Another important criteria for evaluating a scanner is the unit's dynamic range, which is somewhat similar to bit depth in that it measures how wide a range of tones the scanner can record. Dynamic range is measured on scale from 0.0 (perfect white) to 4.0 (perfect black), and the single number given for a particular scanner tells how much of that range the unit can distinguish.

Most color flatbeds have difficulty perceiving the subtle differences between the dark and light colors at either end of the range, and tend to have a dynamic range of about 2.4. That's fairly limited, but it's usually sufficient for projects where perfect color isn't a concern.

For greater dynamic range, the next step up is a top-quality color flatbed scanner with extra bit depth and improved optics. These high-end units are usually capable of a dynamic range between 2.8 and 3.2, and are well-suited to more demanding tasks like standard color prepress.

For the ultimate in dynamic range, the only choice is a drum scanner. These units frequently have a dynamic range of 3.0 to 3.8, and deliver all the color quality one could ask of a desktop scanner. Although they are overkill for most projects, drum scanners do offer high quality in exchange for their high price.

While a high dynamic range is no guarantee of good scanning results (many other factors come into play), it is generally an indication that the scanner manufacturer is striving to please educated buyers by producing a higher-quality product. All other things being equal, go with the scanner that offers the higher dynamic range.