text4_多媒体信息和系统.ppt

1、Technical English For Communication Engineering,2020/8/23,Multimedia Information and Systems,Text 4,The various types of information that multimedia systems handle have different characteristics. If we understand them, we shall also understand why storing, processing, or transporting them raises dif

2、ferent issues.,Text is the historical form of interaction between computers and humans. It may have two broad forms: unformatted, also called plain text（纯文本）, or formatted, sometimes termed rich text. In contrast to the former, the latter has extended character sets, a choice of fonts, size, and typ

3、es. Its appearance is similar to that of text on a printed document. Most human-computer interfaces (HCIs) offer rich text capabilities nowadays.,未格式化的,扩展的字符集,Graphics are internally represented as an assemblages（集合） of objects such as lines, curves, or circles. We say that the representation is awa

4、re of（知道、了解） the semantic contents. They are revisable; that is, objects can be individually deleted, added, moved, or modified later. In contrast, images are not revisable in the sense given above. They ignore the semantic contents. They are described as spatial arrays of values.,可修改的,就意义而言,被描述成一些数

5、值的空间阵列,The smallest addressable image element is called a pixel. The array, and thus the set of pixels, is called a bitmap. Object-based editing is not possible -though autotracing tools which can compute the bounds of bitmap areas may help but image editing tools exist for enhancing and retouching

6、bitmap images. The drawback of bitmap is that they need much more storage capacity than graphics,增强和修饰,up to two or three orders of magnitude. Their advantage is that no processing is necessary before displaying them, unlike with graphics where the abstract definition must be processed first to prod

7、uce a bitmap. Of course, images captured from an analog signal, via scanners or video cameras, are represented as bitmaps, unless semantic recognition takes place such as in optical character recognition.,高达2或3倍的数量级,光学字符识别,When a succession of correlated views is displayed, an effect of movement may

8、 be given to human viewers. One individual view in such a succession is called a frame. The impression of smooth movement starts at 15 or 16 displayed frames per second (fps). Captured motion video refers to a video sequence produced from a video camera, whereas（然而） in synthesized motion imaging, ea

9、ch frame is generated,一连串的关联视图,by a computer, or by an author with the assistance of a computer, and stored as a bitmap. Computer animation is different. Here, similarly to graphics, the moving sequence is described by a set of objects, but with time-dependent directives（指令）. The resulting “program”

10、 must be executed at displaying time, unless the result has been recorded as a succession of bitmap frames prior to its presentation.,在.之前,Speech is a sound, but not all sounds are like speech. The range of frequencies we can generate is narrower than that we can detect. And during a conversation, h

11、opefully, not all participants speak at once. These properties have been exploited by coding, compression, and transmission systems. Speech may be up to 10 times less demanding than, say, music, in terms of digital storage volume. Also, speech has a,被利用,semantic content. The syntactic components of

12、speech can be recognized by computers. Speech recognition where words are identifiedhas made real progress though still needs to be used in well-defined environments. Speech understandthat is, the interpretation of a succession of words poses more difficulties but laboratory implementations work.,除了

13、其实验室实现方法外，还面临着许多的困难,The reverse, speech synthesis that is, the creation by a computer of a physically audible sound from a description of the semantic content is more widespread（广泛普及）. Speech or sound synthesis is different from computer-mediated sound play-out（播出）, which is simply the generation of

14、 the physically audible waveform from a digital sound signal, that is an ordered sequence of coded samples.,语音合成,有序序列,Finally, let us mention two terms found in the multimedia literature. Continuous media refers to information media, such as sound or motion video, the presentation of which requires

15、a continuous play-out as time passes. Conversely, discrete media refers to text, still images, or graphics which are composed of non-time-dependent fragments.,碎片、片段,The line between the two tends to be blurred（模糊）, as modern computer-assisted on-screen presentations include synchronization, and thus

16、 time-dependencies, between elements of text or graphics too. Multimedia systems are computer controlled, integrated, use any information in a digital form, and may offer interactivity.,随着现代计算机辅助屏幕展示技术及同步、时间依赖的发展，,The first key aspect is that the presentation of the information to end-users is contr

17、olled by a computer. In practice, computers are not only involved in the presentation. They also intervene in the production of the information, either when it has to be captured from the physical environment or when it is generated after computation. They also control the devices when the informati

18、on is stored.,介入,The notion of integration is more an objective, that of minimizing the different types of systems involved. In particular, whenever possible, a single computer display is to be used to present all visual information. Similarly, a single type of storage device can be used.,主要为了一个目的,只

19、要可能,概念、想法、主张,The most essential characteristic of multimedia systems lies in the uniformity of the representation of information. Information which human senses can detect and a person can interpret may be represented, after capture, by an analog signal, which is a function of time or space, or of b

20、oth time and space. The process of translation from analog to digital representation, the digitization, involves two,人类感官,steps. First, only a discrete set of values is retained. This is called sampling. Second, every sample is coded in such a way that it may take only a limited number of values. Th

21、is is called quantization and coding. The advantages of digital representation are manifold. First, the storage is simplified as only one type of device may be used. Second, the automated transmission of information may in theory rely on,多方面的,a single type of data network, that is a network capable

22、of handling bits. Third, the digitized information may be processed by computers. For example, its semantic content may be recognized more easily than with analog representation. The content can also be modified manually by computer users, or by programs. Powerful editing such as the creation of multimedia documen