1. The definition of multimedia
The word "Multimedia" is translated from the English word "multimedia", which is a compound of mutiple and media. The original meaning of media is twofold. One refers to entities that store information, such as magnetic disks, optical disks, magnetic tapes, semiconductor memories, etc. , which is often translated into media in Chinese, refers to the carrier of information, such as numbers, words, sounds, graphics and so on. And Chinese translation as a medium. So the word for multimedia is Monomedia. Literally, multimedia is composed of mono media.
Multimedia technology has different definitions from different angles. For example, some people define that "a multimedia computer is a set of hardware and software equipment; Combining various visual and auditory media can produce impressive audio-visual effects. In visual media, it includes graphics, animation, images and words, while in auditory media, it includes language, stereo and music. Users can access various media sources from multimedia computers at the same time. " Others define multimedia as "the combination of traditional computing media (words, graphics, images and logical analysis methods) with video, audio and interactive applications for knowledge creation and expression". To sum up, multimedia technology is the interactive comprehensive processing of multimedia information-words, graphics, images and sounds by computers, which makes all kinds of information logically linked and integrated into a system for interaction. In short, multimedia technology is a computer technology that comprehensively processes audio, video and graphic information, which is integrated, real-time and interactive. )。 Multimedia has its own definition in China. Generally speaking, multimedia technology refers to the technology that can handle information on various carriers (media) and information on various storage bodies (media).
2. Key technologies of multimedia
Because the multimedia system needs to achieve a unified structure code stream of different media data tables, and then convert, reorganize and analyze them for further storage, transmission, output and interactive control. Therefore, the traditional key technologies of multimedia mainly focus on the following four categories: data compression technology, large-scale integrated circuit (VLSI) manufacturing technology, large-capacity optical disk, and real-time multi-task operating system. Due to the breakthrough in these technologies, multimedia technology has developed rapidly and become a high-tech technology with strong ability to handle media information such as sound, text and images as it is today.
However, when talking about the key multimedia technologies to be used in the Internet, some experts think that it can be divided into six aspects: media processing and coding technology, multimedia system technology, multimedia information organization and management technology, multimedia communication network technology, multimedia man-machine interface and virtual reality technology, and multimedia application technology. It should also include multimedia synchronization technology, multimedia operating system technology, multimedia middleware technology, multimedia exchange technology, multimedia database technology, hypermedia technology, content-based retrieval technology, QoS management technology in multimedia communication, multimedia conference system technology, multimedia video-on-demand and interactive TV technology, virtual reality space technology and so on.
3. Components of Universal Multimedia System
A general multimedia system consists of the following four parts:
Multimedia hardware system, multimedia operating system, media processing system tools and user application software.
★ Multimedia hardware system: including computer hardware, audio/video processor, various media input/output devices and signal conversion devices, communication transmission devices and interface devices. Among them, the most important ones are multimedia information processing chips, boards and optical disk drives developed according to multimedia technical standards.
★ Multimedia operating system: or multimedia kernel system, with real-time task scheduling, multimedia data conversion and synchronous control to drive and control multimedia devices, graphical user interface management and other functions.
★ Media processing system tool: or multimedia system development tool software, which is an important part of multimedia system.
★ User application software: an application software customized according to the requirements of the end users of multimedia systems or a user application software system in a certain field, which is a system product for large-scale users.
Composition of the second multimedia computer
1. Interpretation of Multimedia Personal Computer
Before the emergence of multimedia computers, the information processed by traditional microcomputers or personal computers was often limited to words and numbers, which could only be regarded as the primary stage of computer application. At the same time, because the interaction between man and machine can only be through keyboard and display, the way of exchanging information lacks diversity. In order to change the interface of human-computer interaction and enable computers to integrate sound, text, graphics and image processing, humans invented computers with multimedia processing capabilities. Let's focus on the personal computer (that is, the PC now). So now you should understand that the so-called Multimedia Personal Computer (MPC) is nothing more than a personal computer with multimedia processing function (such as the early 586 model), and its hardware structure is not much different from the commonly used personal computer, only adding some software and hardware configurations. There are probably two ways for ordinary users to own MPC: one is to buy a PC with multimedia function directly; The second is to add a multimedia suite to the basic PC to form MPC. Today, when PC II is rampant, MPC has become a necessary technical specification for computer manufacturers and developers.
