quency of elec- tricity in the United States. By the same token, PAL relies on a scan rate that is very close to 50 Hz, the standard in Europe. This odd-even alternation of fields is called interlaced video. Many monitors, on the other hand, use a technique called progressive scan, in which the entire screen is painted 30 times per second, from top to bottom. This is referred to as noninterlaced video. Noninterlaced sys- tems tend to demonstrate less flicker than their interlaced counterparts. Computers often rely on variable graphics array (VGA) monitors, which are much sharper and clearer than television screens. This is due to the density of the phosphor dots on the inside of the screen face that yield color when struck by the deflected electron beams, as well as a number of other factors. The scan rate of VGA is much higher than that of traditional television and, therefore, can be noninterlaced to reduce screen flicker. Another quality factor is color resolution. Most systems resolve color images using a technique called RGB-for the red, green, and blue pri- mary colors. While video does rely on RGB, it also uses a variety of other resolution techniques, including YUV and YIQ. YUV is a color scheme used in both PAL and NTSC. As noted previously, Y represents the lumi- nance component; U and V-hue and saturation, respectively-make up the color component. Varying the hue and saturation components changes the color. Image quality plays a critical role in the final outcome, and the actual resolution varies by application. For example, the user of a slow scan, desktop, videoconferencing application might be perfectly happy with a half-screen, 15-frame-per-second, eight-bit image, whereas a physician using a medical application might require a full frame, 768-by-484 (the NTSC standard screen size) pixel image, with 24-bit color for perfect accuracy. Both frame rate (frames per second) and color density (bits per pixel) play a key role. Finally, spatial resolution comes into the equation. Many PCs have displays tha