Output refers to information derived from the computer. It is the results of data processing from the Central Processing Unit (CPU) conveyed to the user through hardware output devices. Common output devices include monitors, printers, loudspeakers and plotters.
Output devices are classified based on the mode of presenting information to the user. The following categories can be identified:
In this post we will look at display output devices.
Display Output Devices
A display output device is any device that visually conveys presents text, graphics, and video information to the user on a screen. These include but not limited to monitors and projectors.
A monitor, also called Video Display Unit (VDU) is an output device that produces soft copy output displayed on its screen. Three important features of monitors that determine the quality of display are:
- Resolution of a Monitor – A monitor is made of pixels (short for “picture element”). Pixels are the individual dots or picture elements that form images on the screen. This describes the measure of a monitor’s sharpness and clarity, related directly to the number of pixels it can display. A monitor’s resolution is a measure of pixels in width by height. For example, a monitor’s resolution of 640 pixels wide by 480 tall is written as 640 x 480. If a high resolution is selected, such as 1280 x 1024, more information can fit on the screen, but everything will be displayed smaller than a lower resolution such as 800 x 600 or 1024 x 768. The screen resolution of a monitor can be changed by users in the Control Panel to match their preferences.
- Refresh Rate – The refresh rate is the number of times per second that the electron guns scan every pixel on the screen. This is measured in Hertz (Hz) or Cycles per second. The monitor refreshes itself at least several dozen times each second. The refresh rate of the monitor is important because pixels on the screen fade quickly after the electron gun passes over them. If therefore the screen is not refreshed often enough, it appears to flicker (shine unsteadily). Flicker is one of the main causes of eyestrain and the problem gets compounded when the flicker is not even detected though it can still cause eyestrain.
- Dot Pitch – Dot pitch is the distance between the phosphor dots that make up a single pixel. This distance is very small and is typically measured in fractions of millimeters. The dot pitch specification of a monitor tells how sharp the displayed image can be. The smaller the dot pitch, the sharper the image. In a colour monitor there are three dots, one red, one green and one blue, in every pixel. If these dots are not close enough together, the images on the screen will not be sharp and clear.
Types of Monitors
Monitors can be categorized based on their colour display mode and the technology they use. There are two types of monitors based on their colour mode and also two types of monitors based on technology.
These are indicated below:
- Colour display mode
- Monochrome monitors
- Colour monitors
- Cathode Ray Tube (CRT) monitors
- Flat Panel Display monitors
- Liquid Crystal Display (LCD)
- Gas Plasma Display (GPD)
- Light Emitting Diode (LED)
- Field Emission Display (FED)
These monitors are mostly character based and can display information in only one colour on a background colour. They are controlled by display adapter cards which do not support enough graphics and colour in multiple shades. The single colour of characters on a background they display include Black, White, Green and Amber.
Colour monitors are supported with enough memory and sophistication to display images with combination of colours of different shades on the screen. The ability of these monitors to handle complex graphics depends on their resolutions, the memory size and efficiency of their video cards. They can display combinations of different colours ranging from 16 colours to 16 million colours.
Cathode Ray Tube Monitors
These are monitors that are usually very large and heavy with bulky backs and their screens sometimes flat squared or spherical. A glass tube inside it called the Cathode Ray Tube (CRT) is the core of the monitor. The monitor works by firing a beam of electrons with an electron gun through a glass funnel at the screen which is coated with red, green and blue phosphor dots. This stimulates the colours across the screen and cause the phosphor dots to paint a picture of characters and images on the entire viewable area.
CRT monitors have long been the standard for use with desktop computers because they provide the brightest and clearest pictures at a relatively low cost. Their two major disadvantages however are that they are bulky, take up desktop space and can be difficult to move as compared to slim and light weight Flat-panel monitors. CRT monitors require a lot of power and produce heat, and are not practical for notebook computers.
Flat Panel Display Monitors
Flat Panel Display (FDP) monitors use a thin panel design instead of the traditional cathode ray tubes found in televisions and other video displays. They are usually less than 10 centimeters (3.9 in), far lighter and thinner, and can be much more portable. They also have higher resolutions than older models.
Flat panel technology is in many applications, specifically modern portable devices such as laptops, mobile phones, digital cameras, camcorders, PDAs, and many more. Four major types of FDPs are Liquid Crystal Display (LCD), Gas Plasma Display (GPD), Light Emitting Diode (LED), and Field Emission Display (FED).
Liquid Crystal Display (LCD) Monitors
An LCD monitor creates images with a special kind of liquid crystal that is transparent but becomes opaque when charged with electricity. It uses the charged liquid crystals located between two sheets of clear material (usually glass or plastic) to light up the appropriate pixels to form the image on the screen. LCDs are by far the most commercially important flat panel technology because they are used in notebook computers.
Gas Plasma Display (GPD) Monitors
Gas Plasma monitors create images by sending a special gas (such as neon or xenon) between two sheets of glass. When the gas is electrified through a grid of small electrodes, it glows. By controlling the amount of voltage applied at various points on the grid, each point acts as a pixel to display an image.
Plasma displays are generally expensive but they provide high-quality images and can be much larger than typical LCDs.
Light Emitting Diode (LED)
A LED display is a flat panel display which uses an array of light-emitting diodes as pixels for a video display. Their brightness allows them to be used outdoors where they are visible in the sun. They can therefore be used for billboards and store signs.
LED displays are capable of providing general illumination in addition to visual display as when used for stage lighting or other decorative (as opposed to informational) purposes.
Field Emission Display (FED)
This technology is essentially a flat CRT with a thousand cathodes (emitters) per pixel, thereby eliminating the long throw distance of the single scanning electron beam of the CRT. It has most of the advantages of CRT image quality, without the bulkiness or power inefficiency. It has full 160 degree viewing angles horizontally and vertically.
A projector or image/data projector is a display output device that takes the image (or moving images) displayed on a computer screen and projects it onto a screen such that a large audience of people can see the image clearly. Projectors can be large devices attached to the ceiling or wall in an auditorium. Two types of smaller, lower cost are LCD projectors and DLP projectors.
An LCD projector, which uses liquid crystal display technology, is attached directly to a computer and uses its own light source to display the information shown on the computer screen. A Digital Light Processing (DLP) projector uses light mirrors to reflect light, producing crisp, bright, colourful images that remain in focus and can be seen clearly even in a well-lit room.
READ ALSO : Types Of Computer Hardware – Input Devices
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