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Display Devices

 

Ahmed Mohsen Abdel Hafez, Rami Nabil Faker, Kareem Mohamed Abdel Aziz, Kareem

Mahmoud Mustafa, and Nabil Magdy Hassan

Group (71)

 Abstract

This article will focus on demonstrating the

technology of operation for some of the common, new

and experimental electronic display devices such as

Cathode ray tube (CRT), 3D glasses, LCD TV, Laser 

TV and surface-conducting electron-emitter display

(SED).

1. Introduction

Nowadays the various display devices are great

tools in many fields of life; Science, Entertainment,

Education & also Finance. So scientists are searching

& developing a better ways to make the use of the

display devices is more comfortable & easier. The

new display devices became now more preferable &

affordable than ever before. We can say that we are

living the adventures of using these devices daily, &

this is because of the huge steps from the scientists tounderstand the way that these devices operate & how

to get the best performance from them.

2. Cathode Ray Tube (CRT)

The cathode ray tube (CRT) is a vacuum

tube containing an electron gun (a source of 

electrons) and a fluorescent screen, with internal or

external means to accelerate and deflect the electron

beam, used to create images in the form of light

emitted from the fluorescent screen. The image may

represent electrical waveforms (oscilloscope),

pictures (television, computer monitor), radar targets

and others. The CRT uses an evacuated glass envelope which

is large, deep, heavy, and relatively fragile

2.1. CRT structure

A cathode ray tube is a vacuum tube which

consists of one or more electron guns, possibly

Internal electrostatic deflection plates and a

phosphor target.

Figure (1): CRT

In television sets and computer monitors, the entire

front area of the tube is scanned repetitively andsystematically in a fixed pattern called a raster. An

image is produced by controlling the intensity of each

of the three electron beams, one for each additive

primary color (red, green, and blue) with a video

signal as a reference. [1]

In all modern CRT monitors and televisions, the

beams are bent by magnetic deflection, a varying

magnetic field generated by coils and driven by

electronic circuits around the neck of the tube,

although electrostatic deflection is commonly used

in oscilloscopes, a type of diagnostic instrument.

2.2. Color CRT

Color tubes use three different phosphors which

emit red, green, and blue light respectively. They are

packed together in stripes (as in aperture grille

designs) or clusters called "triads" (as in shadow

mask CRTs). Color CRTs have three electron guns,

one for each primary color, arranged either in a

straight line or in a triangular configuration (the guns

are usually constructed as a single unit). A grille or

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mask absorbs the electrons that would otherwise hit

the wrong phosphor. A shadow mask tube uses a

metal plate with tiny holes, placed so that the electron

beam only illuminates the correct phosphors on the

face of the tube.

Figure (2): Colored CRT

The three beams in color CRTs would not strike

the screen at the same point without convergence

calibration. Instead, the set would need to be

manually adjusted to converge the three color beams

together to maintain color accuracy.

Most CRT television sets and computer monitors

have a built-in degaussing (demagnetizing) coil,

which upon power-up creates a brief, alternating

magnetic field which decays in strength over the

course of a few seconds. This degaussing field is

strong enough to remove most cases of shadow mask 

magnetization. [2]

3. Liquid Crystal Display (LCD) 

A liquid crystal display (LCD) is a thin,

flat electronic visual display that uses the light

modulating properties of liquid crystals (LCs). LCs

do not emit light directly. LCDs therefore need a

light source and are classified as "passive" displays.

Some types can use ambient light such as sunlight or

room lighting. There are many types of LCDs that aredesigned for both special and general uses. They can

be optimized for static text, detailed still images, or

dynamic, fast-changing, video content.

They are used in a wide range of applications

including: computer monitors, television, instrument

panels, aircraft cockpit displays, signage, etc. They

are common in consumer devices such as video

players, gaming devices, clocks, watches, calculators,

and telephones. LCDs have displaced cathode ray

tube (CRT) displays in most applications.

