HD High-definition television

Academia

• Handelshøjskolernes erhvervsøkonomiske Diplomuddannelse, a Danish evening course for a Graduate Diploma in Business and Administration
• Higher Diploma, an academic award

[edit] Business

• Harley-Davidson, an iconic American motorcycle manufacturer
• Headphone Dust, a record label run by music artist Steven Wilson
• Hokkaido International Airlines, a Japanese low-cost airline with IATA designator HD
• Home Depot, a chain of home improvement warehouse retailers

[edit] Medicine

• Attention-deficit hyperactivity disorder, known as Hyperactivity Disorder (HD), as in AD/HD
• Hip Dysplasia
• Hodgkin’s disease
• Hormone disruptor
• Huntington’s disease
• The HD gene, a historical name for the huntingtin gene, which can cause Huntington’s disease when it has certain properties.

[edit] People

• Hilda Doolittle, also known as H.D., an American poet

[edit] Science and technology

• Hard drive, a computer device which stores digitally encoded data, also known as HDD
• Henry Draper Catalogue, a sequential numbering system for stars ordered by right ascension
• High-definition, in reference to high-definition video, high-definition television LCD (HDTV), or Intel High Definition Audio
• High density, in reference to a floppy disk, other magnetic media or the optical formats HD DVD and Blu-ray
• Hybrid drive, a type of notebook computer hard drive that utilizes a large buffer
• HD Radio, an abbreviation from the term Hybrid Digital/analog radio
• HD Photo, an image format
• the chemical warfare agent sulfur mustard, which in its distilled form is referred to as HD

[edit] Other

• Harmonisation Document, a normative document in the European Union
• Hit Dice, a statistic related to hit points, indicating role-playing game characters’ health or durability
• Holocaust denial

This disambiguation page lists articles associated with the same title. If an internal link led you here, you may wish to change the link to point directly to the intended article.

Advantages of HDTV expressed in non-technical terms

High-definition television (HDTV) yields a better-quality image than standard television does, because it has a greater number of lines of resolution. The visual information is some 2-5 times sharper because the gaps between the scan lines are narrower or invisible to the naked eye.

The lower-case “i” appended to the numbers denotes interlaced; the lower-case “p” denotes progressive. The interlaced scanning method, the 1,080 lines of resolution are divided into two, the first 540 lines are painted on a frame, the second 540 lines are painted on a second frame, reducing the bandwidth. The progressive scanning method simultaneously displays all 1,080 lines of resolution at 60 frames per second, on a greater bandwidth. (See: An explanation of HDTV numbers and laymen’s glossary)

Often, the broadcast HDTV video signal soundtrack is Dolby Digital 5.1 surround sound, enabling full, surround sound capabilities, while STBC television signals include either monophonic or stereophonic audio, or both. Stereophonic broadcasts can be encoded with Dolby Surround audio signal. Brasil opted to upgrade the ISDB-T Japanese standard to H.264 AVC Mpeg4 part 10 in the video compression and HE-AAC for audio compression because Dolby is not open and the royalty fees are more expensive than that of Mpeg4 H.264 AVC and renamed the upgraded standard to ISDB-Tb that now became the International ISDB-T standard.

[edit] Disadvantages of HDTV expressed in non-technical terms

In practice, the best possible HD quality is not usually achieved. The main problem is that many operators do not follow LCD HDTV specifications fully. They may use slower bitrates or lower resolution to pack more channels within the limited bandwidth.^[12] The operators may use format that is different from the original programming, introducing generation loss artifacts in the process of re-encoding.^[13] Also, image quality may be lost if the television is not properly connected to the input device or not properly configured for the input’s optimal performance, which may be difficult because of customer confusion regarding connections.

You will have to buy the appropriate cable for example in most cases an HDMI cable or component cables. These are often more expensive. For instance, if Composite or S-Video cables are used for connections from a cable box or satellite dish then only an SDTV quality picture will be seen. HDMI provides the best picture and sound but are also generally more expensive than Component cables.

