基本概念 人是用眼睛来观看图像和动画的，人眼的自然特性决定了视频系统的一些重要特性。 Basic Concepts

1. 视频与动画 • 基本概念 • 人是用眼睛来观看图像和动画的，人眼的自然特性决定了视频系统的一些重要特性。 • Basic Concepts • The human eye views pictures and motion pictures. The immanent properties of the eye determine, in connection with neuronal processing, some essential conditions related to video systems. 基本概念

2. 视频信号表示 • 普通的黑白电视机中，视频信号是显示在CRT(阴极射线管)上的。电子束携带了诸如场景光强这样的信息。 • Video Signal Representation • In conventional black-and-white TV sets, the video signal is displayed using a CRT (Cathode Ray Tube). An electron beam carries corresponding pattern information, such as intensity in a viewed scene.

3. 视频信号的表现包括三个方面:视觉表现、传输与数字化。视频信号的表现包括三个方面:视觉表现、传输与数字化。 • Video signal representation includes three aspects: the visual representation, transmission and digitalization.

4. （1）视觉表现 • ⑴垂直分辨率与观察距离 • 电视上图像的几何状受到电视画面宽高比的影响。我们称这个比为宽高比(aspect ratio),这个比一般是4/3=1.33。图5.1为宽高比的示意图。 • （1） Visual Representation • (1) Vertical Detail and Viewing Distance The geometry of the field occupied by the television image is based on the ratio of the picture width W to height H. It is called aspect ratio. The conventional aspect ratio is 4/3=1.33. Figure 5.1 shows an example of aspect ratio.

6. 观察距离D决定了画面高度的比值D/H衡量。 • The viewing distance D determines the angle h subtended by the picture height. This angle is usually measured by the ratio of the viewing distance to the picture height (D/H).

7. 图像中的最小单位是像素。 • 理想情况下，每个像素都能表示场景中的一定信息，但实际上有些细节信息存在于两根扫描线之间，因此这样的像素需要两条扫描线来描述，从而使得垂直分辨率有所损失。 • 测试结果显示所有扫描线只能表示大约70%的垂直细节信息。 • 这个比率称为 Kell 因子，它与扫描线紧凑程度有直接关系，即扫描线是一条紧挨眷着一条紧挨着一条(累进式扫描)还是一条隔一条(隔行扫描)。

8. The smallest detail that can be reproduced in the image is a pixel. • Ideally, each detail of the scene would be reproduced by one pixel. • Practically, however, some of the details in the scene inevitably fall between scanning lines, so that two lines are required for such picture elements. • Thus, some vertical resolution is lost. Measurements of this effect show that only about 70% of the vertical detail is presented by the scanning lines. • The ratio is known as the Kell factor; it applies irrespective of the manner of scanning, whether the lines follow each other sequentially (a progressive scan) or alternately (an interlaced scan).

9. ⑵水平分辨率和画面宽度 • 普通电视机的画面宽度是4/3画面高度。使用宽高比，就能根据水平视角确定水平视野。 • （2）Horizontal Detail and Picture Width • The picture width chosen for conventional television service is 4/3×picture height. • Using the aspect ratio, we can determine the horizontal field of view from the horizontal angle.

10. ⑶图像的细节内容 • 垂直方向上的分辨率等于在画面高度上可表示的像素数，而画面宽度上的像素数则等于水平辨率乘以宽高比，垂直方向像素数与水平方向像素的乘积即为整个画面的像素总数。 • （3）Total Detail Content of the Image • The vertical resolution is equal to the number of picture elements separately presented in the picture height, while the number of elements in the picture width is equal to the horizontal resolution times the aspect ratio. • The product of the number of elements vertically and horizontally equals the total number of picture elements in the image.

11. ⑷观察深度 • 自然视觉中，人主要是通过两只眼睛观察图像的角度差来感知第三个维度━━深度的。而在电视平板画面中，深度信息是通过物体的透视外形获得的。摄像机透镜焦距的选取和变化也可以影响深度感。 • 4.Perception of Depth • In natural vision, perception of the third spatial dimension, depth, depends primarily on the angular separation of the images received by the two eyes of the viewer. • In the flat image of television, a considerable degree of depth perception is inferred from the perspective appearance of the subject matter. Further, the choice of the focal length of lenses and changes in depth of focus in a camera influence the depth perception.