2. Basic configuration (and optional configuration) of multimedia computer
Generally speaking, the basic hardware structure of a multimedia personal computer (MPC) can be summarized into seven parts:
★ At least one powerful and fast central processing unit (CPU);
★ Can manage and control the configuration of various interfaces and devices;
★ Storage space with a certain capacity (as large as possible);
★ High-resolution display interface and equipment;
★ Interfaces and devices that can handle audio;
★ Interface equipment capable of processing images;
★ Configuration that can store a large amount of data, etc.
The configuration provided in this way is the hardware foundation of the most basic MPC, and they constitute the host of MPC. In addition, the configuration that MPC can extend may also include the following aspects:
★ Optical disk drive: including erasable optical disk drive (CD-R), WORM optical disk drive and CD-ROM drive. Among them, the CD-ROM drive has brought cheap 650M storage equipment to MPC, and the CD-ROM drive with graphics, animation, images, sounds, words, digital audio, programs and other resources has been widely used, so now the CD-ROM drive is necessary for the majority of users. While rewritable discs and WORM discs are more expensive and less popular at present. In addition, DVD has appeared in the market for some time, and its storage capacity is larger, reaching about 17GB, which is an ideal product for upgrading.
★ Sound card: Audio input and output devices connected to the sound card include microphones, audio playback devices, MIDI synthesizers, headphones, speakers, etc. Supporting digital audio processing is an important aspect of multimedia computer. Sound card has the function of converting A/D and D/A audio signals. It can synthesize music, mix various audio sources and connect MIDI electronic music equipment.
★ Graphics Accelerator Card: The illustrated multimedia performance requires a graphics card with high resolution and rich colors on the same screen.
Yes, but it also needs a Windows display driver, and the pixel operation speed is faster under Windows. So now the local bus display adapter with GUI accelerator of graphical user interface has greatly accelerated the display speed of Windows.
★ Graphics card: It can be subdivided into special cards such as video acquisition card, video processing card, video playing card, TV encoder, etc. Its function is to connect cameras, video recorders, televisions and other devices in order to collect, process and represent various animation and digital video media.
★ Scan card: It is used to connect various graphic scanners, and is a common input device for still photos, characters and engineering drawings.
★ Printer interface: used to connect various printers, including ordinary printers, laser printers and color printers. Printer is now one of the most commonly used multimedia output devices.
★ Interactive control interface: It is used to connect touch screen, mouse, light pen and other human-computer interactive devices, which will greatly facilitate users to use MPC.
★ Network interface: it is an important MPC expansion component to realize multimedia communication. The era of the combination of computer and communication technology has arrived, which requires special multimedia external equipment to transmit or receive a large number of multimedia information. Devices connected through network interfaces include videophones, fax machines, local area networks and ISDN.
3. The application of media player in WEB
We know that because the audio-on-demand and video-on-demand applications are not fully integrated into the current Web browser, it needs a separate application to help. Usually, we use a media player to play audio and video. A typical media player performs a variety of functions, including decompression, jitter elimination, error correction and user playback. Now, you can use plug-in technology to put the user interface of the media player on the user interface of the Web client. The browser reserves screen space on the current webpage and is managed by the media player. At present, most clients use the following methods to read audio and video files:
★ Transmit sound/video from the Web server to the media player through the Web browser;
★ Send audio/video directly from the network server to the media player.
★ Directly transmit sound/video from the multimedia exile server to the media player;
In this process, the main functions of the media player are as follows:
★ Decompression: Almost all audio and video are compressed and stored in memory, so audio and video from memory or network should be decompressed.
De-jitter: Because the time delay of each voice packet and TV image packet arriving at the receiving end is not a fixed value, if no measures are taken to send the data to the media player, it sounds like jitter, and even the information expressed by voice and TV images cannot be understood. In the media player, a simple way to limit this jitter is to use the buffer technology, that is, the sound or TV image data is stored in the buffer memory first, and then played after a delay.
