How to Buy a Scanner
The Big Picture
Choosing a scanner entails balancing the quality of the output, speed, driver, and software bundle. Fortunately, even moderately priced scanners are acquiring advanced features like 4800-dpi resolution and transparency adapters.
Today's consumer scanners commonly have optical resolutions of 4800 dots per inch, and that's likely to remain the maximum you'll see for a while. Most home and business scanners tend to be inexpensive and have a fairly low profit margin, so instead of upgrading the core hardware, manufacturers are making scanners easier to use. On some of their models, for example, manufacturers have increased the number of slides or film negatives you can place in a template and scan at the same time. Epson offers Easy Photo Fix software, which when prompted attempts to correct signs of age in old photos, such as fading and changes in color.
Optical resolution: For displaying photos on the Web or printing 3-by-5 or 4-by-6 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 photo prints, or to enlarge smaller images, you'll have more flexibility in editing your image if you start with the highest possible resolution. Be warned, however, that high-resolution images take up a lot of hard-disk space--for example, a 2400-dpi, 4-by-6-inch photo can consume 50MB. In addition, 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 usually held in place with a template. Transparency adapters can be built into a scanner's lid, or they can be separate modules that plug in and sit on the scanner glass. A separate transparency adapter lets a scanner maker keep the lid thin or incorporate an automatic document feeder into the lid. Transparency templates come in different sizes: The smallest hold only one slide; many others are sized hold three slides, or to hold one or more 6-inch-long filmstrips; and some are big enough to accommodate one or more large-format transparencies.
Automatic document feeder: For handling high-volume optical character recognition or for scanning pages that are longer than a flatbed's scanning surface, an automatic document feeder can be helpful. ADFs are typically built into or replace the scanner's lid. Epson, HP, and Microtek offer aftermarket ADFs for some of their models, but the total cost (around $200) is higher than if you choose a scanner that includes an ADF at the outset.
Interface: Scanners typically come with a USB 2.0 interface (which is backward-compatible with USB 1.1 connections). Some scanners also offer a FireWire connection; however, FireWire models typically cost more and are designed for professional users.
Color depth: The amount of color (and grayscale) data a scanner can recognize and save, termed color depth, is measured in bits per pixel. Since a scanner can usually capture more data than its driver can save, you'll frequently see a qualifier appended to the bit-depth spec, such as 48-bit internal or hardware color, which describes how much data the scanner can recognize. External or true color describes how much data the scanner's driver can save. For almost all types of general-purpose use, 24-bit external color depth is sufficient.
Sensor technology: Flatbed scanners have one of two types of sensor technology: a charge-coupled device (CCD) or a contact image sensor (CIS). CCDs, the older technology, might sound familiar as they're also used in digital cameras. CIS sensors are a more recent innovation in scanners. Although they produce slightly lower-quality scanned images, CIS-based scanners can be much smaller and use far less power than CCD-based scanners. (CIS-based scanners can be powered through a USB cable.)
Scanner type: Most scanners on the market today are flatbed scanners, so named because the scanning surface is flat. With a flatbed scanner, you place the object you want scanned onto a slab of glass beneath a cover (much like a copy machine).
In addition to flatbed scanners, you'll also see sheet-fed scanners, handheld scanners, film scanners, and multifunction devices (also called "all in ones") that incorporate a printer, a scanner, and sometimes a fax machine. Sheet-fed scanners were once prevalent, but they have decreased in popularity because they're less versatile than flatbed scanners. They work best for individual text pages: Because you slide your document through a feeder, much as you do with a fax machine, photographs can emerge bent out of shape--and you can't cram a book through a feeder.
Software: All scanners come bundled with the necessary software for reading an object, capturing an image from the scan head, and transferring it to your PC. But once you have the image in your computer, you'll probably want to resize or crop it, adjust the brightness and contrast, or remove the red-eye effect flash photography creates.
Most scanners include simplified versions of image-editing software so you can touch up color imperfections and optimize the files for e-mailing or printing. Higher-end scanner models may include Adobe Photoshop for more extensive image manipulation. Additionally, many scanners also ship with optical character recognition, or OCR, software that allows you to scan a printed document and convert it to text that you can edit on your PC.