• Do you want it to provide visual enhancements to your e-mail, your Web page, or your holiday greetings,?
• Do you want to use the scanner primarily to turn your computer into a fax machine?
• Or are you a graphic artist, needing quality images that will be included in your newsletter?

You must also decide how precise you need your scanner to be. This precision is measured as the scanner's resolution. Scanner resolution is measured in terms of dots per inch (dpi).

Think of each dot as an element of a picture that the scanner has scanned You also must decide how precise you need your scanner to be. This precision is measured as the scanner's resolution. Scanner resolution is measured in terms of dots per inch (dpi). A scanner with a high resolution is very precise, while a scanner with a lower resolution is less so. The more elements of a picture that a scanner can detect, the more detailed the picture will be and the higher the resolution will be.

On the scan head in each scanner, there are a certain number of sensors. As the scan head passes under or over the document or image, it stops, - too briefly to be detected - a number of times so that each sensor can take a picture.

The amount of resolution a scanner can produce depends on how many electronic sensors it has on its scan head and how many times it will stop as it moves across the original document or image. If the scanner had 600 sensors for each inch of the scan head, the resolution would be specified as 600 x 600dpi.

Different applications require the use of different types of scanners and each type of scanner has unique features and comes in a different price range.

How Scanners Work

Scanners work a lot like copy machines. But instead of immediately outputting an exact copy of the image, scanners send the information about the original to an electronic storage device connected to a host computer. Most scanners shine a bright light on to an original document or image and then measure the information that is reflected back into the scanner.

These electronic sensors respond to even the slightest variations in light intensity. Some of these sensors are sensitized to various colours; they use filters to block certain colours, which allows other colours to be measured more easily. Or they use prisms to separate the light into colours. Those that use prisms are known as beam splitters and are generally regarded as superior

There are six distinct types of scanners:

• handheld
  
• flatbed
  
• sheetfed
  
• photo drum, and
  
• slide.

Each of these styles has its own practical applications and limitations. Theoretically, you could also include digital cameras as a type of scanner.

Handheld: Once very popular with professionals and hobbyists, these have become less popular, primarily because flatbed and sheetfed scanners have decreased in price. To use a handheld scanner, which looks like a small vacuum cleaner attachment, you simply pass the scanner over the image you want to scan. The drawbacks are obvious.

First, you must move the scanner across the image in one fluid and steady motion.

Second, images wider than the scanner must be stitched back together by software, with varying results.

With the recent drop in prices for flatbed and other scanners, the days of the handheld scanner would appear to be numbered.

Flatbed: The flatbed scanner is the copier's closest cousin. Just as with the copier, you place an image or document on the glass scanning surface, and it remains in place while a mechanically driven scan head passes underneath it. Flatbed scanners provide a much more stable scan than can be produced by either handheld or sheetfed scanners.

Sheetfed: One of the drawbacks of the flatbed scanner is its footprint (the area it takes up on the desk). Users who cannot afford the space a flatbed scanner requires will appreciate the smaller footprint of the sheetfed scanners. These scanners are best for those who only need a scanner as a digitizing device for fax documents, or for keeping a digital record of printed documents.

Photo:This style is a spin-off from the sheetfed family of scanners. Most are relatively low resolution, and are limited to scanning photo prints or similar sized single-sheet reflective originals. Because they are limited in what they can scan, their practical applications are limited. But they are suitable for those who just want a quick scan of a photo to post on a Web page.

Drum: The most efficient and by far the most expensive scanners are the drum scanners. These are used primarily in the publishing industry to digitize the images that appear in books and magazines and are printed on high-quality printing presses.

Slide: Because photographic slides are small and require much higher scanning resolutions than larger documents and images, slide scanners were developed. These scanners are dedicated to scanning only transparencies: either photographic negatives, or slides. They have no capacity for scanning other originals. These slide scanners are in use by many photographers and publishers because they produce high-quality scans.

A scanner is a piece of hardware with which you produce a raw product. After you have created the product - a computer file containing digital data that represents a scanned inage, the image must then be processed to be used in publications, faxed, or read as text.

Drivers: To complete the process from the scan to processed image, the software driver is needed that allows the scanner and the computer to communicate. The driver lets you tell the scanner what to do and where to put the scanned information. Most scanners today are compatible with the TWAIN standard. (TWAIN which stands for "Technology Without An Interesting Name," allows different applications to communicate with the scanner.)