RM video is soft, while ASF video is relatively clear.