 screen or monitor to displays. Video communications technologies rely on dividing an image into lines containing picture bits and transmitting them serially-one after the other. The video image is, therefore, a mosaic of light, and the tiles, or points of light, are called picture elements. The term is abbreviated to pel in broadcast TV parlance. Those in the fields of telecommunications and computing know them as pixels. A video monitor image is constructed before our eyes one pixel at a time. What looks like a continuously moving picture is actually a series of still images called frames. When a series of still image frames arrives fast enough, the images fuse in our minds and appear to be moving. The faster the frame rate, the better the fusion, and the smoother the motion will appear. Color subcarrier (odd harmonics of half-line frequency) Odd harmonics of half-line frequency Half-line frequency 453rd 455th 457th 459th 226th 227th 228th 229th Harmonics of line frequency Frequency Figure 5-9. Color Television Spectral Detail (Michel Bayard). In the early 1820s, Peter Mark Roget, a doctor who specialized in vision (and the father of the Thesaurus) began to experiment with the properties of human vision. In 1824, he delivered a paper to the Royal Society in which he introduced the concept of "persistence of vision." One can define it as the brain's ability to retain the impression of light after the original stimulus has been removed. The brain holds the light for about one tenth of a second, although it starts to fade almost immediately upon receipt. Therefore, if images are sent at a rate of at least 10 fps, they appear to be continuous, though somewhat jerky. Somewhere between 10-20 fps, the jerkiness disappears. A new image is presented long before the old one appreciably fades. The brain fails to perceive that the video monitor is actually just blinking images. The History and Technology of Analog Video A frame of video is displayed by reversing the camera's scanning process. A process called raster-scan p