A slide scanner is a device that is designed to digitize slides and negatives. There are different types of scanners to suit different requirements namely Flatbed Scanners, Hand-held Scanners, Drum Scanners and Sheet-fed Scanners. To scan, place the slide on the scanner. Most of the scanners come with a holder to keep the slides in place, while few have the capability of supporting multiple slides for sequential scanning. The carrier, which is the place where the slides to be scanned are kept can be plastic or metal. Common light sources for slide scanners include LED lights or fluorescent bulbs Either ways, the source of light will be regulated to ensure the lighting is consistent throughout 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 a bunch of diodes, being light sensitive are also responsible for converting analog light to digital signal. Slide scanners are classified into sequential array scanner and full frame sensor. Sequential scanner divides the slide into units for scanning and comes with three rows of sensors. Red, Blue or Green light is measured by each row. Full frame sensor and sequential array have separate sensors for colors yet vary in one aspect. The slide or the sensor is not moved when capturing the image. The carrier moves the slide across the light source and sensor assembly or moves the assemble over the slide. The moving rate of a carrier is determined by, electrical stepping motor which uses a drive belt or a rack and pinion system. With a variation in sensor also comes a variation in scanning process. Light source is on the opposite side and passes through the slide when using a sequential sensor. First step is calibration where measurements of calibrate color balance, contrast and brightness are determined. The the carrier positions itself at the portion where scanning is to be done. The image is divided into portions or "slices" for scanning in sequence. 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 image is then moved to a specified location and scanned as a whole. Once scanning is done, the files are transferred to a computer using a USB or Fire Wire. Scanner is not only for digitizing images but also for high-quality output. DPI or "dots per inch" determine the clarity of the scans. 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.
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