3.1. LCD vs. CRT

They are usually more compact, lightweight,

portable, and lower cost. They are available in a

wider range of screen sizes than CRT and other flat

panel displays. 

LCDs are more energy efficient, and offer safer

disposal, than CRTs. Its low electrical power

consumption enables it to be used in battery-powered

electronic equipment. It is an electronically-

modulated optical device made up of any number

of pixels filled with liquid crystals and arrayed in

front of a light source (backlight) or reflector to

produce images in color or monochrome. [3]

3.2. LCD panel structure

Each pixel of an LCD typically consists of a layerof molecules aligned between

two transparent electrodes, and two polarizing filters,

the axes of transmission of which are (in most of the

cases) perpendicular to each other. With no

actual liquid crystal between the polarizing

filters, light passing through the first filter would be

blocked by the second (crossed) polarizer.

The surface of the electrodes that are in contact

with the liquid crystal material are treated so as to

align the liquid crystal molecules in a particular

direction. This treatment typically consists of a thin

polymer layer that is unidirectional rubbed using, for

example, a cloth. The direction of the liquid crystalalignment is then defined by the direction of rubbing.

Electrodes are made of a transparent conductor

called Indium Tin Oxide (ITO).

Before applying an electric field, the orientation of 

the liquid crystal molecules is determined by the

alignment at the surfaces of electrodes. In a twisted

nematic device (the most common liquid crystal

device), the surface alignment directions at the two

electrodes are perpendicular to each other, and so the

molecules arrange themselves in a helical structure,

or twist.

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Figure (3): LCD panel when light is applied.

This reduces the rotation of the polarization of the

incident light, and the device appears grey. If the

applied voltage is large enough, the liquid crystal

molecules in the center of the layer are almost

completely untwisted and the polarization of the

incident light is not rotated as it passes through theliquid crystal layer.

This light will then be mainly polarized

perpendicular to the second filter, and thus be

blocked and the pixel will appear black. By

controlling the voltage applied across the liquid

crystal layer in each pixel, light can be allowed to

pass through in varying amounts thus constituting

different levels of gray.

The optical effect of a twisted nematic device in

the voltage-on state is far less dependent on

variations in the device thickness than that in the

voltage-off state. Because of this, these devices are

usually operated between crossed polarizers such that

they appear bright with no voltage (the eye is much

more sensitive to variations in the dark state than the

bright state). These devices can also be operated

between parallel polarizers, in which case the bright

and dark states are reversed. The voltage-off dark 

state in this configuration appears blotchy, however,

because of small variations of thickness across the

device.

Both the liquid crystal material and the alignment

layer material contain ionic compounds. If an electric

field of one particular polarity is applied for a long

period of time, this ionic material is attracted to the

surfaces and degrades the device performance. This

is avoided either by applying an alternating current orby reversing the polarity of the electric field as the

device is addressed (the response of the liquid crystal

layer is identical, regardless of the polarity of the

applied field). [4]

3.3 Color LCD

In color LCDs each individual pixel is divided into

three cells, or sub pixels, which are colored red,

green, and blue, respectively, by additional filters

(pigment filters, dye filters and metal oxide filters).

Each subpixel can be controlled independently to

yield thousands or millions of possible colors for

each pixel. CRT monitors employ a similar 'subpixel'

structures via phosphors, although the electron beam

employed in CRTs do not hit exact 'subpixels'.

Because they utilize red, green and blue elements,

both LCD and CRT monitors are direct applications

of the RGB color model and give the illusion of 

representing a continuous spectrum of hues as a

result of the tri-chromatic nature of human vision.

Figure (4): Colored CRT demonstration

Color components may be arrayed in various pixel

geometries, depending on the monitor's usage. If the

software knows which type of geometry is being used

in a given LCD, this can be used to increase the

apparent resolution of the monitor through subpixel

rendering. This technique is especially useful for

text anti-aliasing.

