Author: admin
These are three basic types of monitors that are used with personal computer:
- CRT Monitors
- Flat-Panel Monitors
- Touch Screen Monitors
1. CRT Monitors
A CRT monitor is similar to standard television. It contains a cathode ray tube (CRT). A cathode ray tube is a large, scaled glass tube. The front of the tube is the screen. The back of the screen is coated with phosphor (chemical material that glows when electron beam falls on it). The screen is organized into a grid of tiny dots of phosphor material. Each dot consists of a red, a green and a blue phosphor. The smallest number of phosphor dots that the gun can focus on is called a pixel (short for picture element). A pixel indicates a single point in an electronic image.
CRT monitor contains an electronic gun. The electronic gun shoots a beam of electrons through a magnetic coil and moves back and forth across the back of the screen. This causes the dots of phosphor on the screen to glow, which produces an image on the screen. Actually, the electron gun does not focus on a spot and shoots electrons at it. The electron beam scans each line of pixels across the screen until it reaches the bottom of the screen and then it starts over.
Today, most of the PCs have color monitors. A color monitor works like a monochrome one, except it contains three electron guns; one for red color, second for green color and third for blue color. The beams emitted by electron guns are colorless. In a color monitor, each pixel includes three phosphor tiny dots. These are red, green and blue arranged in a triangle. When the beams of each these guns are combined and focused on a pixel, the phosphors light up. The output is displayed in different colors by combining various intensities of the three guns. A typical monitor can display output in 256 to 65,536 colors.
1. CRT Monitor Size
Like televisions, CRT monitor size is measured diagonally, in inches, across the front of the screen. For example, a 17-inch monitor measures 17 inches from the lower left to the upper right corner. For the past few years, the 15-inch monitor was the standard size used with most PCs. Today, CRT monitors are available in various sizes, i.e., 15, 17, 19, 21 and 22 inches. The large size monitors are more expensive and allow you to view more information on the screen at once.
2. Measuring Quality of CRT Monitor
The quality of CRT monitor depends on the following factors.
- Resolution
- Dot pitch
- Refresh rate
i) Resolution
The resolution refers to the sharpness and clearness of an image. The monitor’s screen that has large number of pixels has high resolution. For example, a resolution of 800 x 600 means that there are 800 pixels horizontally and 600 pixels vertically across the screen. Today the monitors used in desktop computers have resolution 1200 x 600 to 1600 x 1200 or more. A 21-inch monitor may use 1600 x 1200 resolutions and a 17-inch monitor may use 800 x 600 resolutions.
In high-resolution computer monitors more items can fit on the screen or desktop but the items appear in smaller size. The high-resolution monitors are always preferred to see video films as well as for designing graphics.
ii) Dot Pitch
The distance between each pixel on the monitor screen is called dot pitch. It is also referred to as Pixel Pitch. Dot Pitch is another factor that you can use to measure image clarity on a monitor. The smaller the distance between the pixels, the higher the sharpness of image displayed on screen. In a color monitor there are three dots (one red, one green and one blue) in every pixel. The dot pitch should not be greater than 0.28 millimeter. Advertisements usually specify a monitor’s dot pitch.
iii) Refresh Rate
The refresh rate is the number of times per second the electron guns scan every pixel on the screen to redraw the images on the screen. It is measured in Hertz (Hz) or in cycles per second. Refresh rate is also referred to as vertical frequency or vertical scan rate. The monitor refreshes itself at least several dozen times each second. The refresh rate is very important because dots or pixels fade quickly after the electron gun passes over them. Therefore, if the screen is not refreshed, it appears to flicker. The flicker is one of the main causes of eyestrain. In general, a refresh rate of 75 Hz or higher should not cause eyestrain. This means image on the screen redraws itself 75 times in a second.
3. Video Card
Many CRT monitors use an analog signal to create an image on the screen. The video card is installed on the motherboard. Video card is also known as graphics card. It converts the digital output from computer into analog video signal. A cable on the CRT monitor plugs into a port on the video card. The video card sends the analog signal through cable to the monitor and output is displayed on the screen.
The number of colors a video card can display is determined by its bit depth also known as color depth. The color depth is the number of bits it uses to store information about each pixel. For example, an 8-bit video card uses 8 bits to store information about each pixel. Thus this video card can display 256 (i.e. 28) different colors. Similarly, 24-bit video card can display 16.7 (i.e. 224) million colors: The greater the number of bits, the better the resulting image on the screen.
Several video standards have been developed to define the resolution, number of colors and other display properties. Today, VESA (Video Electronics Standards Association) develops video standards. These standards are given below:
| Standard | Maximum Color | |
|---|---|---|
| Monochrome Display Adapter (MDA) | 720 x 350 | 1 |
| Video Graphics Array (VGA) | 640 x 480 | 16 |
| Extended Graphics Array (XGA) | 1024 x 768 | 256 |
| Supper Video Graphics Array (SVGA) | 800 x 600 1024 x 768 1280 x 1024 1600 x 1200 |
16.7 million 16.7 million 16.7 million 16.7 million |
| Beyond SVGA | 1920 x 1440 2048 x 1536 |
16.7 million 16.7 million |
Today, the most commonly used video card supports the SVGA standard and VGA standard. Both the video card and the monitor must support the video standard and video card also must have enough memory to generate the resolution and number of colors you want to display. The memory in a video card stores information about each pixel. The commonly used memories in video cards are VRAM (video RAM), SGRAM (Synchronous Graphics RAM) etc. The storage capacity of video memory is measured in megabytes. Most video cards have 16 MB to 128 MB of video memory. In addition to video memory chips, the video card also contains a processor chip called the Graphics Processing Unit (GPU). The GPU performs calculations used to display images on the screen.
See the next part of this article