12. ⑸ 亮度和色度 • 颜色视觉是由与场景中红、绿、蓝(RGB)三种光线强度成正比的三种信号产生的。这种信号被分别传到显像管的输入端，这样显像管就能在某一点复现摄像机所拍摄到的相应的R，G，B强度。在信号的传输过程中也常使用一种不同于RGB的色彩编码方法。这种色彩编码方法使用一个亮度分量和两个色度分量，我们将在这一节后面介绍。

13. Luminance and Chrominance Color vision is achieved through three signals, proportional to the relative intensities of Red, Green and Blue light (RGB) in each portion of the scene. The three signals are conveyed separately to the input terminals of the picture tube, so that the tube reproduces at each point the relative intensities of red, green and blue discerned by the camera. During the transmission of the signals from the camera to the receiver (display), a different division of signals in comparison to the RGB division is often used. The color encoding during transmission uses luminance and two chrominance signals. We will detail these signals later in this section.

14. ⑹视觉的时间特性 • 人眼视觉的另一特性是观察运动的分辨率有限。 • 与人耳能听连续的声波不一样，一系列离散的独立画面在视觉残留的作用下乍起来就可能像连续的一样。 • 电视和动画利用了这一特性，即一系列前后衔接变化不大的静止图像(帧)的快速切换造成运动的效果。 • 在帧与帧之间的切换时间内是没有光线的。产生视觉真实有两个要求:首先，图像的复现速度必须足以保证帧与帧之间的动作过渡很平滑；其次，图像的复现速度还必须足以使视觉残留能覆帧切换时所产生的闪烁。

15. 6.Temporal Aspects of Illumination • Another property of human vision is the boundary of motion resolution. • In contrast to continuous pressure waves of an acoustic signal, a discrete sequence of individual pictures can be perceived as a continuous sequence. • This property is used in television and motion pictures, i.e., notion is the presentation of rapid succession of slightly different still pictures (frames). • Between frames, the light is cut off briefly. • To represent visual reality, two conditions must be met. • First, the rate of repetition of the images must be high enough to guarantee smooth motion from frame to frame. • Second, the rate must be high enough so that the persistence of vision extends over the interval between flashes.

16. ⑺运动的连续性 • 当帧速率大于15帧/秒时，画面就连续起来了。 • 如果是摄像得到的画面而不是合成出来的视频画面只有达到30帧/秒的速率才能获得平滑的运动效果。 • 电影由于帧速率为24帧/秒，因而看起来常有些抖动，特别是一个大物体快速移向观众时，就像摇头中的场景一样。 • 最新的Showcan技术[Dep80]可以以每秒60帧的速度制作并放映70毫米胶片。 • 这一技术使用了一个更大的画面，它占据了更大的视野空，运动也更为平滑了。

17. （7）Continuity of Motion • It is known that we perceive a continuous notion to happen at any frame rate faster than 15 frames per second. • Video motion seems smooth and is achieved at only 30frames per second, when filmed y a camera and not synthetically generated. • Movies, however, at 24 frames/s, often have a jerkiness about them, especially when large objects are moving fast and close to the viewer, as sometimes happens in a panning scene. • The new Show scan technology [Dep89] involves making and showing movies at 60 frames per second and on 73-millimeter films. • This scheme produces a bigger picture, which therefore occupies a larger portion of the visual field, and produces much smoother motion.

