Image scanners are devices that scan two-dimensional (2D) objects and convert them into digital images. They often use a charge-coupled device (CCD) or contact image sensor (CIS) as their imaging-sensing component. Most image scanners read red-green-blue (RGB) color from an array, and then transfer the scanned image to a computer. Product specifications include the way in which the image scanner physically connects to the computer, and the way in which data is retrieved from the scanner. Connection types for image scanners include parallel, small computer systems interface (SCSI), universal serial bus (USB), and IEEE 1394 or FireWire (Apple Computer). There are many types of image scanners. Examples include drum scanners and flatbed scanners. Drum scanners use upon photomultiplier tubes (PMT) instead a CCD or CIS. Operators place the object to be scanned upon a large, glass drum with an acrylic cylinder that rotates at high speeds. The ability to control aperture and sample-size make drum scanners a good choice for applications that require the enlargement of originals. Unlike drum scanners, flatbed scanners use CCDs and a flat glass pane called a platen. A xenon or cold cathode fluorescent light is used to illuminate the pane. Color flatbed scanners are image scanners with separate sensor arrays with red, green, and blue filters. Film scanners and hand scanners are common types of image scanners. Because they are not designed to scan large areas, film scanners usually provide better resolution than film scanners. With film scanners, uncut strips of film are fed into a carrier which is moved by a stepper motor. Hand scanners are used to scan the surfaces of documents, and in digital design applications. Handheld document scanners are designed to be dragged across the surface of the document to be scanned. Although most devices are monochrome, color hand scanners are also available. Three-dimensional or 3D image scanners are used for industrial design instead of document scanning. Planetary scanners are specialized image scanners that are used in archival applications. Unlike flatbed scanners, which come in contact with a significant part of the object to be scanned, planetary scanners make minimal contact. Designed for use in archives and museums, these image scanners work at a very high rate of speed and do not require books to be open to long periods of time.