istication. Nearly all allow conference participants to annotate shared images in real time with electronic tablets and styli. Applications sharing systems are more sophisticated. These permit users at different sites to interactively share, manipulate and exchange or markup files and move images. Some systems offer high-resolution graphics, including CAD support for engineers to collaborate on product designs, and to view concurrently computer simulations. Most are PC-based, and connect through data ports on the codec that allow them to share the audio/video data stream. Images can be scanned in, retrieved from files, or captured with cameras. When photorealism is required (X-rays, medical images and cases when an entire typed page or detailed diagram must be transmitted) enhanced-resolution systems Video Communications: The Whole Picture are required. These systems are available in monochrome or color and go beyond the PC VGA resolutions of 640H X 480V pixels to produce images containing 3-13 times more pixels. Television cameras cannot scan at such high levels of detail. In very high- resolution applications devices called scanners are required. Flatbed scanners resemble small photocopiers, and capture images that are placed facedown on the clear-glass surface, and scanned from underneath. The scanning area or size of the bed can affect the price of the scanner, particularly when scanners have a bed size of 11" X 17" or more. Within the scanner, one or more CCDs convert incoming light into voltages with amplitudes that correspond to the intensity of the light. Four-bit gray-scale scanners can capture 16 shades of gray; eight-bit gray-scale scanners can capture 256 shades of gray, and are often used in medical applications. Color scanners are usually required in multimedia work; they typically make three scanning passes, one each for red, green, and blue. A scanner should resolve an image at no less than 300 dots-per-inch. Images are stored on hard disk (requirements for saving images add up quickly), printed, 