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Crossing the boundary: analogue universe, digital worlds
Crossing the boundary: analogue universe, digital worlds

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4.11.2 Scanners (again)

In Subsection 4.2.5, scanners came up as devices that can convert text into digital form. They do this by making a digital image of the page and then passing this image to an OCR system to distinguish the various characters. However, they are more often used to take images such as photographs and printed diagrams across the digital boundary. A scanner works by moving a sensing point rapidly across the image, in a series of lines, as illustrated in Figure 25.

Figure 25
Figure 25 Raster scanning

The characteristic pattern shown in Figure 25 is known as raster scanning. The scanner measures the brightness (luminance) and the colouring (chrominance) of a series of points along each line and converts the readings at each point into a number. The quality of the resulting bitmap will obviously depend on the number of lines the scanner follows across the specimen, and the number of measurement points along each line. Most scanners come with software that will compress the bitmap into a number of formats, including JPEG and GIF.