by Staff Writer
Digital scanners are the ideal tool for digitizing documents, photos, slides and other materials. Scanners come in a variety of models, suited for business and home applications. This scanner buying guide will help you better understand how scanners work and what to look for in a quality document scanner of your own.
Document scanners: Also called sheet-fed scanners, these look more like a printer. Document pages roll past the scanner head, so you can scan many pages easily. You can only scan loose sheets with a document scanner, however. Some models are specifically designed to scan and read text documents.
Drum: Designed for professionals, this large-format color scanner rotates the document on a drum while a laser bounces a light off the document into a photo multiplier tube (PMT). This ultimate computer scanner produces a superb image. Unfortunately, prices start in the low five figures.
Film: Occasionally called a picture scanner or slide scanner, film scanners are specialized units designed to digitize film negatives, transparencies and similar non-paper items.
Flatbed: These scanners are the most common for small office and home use. A flatbed scanner works much like a copier, with a flat glass platform on which you place your documents or photos. A good flatbed scanner has a removable or adjustable lid so you can place odd-sized books on the scanner bed. You may also find flatbed photo scanners with high resolutions specifically for digitizing photos.
Handheld: Handheld scanners are great for scanning a few documents when away from the office. The scanner itself is usually about 10 inches long. Depending on the model, you simply pass the scanner light over the document or roll it across on a flat surface, like a table.
Portable: Portable scanners are often paired with laptops or netbooks, connecting through a USB port. They're typically sheet-fed devices and weigh as little as one pound.
Cable connections: Older scanners use a parallel port, a really wide connection that screws into the back of the computer. Most new model scanners use a USB connector. Large-format scanners have a FireWire (IEEE 1394) cable, which allows a higher data transfer rate.
Document feeder: Higher end flatbed scanners and sheet-fed scanners have an automatic document feeder which rapidly moves large numbers of pages through to be scanned.
Sensor: A scanner uses a light-sensitive sensor to capture reflected light from the scanned object; two types are common:
Charge-coupled device (CCD): This is similar to sensors used in digital cameras. CCDs use a mirror to bounce bright light off the page, exciting pixels and capturing an image. CCD scanners produce clearer, higher resolution images with good color reproduction.
Contact image sensor (CIS): These sensors are placed close to or in contact with the document scanned, bouncing light directly off the page through a lens to create the image. CIS scanners can be more compact, more durable and use less power than CCD scanners.
DPI: The image resolution that your scanner produces is measured in dots per inch (dpi). This is the maximum number of pixels that your scanner can produce in the digital image and the maximum resolution of any image you print from that file. The higher the dpi, the more crisp and detailed your scans will be.
Image file formats: Your scanner will probably be capable of saving scanned images in multiple digital image file formats. Some common formats include JPG, PNG, TIFF and BMP files. Certain scanners may also read and convert your files into TXT, PDF or RTF formats.
Optical character recognition (OCR): An OCR software package allows the scanner to read scanned text by recognizing printed characters in the image. This software continues to improve, allowing scanned documents to be searched for their content.