ABSTRACT

This paper generally explains and gives us an overview of the different types of

Image Display Technology which handle data input as character maps or

bitmaps. In character-mapping mode, a display has a preallocated amount of

pixel space for each character. In bitmap mode, it receives an exact

representation of the screen image that is to be projected in the form of a

sequence of bits that describe the color values for specific x and y coordinates

starting from a given location on the screen. Displays that handle bitmaps are

also known as all-points addressable displays.

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INTRODUCTION:

DEFINITION: IMAGE DISPLAY

A display is a computer output surface and projecting mechanism that shows

text and often graphic images to the computer user, using a cathode ray tube (

CRT ), liquid crystal display ( LCD ), light-emitting diode, gas plasma, or other

image projection technology.

BRIEF EXPLANATION:

The display is usually considered to include the screen or projection surface and

the device that produces the information on the screen. In some computers, the

display is packaged in a separate unit called a monitor . In other computers, the

display is integrated into a unit with the processor and other parts of the

computer. (Some sources make the distinction that the monitor includes other

signal-handling devices that feed and control the display or projection device.

However, this distinction disappears when all these parts become integrated into

a total unit, as in the case of notebook computers.) Displays (and monitors) are

also sometimes called video display terminals (VDTs) . The terms display and

monitor are often used interchangably.

Most computer displays use analog signals as input to the display image

creation mechanism. This requirement and the need to continually refresh the

display image mean that the computer also needs a display or video adapter .

The video adapter takes the digital data sent by application programs, stores it in

video random access memory ( video RAM ), and converts it to analog data for

the display scanning mechanism using an digital-to-analog converter ( DAC ).

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DISPLAYS CAN BE CHARACTERIZED ACCORDING TO:

Color capability

Sharpness and view ability

The size of the screen

The projection technology

Color Capability

Today, most desktop displays provide color. Notebook and smaller computers

sometimes have a less expensive monochrome display. Displays can usually

operate in one of several display modes that determine how many bits are used

to describe color and how many colors can be displayed. A display that can

operate in Super VGA mode can display up to 16,777,216 colors because it can

process a 24-bit long description of a pixel . The number of bits used to describe

a pixel is known as its bit-depth. The 24-bit bit-depth is also known as true color

. It allows eight bits for each of the three additive primary colors - red, green,

and blue. Although human beings can't really distinguish that many colors, the

24-bit system is convenient for graphic designers since it allocates one byte for

each color. The Visual Graphics Array (VGA ) mode is the lowest common

denominator of display modes. Depending on the resolution setting, it can

provide up to 256 colors.

Sharpness and View ability

The absolute physical limitation on the potential image sharpness of a screen

image is the dot pitch , which is the size of an individual beam that gets through

to light up a point of phosphor on the screen. (The shape of this beam can be

round or a vertical, slot-shaped rectangle depending on the display technology.)

Displays typically come with a dot pitch of .28 mm (millimeters) or smaller.

The smaller the dot pitch in millimeters, the greater the potential image

sharpness.

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The actual sharpness of any particular overall display image is measured in

dots-per-inch (dots per inch ). The dots-per-inch is determined by a combination

of the screen resolution (how many pixel s are projected on the screen

horizontally and vertically) and the physical screen size. The same resolution

spread out over a larger screen offers reduced sharpness. On the other hand, a

high-resolution setting on a smaller surface will produce a sharper image, but

text readability will become more difficult.

View ability includes the ability to see the screen image well from different

angles. Displays with cathode ray tubes (CRT ) generally provide good view

ability from angles other than straight on. Flat-panel displays, including those

using light-emitting diode and liquid crystal display technology, are often

harder to see at angles other than straight on.

The Size of the Screen

On desktop computers, the display screen width relative to height, known as the

aspect ratio, is generally standardized at 4 to 3 (usually indicated as "4:3").

Screen sizes are measured in either millimeters or inches diagonally from one

corner to the opposite corner. Popular desktop screen sizes are 12-, 13-, 15-, and

17-inch. Notebook screen sizes are somewhat smaller.

The Projection Technology

Most displays in current use employ cathode ray tube (CRT ) technology similar

to that used in most television sets. The CRT technology requires a certain

distance from the beam projection device to the screen in order to function.

Using other technologies, displays can be much thinner and are known as flat-

panel displays. Flat panel display technologies include light-emitting diode

(LED), liquid crystal display (LCD ), and gas plasma. LED and gas plasma

work by lighting up display screen positions based on the voltages at different

grid intersections. LCDs work by blocking light rather than creating it. LCDs

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require far less energy than LED and gas plasma technologies and are currently

the primary technology for notebook and other mobile computers.