High-resolution color displays such as modern

LCD computer monitors and televisions use an active

matrix structure. A matrix of thin-film

transistors (TFTs) is added to the polarizing and color

filters. Each pixel has its own dedicated transistor,allowing each column line to access one pixel. When

a row line is activated, all of the column lines are

connected to a row of pixels and the correct voltage

is driven onto all of the column lines. The row line is

then deactivated and the next row line is activated.

All of the row lines are activated in sequence during

a refresh operation. Active-matrix addressed displays

look "brighter" and "sharper" than passive-matrix

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addressed displays of the same size, and generally

have quicker response times, producing much better

images. [5]

3.4. LCD Efficiency

LCDs are relatively inefficient in terms of power

use per display size, because the vast majority of 

light that is being produced at the back of the screen

is blocked before it reaches the viewer. To start with,

the rear polarizer filters out over half of the original

un-polarized light.

A good portion of the screen area is covered by the

cell structure around the shutters, which removes

another portion. After that, each sub-pixel's color

filter removes the majority of what is left to leave

only the desired color. Finally, to control the color

and luminance of a pixel as a whole, the light has to

be further absorbed in the shutters.

Old LCD sets use several hundred watts of power,

more than would be required to light an entire housewith the same technology. As a result, LCD

televisions end up with overall power usage similar

to a CRT of the same size.

Modern LCD sets have attempted to address the

power use through a process known as "dynamic

lighting". This system examines the image to find

areas that are darker, and reduces the backlighting in

those areas.

CCFLs are long cylinders that run the length of the

screen, so this change can only be used to control the

brightness of the screen as a whole, or at least wide

horizontal bands of it. This makes the technique

suitable only for particular types of images, like thecredits at the end of a movie. Sets using LEDs are

more distributed, with each LED lighting only a

small number of pixels, typically a 17 by 17 patch.

This allows them to dynamically adjust brightness of 

much smaller areas, which is suitable for a much

wider set of images.

Another ongoing area of research is to use

materials that optically route light in order to re-use

as much of the signal as possible. One potential

improvement is to use micro prisms or dichromic

mirrors to split the light into R, G and B, instead of 

absorbing the unwanted colors in a filter. A

successful system would improve efficiency by threetimes. Another would be to direct the light that would

normally fall on opaque elements back into the

transparent portion of the shutters.

Several newer technologies, OLED, FED and

SED (we will discuss the way of operation for some

of them later), have lower power use as one of their

primary advantages. All of these technologies

directly produce light on a sub-pixel basis, and use

only as much power as that light level requires. The

dramatically lower power requirements make these

technologies particularly interesting in low-power

uses like laptop computers and mobile phones. These

sorts of devices were the market that originally

bootstrapped LCD technology, due to its light weight

and thinness. [7]

3.5. LCD image quality

Early LCD sets were widely derided for their poor

overall image quality, most notably the ghosting on

fast-moving images, poor contrast ratio, and muddy

colors. In spite of many predictions that other

technologies would always beat LCDs, massive

investment in LCD production, manufacturing, and

electronic image processing has addressed many of 

these concerns.

Since the total amount of light reaching the viewer

is a combination of the backlighting and shuttering,

modern sets can use "dynamic backlighting" to

improve the contrast ratio and shadow detail. If aparticular area of the screen is dark, a conventional

set will have to set its shutters close to opaque to cut

down the light. However, if the backlighting is

reduced by half in that area, the shuttering can be

reduced by half, and the number of available

shuttering levels in the sub-pixels doubles. This is the

main reason high-end sets offer dynamic lighting (as

opposed to power savings, mentioned earlier),

allowing the contrast ratio across the screen to be

dramatically improved. 

Color on an LCD television is produced by

filtering down a white source and then selectively

shuttering the three primary colors relative to eachother. The accuracy and quality of the resulting

colors are thus dependent on the backlighting source

and its ability to evenly produce white light. [7]

3.7. Recent research

Some manufacturers are also experimenting with

extending color reproduction of LCD televisions.

Although current LCD panels are able to deliver

all RGB colors using an appropriate combination of 

backlight's spectrum and optical filters,

manufacturers want to display even more colors.

