How to buy ... a scanner

Once the domain of imaging and publishing professionals, scanners are now a common PC peripheral for home users. If you want to email a photo taken with a film camera to friends, use a scanner. Need to convert a hard-copy document into digital form so that you can edit it? A scanner can do that, too. But as with any PC-related purchase, it pays to know what you need before you dish out any cash. Whether this is your first scanner purchase or you want to upgrade to a better-quality device, this guide will provide the information you need.

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, transparency adapters, and USB 2.0 connections.

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. HP, for example, will add a 4-by-6-inch photo feeder to an upcoming model so you can scan snapshots faster; Epson is incorporating its Print Image Matching technology into newer units, which will simplify colour calibration between the scanner, your system, and Epson printers. Support for Windows XP is universal among new models, and we have encountered no compatibility problems in our testing.

Key Features

Optical resolution: For displaying photos on the Web or printing 3 x 5 or 4 x 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 x 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 x 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 for three slides or a 6-inch-long filmstrip, 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 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.

Colour depth: The amount of colour (and grayscale) data a scanner can recognize and save, termed colour 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 colour, which describes how much data the scanner can recognize. External or true colour describes how much data the scanner's driver can save. For almost all types of general-purpose use, 24-bit external colour 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 peripherals that incorporate a printer, scanner, and fax machine into one device. 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 colour imperfections and optimize the files for emailing 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.

The Specs Explained

As with any piece of high-tech equipment, a scanner's specifications can't tell the whole story. But you can use price, along with resolution, colour depth, and other specs, to weed out the ones you don't want. With scanners in particular, higher prices indicate better components--so you really do get what you pay for.

When reading the resolution figures, note that the lower of the two numbers indicates how many dots the scanner can capture in each linear inch of the scan head (called the optical resolution). The larger number is the number of "lines" the head captures as the head scans each inch of the photo or document.

In general, ignore interpolated resolution, which uses software to add more information to an image. This attempt to sharpen images is generally not very useful.

On high-end scanners you may see a specification for dynamic range (or Dmax)--this indicates the sensitivity of the device in accurately rendering the lightest and darkest colours and shades in an image. Dmax readings of 3.2 or higher are considered good. It's worth noting that Dmax is a logarithmic system, so a scanner with a 3.6 or 4.2 rating has a significantly better dynamic range than a 3.2-Dmax-rated scanner.

Scanner Shopping Tips

For most uses, go flatbed. These common models are easy to use and versatile enough for most tasks.

Handhelds find their niche. A handheld in the $200 to $300 range may work for you if you plan to scan short text passages frequently. Students and lawyers, take note: A handheld scanner will save you money over the long run if you often have to pay to make copies at libraries that don't allow you to remove books from the premises.

Look for at least 2400-dpi optical resolution. Although these models cost a bit more than lower-quality units, they are worth the investment. Scanners with this level of resolution and colour depth allow you to make reprints using state-of-the-art photo printers that will be almost indistinguishable from reprints made by photo outlets. Even if you don't need these capabilities now, it's better to anticipate growing needs rather than having to buy another new scanner when you need better resolution.

Check your PC's USB port. Almost all scanners can connect to a PC through a USB port. If you have a computer that is more than a couple years old, it likely has a USB 1.1 port. Current scanner models have USB 2.0 connectivity, which provides faster transfer speeds. To use a USB 2.0 scanner at its optimum transfer speed, you'll either have to buy a new PC that has USB 2.0 ports or install a USB 2.0 card in your PC. Bottom line: If you scan a lot of large, high-resolution images, a fast interface can save you a lot of time.

One-touch buttons are a plus. Find a model that has preprogrammed buttons for photo scanning, emailing, and other common tasks. One-touch buttons can save you time and effort if you scan a lot of items.

Advanced options get big jobs done. For business users and others who do high-volume or specialty scanning, advanced options such as automatic document feeders, transparency adapters, and a scan bed large enough for legal-size documents can make all the difference. Legal-size scan beds are also a huge plus for scanning large illustrations, diagrams, paintings, and labels (on product boxes, for instance), as well as tabloid-size pages.