Chapter 22. Scanners

The scanner is a science- fiction aficionado's dream, a device that shifts between dimensions. It takes three-dimensional objects ”your artwork, pages from books and magazines, even small objects such as coins ”and reduces them to two-dimensional images by looking at them one dimension at a time. Without a trace of the alien technology or the supernatural, the scanner converts images you see in the real world and hold in your hand into the flatland of graphics, ready to adorn your documents or edit into arresting artwork.

The essence of any scanner is elementary. As you would expect, it scans . That is, it uses a long array of light sensors to scan across whatever you put into its range of sight. Each light sensor detects the differences in the brightness of reflections off a tiny spot of the object or image you scan.

In the typical scanner, the light sensors comprise a linear (hence, one-dimensional) array of charge- coupled devices (CCDs), squeezed together hundreds per inch in a narrow strip that stretches across the full width of the largest image that can be scanned. The width of each scanning element determines the smallest area that can be individually judged, thus the finest resolution the scanner can detect within a single line. The narrower each scanning element and the closer they are all packed together, the higher the resolution and the finer the detail the scanner can capture.

Circuitry inside the scanner reads each sensing element in the line, one by one, and in order. From that data, it creates a string of serial data representing the brightness of each point in each individual scan line. Once the scanner has collected and arranged the data from each dot on the line, it advances the sensing element to read the next line.