One of the approaches is to use a fourth or evenfifth and sixth color in the optical color filter array.

Another approach is to use two sets of suitably

narrowband backlights (e.g. LEDs), with slightly

differing colors, in combination with broadband

optical filters in the panel, and alternating backlights

each consecutive frame. Fully using the extended

color gamut will naturally require an appropriately

captured material and some modifications to the

distribution channel. Otherwise, the only use of the

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extra colors would be to let the looker boost the color

saturation of the TV picture beyond what was

intended by the producer, but avoiding the otherwise

unavoidable loss of detail ("burnout") in saturated

areas.

4. Field emission display (FED) A field emission display (FED) is a flat panel

display technology that uses large-area field electron

sources to provide electrons that strike colored

phosphor to produce a color image. In a general

sense, a FED consists of a matrix of  cathode ray

tubes, each tube producing a single sub-pixel,

grouped in threes to form red-green-blue (RGB)

pixels. 

FEDs combine the advantages of CRTs, namely

their high contrast levels and very fast response

times, with the packaging advantages of  LCD and

other flat panel technologies. They also offer the

possibility of requiring less power, about half that of an LCD system. To date, however, manufacturing

problems have prevented any FED system from

entering commercial production.

4.1. FED structure 

The key lies in giving each pixel separate electron

guns situated very close behind the phosphor coated

screen. Conventionally these guns have been

fabricated using the Spindt process, in which arrays

of small sharp silicon or molybdenum cones are

deposited onto a substrate within an etched hole.

The result is a triode structure of between a few

and less than one micron in diameter, of which there

are thousands per individual pixel. Electrons can

leave the sharp tips with relatively low extraction

voltages at the gate.

The advantages are CRT-like viewing

characteristics using mature phosphor technology for

the anode, and energy efficient low voltage control at

the gate. The main problem is, not surprisingly,

fabricating an array over a large area. To date, full

color 35cm flat panels have been demonstrated, and

12cm versions are in production, but this approach is

highly unlikely to achieve broad area status.

Figure (5): Demonstration for step one.

The traditional tip-based structure relies on a sharp

cone in a small hole, requiring some fine lithography

and difficult processing. This three electrode (triode)

structure enables the emission to be controlled by

lower voltages on the intermediate electrode (gate).

Figure (6): Demonstration for step two.

A predominantly flat cathode like the PFE (Printable

Field Emitters, will be discussed later) printed

composite allows the gated structure to be wider and

produced with greater ease and less expense.

Figure (7): Demonstration for step three.

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Nanotubes (will be discussed later) give hairy

structures that emit at low fields, but would require

much deeper gated structures to accommodate the

irregular morphology and avoid short circuits

between the electrodes.

The solution would be to achieve field emission

from a flat cathode plane. This would reduce the need

for fine lithographic features and relax the tolerances

demanded of the triode structure. Materials that have

been investigated include polycrystalline diamond

thin films, amorphous carbon thin films, and various

other amorphous thin films such as silicon and boron

nitride.

All of these thin film materials are believed to

have the electronic band structure necessary for

electrons to leave the material under the application

of a modest electric field and travel into the vacuum.

However, they all require plasma-based deposition in

costly vacuum equipment. [8]

4.2. Carbon Nanotubes 

Carbon nanotubes and related structures (placed in

figure 7) have also been found to field emit electrons

at very low fields. However, their aspect ratio has

made it difficult to fit them into triodes without

losing this advantage.

They are also relatively difficult to produce in

large uniform batches, are very sensitive to adsorbed

gases, and are rather difficult to bind securely within

the device. However, Samsung and Motorola are both

actively researching these materials for displayapplications, and have looked at related carbon

materials that appear to emit electrons well without

some of these drawbacks. [9]

4.3. Printable Field Emitters (PFE) 

It’s an emitting structure consists of a tailored

composite of semiconducting or conducting particles

in an insulating matrix.

