ng a telecultural shift, with the introduction of interactive television. Before we begin our detailed discussion of video compression and DTV stan- dards, it makes sense to provide a brief explanation of the key parameters that deter- mine not only the viewing experience but the bandwidth required: Number of pixels on a screen-A pixel (which is short for picture element) is one of the thousands of small rectangular dots that comprise television and computer screen images. Basically, the more pixels per screen, the greater, or better, the resolution-that is, the more defined, detailed, and crisp the image appears. Frame rate-The frame rate is a measure of how fluid or natural the motion onscreen appears. As a quick reference, motion pictures use 24 frames per second (fps), the North American NTSC television standard uses 30fps, and the European PAL standard uses 25fps. (Television standards are discussed later in this chapter.) Number of bits per pixel-The number of bits per pixel is a measure of the color depth; the more bits per pixel, the more colors can be represented. Remember that the human eye can perceive more than 16 million colors. A digitally encoded image, using 24 bits per pixel, can display more than 16 million colors, providing a rich and natural experience. As we talk about compression techniques and digital television standards, you will notice that most of the standards define the number of pixels and frames per sec- ond that can be supported. Multimedia Networking Requirements Video Compression To make the most of bandwidth, it is necessary to apply compression to video. Full- motion digital video needs as much compression as possible in order to fit into the precious spectrum allocated to television and wireless communications, not to men- tion to fit on most standard storage devices. Moving Picture Experts Group (MPEG; www.chiariglione.org/mpeg) is a working group of the International Organization for Standardization (ISO; www.iso.ch) and the International Electrotechnical Commis- sion (IEC; 