问题 问答题 简答题

阐述多媒体信息服务系统中运动图像压缩编码标准MPEG。

答案

参考答案:

MPEG标准是ISO/IEC委员会的第11172号标准,是针对全活动视频的压缩标准。该标准包括MPEG视频、MPEG音频和MPEG系统三大部分。MPEG视频是面向位速率约1.5Mbit/s全屏幕运动图像的数据压缩;MPEG音频是面向每通道数率为64,128和192kbit/s的数字音频信号的压缩。

MPGE输入图像亮度信号的分辨率为360×240,色度信号的分辨率为180×120,每29.97帧,采用双向运动补偿。MPEG把输入的视频信号分成组,用帧内图像、预测图像和差补图像三种格式标出。每组中的第一帧用帧内图像格式编码,第1M、2M、3M帧(M一般选为3)用预测图像格式编码,其它各帧使用差补图像格式编码。差补图像不仅利用过去的帧内图像或预测图像,也利用未来的帧内图像或预测图像进行运动补偿,因此可以达到更高的图像压缩率。

(1)MPEG-I标准。MPEG-I标准是运动图像专家小组1981年制订的数字存储运动图像及伴音编码标准。该标准分为视频、音频和系统三部分。它是一个通用标准,既考虑了应用要求,又独立于具体应用之上。视频部分为1.5Mbit/s活动图像压缩编码算法,对于带宽为1.5Mbit/s的位流,能够获得可接受的图像质量。该算法帧内编码采用二维余弦变换、自适应量化、行程编码、变字长编码和DPCM技术,帧间编码采用运动补偿预测和运动补偿内插技术。MPEG-I对于较低的传输速率、窄带宽的应用(如单速CD-ROM)是相当完善的,并通过插值可处理大于352×240的画面。

(2)MPEG-II标准。MPEG-II是MPEG-I的扩充,丰富和完善。MPEG-II标准的视频数据速率为4-5Mbit/s,能提供720×480(NTSC)或720×576(PAL)分辨率的广播级质量的视像,适用于包括宽屏幕和高清晰度电视(HDTV)在内的高质量电视和广播。

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Today’s children are not satisfied with playing simple games with simple toys.   71   The electronic models are marketed. They can move and communicate. Children need toys that fit well into their renewed idea of playing pleasure.

72   These toys are among the top ten “must haves” for every boy and girl. Their sales largely depend on the rapidly changing toy trade. Besides, the demand by parents and children for more advanced features can make a robot toy sell well.

There are different types of robot toys in the market today.   73   However, video games are not considered as robot toys. While video games are just electronic role-playing mind games, robot toys are highly dependent on the interaction(互动) between the toy and the user. In a video game, the player has a specific goal or task that must be accomplished. The robot toy is a simulation(模仿) of an animal or human.

There are a number of different types of robot toys in the world market today. They are all very costly. There are high-tech robot toy pets that have life-like actions and movements.   74    Not only children but even adults like robot toys and are now spending a lot of money on them in the market.

Robot toys are great educational toys that interact with and within their environment.   75   The robot toys have sensors that enable them to see, hear and feel, making them the ideal companions. And many robot toys are also designed to express emotions,

A.In fact, their demand today has changed.

B.Robot toys are popular with adults as well as children.

C. A robot toy is an electronic toy that is the gift of modern technology.

D.Video games are common in the world of games for children.E. The toys enable the user to experiment and increase creativity.

F. Some of the robot toy pets can actually fetch and carry.

G. Now robot toys are playing an important part in the growth of children.

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