This approach was derived from investigations of 

high voltage hold off between polished but

contaminated electrodes at the University of Aston.

The PFE materials are produced as an ink and can

be deposited using, for example, screen-printing

technology, instantly making them appealing for use

on broad area substrates.

The electronic band structure of the combined

matrix and particle means that each particle in the

composite acts as an individual field emitting site.

Unlike microtips, the PFE cold cathode materials are

extremely robust and relatively insensitive to poor

vacuum.

Figure (8): The concept of printing a field emitter cathode plane

and the components required to assemble a working display.

A further advantage of PFE's materials is that they

are predominantly flat. They can therefore operate

within relatively large triode structure, which means

that the feature size is also compatible with screen

printing technology. Because, as in the PDP case, the

electrodes and dielectric are also screen printable,

fabricating the entire device on slightly modified

PDP production lines is feasible. This will drastically

reduce the time taken for a display to reach themarketplace.

It is worth highlighting that packaging a complete

FED presents other materials related challenges. The

cathode plane needs to be fabricated on a glass

substrate, and, in the case of the PFE device, will

undergo a series of printing and air baking cycles.

The resulting low cost sandwich must be expansion

matched, adhere well at each interface and consist of 

material that will be vacuum compatible. The cathode

plane must then be brought up to a suitable anode

plane comprising the phosphors and the black matrix

material that separates the pixels.

These two sheets must be mated with a closely

controlled spacing between the two halves. This is

achieved by using small, high aspect ratio ceramic or

glass spacers, designed to prevent the glass bowing

under the forces of the external atmospheric pressure.

These spacers must be located invisibly at regular

intervals throughout the display, and be conductive

enough to dissipate stray charge that may build up,

but without conducting an excessive leakage between

the anode and cathode.

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from the usually inorganic contacts. To solve this

problem, often the structure includes an electron

transport layer (ETL) and/or a hole transport layer

(HTL), which facilitate the injection of charge

carriers. All of these layers must be grown on top of 

each other, with the first grown on a Substrate.

Figure (10): OLED structure

When voltage is applied, one layer becomes

negatively charged relative to another transparent

layer. As energy passes from the negatively charged

(cathode) layer to the other (anode) layer, it

stimulates organic material between the two, which

emits light visible through an outermost layer of 

glass.

6.2 Principle behind the emittance of 

photons:

A hole is injected into one layer of the device and

an electron is injected into the other side of the

device. The two charge carriers move along the

polymer chains in the emitting layer, and when these

two charge carriers combine, they emit a photon

(they produce light). [13] 

6.3 OLED advantages

OLEDs have the following advantages over today's

flat-panel tech (LCD, CRT):

  Low power consumption - OLEDs are a far

better choice for portable devices.

  Faster refresh rate and better contrast.

  Greater brightness - The screens are

brighter, and have a fuller viewing angle.

(Because an OLED becomes self-emissive

through organic material, its viewing angle

is far wider than an LCD. This wide viewing

angle can provide great improvements in a

wide variety of product applications. It also

offers new design concepts to industrial

designers who were before limited by the

constraints of traditional LCD -140 degrees

wide angle visibility-).

  Exciting displays - new types of displays,

which we do not have today, like ultra-thin,flexible or transparent displays.

  Better durability - OLEDs are very durable

and can operate in a broader temperature

range

  Lighter weight - the screen can be made

very thin, and can even be 'printed' on

flexible surfaces

6.4. OLED Disadvantages:

  OLEDs have limited lifetime (compared

with the current display panels).

  OLEDs can also be problematic in directsunlight, because of their emissive nature.

7. LASER TV

Most projection displays are now using the lamp as

a light source, so the effort for using the laser as a

light source is continued for the merits of laser.

7.1. Laser TV advantages 

The advantages of using the laser light for

projection displays are come from the original

characteristics of laser. The main advantages of scanning laser projection displays are high contrast

ratio, excellent expression of natural color and

infinite depth of focus. Laser light is polarized, so it

can yield a higher contrast ratio by using the proper

polarized optics.

