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Computer Graphics | Light Pen

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Light Pen

Light Pen (similar to the pen) is a pointing device which is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube. When its tip is moved over the monitor screen, and pen button is pressed, its photocell sensing element detects the screen location and sends the corresponding signals to the CPU.

Light Pen


  1. Light Pens can be used as input coordinate positions by providing necessary arrangements.
  2. If background color or intensity, a light pen can be used as a locator.
  3. It is used as a standard pick device with many graphics system.
  4. It can be used as stroke input devices.
  5. It can be used as valuators


The digitizer is an operator input device, which contains a large, smooth board (the appearance is similar to the mechanical drawing board) & an electronic tracking device, which can be changed over the surface to follow existing lines. The electronic tracking device contains a switch for the user to record the desire x & y coordinate positions. The coordinates can be entered into the computer memory or stored or an off-line storage medium such as magnetic tape.



  1. Drawing can easily be changed.
  2. It provides the capability of interactive graphics.


  1. Costly
  2. Suitable only for applications which required high-resolution graphics.

Touch Panels:

Touch Panels is a type of display screen that has a touch-sensitive transparent panel covering the screen. A touch screen registers input when a finger or other object comes in contact with the screen.

When the wave signals are interrupted by some contact with the screen, that located is recorded. Touch screens have long been used in military applications.

Voice Systems (Voice Recognition):

Voice Recognition is one of the newest, most complex input techniques used to interact with the computer. The user inputs data by speaking into a microphone. The simplest form of voice recognition is a one-word command spoken by one person. Each command is isolated with pauses between the words.

Voice Recognition is used in some graphics workstations as input devices to accept voice commands. The voice-system input can be used to initiate graphics operations or to enter data. These systems operate by matching an input against a predefined dictionary of words and phrases.


  1. More efficient device.
  2. Easy to use
  3. Unauthorized speakers can be identified


  1. Very limited vocabulary
  2. Voice of different operators can’t be distinguished.

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