... input devices but pointing devices can be used to control a computer or select items from a menu. These include a mice, joysticks, tracker balls and touch screens. Sound Samplers These will convert an audio signal into a digital form that can be stored and processed by a computer. Video Digitisers These will convert a video signal into a digital form that can be stored and processed by a computer. These are useful for capturing pictures of three dimensional objects. Scanners These will convert an image on a flat sheet of paper into a digital form that can be stored and processed by a computer. The speed, resolution, data transfer rate and connecter interface are essential features of a scanner. How a scanner works For a black and white picture the scanner measures the reflected light from each position on the paper (Say at 100 dots per inch). If the reflected light is above a certain level the ...

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