The monochromatic property and color saturation

of the laser light can increase the color space about

three times larger than that of the conventional

phosphor system (the ordinary TV). The wavelengths

of lasers cover more than 90% of all colors which can

be perceived by the human eye. Laser has a long

coherence length and a low beam divergence, so one

can achieve infinite depth of focus with the properdisplay technology, such as a raster scanning.

Projection image is no longer limited to a flat screen

and it can be projected at any other surface.

We can conclude the previous talk into the

following points:

  be half the weight and cost of plasma

displays

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  require around 25% of the power required

by plasma displays

  be very slim like plasma and LCD displays

are today

  Have a very wide color gamut, twice that of 

current HDTVs.

  have a very long life  maintain full power output for the lifespan

of the laser, resulting in a picture that doesn't

progressively degrade over time (which

happens with technologies such as plasma,

LCD, and CRT)

  Never suffer from screen burn-in; Burn-in is

caused by uneven use of color reproduction

elements across a screen's surface, but laser

TVs bypass this completely.

7.2. Laser TV realization obstacles

In spite of these excellent characteristics; laser TVfor home theater could not be realized yet, for the

lack of industrial laser-related technologies, also wecan’t neglect the cost issue.

7.3. Laser TV structure & way of operation 

The figure shows a schematic drawing of the basic

layout of the laser TV. It is mainly composed of blue,

green and red laser light sources, three acousto-optic

modulators, a laser beam combining part (a high-

reflection mirror and two dichroic mirrors), a

polygon scan mirror, a galvanometer and optical

lenses.

Figure (11): Schematic drawing of the basic layout of the laser TV.

Blue, green diode-pumped solid state (DPSS)

lasers and a red diode laser are used as a light source.

The wavelengths of the blue green and red are 457

nm, 532 nm and 748 nm, and the output powers are

350 mW, 700 mW and 500 mW, respectively. The

power levels of lasers are adjusted for white color

balance. Diode-pumped solid state (DPSS) lasers are

an exciting tool that combines the beam quality of a

gas laser, small size and efficiency of a diode laser

with single line output.

Blue, green and red laser beams are modulated at

acousto-optic modulators (AOMs) according to the

video signals.

Laser beam modulation in the acousto-optic device

is implemented by varying the amplitude of the

acoustic drive signal, which in turn varies the

amplitude of the light passed to the first order.

Separated RGB color signals are amplified by a high

frequency signal amplifier and are used in

modulating each laser beam by the acousto-optic

modulator.Modulated red, green and blue light beams are

combined by dichroic mirrors and a high-reflection

mirror. Then the combined beam is projected to the

screen by the scanning part. The dichroic mirror

(DM2) for combining the green light with the red

light has a transmittance over 95% in the red light,

and a reflectance of 99% in the green light.

The dichroic mirror (DM1) for combining the blue

light with the green and red light has a transmittance

over 95% in the blue light, and a reflectance of 99%

in the green and red light. All dichroic mirrors are

designed to obtain the best performance with the 45°

incident angle.Combined laser beam is horizontally scanned by a

polygon scan mirror and vertically scanned by a

galvanometer. The galvanometer is running at a rate

of 70 Hz. The polygon scan mirror has 25 facets and

is rotating at the speed of 75,700 rpm for VGA

resolution (740 × 480 Progressive scanning).

Therefore the scan rate is 31.5 kHz in coinciding with

VGA video signal format which has 525 scanning

lines (including blanking signal lines) and video

images of 70 frames per second.

When the RGB video signals are inserted to the

AOM rf drivers, acoustic wave is generated at the

transducer and it is traveled to the AO crystal, and thelaser beam is diffracted and modulated. So some time

delay is exist between the video signal and the

modulation.

This time delay must be controlled to have the

same value at three AOMs. If not, color mismatch at

the image could be happen. It can be done by

adjusting the distance between the laser beam path

and the transducer of the AOM, but some loss of 

diffraction efficiency is happened due to the

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manufacturing variations of AOMs. So the control

circuit is applied to solve this problem, and the time

delay is controlled at the RGB video signals.

