Page 31 - DCAP504_Computer Graphics

Computer Graphics

3. Trackball: The trackball functions similar to the joystick. This device comprises a ball that can be
rotated in any direction using figures or palm. When the ball is moved the cursor moves
accordingly. A potentiometer is attached to the ball to measure the direction of rotation. It can be
used as a substitute to the mouse.
4. Mouse: Mouse is the most important input device which consists of an upside-down trackball
mounted in a small, lightweight box. As you move the mouse across a surface, the ball rotates and
drives the shafts of two valuators, that is, either potentiometers or digital shaft encoders. The
movement of the shafts provide (x, y) coordinates. The Optical mouse and mouse that is based on
magnetic principles use small light source and a small photo electric cell that produces light
pulses, which are counted and converted into (x, y) coordinates.
5. Light Pen: The light pens are pencil shaped devices used to select screen positions by detecting the
light coming from the screen. It consists of a light sensitive diode to sense the light from the
screen. These screens are sensitive to only short burst of light that gets emitted from the light pens.
Other lights such as the background light in a room are not detected by the light pen.
3.2 Output Devices
Output devices play a major role in a computer system. These devices are used to display or
communicate the information that is processed by the computers. The output devices connected to the
computer takes various forms, such as display, print, graphics or audio. Even though there are
numerous output devices, only a few of them are related to computer graphics.
3.2.1 Display Devices
In terms of computer graphics display devices are output devices that help to display graphics. The
graphical outputs can be of two forms:
1. Hard Copy: Hard copy refers to the physical form of output that is recorded from a computer
onto a paper or some other durable surface, such as a microfilm. Output in the form of hard copy
is permanent and stable. Generally, paper is the widely used form of hardcopy.
2. Soft Copy: Soft copy refers to the electronic version of an output, which resides in computer
memory or on disk, and is displayed on a screen. It is not a permanent form of output as the hard
copy. Outputs in the form of soft copy can be in audio visual or graphical form.

Depending on the hard copy and soft copy outputs, the display devices are classified into two types:
1. Hard copy display devices
2. Soft copy display devices
Both the hard copy and the soft copy display devices are capable of converting the electrical signals of a
computer into visible images at higher speeds.

24 LOVELY PROFESSIONAL UNIVERSITY