★ Error handling: Due to unacceptable traffic congestion on the Internet, some information in the data packet may be lost during transmission. If too many packets are lost continuously, the sound and image quality received by users will be unbearable. The method used is often retransmission.
User-controllable interface: This is the actual interface where the user directly controls the media player to play media. The control functions provided by media players for users usually include volume, pause/restart, jump and so on.
The third article images and graphics
1. Basic knowledge about color
We know that all colors can be described by brightness, hue and saturation, and any colored light seen by human eyes is a combination of these three characteristics. So what do brightness, hue and saturation mean respectively?
★ Brightness: it is the bright feeling produced by light acting on human eyes, which is related to the luminous intensity of the observed object; ★ Tone: It is the color feeling of human eyes when they see light with one or more wavelengths, which reflects the types of colors and is the basic characteristic that determines colors. For example, red and brown refer to hue;
★ Saturation: refers to the purity of color, that is, the degree of white light mixing, or the depth of color. For light with the same hue, the deeper the saturation, the brighter or purer the color. Usually we call hue and saturation chroma. Now you should understand that brightness is used to indicate the brightness of a certain color light, while chromaticity is used to indicate the category and depth of color. In addition, various colors of light that are common in nature can be composed of red (R), green (G) and blue (B) in different proportions. Similarly, most colors of light can be decomposed into three colors: red, green and blue, which forms the most basic principle in colorimetry-the three primary colors principle (RGB).
2. The common graphic (image) formats at present
Generally speaking, the current graphic (image) formats can be roughly divided into two categories: one is bitmap; The other is called drawing class, vector class or object-oriented graphics (images). The former describes a graph (image) in the form of a lattice, and the latter is a graph (image) composed of geometric elements described by mathematics. Generally speaking, the latter expresses the image carefully and truly, and the resolution of the graphics (images) remains unchanged after scaling, so it is widely used in professional graphics (images) processing.
Before introducing the graphic (image) format, it is really necessary for us to know some related technical indicators of the graphic (image): resolution, color number and graphic gray level.
★ Resolution: It can be divided into screen resolution and output resolution. The former is expressed in lines per inch, and the higher the value, the better the quality of graphics (images). The latter measures the accuracy of the output device, expressed in pixels per inch;
★ Color number and graphic gray level: expressed in bits, generally written as the n power of 2, where n represents the number of bits. When the figure (image) reaches 24 bits, it can represent16.77 million colors, that is, true color. The representation of gray scale is similar;
Let's learn about the common graphic file formats one by one through the feature suffix names of graphic files (as shown in figure. Bmp): BMP, DIB, PCP, DIF, WMF, GIF, JPG, TIF, EPS, PSD, CDR, IFF, TGA, PCD and MPT.
★ BMP (bitmap picture): the most commonly used bitmap format on PC, which has two forms: compression and decompression. The format can represent colors from 2 bits to 24 bits, and the resolution can also range from 480x320 to 1024x768. This format is quite stable in the Windows environment, and it is widely used when the file size is not limited.
★ DIB (Device Independent Bitmap): The ability to describe images is basically the same as that of BMP, and it can run on various hardware platforms, but the file is large.
★ PCP (PC Paint Brush): A compressed and disk-saving PC bitmap format created by Zsoft Company, which can represent up to 24-bit graphics (images). There used to be a certain market, but with the rise of JPEG, its position gradually faded.
★ DIF (Drawing Interchange Format): A graphic file in AutoCAD, which stores the graphics in ASCII code, displays the graphics with very accurate size, and can be called and edited by large software such as CorelDraw and 3DS.
★ WMF (Windows metafile format): Microsoft Windows metafile, which has the characteristics of short file and modular modeling. This kind of graphics is rough, and editing can only be called in Microsoft Office.
★ GIF (Graphics Interchange Format): A compressed graphics format that can be processed by various graphics processing software on various platforms. The disadvantage is that only 256 colors can be stored.
★ JPG (Joint Photographic Graphics Expert Group): A graphics format that can greatly compress graphics files. For the same picture, the files stored in JPG format are from110 to 1/20 of other types of graphic files, and the number of colors can be up to 24, so it is widely used in home pages or picture libraries on the Internet.