TYPES OF DISPLAY UNITS

1. Liquid Crystal Display

2. Cathode Ray Tube

3. Light-Emitting Diodes

4. Plasma

1. LIQUID-CRYSTAL DISPLAY

A liquid-crystal display (LCD) is a flat-panel display or other electronic

visual display that uses the light-modulating properties of liquid crystals.

Liquid crystals do not emit light directly.

LCDs are available to display arbitrary images (as in a general-purpose

computer display) or fixed images with low information content, which can

be displayed or hidden, such as preset words, digits, and 7-segment displays

as in a digital clock. They use the same basic technology, except that arbitrary

images are made up of a large number of small pixels, while other displays

have larger elements.

LCDs are used in a wide range of applications including computer monitors,

televisions, instrument panels, aircraft cockpit displays, and signage. They are

common in consumer devices such as DVD players, gaming devices, clocks,

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LIQUID-CRYSTAL DISPLAY

watches, calculators, and telephones, and have replaced cathode ray tube (CRT)

displays in nearly all applications. They are available in a wider range of screen

sizes than CRT and plasma displays, and since they do not use phosphors, they

do not suffer image burn-in. LCDs are, however, susceptible to image

persistence.

The LCD screen is more energy-efficient and can be disposed of more safely

than a CRT can. Its low electrical power consumption enables it to be used in

battery-powered electronic equipment more efficiently than CRTs can be. It is

an electronically modulated optical device made up of any number of segments

controlling a layer of liquid crystals and arrayed in front of a light source

(backlight) or reflector to produce images in color or monochrome. Liquid

crystals were first discovered in 1888. By 2008, annual sales of televisions with

LCD screens exceeded sales of CRT units worldwide.

The native resolution of a LCD, LCoS or other flat panel display refers to its

single fixed resolution. As an LCD consists of a fixed raster, it cannot change

resolution to match the signal being displayed as a CRT monitor can, meaning

that optimal display quality can be reached only when the signal input matches

the native resolution. An image where the number of pixels is the same as in the

image source and where the pixels are perfectly aligned to the pixels in the

source is said to be pixel perfect.

In 1888, Friedrich Reinitzer (1858–1927) discovered the liquid crystalline

nature of cholesterol extracted from carrots (that is, two melting points and

generation of colors)

2. CATHODE RAY TUBE

The cathode ray tube (CRT) is a vacuum tube containing one or more electron

guns, and a phosphorescent screen used to view images. It has a means to

accelerate and deflect the electron beam(s) onto the screen to create the images.

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The images may represent electrical waveforms (oscilloscope), pictures

(television, computer monitor), radar targets or others.

 

While CRT monitors can usually display images at various resolutions, an LCD

monitor has to rely on interpolation (scaling of the image), which causes a loss

of image quality. An LCD has to scale up a smaller image to fit into the area of

the native resolution. This is the same principle as taking a smaller image in an

image editing program and enlarging it; the smaller image loses its sharpness

when it is expanded. This is especially problematic as most resolutions are in a

4:3 aspect ratio (640×480, 800×600, 1024×768, 1280×960, 1600×1200) but

there are odd resolutions that are not, notably 1280×1024. If a user were to map

1024×768 to a 1280×1024 screen there would be distortion as well as some

image errors, as there is not a one-to-one mapping with regard to pixels. This

results in noticeable quality loss and the image is much less sharp.

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In theory, some resolutions could work well, if they are exact multiples of

smaller image sizes. For example, a 1600×1200 LCD could display an 800×600

image well, as each of the pixels in the image could be represented by a block

of four on the larger display, without interpolation. Since 800×600 is an integer

factor of 1600×1200, scaling should not adversely affect the image. But in

practice, most monitors apply a smoothing algorithm to all smaller resolutions,

so the quality still suffers for these "half" modes.

Most LCD monitors are able to inform the PC of their native resolution using

Extended display identification data (EDID); however, some LCD TVs,

especially those with 1366x768 pixels, fail to provide their native resolution and

only provide a set of lower resolutions, resulting in a less than pixel perfect

output.

Some widescreen LCD monitors optionally display lower resolutions without

scaling or stretching an image, so that the image will always be in full

sharpness, although it will not occupy the full screen. This is most often

recognizable upon close inspection, as there will typically be black edges visible

on either side of the panel horizon. A cathode ray tube consists of several basic

components, as illustrated below. The electron gun generates an arrow beam of

electrons. The anodes accelerate the electrons. Deflecting coils produce an

extremely low frequency electromagnetic field that allows for constant

adjustment of the direction of the electron beam. There are two sets of

deflecting coils: horizontal and vertical.(In the illustration, only one set of coils

is shown for simplicity.) The intensity of the beam can be varied. The electron

beam produces a tiny, bright visible spot when it strikes the phosphor-coated

screen.

