Optical Input Devices

For a long time, futurists and computer scientists have had the goal of enabling computers to "see". Computers may never see in the same way that humans do, but new technologies allow computers to use light as a source of input. these tools fall into the category of optical input devices.

Bar Code Readers:

The most widely used input device after the keyboard and mouse is a bar code reader. The most common type of bar code reader is the flatbed  model, which is commonly found in supermarkets and department stores. Workers for delivery services, such as Federal express, also use handheld bar code readers to identify packages in the field.
                           These devices convert a bar code , which is a pattern of printed bars on products , into a code the computer can understand. The bar code reader emits  a beam of light - frequently a laser beam - that is reflected by the bar code image. A light - sensitive detector identifies the bar code image by recognizing special bars at both ends of the image.  These special bars are different , so the reader can tell whether the bar code has been read   right side up or upside down.

After the detector has identified the bar code, it converts the individual bar patterns into numeric digits. the code reader then feeds that number to the computer, as though the number had been typed on a keyboard.