Input Devices in Computer Graphics

Input Devices in Computer Graphics

Input Devices in Computer Graphics

An input device is any machine that feeds data into a computer. For example, a keyboard is an input device, whereas a display monitor is an output device. Input devices other than the keyboard are sometimes called alternate input devices. Mice, trackballs, and light pens are all alternate input devices.

Some of these devices are as below:

Input Devices

  • Keyboard
  • Mouse
  • Tablets
  • Trackball
  • Joystick
  • Touch Panels
  • Light Pen
  • Image Scanners
Input Devices


Keyboard is used to enter data and programs. A simple layout of a keyboard is shown in figure 1.18. 


Figure 1.18 Keyboard

The keyboard is one of the most popular input devices used to enter text information into a computer. Character-based commands to a computer are input by using the keyboard. The computer keyboard has undergone various modifications. It consists of keys for all the letters and numerals, and also some special characters.

Modern keyboards have about 102 to 110 keys, with some new keyboards having keys assigned with special functions.

Parts of Keyboard

The keyboard is divided into three portions/parts.

1) The upper portion/parts are called function keys,

2) The middle portion/parts is the main keyboard

3) The rightmost portions/parts are called numeric keypads.


The mouse is a device that controls the movement of the cursor or pointer on a display screen (figure 1.19). A mouse is a small object that can be rolled along a hard, flat surface. Its name is derived from its shape, which looks a bit like a mouse, its connecting wire that one can imagine to be the mouse’s tail, and the Tact that one must make it scurry along a surface.

As the mouse is moved, the pointer on the display screen moves in the same direction. Mice many as depending S three, which have different functions on what program is running.

The mouse is one of the great breakthroughs in computer ergonomics because it frees the user to 


Figure 1.19 Mouse


This is another device to select screen positions. Using tablets, the position is selected by activating a hand stylus at corresponding positions on a flat surface, called a graphics tablet or digitizer.

This hand cursor contains the crosshairs for sighting positions, while a stylus is a pencil-shaped device. Either of these devices is pointed at positions on the tablet.

Tablet is a rectangular grid of wires on a tablet surface. Each surface has a different voltage, which is correlated with the coordinate position of the wire. Voltage differences correspond to coordinate differences in horizontal and vertical directions on the screen. The voltage of that wire set where the stylus is activated is recorded. This voltage is then converted to the corresponding screen positions. A digitizing tablet with a pen is shown in figure 1.20.


Figure 1.20: A Digitizing Tablet with Pen


The trackball is another pointing device. Essentially, a trackball is a mouse lying on its back. To move the pointer, the ball is rotated with the thumb, fingers, or the palm of the hand. There are usually one to three buttons next to the ball, which you use just like mouse buttons.

Track Ball

Figure 1.21: Track Ball


A lever that moves in all directions and controls the movement of a pointer or some other display symbols and a joystick is similar to a mouse, except that with a mouse the cursor stops moving as soon as you stop moving the mouse. With a joystick, the pointer continues moving in the direction the joystick is pointing. To stop the pointer, the user must return the joystick to its upright position. Most joysticks include two buttons called triggers.

Joysticks are used mostly for computer games, but they have also been used occasionally in manufacturing) systems and other applications.


Figure 1.22: A joystick

Touch Panels

As implied from the name this device allows the screen positions to be selected with the touch of a finger. A touch panel is a transparent plate that fits on the screen. When the plate is touched, the contact position is recorded by an optical, acoustical or electrical method.

Types of Touch Panel

A touch panel monitor is shown in figure 1.23.

1)     Optical Touch Panel: In an optical touch panel, one vertical and one horizontal edge of the panel or frame arc is fitted with light-emitting diodes (LEDs). The opposite horizontal and vertical edges are fitted with light detectors one for each led. When the panel is touched at some position, the optical beams at that point get interrupted which are not detected by the corresponding light detectors.

Touch Panel

Figure 1.23: A Touch Sensitive Monitor

The two crossing beams that are interrupted identify the horizontal and vertical coordinates of the screen position selected. Since LEDs are closely fitted, so more than one beam is likely to be interrupted. At that time average position is recorded. The LEDs emit infrared rays so they are not visible to the user.

2)     Acoustic Touch Panel: In acoustic touch panels, high-frequency sound waves are generated in the horizontal and vertical directions of the panel. The working principle is that of optical touch panels and acoustic tablets. Like acoustic tablets in the acoustic touch panel microphones are fitted on one horizontal and vertical side of the touch panel.

3)     Electrical Touch Panel: In electrical touch panels, there are transparent plates very close to each other. One Plate is coated with some conducting material and the other plate is coated with some resistive material. When the outer plate is touched, it comes in contact with the inner plate and a voltage drop takes place at that point. That voltage drop is captured, converted to the cursor location, and recorded.

Light Pen

This is another device that is used for selecting the cursor position (figure 1.24). These are pencil-shaped devices that are used to select the screen positions by moving the pen across the CRT screen.

These pens are sensitive to short bursts of light emitted from phosphor coating at eh instant an electron beam strikes a particular point.

An activated pen is pointed at a spot on the screen as an electron beam lights up that spot, and generates an electrical pulse that tells the computer to record the coordinate position of the electron beam.

To activate the pen a button is used which is mounted either on the top of the pen or on the side. 

Light Pen

Figure 1.24: A Light Pen

Image Scanners

The scanner is an input device that can read text or illustrations printed on paper and translate the information into a form that the computer can use. The primary purpose of image scanners is to capture the image of anything already written, typed, drawn, or printed on paper, whether in color or in black and white.

Each scanner has its own software that one uses to pass to the scanner properties of the image to be scanned and control the scanning process.

Types of Image Scanners

There are several main kinds of image scanners in common use. Some of them are defined as below:

1)         Flatbed Scanners: A flatbed scanner looks like a box with a hinged top cover that can be opened to expose a clear glass platform. Figure 1.25 shows a scanner with the top cover open:

Flatbed Scanner

Figure 1.25: Flatbed Scanner

A flatbed scanner is used for scanning images from both single sheets of paper as well as images from pages of a book or a magazine. A lamp located below the glass platform within the scanner moves from one end of de scanner to the other end, thus capturing the image, one row at a time.

to scan a page, you open the top cover of the scanner and then lay the paper to be scanned face-down on the scanner’s glass platform, and then close the cover.

2)         Hand-Held Scanners: As its name suggests, a hand-held scanner is small in size, about 4 inches (or 10cm) wide. It is also very affordable and, therefore, preferred by persons venturing into scanning for the first time. Because of its small size and weight, it is easy to store and carry around. Figure 1.26 shows a hand-held scanner is used to scan a document.

To use a hand-held scanner, you press and hold down a spring-loaded switch on the scanner, which lights up a lamp inside the scanner. You then slowly slide the scanner along the length of the page to be scanned. As you slide the scanner, it captures an image from the page and displays it on the computer’s screen.

Hand-Held Scanners

Figure 1.26: Using a Hand-Held Scanner to Scan a Document