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To produce an image on the screen, complex signals are applied to the

deflecting coils, and also to the apparatus that controls the intensity of the

electron beam. This causes the spot to race across the screen from right to left,

and from top to bottom, in a sequence of horizontal lines called the raster. As

viewed from the front of the CRT, the spot moves in a pattern similar to the way

your eyes move when you read a single-column page of text. But the scanning

takes place at such a rapid rate that your eye sees a constant image over the

entire screen.

The illustration shows only one electron gun. This is typical of a monochrome,

or single-color, CRT. However, virtually all CRTs today render color images.

These devices have three electron guns, one for the primary color red, one for

the primary color green, and one for the primary color blue. The CRT thus

produces three overlapping images: one in red (R), one in green (G), and one in

blue (B). This is the so-called RGB colormodel.

In computer systems, there are several display modes, or sets of specifications

according to which the CRT operates. The most common specification for CRT

displays is known as SVGA (Super Video Graphics Array). Notebook

computers typically use liquid crystal display. The technology for these displays

is much different than that for CRTs.

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How LCD Panels Work

LCD is short for liquid crystal display, and while the TVs made with this

tech come in a few different varieties (namely CCFL-backlit and LED-

backlit), the panels they use are the same. LCD panels are typically

composed of two sheets of polarized material with a liquid crystal

solution between them, so when an electric current passes through the

liquid, it causes the crystals to align so that light can (or can’t) pass

through. Think of each crystal as a shutter or gate, either allowing light to

pass through or blocking it out. After passing through the front most

polarized pane, the light then passes through a color filter that leaves it

either red, green, or blue. Each cluster of red green and blue makes up

one pixel on the screen. By selectively illuminating the colors within each

pixel, a wide range of hues can be produced on the larger display.

3. LIGHT EMITTING DIODES

An 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 in store signs and billboards, and in recent years they have also

become commonly used in destination signs on public transport vehicles.

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.

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The first true all-LED flat panel television screen was possibly developed,

demonstrated and documented by James P. Mitchell in 1977. Initial public

recognition came from the Westinghouse Educational Foundation Science

Talent Search group, a Science Service organization. The paper entry was

named in the "Honors Group" publicized to universities on January 25, 1978.

The paper was subsequently invited and presented at the Iowa Academy of

Science at the University of Northern Iowa. The operational prototype was

displayed at the Eastern Iowa SEF on March 18 and obtained a top "Physical

Sciences" award and IEEE recognition. The project was again displayed at

the 29th International SEF at the Anaheim Ca. Convention Center on May

8–10. The ¼-inch thin miniature flat panel modular prototype, scientific

paper, and full screen (tiled LED matrix) schematic with video interface

were displayed at this event. It received awards by NASA and General

Motors Corporation. This project marked some of the earliest progress

towards the replacement of the 70+ year old high-voltage analog CRT

system (cathode-ray tube technology) with a digital x-y scanned LED matrix

driven with a NTSC television RF video format. Mitchell's paper projected

the future replacement of CRTs and included foreseen application to battery

operated devices due the advantages of low-power. Displacement of the

electromagnetic scan systems included the removal of inductive deflection,

electron beam and color convergence circuits and has been a significant

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achievement. The unique properties of the light emitting diode as an

emissive device simplifies matrix scanning complexity and has helped the

modern television adapt to digital communications and “collapse” into its

current thin form factor.

4. PLASMA

A plasma display panel (PDP) is a type of flat panel display common to

large TV displays 30 inches (76 cm) or larger. They are called "plasma"

displays because they use small cells containing electrically charged ionized

gases, which are plasmas.

Plasma displays have lost nearly all market share, mostly due to competition

from low-cost LCD and more expensive but high-contrast OLED flat-panel

displays; manufacturing for the United States retail market ended in 2014,

and manufacturing for the Chinese market is expected to end around 2016.

Plasma displays are bright (1,000 lux or higher for the module), have a wide

color gamut, and can be produced in fairly large sizes—up to 3.8 metres

(150 in) diagonally. They had a very low-luminance "dark-room" black level

compared with the lighter grey of the unilluminated parts of an LCD screen at

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least in the early history of the competing technologies (in the early history of

plasma panels the blacks were blacker on plasmas and greyer on LCDs).

How Plasma TV’s Work

Plasma displays work in an entirely different way. Instead of using a

backlight and a set of filters to illuminate pixels on the screen, images on

a plasma TVs are created by ionized gas (plasma) that lights up when you

run an electrical current through it. The easiest way to understand it is by

thinking of each individual sub pixel on the TV as a tiny neon light, or

perhaps a miniature version of the florescent tubes you might be sitting

under right now. The pixels that make up a plasma display are almost

exactly the same technology, just on a much smaller scale. 