As high-definition video broadcasts are digital, the disadvantages of digital video broadcasting also apply here. For example, digital video responds differently to analogue video when subject to interference. As opposed to a lower-quality signal one gets from interference in an analogue television broadcast, interference in a digital television broadcast will freeze, skip, or display “garbage” information. Broadcasters may aggressively compress video to save bandwidth and therefore broadcast more channels – this compression manifests itself as reduced video quality.

In order to view HDTV broadcasts, viewers may have to upgrade their TVs which come at expense. Adding a new aspect ratio makes for consumer confusion if their display is capable of one or more ratios but must be switched to the correct one by the user. Traditional standard definition TV shows and feature films (mostly movies from before 1953) originally filmed in the standard 4:3 ratio, when displayed correctly on a HDTV monitor, will have empty display areas to the left and right of the image. Many consumers aren’t satisfied with this unused display area and choose instead to distort their standard definition shows by stretching them horizontally to fill the screen, giving everything a too-wide or not-tall-enough appearance. Alternatively, they’ll choose to zoom the image which removes content that was on the top and bottom of the original TV show.^[14]

Broadcasters may demand, or cable-television operators may elect, to place HD signals in a premium band that requires higher cable fees. Some satellite companies may offer local HD channels as a service at additional cost (transmission comes from satellite). This leads some broadcasters to offer on-air broadcasts of local HD signals as a premium service to subscribers. Viewers may be denied some television channels that they expected, be allowed only access to the non-digital, and obviously sub-standard non-digital signal, or have to install an antenna to receive the digital broadcasts. Such issues more entail economic and legal disputes than they entail technology.

Another disadvantage of HDTV compared to traditional television has been consumer confusion stemming from the different standards and resolutions, such as 1080i, 1080p, and 720p. Complicating the matter have been the changes in television connections from component video, to DVI, then to HDMI. Finally, the HD DVD vs. Blu-ray Disc high definition storage format war for a period of time created confusion for consumers. This particular format war was recently “settled” with Blu-ray emerging as the victorious standard.

HDTV sources computer graphics digital

The rise in popularity of large screens and projectors has made the limitations of conventional Standard Definition TV (SDTV) increasingly evident. A HDTV compatible television set will not improve the quality of SDTV channels. To display a superior picture, high definition televisions require a High Definition (HD) signal. Typical sources of HD signals are as follows:

• Over the air with an antenna. Most cities in the US with major network affiliates broadcast over the air in HD. To receive this signal an HD tuner is required. Most newer high definition televisions have an HD tuner built in. For HDTV televisions without an built in HD tuner, a separate set-top HD tuner box can be rented from a cable or satellite company or purchased.
• Cable television companies often offer HDTV broadcasts as part of their digital broadcast service. This is usually done with a set-top box or CableCARD issued by the cable company. Alternatively one can usually get the network HDTV channels for free with basic cable by using a QAM tuner built into their HDTV or set-top box. Some cable carriers also offer HDTV on-demand playback of movies and commonly viewed shows.
• Satellite-based TV companies, such as DirecTV and Dish Network (both in North America), Sky Digital (in the UK and Ireland), Bell ExpressVu and Star Choice (both in Canada) and NTV Plus (in Russia), offer HDTV to customers as an upgrade. New satellite receiver boxes and a new satellite dish are often required to receive HD content.
• Video game systems, such as the Xbox, PlayStation 3, and Xbox 360, and digital set-top boxes that rely on an Internet connection, such as the Apple TV, can output a HD signal. The Xbox Live Marketplace, iTunes Music Store, and PlayStation Network services offer HD movies, TV shows, movie trailers, and clips for download, but generally at lower bitrates than Blu-ray Disc.
• Most newer computer graphics cards have either HDMI or DVI interfaces, which can be used to output images or video to a HDTV.
• The optical disc standard Blu-ray Disc (25GB-50GB) can provide enough digital storage to store hours of HD video content.^[9]

High-definition television(HDTV)

High-definition television (HDTV) is a digital television broadcasting system with higher resolution than traditional television systems (NTSC, SECAM, PAL). HDTV is digitally broadcast because digital television (DTV) requires less bandwidth if sufficient video compression is used.

