| Dynamic Range The dynamic range of a scanner is an indication of the tonal range of the original image that the scanner is capable of capturing. By tonal range we mean the detail between the highlight and shadow areas. The dynamic range is expressed as a logarithmic value, thus a range of 2.0D is 100:1, 3.0D is 1000:1. and so on. For reflective originals a dynamic range of less than 2.0D is sufficient, however, for transparencies you need a much higher dynamic range scanner. The density range on a properly exposed transparency can be as high as 3.2D. If your scanner has a low dynamic range, what you will notice first is lack of detail in the shadow areas. Entry level scanners with transparency options typically have a dynamic range of 2.3D for transparency scanning. This is not sufficient for high quality scanning of transparencies but is sufficient for the office market and for position only work. These scanners are far better suited to reflective scans and line art scans at 600 dpi and below. Mid-level scanners have a dynamic range of 2.8D. This may not seem like a big improvement over the entry level ones, but remember this is a logarithmic scale so the difference is quite significant. It is, in fact, the difference between 200:1 and 650:1, or an increase in dynamic range by a factor or more than three. Thus the shadow details from scanners in this range are greatly enhanced. This makes the scanner more capable of fulfilling the expectations of the mid-level end of the desktop market. These scanners are typically 600 x 1200 ppi. Professional model flatbed scanners have a dynamic range of 3.0D to 3.2D and can capture two to four times the range of the mid-level scanners. These scanners are typically in the 1200 x 1200 ppi range with interpolation to 2400 for line art. How Much Dynamic Range Do I Need? The dynamic range you need depends on the type of original you use and the intended end-use of the scan. Vacation-type transparencies like slides tend to be more exposed and have low density ranges. If these images are to be used in a newsletter, a low end scanner might be sufficient. If the intended use is in a magazine where different film types and non-ideal conditions are encountered, then a mid-level scanner would be better suited. For professional studio shots, publishers are intent on getting the maximum quality from the film. Scanning these requires a drum scanner with a high dynamic range. Professional model scanners are used almost exclusively in the publishing market because of their raw scanning speed and ability to capture great detail throughout the tonal range.
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