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You can use a scanner to make digital copies of existing paper photos, documents, drawings, and more. Better scanners give you the option of copying directly from a photographic negative or slide, providing images of stunning visual quality—assuming the original photo was halfway decent, of course! In this section, you’ll look at how scanners work and then turn to what you need to know to select the correct scanner for you or your clients.

How Scanners Work

All consumer-level scanners—called flatbed scanners—work the same way. You place a photo or other object facedown on the glass, close the lid, and then use software to initiate the scan. The scanner runs a bright light along the length of the glass tray once or more to capture the image. Figure 18-29 shows an open scanner.

Figure 18-29 Scanner open with photograph face down

The scanning software that controls the hardware can be manifested in a variety of ways. Nearly every manufacturer has some sort of drivers and other software to create an interface between your computer and the scanner. When you push the front button on the Epson Perfection scanner in Figure 18-30, for example, the Epson software opens the Photoshop program as well as its own interface.

You can also open your favorite image-editing software first and choose to acquire a file from a scanner. Figure 18-31 shows the process of acquiring an image from a scanner in the popular shareware image-editing software, Paint Shop Pro. As in most such software, you choose File | Import and then select a source. In this case, the scanner uses the traditional TWAIN drivers. TWAIN stands for Technology Without an Interesting Name—I’m not making this up!—and has been the default driver type for scanners for a long time.

Figure 18-30 Epson software with Photoshop open in the background

At this point, the drivers and other software controlling the scanner pop up, providing an interface with the scanner (as shown in Figure 18-31). Here you can set the resolution of the image as well as many other options.

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NOTE In addition to loading pictures into your computer, many scanners offer a feature called optical character recognition (OCR), a way to scan a document and have the computer turn the picture into text that you can manipulate by using a word processing program. Many scanners come with OCR software, such as ABBYY FineReader.

Figure 18-31 Acquiring an image in Paint Shop Pro

How to Choose a Scanner

You must consider five primary variables when choosing a scanner: resolution, color depth, grayscale depth, connection, and scan speed. You can and will adjust the first three during the scanning process, although probably only down from their maximum. You need to decide on the connection before you buy. The scan speed relates to all four of the other variables, and the maximum speed is hard-coded into the scanner.

Configurable Variables Scanners convert the scanned image into a grid of dots. The maximum number of dots determines how well you can capture an image and how the image will look when scaled up in size. Most folks use the term resolution to define the grid size. As you might imagine, the higher the resolution, the better the scanned image will look and scale.

Older scanners can create images of only 600 × 600 dots per inch (dpi), while newer models commonly achieve four times that density and high-end machines do much more. Manufacturers cite two sets of numbers for a scanner’s resolution: the resolution it achieves mechanically—called the optical resolution—and the enhanced resolution it can achieve with assistance from some onboard software.

The enhanced resolution numbers are useless. I recommend at least 2400 × 2400 dpi optical resolution or better, although you can get by with a lower resolution for purely Web-destined images.

The color depth of a scan defines the number of bits of information the scanner can use to describe each individual dot. This number determines color, shade, hue, and so forth, so a higher number makes a dramatic difference in your picture