★ TIF(tagged image file format): The file is huge, but the amount of information stored is also huge, with many subtle levels of information, which is conducive to the reproduction of the original tone and color. There are compressed and uncompressed formats, and the maximum number of colors supported can reach 16M.
★ EPS(encapsulated PostScript): an ASCII graphic file described in PostScript language, which can print high-quality graphics (images) on a PostScript graphic printer, and can represent 32-bit graphics (images) at most. The formats can be divided into Photoshop EPS format, adobeillustrator EPS format and standard EPS format, among which the latter can be divided into graphic format and image format.
★ PSD (Photoshop standard): the standard file format in Photoshop, which is specially optimized for Photoshop.
★ CDR (CorelDRAW): the file format of CorelDRAW. In addition, CDX is a graphic (image) file that can be used by all CorelDraw applications, and it is a mature CDR file.
★ IFF (image file format): It is used for large-scale super graphics processing platforms, such as AMIGA, and this graphics format is mostly used for Hollywood stunts. Graphic (image) effects, including colors and textures, vividly reproduce the original scene. Of course, this format will consume a lot of computer resources such as memory and external storage.
★ TGA(tagged graphic): It is a graphic file format developed by True vision for its graphics card. It was established earlier and the maximum number of colors can reach 32. VDA, Pixar, Wen, BPX, ICB, etc. All belong to its collateral.
★ PCD(Photo CD): It is developed by Kodak Company and can only be read by other software systems.
★ MPT(macintosh pen) or MAC:Macintosh pen uses gray graphics (image) mode, and the resolution can only be 720x567.
In addition, graphics (images) formats special for Macintosh computers include PNT, PICT, PICT2, etc.
The fourth sound (audio)
1. Audio processing technology in multimedia
Multimedia involves many audio processing technologies, such as audio acquisition, speech coding/decoding, text-to-speech conversion, music synthesis, speech recognition and understanding, audio data transmission, audio and video synchronization, audio effect and editing. Among them, digital audio is a key concept, which refers to a data sequence used to express sound intensity. It is obtained by sampling (that is, taking an amplitude value on the analog sound waveform every other time interval), quantizing and coding (that is, writing the sound data into a computer data format). Digital sound is stored in computer digital CD and DAT. The analog-to-digital converter converts analog sound into digital sound; Digital-to-analog converter can recover analog sound.
Generally speaking, there are two ways to realize computer voice output: one is recording/playback, and the other is text-to-speech conversion. The second method is sound generation technology based on sound synthesis technology, which can be used for speech synthesis and music synthesis. The first method is the simplest music synthesis method, and music synthesis technology using frequency modulation (FM) and wave table has been produced successively.
2. The concept of musical instrument digital interface MIDI
MIDI (Musical Instrument Digital Interface) is one of the most frequently used audio terms, which appears as the abbreviation of Musical Instrument Digital Interface and is used to refer to the international standard of digital music. Because it defines the way for electronic devices such as computer music programs and synthesizers to exchange information and electronic signals, it can solve the incompatibility problem between different electronic musical instruments. In addition, the standard multimedia PC platform can play MIDI files through a built-in synthesizer or an external synthesizer connected to the computer MIDI port, and use MIDI files to play music, which requires the least storage.
As for MIDI file, it refers to the standard file format for storing MIDI information. MIDI files contain notes, timing and performance definitions for up to 16 channels. This file includes information about the playing notes of each channel: key channel number, sound length, volume and intensity (the speed at which the key reaches the lowest position when pressed). Because MDDI file is a series of instructions, not waveforms, it needs little disk space. And now it is much easier to load MIDI files than waveform files. In this way, when designing multimedia programs, you can specify when to play music, which will have great flexibility. In the following cases, using MIDI files is more suitable than using waveform audio: it takes a long time to play high-quality music, and if you want to store music on the hard disk for more than 4 minutes, the hard disk does not have enough storage capacity; You need to use music as the background sound effect, and load other data from the CD, such as the display of images and words; It is necessary to use music as background sound effect, play waveform audio at the same time or realize the conversion from text to language, so as to realize the simultaneous output of music and voice.