Anatomy of a plasma TV subpixel

For those of you who care to understand the science behind it all, here’s

how the magic happens: An electrode applies an electrical current to a

small cell filled with a noble gas mixture (usually neon and xenon). This

excites the gas, ionizing it and transforming it into a plasma. This plasma

emits ultraviolet light – which we can’t see – but when the UV light hits

a phosphor coating that lines each cell, it causes the phosphor to glow and

put out light that we can see. Depending on which particular phosphor the

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cell is coated with, it will create a red, green, or blue glow. Just like with

LCD displays, each cluster of red green and blue subpixels makes up one

pixel on the screen (see header image).

Advantages of Plasma

Deep Blacks

Due to the fact that plasma displays have the ability to completely turn

off individual pixels, they boast far better black levels than LCD displays.

Although LCD tech has improved over the years, the panels still aren’t

that great at blocking out light completely, which makes it really hard for

them to achieve true blackness on dark scenes. This is especially true of

CCFL-backlit LCD screens. Some LED-backlit LCD TVs with local

dimming can achieve black levels comparable to those of plasma TVs,

but they’re generally much more expensive. 

Strong Color Saturation 

Because of the way they’re designed, plasma TV’s are also better at

controlling the relative level of brightness of each red, blue, or green sub

pixel, so they typically produce greater contrast, more realistically

textured images, and richer colors than their LCD counterparts.

Disadvantages of Plasma

Burn In?

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If you’ve done even a small amount of research on plasma screens,

there’s a good chance you’ve come across a thing called burn-in. This

refers to an image that persists on the screen even after the image that

created it is long gone  – kind alike when somebody shines a flashlight in

your face and you can still see streaks when you close your eyes. Burn-in

works in the same way, but on your TV. If something bright stays on a

plasma screen for too long (like CNN’s ticker or the Discovery Channel

logo) it can sometimes leave a visible ghost behind after the image has

gone away. This was a big problem in early plasma displays, but burn-in

has largely been eradicated now that manufacturers have devised ways to

cycle power to the phosphors and keep them from staying lit for too long.

Still, it’s probably not a good idea to leave a static image on your screen

for days on end.

Energy Consumption

Plasma TV’s are much more power-hungry than their LCD counterparts.

Screen Reflectivity and Brightness

Despite all the advances plasma technology has seen over the years, it

still can’t match the brightness enjoyed by LED or CCFL-backlit LCD

screens. This makes LCD TVs a better option for rooms with lots of light

– especially since plasma TVs almost always have glossy, reflective

screens. 

ADVANTAGES

Very compact and light.

Low power consumption. Depending on the set display brightness and

content being displayed, the older CCFT backlit models typically use 30–

50% of the power a CRT monitor of the same size viewing area would

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use, and the modern LED backlit models typically use 10–25% of the

power a CRT monitor would use.

Very little heat emitted during operation, due to low power consumption.

No geometric distortion.

The possible ability to have little or no flicker depending on backlight

technology.

Usually no refresh-rate flicker, because the LCD pixels hold their state

between refreshes (which are usually done at 200 Hz or faster, regardless

of the input refresh rate).

DISADVANTAGES

Limited viewing angle in some (mostly older or cheap) monitors, causing

color, saturation, contrast and brightness to vary, even within the intended

viewing angle, by variations in posture.

Uneven backlighting in some (mostly older) monitors, causing brightness

distortion, especially toward the edges.

Black levels may appear unacceptably bright because individual liquid

crystals cannot completely block all light from passing through.

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RECOMMENDATION

So which type of TV should you go with? It depends on a few different

factors, but if you’re looking for the best picture at the lowest price,

definitely go with a plasma TV. Plasma sets cost roughly as much as your

typical CCFL-backlit LCD TV, but offer a picture that’s on par with or

better than some of the best, most expensive LED TV’s on the market. 

I recommend that homes, hospitals, industries and research institutions

should go for plasma display units for their CCTV and other security

implementation.

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REFERENCES:

http://money.cnn.com/2014/10/30/technology/plasma-tv/

HDGuru.com – Choosing The HDTV That’s Right For You

PlasmaTelevisions.org – How to Calibrate Your Plasma TV

"History of the Cathode Ray Tube". About.com. Retrieved 4 October 2009.

Topic 7 The Cathode-Ray Tube. aw.com. 2003-08-04

How Computer Monitors Work'". Retrieved 4 October 2009.

Ohaka Chimene Nyemaovuchi Initiatives.com 2016-17-08

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