18. 好几种动态视频频标准规定了一定运动连续性所需要的帧速度。动态视频信号的美国标准NTSC(国家电视系统委员会)开始规定帧速率为30帧/秒，后来又改为29.97Hz以维持4.5MHz时的声像载波分离。好几种动态视频频标准规定了一定运动连续性所需要的帧速度。动态视频信号的美国标准NTSC(国家电视系统委员会)开始规定帧速率为30帧/秒，后来又改为29.97Hz以维持4.5MHz时的声像载波分离。 • NTSC扫描显示设备以24Hz的标准切换图像，但要将其转换为29.97的扫描频率。动态视频的欧洲标准PAL(Phase Alternating Line,相位交错扫描线)采用25Hz的复现频率，因而帧速率也是25帧/秒。

19. There are several standards for motion video signals, which determine the frame rate to achieve proper continuity of motion. The USA standard for motion video signals, NTSC (National Television Systems Committee) standard, specified the frame rate initially to 30 frames/s, but later changed it to 29.97 Hz to maintain the visual-aural carrier separation at precisely 4.5 MHz. • NTSC scanning equipment presents images at the 24 Hz standard, but transposes them to the 29.97 Hz scanning rate. The European standard for motion video, PAL (Phase Alternating Line), adopted the repetition rate of 25 Hz, and the frame rate therefore is 25 frames/s.

20. ⑻闪烁 • 可觉察到的亮度的缓慢变化和周期性起伏就是闪烁。避免闪烁的边际条件是画面每秒至少要有50次刷新，因此为了使画面连续而且不闪烁，我们需要一个相对更高的刷新频率。与电视一样，电影也采用了一些技术措施来处理运动频率过低这个问题。 • （8）Flicker • Through a slow motion, a periodic fluctuation of brightness perception, a flicker effect, arises. The marginal value to avoid flicker is at least 50-refresh cycles/s. To achieve continuous flicker-free motion, we need a relatively high refresh frequency. Movies, as well as television, apply some technical measures to work with lower motion frequencies.

21. 比如每秒只有16幅画面的电影，如不加技术处理，电影会抖动得很历害。为了减轻闪烁，可以在一幅画面的投映过程中额外将光线中断两次，这样同一幅画面就被多刷新了两次，因而获得了3×16=48Hz的刷新频率。比如每秒只有16幅画面的电影，如不加技术处理，电影会抖动得很历害。为了减轻闪烁，可以在一幅画面的投映过程中额外将光线中断两次，这样同一幅画面就被多刷新了两次，因而获得了3×16=48Hz的刷新频率。 • For example, to run a movie with 16 pictures per second without any technical measures taken would be very disturbing. To reduce the flicker effect, the light wave is interrupted additionally two times during the picture projection, so that additionally to the original picture projection, the picture can be redrawn twice during the interruptions; thereby, a picture refresh rate of 3×16Hz=48Hz is achieved.

22. 对于电视而言，可以通过设置一个显示刷新缓冲来减轻闪烁。数据以略高于连续运动要求的频率写入刷新缓冲(例如25Hz)，而显示器用足消除闪烁的频率显示缓冲的内容(比如70Hz)，70Hz刷新频率的显示效果是相当不错的。对于电视而言，可以通过设置一个显示刷新缓冲来减轻闪烁。数据以略高于连续运动要求的频率写入刷新缓冲(例如25Hz)，而显示器用足消除闪烁的频率显示缓冲的内容(比如70Hz)，70Hz刷新频率的显示效果是相当不错的。 • 另一川方法是将一幅完整的电视图像用一行间一行抽取的方式分为两半，再使用线嵌入的方法依次传送这两部分部分。如果全屏电视图像的传输频率是30Hz(实际29.97Hz)或25Hz(欧洲)，那么半幅就应以2×30=60Hz或2×15=50Hz的速率扫描，来获得相应的全幅图像的30Hz和25Hz，如图5.2所示。

23. In the case of television, flicker effect can be alleviated through a display refresh buffer. The data are written in the refresh buffer at a higher frequency than the motion resolution requires (e.g., 25Hz). The picture is displayed at a frequency so that the flicker effect is removed (e.g., a70Hz). • For example, the 70-Hz-motion frequency corresponds to the motion frequency of a good computer display. A full TB picture is divided into two half-pictures, which consist of interleaved scanning lines. • Each half-picture after another is transmitted, using the line-interleaving method. In the case of a full TB picture, where the transmission occurs at 30Hz (actually 29.97Hz), or 25Hz in Europe, the half-pictures must be scanned at higher frequency of 2×30Hz=60Hz, or 2×25Hz=50Hz, to achieve the scanning rate of 30Hz, respectively 25Hz, for the full pictures. Figure 5.2 shows the situation described above.

