Buyers' Guide to Scanners

Key Features

Optical resolution: For displaying photos on the Web or printing snapshots, 100 dots per inch is plenty of resolution; for capturing text using optical character recognition, 300 dpi is standard; any scanner on the market can easily perform those tasks. But if you want to make 8-by-10-inch or larger prints, or enlarge smaller images, opt for a scanner with 1200 dpi or 2400 dpi of optical resolution. You'll have more image-editing flexibility if you start with the highest possible resolution. Be warned, however, that high-resolution images take a lot of hard disk space--even a modest 1200-dpi, 2-by-2-inch photo can consume 17MB. Also, scanning at high resolutions tends to take longer.

Transparency adapter: Scanning slides or film requires a transparency adapter--a light source that shines through the film, which is normally held in place with a template. Transparency adapters can be built into a scanner's lid, or they can be separate modules. The separate adapters let scanner makers keep the lid thin or put an automatic document feeder into the lid. Transparency templates come in different sizes: Many are sized for three slides or a 6-inch-long filmstrip, and some are big enough for one or more large-format transparencies.

Automatic document feeder: An automatic document feeder is helpful if you need to handle high-volume optical character recognition or scan extra-long pages. HP and Microtek sell aftermarket ADFs (for around $200) for some models, but buying a scanner and ADF separately is more expensive than purchasing a scanner that includes an ADF at the outset.

Interface: Scanner makers are currently releasing products that come with USB 2.0 interfaces (which are backward-compatible with USB 1.1 connections). We have not seen great speed jumps from USB 2.0 scanners so far.

Color depth: The amount of color (or gray-scale) data a scanner can recognize and save, called bit depth, is measured in bits per pixel. Since a scanner usually can capture more data than its driver can save, you'll frequently see bit depth qualified with a term such as internal or hardware, referring to how much data the scanner can recognize. External or true bit depth describes how much data the scanner's driver can save. For almost all forms of general-purpose use, 24-bit external color depth is sufficient.