 | in scanners |
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Color depth |
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This tricky phrase refers to the number of bits captured per pixel, which correlates with the number of possible colors. Manufacturers always give the internal color depth, typically 48 bits, rather than the output color depth, which is limited by the 24-bit maximum that most applications can handle. This translates to a photorealistic 16,777,216 colors. (Adobe Photoshop is among the apps that can handle up to 48 bits of image data.) Higher internal color-depth numbers generally result in better images, but the real test of an inexpensive scanner is how well it converts the scan to 24-bit output. That can be determined only by viewing the results. |
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Optical resolution |
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A scanner's optical resolution refers to the maximum number of dots per inch (dpi) a scanner can capture. With commodity flatbed scanners, the optical resolution ranges from 600x600dpi to 1,200x2,400dpi. The low end of that range generally works fine, even for scanning and printing photographic images the same size as the original (in fact, 300dpi will do). But if you want to scan small originals and enlarge them--photographic slides, for example--look for a resolution on the high end. Scanners with resolutions of more than 1,200x2,400dpi cater to professionals and cost a lot. |
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Interpolated resolution |
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A largely meaningless but widely used specification, the interpolated resolution derives from a software process that fills in spaces between scanned dots with other, artificially generated dots. Pay attention to this number only if you plan to scan line art and enlarge it dramatically (or send it to a phototypesetter) since interpolation can in some cases eliminate jagged fine lines. Commodity flatbed scanners typically offer interpolated resolutions of 9,600x9,600dpi, though some claim 19,200x19,200dpi. Either should be plenty. |
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Maximum supported media size |
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This spec is also known as the maximum scan area. Low-cost flatbed scanners, now commodity items, scan media up to 8.5x11 inches (letter-sized) or 8.5x11.7 inches (A4-sized). A handful of inexpensive scanners handle 8.5x14-inch (legal-sized) media. Photo scanners generally accept media no larger than 5x7 inches, but ordinary flatbeds produce scans of equal quality. Film scanners, designed for slides or negatives only, generally do better than flatbeds that come with slide adapters. Scanners that support large media, such as 11x17 inches (ledger size), cost thousands and are for professional use. |
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Scan element type |
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The technology used to capture an image can make a difference. Most ordinary flatbed scanners use a CCD (charged coupled device) scanning element, but some compact scanners use the smaller CIS (contact image sensor). All things being equal, scanners that use a CCD produce better results. |
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Service and support |
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Most major scanner manufacturers offer a one-year warranty on parts and labor. In addition to thorough printed and electronic documentation, the scanner should include technical support via telephone, e-mail, and the Web. A toll-free number and 24/7 telephone support are less common. |
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