Consider how much resolution you need. If you scan only printed graphics, text documents and original photos (to the same size), the most you'll need is 1200-dpi. (You can always lower a scanner’s setting to the resolution required--and you should, to keep scan times short and file sizes small.)

For enlarging photos or graphics, or scanning film and slides, 2400-dots-per-inch (dpi) is the minimum you’ll need, but you’ll get better results with 3200 dpi and up. The higher resolution allows you to capture more detail when enlarging a 35-mm original or zooming in on a portion of an image. In our film and slide tests, we got the best (very good) performance with a 6400-dpi model. But the best 4800-dpi models produced good results, and prints from those scans would look much the same as those from better performers, providing they were printed only as 4x6s. If you plan to print images larger than 4 by 6, however, consider a model with higher resolution. Color-bit depth is another spec to watch if you’re enlarging prints or scanning negatives or slides. The greater the color-bit depth, the better the scanner can differentiate among subtle gradations of shading; 24-bit (8 bits per color channel) is basic, 48-bit (16 bits per channel) is better.

When comparing specs, focus on native optical resolution. “Interpolated” or “enhanced” resolution comes in handy only for scanning line art.

Resolution isn’t everything, however. As with a camera’s megapixels, a scanner’s resolution is only one component of performance; sensors, circuitry, and other design also comes into play.  In our recent tests, performance tracked roughly with resolution, but one 3200-dpi model outperformed some 4800-dpi scanners.

Choose quality and speed that suit your needs. Most of the tested scanners did very well at reproducing a color photo at 300 dpi. Those judged good produced decent but less crisp scans, with less accurate colors. Fewer models did well with film.

Speed matters if you expect to be scanning regularly. In our tests, the fastest took about 11 seconds to scan an 8x10-inch photo at 300 dpi, while the slowest took about 30 seconds.

Don’t sweat the software. All the scanners we tested came with software for scanning, image editing, and optical character recognition for scanning text into a word-processing program. Some have software for making digital photo albums or other projects.

Automated buttons let you perform frequent tasks, such as scanning an image for e-mail, with one touch. You can handle other tasks, such as adjusting brightness or contrast, through the software.