Flatbed Scanners

The most popular type of scanner today is the flatbed scanner, so called because it uses a flat imaging surface, very similar to that of a photocopier (see Figure 19.1). Most flatbed scanners sold today support scanning 8.5x11-inch sheets of paper, or possibly slightly larger sizes, such as 8.5x14-inch (legal size). The scanners themselves are therefore slightly larger than this, although most units aren't larger by much.

The route taken by light within a flatbed scanner is actually quite circuitous, as shown by Figure 19.2. This design is fairly complex—it involves three mirrors (two of which must pivot in precisely controlled ways), a lens, a CCD, and a moving light source. When you use a flatbed scanner, you can usually spot the light source moving its way down the page, even with the lid closed. This action is much like the scanning action on a photocopier. In both technologies, the device images a portion of the document at a time. Photocopiers use a rotating photosensitive drum similar to that in a laser printer, but scanners use a light-sensitive CCD array.

Chapter 19

Figure 19.1

You place a document to be scanned on a flatbed scanner's flat glass plate, as if the scanner were a photocopier.

Figure 19.1

You place a document to be scanned on a flatbed scanner's flat glass plate, as if the scanner were a photocopier.

Light Path from Light Source to A/D Converter

Cover Glass

Pivoting Mirror

Drive Mechanism


Light-sensing Diodes and A/D Converter

Light Source and Mirror f

Pivoting Mirror

Interface (SCSI, Parallel, or USB)

Figure 19.2

Flatbed scanners are more expensive than other consumer scanners in part because they require several precision moving parts.

Part IV

Characteristics of flatbed scanners that are important to most consumers include

• Size Flatbed scanners are larger than most other consumer-oriented scanners. Because you typically lift the lid to insert a sheet of paper, you can't stack other items atop these devices, so they consume their desk space quite thoroughly.

• Quality Flatbed scanners produce higher-quality scans than do most other types of scanner. This is largely because they scan at higher resolutions than do most other scanner types.

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