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Saturday, 15 February 2014

Computer Graphics Notes Lab 4

INPUT DEVICES


1)     Keyboard: The keyboard is a primary input device for any graphics system. Standard keyboard consists of
   Alphanumeric key
    Function keys
    Modifier keys
   Cursor movement keys
   Numeric keypad
A standard known as ASCII has been developed to allow computer to encode keyboard characters. When we press a key on the keyboard, keyboard controller places a code corresponding to key pressed into a part of its T- memory, called keyboard buffer. This code is called scan code. The keyboard controller informs CPU of the computer about the key press with the help of an interrupt signal. The CPU then reads the scan code from the keyboard buffer.


Getting the scan code from keyboard

2)     Mouse: A mouse is a palm-sized box used to position the screen cursor. It consists of ball on the bottom connected to wheels or rollers to provide the amount and direction of movement. In general mouse has three buttons. When user presses one of the buttons, the mouse marks the places on the screen. Now-a-days mouse consists of one more wheel on the top to scroll the screen pages.


3)     Trackball: A trackball is a ball that can be rotated with the fingers or palm of the hand to produce screen cursor movement. A trackball uses a hard sphere control movement. The ball can be rotated by hand in any direction. The trackball translates the sphere's direction and speed of rotation into a digital signal used to control the cursor.

4)     Joysticks: It is the most important input device used to play video games. A joystick has a small, vertical lever (called stick) mounted on the base and used to steer the screen cursor around. Joysticks are inexpensive and are quite commonly used.

5)     Light pen: Light pen is a pencil shaped device used to select positions by detecting the light coming from points on the CRT screen. It is a pointing device that can be used to choose a displayed menu option. The pen consists of a photocell placed in a small tube. The pen will send a pulse whenever the phosphor below it is illuminated. The system can identify the part of the graphics to which the pen is pointing. The response time of the pen is also important.
  
6)     Data Glove: The data glove is used to grasp a virtual object. It is constructed with a series of sensors that detect hand and finger motions. Each sensor is a fiber optic cable, with a LED at one end and photo transistor at the other end. The input from the glove can be used to position or manipulate objects in a virtual scene. Thus by wearing the data glove, a user can grasp, move and rotate objects and then release them.
  
7)     Image Scanners: The scanner is a device, which can be used to store drawing, graphs, photos or text available in printed form computer processing. The scanners use the optical scanning mechanism to scan the information. The scanner records the gradation of gray scales or color and stores them in the array. Finally, it stores the image information in a specified file format such as JPEG, GIF, TIFF, BMP and so on. Once the image is scanned, it can be processed or we can apply transformations to rotate, scale the image using image processing software's such as photo-shop or photo-paint. Scanners are available in variety of sizes and capabilities.
  
8)     Touch panels: Touch panels allow displayed objects or screen positions to be selected with the touch of a finger. The touch panels are the transparent devices which are fitted on the screen. They consist of touch sensing mechanism over the video monitoring screen.
  
9)     Voice systems: Speech recognizer are used in some graphics systems as input devices to accept voice commands. Such a voice-system input can be used to initiate graphics operations or to enter data. These systems operate by matching an input with a pre defined dictionary of words and phrases.


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