24. ⑼视频带宽的时间特性 • 用何种带宽传输动态视频在很大程度上取决于它的时序说明。时间标准与视频系统的扫描频率有关，也与人眼对扫描的观察能力有关。例如普通电视扫描所用时间是用微秒来衡量的。而在HDTV(高清晰度电视)中，扫描一个点所用时间不到千万分之一秒。从人眼的观察能力讲，每秒扫描25帧正好可以消除闪烁。 • （9）Temporal Aspect of Video Bandwidth • An important factor to determine which video bandwidth to use to transmit motion video is its temporal specification. Temporal specification depends on the rate of the visual system to scan pixels, as well as on the human eye’s scanning capabilities. • For example, in a regular TV device, the time consumed in scanning lines and frames is measured in microseconds. In an HDTV (High Definition TV) device, however, a pixel can be scanned in less than a tenth of a millionth of a second. From the human visual perspective, the eye requires that a video frame be scanned every 1/25 second. This time is equivalent to the time during which a human eye does not see the flicker effect.

26. 2、传输 • 视频信号是通过各个电视频道传送到接收机的。NTSC频道如图5.3所示。 • Transmission • Video signals are transmitted to receivers through a single television channel. The NTSC channel is shown in Figure 5.3.

27. 视频信号是由三具颜色分量组成的。在传输中使用一个亮度信号和两个色度信号。NTSC和PAL制式规定色度副载波是行扫描频率的一半的厅数倍，这样亮度信号和色度信号就可以共用一个频道复合传输，复合传输时色度分量是交替出现的，这样做是为了接收时的信号分离能避免两者之间的互相干扰，恢复原来的颜色信号。视频信号是由三具颜色分量组成的。在传输中使用一个亮度信号和两个色度信号。NTSC和PAL制式规定色度副载波是行扫描频率的一半的厅数倍，这样亮度信号和色度信号就可以共用一个频道复合传输，复合传输时色度分量是交替出现的，这样做是为了接收时的信号分离能避免两者之间的互相干扰，恢复原来的颜色信号。 • 实际应用中颜色串扰和亮度串扰现象导致的图像质量下降迫使NTSC电视接收机将亮度带宽限制在低于色度副载波频率3.58MHz的3MHz以内，远远低于发送信号的最大频率对应的简单V型滤波器，现在这一过程使用的是一个梳形滤波器，在亮度-色度编码中也使用梳形滤波器。

28. To encode color, a video signal is a composite of three signals. For transmission purposes, a video signal consists of one luminance and two chrominance signals In NTSC and PAL systems, the composite transmission of luminance and chrominance signals in a single channel is achieved by specifying the chrominance sub carrier to be an odd multiple of one-half of the line-scanning frequency. This causes the component frequencies of chrominance to be interleaved with those of luminance. The goal is to separate the two sets of components in the receiver and avoid interference between them prior to the recovery of the primary color signals for display. • In practice, degradation in the image, known as cross-color and cross-luminance, occurs. These effects have pushed manufacturers of NTSC receivers to limit the luminance bandwidth to less than 3MHz below the 3.58MHz sub carrier frequency and for short of the 4.2MHz maximum of the broadcast signal. This causes the horizontal resolution in such receivers to be confined to about 25 lines. The filtering employed to remove chrominance from luminance is a simple notch filter tuned to the sub carrier’s frequency; currently it is the comb filter. The transmitter also uses the comb filter during the luminance-chrominance encoding process.

