Instead of megapixels, the numbers game for scanners starts with optical resolution—how many pixels or how fine a grid the sensor uses to convert the source to digital data, with higher resolution meaning more detail (but slower scanning and larger image files). Horizontal and vertical resolution are listed in dots per inch; 300 dpi may be fine for line art, but photo imaging calls for as much as you can afford, whether it’s 1200 x 2400 dpi; 3600 x 7200 dpi; or more.

Enhanced or interpolated resolution means the scanner can conjure up more pixels than its sensor can actually see—inserting gray dots between black and white ones, so to speak, to produce images at resolutions as high as 19200 dpi. It isn’t as ugly as a camera’s digital zoom, but it’s no substitute for optical resolution.

The other important number (and another factor in file size) is bit depth. The more bits of data assigned to each pixel, the more colors and tones to choose from. Civilian scanners are usually content with a 24-bit palette—a range of 16.7 million colors— but design shops crave 48-bit color depth … with over 281 trillion possible colors.

SIDEBAR: Before you buy
1. If you sometimes import images from 35mm slides or negatives, many generalpurpose flatbeds come with an adapter or holder (like the “photo door” built into the lid of HP’s Scanjet 4070) for scanning transparent materials. If scanning transparencies is a frequent part of your job, however, a specialized or dedicated slide scanner will give you better results.

2. A flatbed document scanner turns printed or typed pages into PDF or other archive files, or works with optical character recognition software to turn pages into editable word processing files. For the latter jobs, you’ll want a flatbed model with a sheetfed-style automatic document feeder that lets you do other work instead of inserting and removing pages one at a time.

Top and middle: HP Scanjet 4890; bottom: Canon LiDE 60