Slide Scanner is the equipment invented to digitize slides and negatives. Flatbed Scanners, Hand-held Scanners, Drum Scanners and Sheet-fed Scanners are different variations of a slide scanner and utilized for different purposes.
The slide that is to be scanned is placed in a scanner. While most of the scanners come with a slide holder, few also feature multiple slide scanning option for sequential scanning. The place where the slides are placed in the scanner is called a carrier and can be of metal or plastic. Scanners use LED lights or fluorescent bulbs for light Irrespective of the source, the lighting remains consistent during the scanning process. Sensors perform the function of converting analog light passing through the scan to digital format. The slide scanner sensors vary with type of scanner. CCD (Charged Coupled Device) array is the sensor that is used often. Sensors have several diodes which are light sensitive and perform the function of converting analog light to digital signal.
The two main classifications of a slide scanner are sequential array scanner and full frame sensor. Sequential scanner divides the slide into units for scanning and comes with three rows of sensors. Each row is meant to measure red,blue or green light. Full frame sensor and sequential array have separate sensors for colors yet vary in one aspect. It's the way the slide is scanned, the entire slide is captured without any movement in sensor or slide. Almost all scanners come with a carrier, which either moves the slide across the light source and sensor assembly or moves the assemble over the slide. Carrier moves constantly and it's moving rate is calculated by electrical stepping motor that uses a drive belt or a rack and pinion system.
With a variation in sensor also comes a variation in scanning process. For a sequential sensor the slide is kept on the carrier and light source will be the opposite direction enabling light to pass through the slide. The first is calibration which means the calibrate color balance, contrast and brightness are determined. The the carrier positions itself at the portion where scanning is to be done. Scanning is done in a sequence, which means portions or "slices" of the image are taken. After scanning is done, they are then arranged systematically and transferred to a PC. Slide carrier is taken into the carriage for scanners that come with full frame sensor. The scanner then scans the image as a whole after it's moved to the pre-defined location. Once scanning is done, the files are transferred to a computer using a USB or Fire Wire.
Scanning is done for two reasons: digitizing images and to get a clearer picture of them. Resolution of a scanner is an important aspect as the clarity of the scans will be proportional to the "dots per inch" or DPI. A scanner with 300 DPI or more is ideal. With the innovation of slide scanner, you no longer need to preserve the documents as they can be easily digitized.