3. Common sound file formats
Next, we introduce seven most popular multimedia sound file effects for your understanding:
★ WAVE, extension WAV: This format records the waveform of sound, so as long as the sampling rate is high, the sampling bytes are long and the machine speed is fast, the sound file recorded in this format can be basically consistent with the original sound, and the quality is very high, but the price of doing so is that the file is too large.
★ MOD, extended MOD, ST3, XT, S3M, FAR, 669, etc. This format file stores all kinds of timbre samples used in score and music, which has the advantages of clear playback effect and unlimited timbre types. But it also has some fatal weaknesses, so that it is gradually eliminated. At present, only MOD fans and some game programs are still in use.
★ MPEG-3, Extended MP3: The most popular audio file format is widely used in network videophone communication because of its high compression rate, but its sound quality is not ideal compared with CD records.
★ Real Audio, extension RA: This format is really the soul of the network. Its powerful compression and minimal distortion make it stand out among many formats. Like MP3, it is also to solve the network transmission bandwidth resources, so the main goal is compression ratio and fault tolerance, followed by sound quality.
★ Creative music format, extended CMF: A special music format of creative companies, similar to MIDI, but with some characteristics in timbre and effect. It is specially used for FM sound cards, but its compatibility is also poor.
★ CD Audio music CD, extension CDA: the format adopted by the record, also known as the "red book" format, records the waveform stream and is absolutely pure HIFI. But the disadvantage is that it can't be edited and the file length is too large.
★ MIDI, extension MID: At present, the most mature music format has actually become an industrial standard, and its scientificity, compatibility, complexity and other aspects certainly far exceed all the standards introduced in this paper (except symphony CD and Unplug CD, other CDs are often made by MIDI), and its universal MIDI is the most common standard. MIDI, as a data communication standard in the music industry, can direct the operation of all kinds of music equipment. It has a unified standard format, can imitate all kinds of playing skills of original musical instruments and even can't play them. The file length is very small.
In short, if there is a professional audio source equipment, then the degree to which HIFI listens to the same song is:
Acoustic instrument performance > MIDI > CD > MOD > MIDI is on the so-called sound card > CMF, while MP3 and RA depend on whether the program source is MIDI, CD or MOD.
In addition, in multimedia materials, file formats for storing sound information also need to be identified, including:
WAV file, VOC file, MIDI file, RMI file, PCM file and AIF file.
★ WAV file: Microsoft's audio file format, which is derived from the sampling of sound analog waveform. By sampling the analog WAVeform of sound with different sampling frequencies, a series of discrete sampling points can be obtained, and the values of these sampling points are converted into binary numbers with different quantization bits (8 bits or 16 bits), and then stored in disk, thus a wav file of sound, that is, a waveform file, is generated. Microsoft sound system software Sound Finder can convert AIF SND and VOD files into WAV format.
★ VOC file: The waveform audio file format of creative company is also the audio file format used by Sound Blaster. Each VOC file consists of a file header block and an audio data block. The file header contains an identification version number and a pointer to the beginning of the data block. Data blocks are divided into various types of sub-blocks. For example, the mute mark of sound data indicates the result repetition, termination mark, expansion block and so on of ASCII code file repetition.
★ MIDI file: the abbreviation of musical instrument digital interface. It is a communication standard formulated by the world's major electronic musical instrument manufacturers, which stipulates the method of exchanging information and control signals between computer music programs, electronic synthesizers and other electronic devices. The MIDI file contains the note timing and instrument definitions of up to 16 channels, and each note contains information such as the duration, volume and intensity of key channel numbers. Therefore, MIDI files record not the music itself, but some instructions describing music performance.
★ RMI file: MIDI file format of Microsoft, which can contain picture labels and text.
★ PCM file: a binary sequence directly formed by analog-to-digital conversion (A/D conversion) of analog audio signals. This file has no attached file header and file end tag. In the software provided by Sound Blaster Card, VOC-HDR program can be used to add file headers to PCM format audio files to form VOC format. Windows conversion tools can convert PCM audio files into Microsoft WAV files.