30. 颜色编码的几种方法简列如下: • ⑴RGB信号 • RGB编码分别使用信号来表示红、绿和蓝三种颜色，它将其他颜色看成是这些原色的组合。如果规一化后的R值、G值和B值有R+G+B=1，那么就得到了中性的白色。 • Several approaches of color encoding are summarized below: •  RGB signal • In the case of separate signal coding the color can be encoded in the RGB signal, which consists of separate signals for red, green, and blue colors. Other colors can be coded as a combination of these primary colors. For example, if the values T (red), G (green) and B (blue) are normalized with R+G+B=1, we get the neutral white color.

31. ⑵YUV信号 • 由于人的视觉系统对亮度比对色度敏感得多，因此将亮度和色度分开编码更为合适。这意味着不再使用色彩分离，而是进行亮度信息(亮度Y)和色彩信息(两个色度分量U和V)的分离。由于兼容性的原因，亮度分量是必须传送的。黑白接收机对色彩分量的利用情况取决于它本身的色彩能力。 • YUV signal • As human perception is more sensitive to brightness than any chrominance information, a more suitable coding distinguished between luminance and chrominance. This means instead of separating colors, one can separate the brightness information (luminance Y) form the color information (two chrominance channels U and V). The luminance component must always be transmitted because of compatibility reasons. For black-and-white reception, the utilization of chrominance components depends on the color capability of the TB device.

32. YUV信号的分量计算公式如下: • Y=0.30R+0.59G+0.11B • U=(B-Y)×0.493 • V=(R-Y)×0.877 • 由于亮度分辨率中的误差要比色度中的误差影响更大，因此亮度值编码的带宽可以大于色度的带宽。 • The component division for YUV signal is: • Y=0.30R+0.59G+0. 11B • U=(B-Y) ×0.493 • V=(R-Y) ×0.877 •  Any error in the resolution of the luminance (Y) is more important than in the chrominance (U, V) values. Therefore, the luminance values can be coded using higher bandwidth than the chrominance values. 

33. 因为亮度和色度分量有不同的带宽，所以通常用亮度与两个色度的带宽比来标识不同的编码方式，例如YUV编码可以表述为4:2:2。有时YUV编码还被表述为Y,B-Y,R-y,因为U与B-Y，V与R-Y之间存在着对应关系。因为亮度和色度分量有不同的带宽，所以通常用亮度与两个色度的带宽比来标识不同的编码方式，例如YUV编码可以表述为4:2:2。有时YUV编码还被表述为Y,B-Y,R-y,因为U与B-Y，V与R-Y之间存在着对应关系。 • CD-I(compact disc-interactive)及DVI视频采用的是YUV信号分解方式。 • Because of these different component bandwidths, the coding is often characterized by a ratio between the luminance component and the two-chrominance components. For example, the YUV encoding can be specified as (4:2:2) signal. Further, the YUV encoding is sometimes specified as the Y, B-Y, and R-Y signal because of the dependencies between Y and B-Y and V and R-Y in the above equations. • The CD-I (Compact Disc-Interactive) and DVI video on demand CD developments adopted the YUV signal decomposition.

34. ⑶YIQ信号 • YIQ信号与YUV信号类似，它是NTSC制式的基础，计算公式如下: • Y=0.30R+0.59+0.11B • I=0.60R-0.28G-0.32B • Q=0.21R-0.52G+0.31B • YIQ signal • A coding similar to the YUV signal described above is the YIQ signal, which builds the basis for the NTSC format. • Y=0.30R+0.59G+0.11B • I=0.60R-0.28G-0.32B • Q=0.21R-0.52G+0.31B

36. 图5.4所示是一个典型的NTSC编码器。它首先分离出I信号和Q信号，指定了它们的传输频带，并用它们对副载波进行正交调制，然后将调制过的副载波信号叠加到亮度信号Y和同步信号波形上。图5.4所示是一个典型的NTSC编码器。它首先分离出I信号和Q信号，指定了它们的传输频带，并用它们对副载波进行正交调制，然后将调制过的副载波信号叠加到亮度信号Y和同步信号波形上。 • A typical NTSC encoder is shown in figure 5.4. It produces the I and Q signals, limits their pass bands, uses them to modulate the subcarrier in a quadrature and adds the moduled subcarrier to the luminance Y, blanking and synchronizing signal waveform.

