t of the United Nations) defines a digitized version of NTSC in its Recommendation CCIR-601 in which 525 vertical lines are each painted with 720 horizontal pixels (For more on CCIR-601, please refer Coding and Compression to Appendix C). HDTV in North America will have yet a different resolution, as will that little window on the PC that contains video clips downloaded from the World Wide Web. To match image-sharpness with application requirements, one can use various pixel reduction techniques. One approach is to shrink the viewing window using a technique known as scaling. Scaling works because smaller viewing areas require fewer pixels. The image displayed in a quarter-screen PC monitor is painted with far fewer pixels than the 27-inch monitor on a videoconferencing room-system requires. Reducing the frame rate is another way to compress a motion video sequence. Although the NTSC standard calls for 30 frames per second, one rarely gets 30 in a videoconference, especially when using a desktop system. When there is little or no motion taking place on the distant end, one may receive 15 to 20 frames per second, possibly even more. However, the moment someone moves the camera, or gets up and walks across the room, a flood of new bits must be shipped to the receiving end and the frame rate drops substantially. Dropping the frame rate allows transmission bandwidth to be significantly compressed with little corresponding degradation. Unlike a car race, most business related video applications include limited motion. Nevertheless, even business meetings can generate more motion than a low-bandwidth channel can accommodate. A person who is rising from a chair and walking to a whiteboard will translate to a large amount non-zero information that must be sent. It may begin to exceed the channel's bandwidth. At that point, some of the signal must be discarded. As more and more people get up and walk around, the codec gets frantic. It eventually falls behind, discarding excessive numbers of frames. The picture degrades to