★ AIF file: the audio file format of Apple computer. Windows conversion tools can also convert files in AIF format into Microsoft WAV format.
The fifth video (animation)
1. synthesis of dynamic images
Dynamic images, including animation and video information, are continuous and progressive static images or graphic sequences, which are displayed in turn along the time axis, thus forming a moving visual medium. When every image in the sequence is a human or computer-generated image, we usually call it animation; When every image in the sequence captures a natural scene or a moving object in real time, we often become a video, or simply a video. Dynamic image demonstration is often carried out in cooperation with sound media, and their common basis is time continuity. Generally speaking, when it comes to video, it often includes sound media. But here, video (animation) is specially made for dynamic images without sound media.
2. The definition of animation
What is animation? The so-called animation is to play still image frames in sequence at a speed of 15 to 20 frames per second (quite close to the full motion video frame rate), creating the illusion of motion. Because the eye can keep the image long enough for the brain to connect the frames in a continuous order, it can create the illusion of movement. We can generate simple animation by changing the displayed image. The simplest method is to repeat between two different frames. This method is a good way to say "yes" or "no". Another way to make animation is to play several image frames in a circular form to produce a rotation effect, and you can rely on calculating time to get a better playback effect, or use a timer to control animation.
3. Common video file formats
There are many formats for storing video information in a computer. At present, the two most popular formats are:
Apple's Quicktime and Microsoft's AVI.
★ Quicktime: It is a low-cost, full-motion video mode adopted by Apple for end-user desktop systems, and now it is also used for software compression and decompression. Its vector quantization is one of the compression technologies of Quicktime software. It provides a video resolution of 320x240 at a maximum speed of 30 frames per second, and the compression ratio can range from 25 to 200.
★ AVI: Similar to Quicktime, it is an audio-video interlaced format adopted by Microsoft and a low-cost and low-resolution video format on the desktop system. AVI can play back video with 8-bit sound at the speed of 15 frames per second in the window of 160x 120, or play it on VGA or super VGA monitor. An important feature of AVI is scalability, and the performance of AVI algorithm depends on the basic hardware used with it.
Article 6 Technical Standards for Multimedia Data Compression and Coding
At present, there are four universal compression coding standards widely recognized and applied by the international community:
H.26 1，JPEG，MPEG，DVI。
★ H.261:The video codec (also called Px64 standard) of audio and video services adopted by CCITT adopts two compression modes: intra-frame lossy compression (based on DCT) and inter-frame lossless coding, and on this basis, the encoder adopts a mixed mode of DCT plus motion estimation and DPCM (differential pulse code modulation). This standard has obvious similarities with JPEG and MPEG standards, but the key difference is that it is designed for dynamic use and provides complete organization and advanced interactive control.
★ JPEG: the full name is Joint Photographic Coding Experts Group, which is a still image compression and decompression algorithm based on DCT. Developed jointly by ISO (International Organization for Standardization) and CCITT (International Telegraph and Telephone Advisory Committee), it became an international standard after being widely adopted by 1992. It removes redundant image signals and other types of still images, and even reduces them to 1% of the original image (compression ratio 100: 1). But at this level, the picture quality is not good; When the compression ratio is 20: 1, we can see that the image changes slightly; When the compression ratio is greater than 20: 1, generally speaking, the image quality begins to deteriorate.
★ MPEG: abbreviation of moving picture expert group, which actually refers to a set of video, audio and data compression standards issued by ITU and ISO. It uses compression algorithm to reduce redundant information of images. The compression ratio it provides can be as high as 200: 1, and the quality of images and sounds is also very high. Now there are usually three versions: MPEG- 1, MPEG-2 and MPEG-4 to meet the requirements of different bandwidths and digital image quality. Its three most remarkable advantages are good compatibility, high compression ratio (up to 200: 1) and low data distortion.
★ DVI: The performance of its video image compression algorithm is equivalent to that of MPEG- 1, that is, the image quality can reach the level of VHS, and the data rate of the compressed image is about1.5mb/s. In order to expand the application of DVI technology, Intel recently introduced a software decoding algorithm of DVI algorithm, called Indeo technology, which can be used as compressed digital video text.