All computers are connected to some type of display unit, which is called a monitor. The monitor is a part of the computer video system and monitors are available in many different types and size. The on-screen display enables us to see how applications are processing our data, but Visual display unit is important to remember that the screen display is not permanent record i.e. the outputs are lost where the power is off. The thinner monitors used on notebook and other small computer are known as flat-panel displays. Compared to CRT (Cathode Ray Tube) based monitors, flat panel displays consume less electricity and take up much less room.
Most flat panel displays use Liquid Crystal Display (LCD) technology. LCD displays sandwich cells containing tiny crystals between two transparent surfaces. By varying the electrical current supplied to each crystal, an images forms. Quality of monitor is often judged in terms of following four factors:
None The most important aspect of a monitor is its size. Like televisions, screen sizes are measured in diagonal inches, the distance from lower left corner to the upper right corner diagonally.
Typical monitors found in the market are of size 14 inches, and 17 inches and above. The size of display are determines monitor quality. In larger monitors the objects look bigger or more objects can be fitted on the screen.
None The screen image is composed of a number of pixel elements. A team pixel is the smallest unit of display screen (the word comes from combination of picture and elements). Each pixel is composed of three phosphor dots, Red, Green and Blue. Now the Dot- pitch is the distance between the phosphor dots that make up a single pixel.
The Dot-pitch of color monitors for PCs ranges from about 0.15 mm to 0.30 mm.
None resolution. The resolution of a monitor indicates how densely the pixels (a single point in a graphic image) are packed. On color monitors, each pixel is actually composed of three dots - a Red, Green and Blue. Ideally the three points should converge at the same point. Resolution indicates the quality of monitor.
Greater the number of pixels, better the resolution and sharper the image. Actually the resolution is determined by the video controller or video adapter card. IBM has provided following adapter cards: The maximum under of points that can be displayed without overlap on a monitor screen is referred to as the. The resolution of a monitor indicates how densely the pixels (a single point in a graphic image) are packed. On color monitors, each pixel is actually composed of three dots - a Red, Green and Blue.
Ideally the three points should converge at the same point. Resolution indicates the quality of monitor. Greater the number of pixels, better the resolution and sharper the image. Actually the resolution is determined by the video controller or video adapter card. IBM has provided following adapter cards:
Refresh Rate: Refresh Rate is the number of times per second at which each pixel on a screen is refreshed. Display monitors must be redrawn many times per second. The refresh rate for a monitor is measured in hertz (HZ) or cycles/second. Generally monitors refresh rates are 60 HZ or 70 HZ. The faster the refresh rate the less the monitor flickers. Monitors are classified into three categories according to its display color
Monochrome: Monochrome monitors actually display two colors, one for the background and another for foreground.
The color can be black (background) and white (foreground), black (background) and green (foreground).
Grey-scale: Gray-scale is a special type of monochrome monitor capable of displaying different shades of gray. Background color is usually white in such monitors. Color: Color monitors can display from 1 to 16 million different colours. These monitors are sometimes called RGB (Red, Green, and Blue) monitors because three primary colors Red, Green and Blue are used to make other colours. An RGB monitor consists of cathode ray tube with three-electron guns-one each for Red, Green and Blue at one end and screen at the other end.
Color and gray-scale monitors are often classified by the number of they use to represent each pixel. For example, a 14-bit monitor represents each pixel with 24 bits. The more bits per pixel, the more colors and shades the monitor can display. A traditional picture tube is like a big glass bottle. There are electron guns in the narrow end.
They fire towards the large flat surface facing the user. The inside of the glass surface is coated with tiny phosphorus dots. There are arrange in groups of three- Red, Blue and Green (for color monitor) phosphorus dot. These dots light up or grow when hit by electrons from the electron gun. The more powerful beam is, the brighter they get. The electron beams are guided by electromagnets, where bend the beams, so they hit the exact desired phosphorus dot.
Data imaged is product by moving the electron beam across the phosphor coated screen. Phosphor coating can be made to glow with different intensities by varying the strength of the electron beam, which finally forms character on screen. CRT monitor contains a shadow mask, which is fine mesh made of up metal., fitted to the shape and size of the screen. The holes in the shadow mask's mesh are used to align the electron beams, to insure that they strike precisely the correct phosphorus dot. Mostly, these holes are arranged in triangles.
CRT monitor are popular with desktop computers. These are available in monochrome and color monitors. The CRT has display screen of 25 lines of 80 characters each. There are two types of CRT monitors:
Composite CRT monitor is used only one electron gun to control the intensity of all these phosphorus dots in each pixel. RGB CRT monitor uses three individual guns, one for its dot, to control the intensity.
Each of the sub dots are hit by its own electron gun that is why these monitors give sharper picture.
a) As the phosphor dots start to fade after sometime they are hit by the electron gun, they need to be refreshed again.
c) They are bulky and heavy. A CRT screen is reliable but it is bulky & consumes a lot of power so it is not used for portable computers. For small computers, flat panel display is used. The most common type of flat panel display are:
LCD produces images by aligning molecular crystals. When a voltage is applied, the crystals line up in a way that blocks light from passing through them and the absence of light is seen as characters on the screen.
The LCD screen is flat, since it does not have picture tube. Instead the screen image is generated on a flat plastic disk. Thus LCD screens are much thinner, soft and do not flicker as compared to CRT.
None LCD is light weight, flat, thin and require less space.
None LCD have smaller viewing angle so picture is best viewed when the person is in straight position from the centre of monitor.
None The liquid crystals do not emit light so the images are less sharp.
None There is a need of backlight setting to enhance sharpness of images. One of the advancement in flat panel display is GPD. Gas Plasma diplay offers flicker free viewing and has higher contrast than LCDs. GPD contains ionized gas (Neon or Xenon) in between two glass plates. Among the two glass plates, one has serial of vertical wires or electrodes while other has series of horizontal wires.
When the two placed together, the intersection of horizontal and vertical wire identifies a pixel. When current is applied through appropriate vertical and horizontal lines, the gas at the pixel emits light. Thus characters are formed by glowing combination of appropriate pixels.
Given current technology, could TV display screens double as video camera sensors?
Even IF - Why would you want to take a photo with zero (or near few mm) field of vision and a lot of blur? Because TV screen would (could) act like a photosensitive paper (or if you are old enough camera film). There would be no lens to focus, no apertures to set the amount of light, no pinholes that would allow you to point to certain area. Screen would take light from everywhere that is not behind the TV. And what would be behind the TV would (could) still have ambient light. So a photo taken with such screen would be very bright (white) on border going to greyish in the middle. Just put a normal camera in the TV. Speakers can work as microphones anyway.
Bao’an District Shenzhen City, China
+86 189 3806 5764