The controllable time delay is 257 pixels. The

sync signals are used to control the scanning part.

The horizontal sync signal is used to clock for driving

the polygon scan mirror. The vertical sync signal is

integrated to ramp signal for driving the

galvanometer. [14]

8. 3D glasses and other 3D display devices

8.1. How 3D effect works 

Our ability to see stereo-vision comes from each

of our eyes seeing a slightly different view of the

world. Our brain integrates these two images into one

three-dimensional picture. The key element in

producing the stereoscopic depth effect is parallax.

Parallax is the horizontal distance between

corresponding left and right image points. Thestereoscopic image is composed of two images

generated from two related perspective viewpoints,

and the viewpoints are responsible for the parallax

content of a view. [15]

8.2. How 3D displays work

Electro-stereoscopic displays provide parallax

information to the eye by using a method related to

that employed in the stereoscope. The 3D display

systems normally in use one of the following

methods:

  Separate display for each eye (used in

HMDs)

  Shutter glasses (most common method)

  Color filter glasses (used in some old 3D

movies)

  Polarizing glasses (used in some modern 3D

movies)

8.3. Color filter glasses

Color filter glasses were one of the oldest 3D

glasses. The system works so that both eyes have adifferent color filter in front of them. This causes

that left eye can only see few colors and right eye

some other colors. When the led eye's colors are

used to draw the image which it should see and same

is used for right eye, the combined image can be

viewed with suitable glasses in 3D. The most

common color combinations are red+green and

blue+green. The color filtering limits that there are

only few possible colors in use in the picture so the

images made using this method are not very nice to

look.

Color filter glasses have been used in 3D movies

and some early computer games. The advantage of 

this method is that the 3D material can be stored to

any standard color video media and viewed withnormal display devices as long as you wear the right

color filter glasses. The glasses are very inexpensive

because you only need very cheap plastic filters for

them. You can even make your own glasses from

piece of cardboard and suitable filters (standard

lighting GEL numbers R27 and R83 should be quite

suitable for red+green glasses).

Figure (12): red+green glasses.

This technique causes colors in the image to be

compromised because you have too many different

colors in different eyes. Practically you lose almost

all your color, so you can see objects coming out of 

the screen but they are gray. The colors also create

some eyestrain and distortion.

8.4. Polarizing glasses 

This method is usually used with projection

displays when 3D material needs to be displayed.

Every viewer has to wear special glasses which have

two polarizing lenses which have their polarization

directions adjusted to be 90 degrees different. This

makes is possible that left eye sees its picture without

problems but everything meant to right eye (sent out

at different polarization) seems to be black. Same

applies also to right eye.

Figure (13): Polarizing glasses.

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The material which has to be shown is typically

projected using two projectors (film projector, slide

projector or video projector) which each have

polarizing lenses in front of them (adjusted to meet

the polarization directions of the glasses). The

projection surface must be specially made so that it

does not do any harm to the polarization (many

traditional projection surface materials are not

suitable, silver stripe screen is recommended). The

advantage of this method is that the pictures can be in

full color and the viewing glasses are still quite

inexpensive.

8.5. LCD shutter glass method

In the LCD shutter glass 3D display, the left and

right images are alternated rapidly on the monitor

screen. When the viewer looks at the screen through

shuttering eyewear, each shutter is synchronized to

occlude the unwanted image and transmit the wantedimage. Thus each eye sees only its appropriate

perspective view. The left eye sees only the left view,

and the right eye only the right view.

A field-sequential 3D (stereoscopic) video signal is

a normal video signal (PAL, NTSC or SECAM)

which has been specially recorded with left and right

images stored on the even and odd fields of the video

signal. The 3D video signal is usually viewed while

wearing a pair of LCD shutter glasses which only

allow the left eye to see left images and the right eye

to see right images.

