Sheikh Mujib Amar Pita By Sheikh Hasina.pdf

Lesson 2 : Optical Input Devices

2.1. Learning Objectives
On completion of this lesson you will be able to describe:
 Different optical input devices
 Working principle of different optical input devices.

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2.2. Introduction

Optical input devices covert any image to digital form. The object or an image of the object is placed in front of the optical input device. The device then scans the object or its image, convert the scanned image into pixels. Scanner, digital camera etc. are optical input devices. They convert an image to bit-mapped graphics and deliver the graphics image to the computer. This image is hen store in the computer in different picture file formats (with BMP, TIF, and JPG etc. extensions). Optical character recognizer is a software package. It recognizes characters from a scanned image that exists in a picture file format.

2.3. Scanner

A scanner scans an image, converts it in bitmapped graphics and delivers to the computer. It is just like the photocopier machine, whereas the photocopier machine delivers the scanned output on paper, and the scanner delivers the scanned output as a packet of digital data, to the computer.

The scanners have a row of light-sensitive diodes. These diodes can convert light with different color and intensity to different voltage. This is moved on the paper from its top to bottom. For each position of the row, a line of pixel is produced from the color and intensity of the reflected light from the paper. These pixels are delivered to the computer.

2.4. Digital Camera

Digital camera gets the image of a still or moving object, converts it to pixels and delivers to the computer. Still and movie both types of digital camera exist. Digital still camera has a light sensitive plate. When light from the object falls upon the plate, the plate supplies different voltage for different color and intensity of the fallen light from different points of the object. From these voltages, a digital image is produced and delivered to the computer. Digital movie camera takes many shots (more than 25 per second) of a moving object, then converts each shot to a digital image and delivers to the computer.