1. DISPLAY DEVICES.

1.  DISPLAY DEVICES.

A display device is an output device that conveys text, graphics and video information to the user.  Information on a display device is called a Soft Copy because it exists electronically and displays only for a short period.  Display devices can be;

(a)    Polychromes (Coloured)

(b)   Monochrome (means that information displays in our colour on a different background e.g white and black.

Advantages of using colours

➢    Colours make the screen displays attractive.

➢    Colours can be used to highlight error messages and menu options.

Disadvantages

➢    Screens with a lot of colours take long to process.

➢    More memory is required to display a lot colours.

 Two main types of display devices are CRT monitors and LCD monitors.

CRT monitors works like a standard television because it also contains a Cathode Ray Tube (CRT).  The front of the CRT is the screen, which is coated with tiny dots of phosphor material.

Each dot consists of a red, green, green and blue phosphor and the three dots combine to make up each pixel.

Advantages of CRT Monitors

➢    Can produce fast and rich colour output.

➢    Can be viewed from a very wide angle.

➢    Cheaper than LCD monitors in general.

Disadvantages

➢    Emit higher electromagnetic radiation (EMR) than LCD monitors.

➢    Consume more energy than LCD monitors.

LCD (Liquid Crystal Display) rather than a cathode ray tube uses liquid crystal to create images on the screen.  LCD monitors produce colour using either passive matrix or active matrix technology.

Advantages of LCD monitors

➢    They require less than one third of the power and take up less space than traditional CRT monitors.

➢    Radiation emitted by LCD monitors is neglectable.

Disadvantages.

➢    They are usually more expensive than CRT monitors.

➢    They can only be viewed from a very narrow angle.

TYPES OF DISPLAYS

They are two types of displays;

(i) Character:

-       Displays character as a dot pattern.

-       Needs less memory than graphics.

(ii) Graphics  

-       Use a technique called BIT mapping in which each pixel is stored in one or more bits in memory.

-       These screens take up a lot of memory and operate more slowly.

A VIDEO CARD

A Video card also called a graphics card or video adapter converts digital output from the computer into analog video signal that is sent through a cable to the display device.  It is required to display colour on a monitor.

The number of colours that a video card can display is determined by its bit depth.

Types of Video display cards/Graphic adaptors.

(a)    CGA (Colour Graphics adaptors) displays 320 x 200 pixels in 4 colours.

(b)   EGA (Enhanced Colour Graphic Adaptor) displays 640 x 480 pixels in 16 colours later changed to extended EGA (320 x 200) pixels in 256 colours.

(c)    VGA (Video Graphic Array) took the place of EGA

(d)   SVGA.  Today every monitoe supports the super video graphics Array standard.

N.B:  Resolution describes the sharpness and clearness of an image.  The higher the resolution, the better the image quality.  Resolution is often expressed in dot per inch (dpi)

Advantages of display devices

➢    Time to display the image is fast.

➢    Screen displays can include text, graphics and colours.

➢    Display devices are usually quite.

➢    No paper is wasted for obtaining the output.

Disadvantages of display devices

➢    Information produced on the screen is only temporary and will be lost when the power of the display device is turned off.

➢    Unsuitable for users with visual problems.

➢    Needs a separate device to produce a hard copy.