The basic idea
A scanner reads a picture or page by looking at it a tiny piece at a time. Instead of capturing the whole image at once, as a camera does, it measures the brightness, and often the color, of each small spot along a line, and then moves on to the next line. Put the measurements in order and the original can be rebuilt, either as marks on another sheet far away or, in modern machines, as a grid of numbers. This line-by-line approach is the thread that runs from nineteenth-century telegraph experiments to the flatbed scanner on a desk.
Picture telegraphy
In 1843, the Scottish inventor Alexander Bain patented an electric telegraph device that could copy marks by scanning a surface with a stylus. It is often cited as the first fax-like idea. Giovanni Caselli, an Italian priest and physicist working in France, built a more practical machine called the pantelegraph in the 1850s, and it was used for transmitting handwriting and drawings between Paris and Lyon in the 1860s. These machines used a stylus that moved over an image drawn in conductive ink, and they were limited and slow.
In the early twentieth century, the German physicist Arthur Korn transmitted photographs by wire. His systems used a light-sensitive selenium cell to measure the brightness of a photograph wrapped around a rotating cylinder, and they sent newspaper photographs between cities in Europe by the 1900s and 1910s. The Bartlane system, developed in Britain around 1920, sent pictures by cable across the Atlantic for newspapers, with the image coded in a few tones of gray. Later, wirephoto services, such as the one begun by the Associated Press in the 1930s, allowed news photographs to be sent around the country by telephone line. These machines are the ancestors of both facsimile machines and modern scanners.
The first digital image
In 1957, Russell Kirsch and colleagues at the U.S. National Bureau of Standards in Washington built a drum scanner connected to the SEAC computer, one of the earliest stored-program computers in the United States. They scanned a small photograph, reportedly of Kirsch’s infant son, at a resolution of 176 by 176 pixels. It is often described as one of the first digitized photographs. The pixels were stored as just two values, black or white, so the picture was crude, but it demonstrated that an image could be handled as numbers.
Drum scanners and the printing industry
From the 1950s and 1960s, printers used drum scanners to separate color pictures into the cyan, magenta, yellow and black plates required for printing. A transparency was mounted on a spinning glass drum, and a light and photomultiplier tube read it at very high quality. Drum scanners remained the standard for demanding color reproduction long after cheaper machines appeared.
Text and reading machines
Scanning was also used to make printed words readable by machines and by blind people. In 1913, the British physicist Edmund Fournier d’Albe built the optophone, which converted printed letters into audible tones. Optical character recognition, in which a computer identifies letters in a scanned image, developed in the following decades for sorting mail and processing forms. In 1976, Ray Kurzweil introduced a reading machine for blind users that combined a flatbed scanner, software to recognize text in different fonts, and speech synthesis. It was an early demonstration that scanning could be combined with computation to give practical results.
Flatbed and desktop
The flatbed design, in which the original lies face down on a glass plate and a sensor array moves beneath it, took advantage of charge-coupled device sensors. Instead of rotating a drum, a moving light bar illuminates a strip of the page, and a lens focuses it onto a line of sensors. Consumer flatbed scanners appeared in the late 1980s. The Hewlett-Packard ScanJet of 1987 is often cited as one of the first, and prices fell through the 1990s. Handheld scanners that the user dragged across a page were also sold, though they were harder to use. Scanning software became part of the home computer, and people digitized family photographs, documents and artwork. Archives, libraries and businesses started large digitization projects.
Related kinds of scanning
The word is now used for several different technologies that share the line-by-line approach or the idea of reading a surface:
- Barcode scanners read patterns of lines at supermarket checkout.
- Fingerprint scanners capture the ridge pattern of a finger.
- 3D scanners measure shape, often with lasers.
- Multi-function printers fold a scanner into a copier or fax.
- Phone cameras now function as scanners with the right app, correcting the perspective of a page photographed at an angle.
Caveats
Early dates and the “first” labels vary by source. The claim that Kirsch’s 1957 image was the first digital photograph depends on definitions, since other experiments in image digitization took place around the same time. Specifications of early machines, such as resolution and speed, are often quoted from memory and should be treated as approximate.