Scanners are input devices that are comprised of a Charge Coupled Device (CCD) array. This array is like a series of "eyes" that read and record light intensities and stores them in digital form. This is achieved when the scanners internal light source passes over the image that is being scanned.
Scanners come in three basic types. The simplest type of scanner is the hand held in which the scanning device is moved across images or text. A Page scanner works by inserting a page into the top of the scanner which is pulled via rollers through the scanner. The most common type of scanner is the flatbed scanner which allows you to place a image or document on the top of its surface, much like a photocopier.
Most scanners sold today use a plug-and-play USB or firewire connection. Older scanners typically used a SCSI, parallel, or proprietary connection method depending on the scanner model.
To scan a document, simply place it face down on the scanner's glass and close the lid. Most scanners will allow you to initiate the scan from the front panel or from the software/driver that is included with it. If you initiate the scan from the front panel, the software will open on the PC anyway. This software will allow you to control important scan settings that are discussed below:
Resolution - Scanner quality is measured in DPI or dots per inch. 300 DPI is usually adequate for normal scanning, however, modern scanners can scan at resolutions of 9600 DPI and higher. The higher the resolution, the larger the resultant scanned file will be.
Color Depth - This describes the number of bits of information that the scanner can use to describe each dot. The higher the bits, such as 36 and 48-bit scanners sold today, the greater the variations in color, shade, hue, etc. the scanner can reproduce.
Grayscale Depth - This is the same as color depth, but is a measure of how many shades of gray the scanner can reproduce. Once again, higher is better.
When buying a scanner, you need to take the above capabilities into consideration along with the scanner's speed and connection type.
Most scanning problems are the result of the scanner's glass getting dirty or getting fingerprints on it. The glass should be cleaned with a glass cleaner that does not have ammonia in it and a soft cloth. Do not pour or spray the cleaner onto the glass - spray the cloth lightly. Do not use any type of cloth that might scratch the glass.
Most scanners have a lock for the light assembly. Make sure you lock this when moving a scanner or you may damage the light assembly. Make sure you unlock this before you try to scan again.