当代通讯网正在迅速地向数字化方向发展。数字化技术虽然有许多根本性的优点,但是却占用很宽的频带。例如,若传输一帧中等分辨率的彩色图像,每帧含640×480个像素,每个像素以24位编码,每秒传输30帧,则传输速率为:640×480×24×30≈221.2Mb/s这样高的传输速率,不仅一般的电话网难以传输,就连现有的窄带综合业务数字网(NISDN)也难以胜任。因此,必须采用图像压缩技术,将可视电话或会议电视的活动图像信息加以压缩进行传输。 目前,有多种方法可以实现图像压缩。例如,JPEG(多灰度静止图像和数字压缩编码)方式主要是为静止图像设计的,但在会议电视的场合下,由于活动信息较少,也可以采用。JPEG方式的压缩比约为40∶1。此外还有MPEG方式和 Contemporary communications networks are rapidly moving toward digitization. Although there are many fundamental advantages of digital technology, but it occupies a very wide band. For example, if a frame of medium resolution color image is transmitted with 640 × 480 pixels in each frame and each pixel is encoded in 24 bits at 30 frames per second, the transmission rate is: 640 × 480 × 24 × 30≈221.2 Mb / s such a high transmission rate, not only the average telephone network is difficult to transmit, even the existing narrowband Integrated Services Digital Network (NISDN) is not competent. Therefore, the image compression technology must be used to compress the moving picture information of the videophone or the conference television for transmission. Currently, there are many ways to achieve image compression. For example, the JPEG (multi-grayscale still image and digital compression coding) method is mainly designed for still images, but in the case of a videophone, the activity information may also be used less. The JPEG compression ratio is about 40: 1. In addition there are MPEG methods and