Magazine article Technology & Learning

Scanners Make the Grade

Magazine article Technology & Learning

Scanners Make the Grade

Article excerpt

Pictures may be worth a thousand words, but to get them into digital form, you need a scanner: Here's a rundown on how scanners work, and how teachers are putting them to work

Nothing brightens the appearance of student projects like an eye-catching picture. Popular integrated software applications often come with clip art for just that purpose. But when accessible choices don't quite fit the project, or students have neither time nor inclination to produce computer-drawn illustrations, a scanner can be a huge help.

Scanner Technology

Scanners come in all shapes and sizes. Yet all scanners do virtually the same thing: capture images from paper, photographs, transparencies, or slides, then translate scanned information into digital data for computer use.

Handheld, sheetfed, flatbed, and slide scanners typically have built-in microelectronic light-sensors for image detection. These photo-sensitive elements are called charge-coupled devices (CCDs). When a scanner's fluorescent or halogen light source passes over an image, CCDs interpret the color and intensity of light that bounces off. Grayscale scanners read this light only once. Color scanners take three readings (one for each red, green, and blue color filter).

"Three-pass" color scanners move a light source over an original image three separate times. On each pass, the scanner captures brightness information for a different color. With "single-pass" scanners, the light sensors read all three colors simultaneously. Once transferred to a PC or Macintosh, a scanned image may be displayed on the screen, edited, stored on disk, or printed.

"Handheld" scanners are generally the least expensive CCD-based scanners. They are T-shaped, with the upper portion of the "T" containing a scanning window measuring about four inches wide. The unit's handle sports an activity indicator light and scanning controls. To scan, you place the device on a document or image, check the alignment of the source material, press the start button, then slowly drag the scanner down the page. The activity indicator light will flash if you move too quickly. If your hand wobbles or you do not scan slowly enough, the image will distort. Source material cannot be wider than four inches, although some handheld scanners include software that allows you to "stitch" or merge together two four-inch-wide strips.

"Sheetfed" scanners produce higher-quality scans than handheld scanners. The user feeds an image under a stationary scanning device (much like a fax machine). Sheetfed scanners do not scan three-dimensional objects like coins or cloth, nor can they handle pictures mounted on thick paper stock, or pages in books. Sheetfed scanners are typically teamed with an automatic document feeder and optical character recognition software (see below) to convert large amounts of handwritten, typewritten, photocopied, or faxed documents into electronically formatted text.

"Flatbed" scanners are the most popular because they are flexible enough to handle both small and large, flat or even three-dimensional originals. With adaptations, they can accommodate transparencies as well. Lift the cover of the photocopier-like device, place an item to be scanned face-down on the glass, close the cover, then press Start. The unit's scanning mechanism passes under the image, capturing information as it moves.

"Slide" scanners scan images from transparent materials such as 35mm slides. They operate at much higher resolutions than either flatbed or sheetfed scanners, because a small 35mm slide image must be enlarged once it's digitized. It's not unusual for a slide scanner to record at least 2,700 dots per inch (dpi), compared to the 300 or 600 dpi resolution of a flatbed scanner.

Some scanners are so versatile that they do much more than simple scans. For example, some come with a copy utility that teams the scanner with a printer for photocopies. "Multi-function" scanners combine scanner, printer, copier, and fax functions into one desktop unit. …

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