37. ⑷复合信号 • 另一种方法是将所有的信息复合编入一个信号中，也就是把各个分量(RGB，YUV或YIQ)组合到同一个信号中。基本信息由亮度信息色差信号组成，由于在合成中，色度信号可能会干扰亮度信号，因此，还要采用适当方法消除色度信号和亮度信号之间的干扰。 • Composite signal • The alternative to component coding composes all information into one signal; consequently, the individual components (RGB, YUV or YIQ) must be combined into one signal. The basic information consists of luminance information and chrominance difference signals. During the composition into one signal, the chrominance signals can interfere with the luminance. Therefore, the television technique has to adopt appropriate modulation methods to eliminate the interference between luminance and chrominance signals. 

38. NTSC标准中亮度信号和色度信号传输所要求的基本视频带宽是4.2MHz。而HDTV的视频带宽至少要是常规(比如NTSC)标准的两倍。在分量分离传输方式中，三种信号(RGB或YUV)总带宽将达到20～30MHz。NTSC标准中亮度信号和色度信号传输所要求的基本视频带宽是4.2MHz。而HDTV的视频带宽至少要是常规(比如NTSC)标准的两倍。在分量分离传输方式中，三种信号(RGB或YUV)总带宽将达到20～30MHz。 • The basic video bandwidth required to transmit luminance and chrominance signals is 4/2 MHz for the NTSC standard. IN HDTV, the basic video bandwidth is at least twice of the conventional standard (e.g., NTSC). Moreover, in the separate component method of transmission, the bandwidths occupied by the three signals (RGB or YUV) are additive, so the total bandwidth prior to signal processing is of the order of 20-30MHz.

39. 3、数字化 • 必须首先将图像转换为数字格式然后才能进行计算机处理或网络传输。一般情况下，数字化即对图像进行M行×N列的灰度或色彩采样。由于灰度值可以是连续范围上的任一值，因此还需进行量化，量化就是将整个灰度域分为K个等份，灰度值只在这些等分点上取值。为了保证量化后图像的质量，灰度量化等级要大小等于100。如果采样区域内的灰度(色彩)变化很缓慢，那么精细的量化就显得尤为重要。

40. Digitalization  • Before a picture or motion video can be processed by a computer or transmitted over a computer network, it needs to be converted from analog to digital representation. In an ordinary sense, digitalization consists of sampling the gray (color) level in the picture at M×N array of points. Since the gray level at these points may take any value in a continuous range, for digital processing, the gray level must be quantized. • By this we mean that we divide the range of gray levels into K intervals, and require the gray level at any point to take on only one of these values. For a picture reconstructed from quantized samples to be acceptable, it may be necessary to use 100 or more quantizing levels. When samples are obtained by using an array of points of finite strings, a picture where the gray (color) levels change slowly [RK82].

41. 经过采样和量化就得到了数字图像，它的主要部分是一个矩形数组，每个元素是代表像素灰度或色彩的一些整数值。详见4.1节。经过采样和量化就得到了数字图像，它的主要部分是一个矩形数组，每个元素是代表像素灰度或色彩的一些整数值。详见4.1节。 • 要生成数字动态视频，下一步就得按时间顺序数字化图像，用得到数字图像序列近似模拟动态视频。 • The result of sampling and quantizing is a digital image (picture), at which point we have obtained a rectangular array of integer values representing pixels. Digital images were described in more detail in Section 4.1. • The next step in the creation of digital motion video is to digitize pictures in time and get a sequence of digital images per second that approximates analog motion video.

42. 计算机视频格式 • 计算机视频格式与动态视频输入输出设备有关 • 数字动态视频的输出与显示设备有关，最常用的显示是前一章讲过的光栅显示器。普通光栅显示器的系统结构如图5.5所示。 • Computer Video Format • The computer video format depends on the input and output devices for the motion video medium. • The output of the digitalized motion video depends on the display device. The most often used displays are raster displays, described in the previous chapter. A common raster display system architecture is shown in Figure 5.5.

