Guide to Scanner Specifications
The first step in making a good purchasing decision on anything is to understand the specifications of the product and what they mean. Reading that a scanner has a 4800 dpi is basically meaningless to you if you have no idea what dpi is.
You don’t have to be a total technological guru to decipher the basics of scanner specifications, however. Take a few moments to review the basic definitions and you’ll be armed with all of the knowledge you need to find the best scanner for your situation.
Resolution
The term resolution refers to nothing more than the quality a scanner is able to produce based on how many pixels it is able to sample. Resolution takes place on a grid, and the number used for dpi (dots per inch) refers to how many squares are contained within that grid.
Most common flatbed scanners have a resolution of at least 1200 dpi. Remember that no matter how many times the scanner head is programmed to stop, the resolution will never be more than how many sensors are contained in the head, so the lowest number is all that matters. A 1200 X 2400 dpi scanner will still only produce a 1200 dpi image.
Bit-Depth
Bit-depth is simply the amount of information a scanner is capable of recording for every pixel it looks at and is responsible for the colors a scan can produce. Low bit scanners can only see black and white and generally produce low quality scans. Most color scanners today operate at 48 bits, although some manufacturers are still making lower bits of 24 and 36 available.
There are some compatibility issues with these very high bit depths, however, as most personal PCs are not able to handle the amount of information. 24 bit is very close to photo quality and is sufficient for the purposes of most but most of the newer flatbed scanners seem to come with 48 bit.
Dynamic Range
Dynamic range is similar to bit-depth, but focuses on the range of colors a scanner is capable of capturing. Higher dynamic ranges mean truer colors. It is measured from perfect white to perfect black, 0.0 to 4.0 respectively. Most flatbeds offer 2.4, which is good enough for most personal projects, but does not produce high photo quality. For that, you will need 3.2 or higher.
Scanning Method
There are two types of scanning methods that are used: the charge-coupled devices, or CCDs, and contact image sensors, or CIS. CCSs produce higher quality images because they use an intricate sensor, light, photo cells, and mirror approach to capture the image to be scanned. They are generally what would be found in a traditional flatbed scanner. CIS, on the other hand, use only light and a single row of sensors in very close proximity to the document, creating an ultra thin scanner, but one that does not produce as high quality of an image.
Scanning Area
The scanning area quite simply refers to the document size a scanner is able to accommodate. Sheetfed scanners can generally handle any sized document while flatbed scanners are limited to their size. Most will only accommodate standard letter sized paper, but large flatbed scanners will be able to scan letter-sized documents as well as 11×17 inch documents.
Scanning Speed
Short of taking a scanner for a test run, it can be difficult to determine the speed since there is no established standard. Generally speaking, however, higher quality resolutions will require longer scanning times than low resolution scans. Scanning software usually allows you to choose the resolution you wish to scan at, so for non-images you can go faster by choosing a lower resolution.
Speed may be more important to you if you have the need to scan many items a day. Document scanners are usually the fastest at scanning because of their auto-feeding features. Scanning with a flatbed scanner will always take longer.
The Bottom Line
You should not make the mistake of focusing in on any one of these specifications in scanner reviews to determine the overall quality of a scanner. Each of them is important for determining the ultimate quality of an image. A high resolution with a low dynamic range may produce excellent quality document scans, but will disappoint you if you are looking to scan photos. Consider what your needs are and focus on getting the highest specs that are vital to that purpose and you will have the best scanner.
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