An image scanner is a device designed to scan pictures, text, or objects and convert them into digital images. The main types of image scanners include flatbed, hand, film, and drum scanners. Flatbed scanners, commonly found in Xerox machines, involve placing an object or document on a glass pane covered by an opaque lid. A sensor and light move along the pane, capturing the reflected image, and the cover prevents external light interference.
There are three primary types of image scanners: hand scanners, film scanners, and drum scanners. Hand scanners, available in document or 3D forms, require manual movement across the object or image to be scanned. Once an image is scanned, the data is processed and sent to a computer. Most scanners read red-green-blue (RGB) color from the color array, with color depth typically at least 24 bits, and higher-quality models offering 48 bits or more. The resolution of the image is measured in pixels per inch (PPI).
Image scanners produce light using green LEDs to highlight and scan the image onto a computer for viewing. 3D scanners, a popular form of hand scanners, compensate for uneven hand movements using reference markers. Film scanners, used in photography and slides, capture images by moving film strips or slides across a lens and sensor, often employing charge-coupled device (CCD) arrays for image capture.
Drum scanners use photomultiplier tubes (PMTs) instead of CCD arrays and can gather image information from both transmissive and reflective originals. They are mounted on an acrylic cylinder that rotates while passing the object in front of precision optics, transferring image information to the PMTs. In summary, image scanners play a vital role in converting various physical content into digital formats, each type catering to specific applications and requirements.