44. 下面举一些视频控制器标准为例进行介绍。每个体系都支持不同的分辨率和颜色表示方法。下面举一些视频控制器标准为例进行介绍。每个体系都支持不同的分辨率和颜色表示方法。 彩色图形适配器(CGA,color graphics adapter)分辨率为320×200，可同时表示4种颜色，每幅图像所需存储空间为: 2位/像素 320×200像素×─────── = 16 000字节 8位/字节 Some computer video controller standards are given here as examples. Each of these systems supports different resolution and color presentation. The Color Graphics Adapter (CGA) has a resolution of 320×200 pixels with simultaneous presentation of four colors. Therefore, the storage capacity per image is: 2 bits/pixel 320×200 pixels×─────── = 16 000 bytes 8 bits/pixel

45. ·超级VGA(SVGA，super VGA)支持1 024×768分辨率下24位颜色的表示。每幅图像所需存储空间为: • 24位/像素 • 1 024×768×─────── =2 359 296 字节 • 8位/字节 • The Super VGA (SVGA) offers resolutions up to 1024×768 pixels and color formats up to 24 bits per pixel. The storage capacity per image is: • 24 bit/pixel • 1024×768×─────── =2 359 296 byte • 8 bit/pixel

46. 视频加速芯片与SVGA视频适配合使用可以克服高分辨率和大量颜色带来的速度下降，从而降低了SVGA的使用代价[Lut94]。视频加速板使得原来仅在将大小为160×120的窗口中播放的图像扩展成全屏播放，因此，视频加速器提高了视频播放的速度和质量。视频加速芯片与SVGA视频适配合使用可以克服高分辨率和大量颜色带来的速度下降，从而降低了SVGA的使用代价[Lut94]。视频加速板使得原来仅在将大小为160×120的窗口中播放的图像扩展成全屏播放，因此，视频加速器提高了视频播放的速度和质量。 Low-cost SVGA video adaptors are available with video accelerator chips that pretty much overcome the speed penalty in using a higher resolution and/or a greater number of colors [Lutt94]. The role of video accelerator boards is to play back video that would originally appear in a 160×120 window at full screen. Hence, video accelerators improve the playback speed and quality of captured digital video sequences [Ann94c].

47. 电 视 传统系统 • 1.NTSC • 美国所制定的NTSC(National Television Systems Committee,美国国家电视系统委员会)标准是历史最久也是应用得最为广泛的一个电视标准。NTSC的色彩载波使用接近4.9MHz或3.57MHz的频率，它使用颜色载波进行正交调幅，画面运动频率约为30Hz，每幅画面有525线。 Conventional Systems • NTSC • NTSC National Television Systems Committee, developed in the U.S., is the oldest and most widely used television standard. The color carrier is used with approximately 4.429 MHz or with approximately 3.57 MHz. NTSC uses a quadrature amplitude modulation with a suppressed color carrier and works with a motion frequency of approximately 30 Hz. A picture consists of 525 lines.

49. 在NTSC制式的电视中，将4.2MHz分配给亮度频道，1.5MHz分配给两个色度频道，而家用电视和VCR给色度分配的频道只有0.5MHz。在NTSC制式的电视中，将4.2MHz分配给亮度频道，1.5MHz分配给两个色度频道，而家用电视和VCR给色度分配的频道只有0.5MHz。 • For NTSC television, 4.2 MHz can be used for luminance and 1.5 MHz for each of the two chrominance channels. Home television and VCRs employ only 0.5 MHz for chrominance channels.

50. 2.SECAM • SECAM(Sequential Couleur Avee Memoive [法语]，序列颜色和存储)标准主要在法国和东欧使用。与NTSC和PAL制式相比，它是调频的，画面运动频率为25Hz，有625线。 • SECAM • SECAM (Sequential Couleur Avec Memoire) is a standard used in France and Eastern Europe. In contrast to NTSC and PAL, it is based on frequency modulation. It uses a motion frequency of 25 Hz, and each picture has 625 lines.