Figure (14): LCD shutter glass

If the images (the term "fields" is often used for

video and computer graphics) are refreshed (changed

or written) fast enough (often at twice the rate of the

planar display), the result is a flickerless stereoscopicimage. This kind of a display is called a field-

sequential stereoscopic display.

The biggest drawback of LC-Shutter glasses

besides the compatibility issue is Crosstalk. Due to

the persistence of the monitor tube, the inability of 

the LC-panels to block the light entirely, sync errors

and other factors one see "Ghost images" sometimes. 

The right eye sees some residue of the image

dedicated to the left eye and vice versa. [16]

8.6. Head Mounted Displays (HMD) 

Head Mounted Displays, or HMD for short, is one

of the oldest stereoscopic 3D technologies on themarket. Unlike their predecessors, modern HMDs are

lightweight helmets or headbands that place

miniature screens directly in front of the viewer’s

eyes.

Figure (15): modern commercial HMD

By having the screens directly in front of their eyes

in an enclosed environment, the viewer is left with

the illusion that they are seeing their favorite games

or movies with a very large screen. While this

illusion is subjective, head mounted displays are

considered one of the most immersive stereoscopic

3D experiences possible.

HMD consists of:

  One or two small display units (CRT, LCD)

with lenses.

  Semi-transparent mirrors.

  Eye-glasses (called data-glasses).

Types of HMD:

  Display a computer generated image (CGI).

  Display a combination between the real

world image & the CGI (this is called

augmented reality).

Their biggest benefits include full color immersion

and absolutely no ghosting. There is no ghosting

because each eye is getting its own personal screen.

Modern HMDs often include additional featureslike earphones and head tracking that adjust the

game’s perspective as the viewer’s head moves.  

The nature of an HMD’s immersion also causes

nausea for the inexperienced gamer. When we move

our heads, our brain expects our vision to correlate

with our movement. When we are wearing an HMD,

and the image doesn’t change according to where our 

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brain thinks our eyes should be looking, this

incongruity creates nausea. [17]

Acknowledgment

We thank the anonymous references for their

comments that greatly improve the presentation of this paper.

References

[1] "The Cathode-Ray Tube". Pearson Education.Retrieved 2009-10-05.

[2] "How CRT and LCD monitors work". bit-tech.net.Retrieved 2009-10-04.

[3] Ergonomics Considerations of LCD versus CRTDisplays. Professor Alan Hedge, Dept. Design &

Environmental Analysis, Cornell University.

[4] The History of Liquid-Crystal Displays, HiroshiKawamoto, Proceedings of the IEEE, 90, #4 (April 2002).

[5] How LCDs Work, by Jeff Tyson, Microsoft-certifiedsystems engineer.

[6] Fundamentals of Liquid Crystal Displays  – How TheyWork and What They Do, FUJITSU

MICROELECTRONICS AMERICA.

[7] Characteristics of CRT and LCD displays, GeertCarrein Product Manager, Display systems.

[8] Materials World, vol. 8, pp. 22-25, July 2000, Dr.Adrian Burden.

[9] Huhtala, Maria (2002). "Carbon nanotube structures:molecular dynamics simulation at realistic limit". Computer

Physics Communications.

[10] Materials World, vol. 8 , July 2000, Dr. Adrian Burden

[11] A closer look at SED, FED Technologies, By RichardFink VP of Engineering

[12] How SED makers inflate their contrast ratio scores, By

George Ou .

[13] Jill A. Rowehl. OLEDs:Modifiability andApplications. 21 May 2007.

[14] Laser TV for Home Theater Jin-Ho Lee, Yong-KweunMuna, cKorea Advanced Institute of Science andTechnology.

[15] 3D glasses and other 3D display devices, Tomi

Engdahl .

[16] Fay Huang, and Karsten Scheibe: Panoramic Imaging(Sensor-Line Cameras and Laser Range-Finders).

[17] A Three Dimensional Helmet Mounted Primary FlightReference for Paratroopers.