History of high-definition television

Further information: Analog high-definition television system

The term high definition described the television systems of the 1930s and 1940s beginning with the British 405-line black-and-white system, introduced in 1936; however, it, and the American 525-line NTSC system established in 1941, were only high definition in comparison with previous mechanical and electronic television systems. Today, the American 525-line NTSC system and the European 625-line PAL and SECAM systems are only regarded as standard definition. The post–WWII French 819-line black-and-white system was high definition in the contemporary sense, but was discontinued in 1986, a year after the final British 405-line broadcast.

In 1958, the U.S.S.R. created Тransformator (Russian: Трансформатор, “Transformer”), the first high-resolution (definition) television system capable of producing an image composed of 1,125 lines of resolution for the purpose of television conferences among military commands; as it was a military product, it was not commercialized.^[1]

In 1969, the Japanese state broadcaster NHK first developed consumer high-definition television with a 5:3 aspect ratio, a slightly wider screen format than the usual 4:3 standard.^[2] However, the system was not launched publicly until late in the 1990s.

In 1981, the first HDTV demonstration in the United States was held. It had the same 5:3 aspect ratio as the Japanese system.^[3]

In 1983, the International Telecommunication Union’s radiotelecommunications sector (ITU-R) set up a working party (IWP11/6) with the aim of setting a single international HDTV standard. One of the thornier issues concerned a suitable frame/field refresh rate, with the world already strongly demarcated into two camps, 25/50Hz and 30/60Hz, related by reasons of picture stability to the frequency of their mains electrical supplies. The WP considered many views and through the 1980s served to encourage development in a number of video digital processing areas, not least conversion between the two main frame/field rates using motion vectors, which led to further developments in other areas. While a comprehensive HDTV standard was not in the end established, agreement on the aspect ratio was achieved. Initially the existing 5:3 aspect ratio had been the main candidate, but due to the influence of widescreen cinema, the aspect ratio 16:9 (1.78) eventually emerged as being a reasonable compromise between 5:3 (1.67) and the common 1.85 widescreen cinema format. An aspect ratio of 16:9 was duly agreed at the first meeting of the WP at the BBC’s R & D establishment in Kingswood Warren.

The resulting ITU-R Recommendation ITU-R BT.709-2 (“Rec. 709″) includes the 16:9 aspect ratio, a specified colorimetry, and the scan modes 1080i (1,080 actively-interlaced lines of resolution) and 1080p (1,080 progressively-scanned lines). It also includes the alternative 1440 x 1152 HDMAC scan format. (According to some reports, a mooted 720p format (720 progressively-scanned lines) was viewed by some at the ITU as an “enhanced” television format rather than a true HDTV format^[4], and so was not included, although 1920×1080 and 1280x720p systems for a range of frame and field rates were defined by several US SMPTE standards.)

However, even that limited standardization of HDTV did not lead to its adoption, principally for technical and economic reasons. Early HDTV commercial experiments such as NHK’s MUSE required over four times the bandwidth of a standard-definition (SDTV) broadcast, and despite efforts made to shrink the required bandwidth down to about 2 times that of SDTV, it was still only distributable by satellite. In addition, recording and reproducing a HDTV signal was a significant technical challenge in the early years of HDTV.

HDTV technology was introduced in the United States in the 1990s by the Digital HDTV Grand Alliance, a group of television companies and MIT.^[5][6] On 6th April 1997, CBS went on the air with WCBS-HD from the top of the Empire State Building, New York, doing demos and evaluations.^[7] The first HDTV sets went on sale in the United States in 1998.

In Europe, analog 1,125-line HD-MAC test broadcasts were performed in the early 1990s, but did not lead to any established public broadcast service.

Japan remains the only country with successful public broadcast analog HDTV, known as “Hi-vision”, featuring a 5:3 aspect ratio screen with 1,125 interlaced lines (1,035 active lines) at the rate of 60 fields per second.

It was not until the early 2000s that technology had progressed enough to deliver sufficient storage capacity and processing power to support compression algorithms powerful enough to make HDTV affordable for consumers and profitable for broadcasters and other programme makers. The main enabling factor was the transition from analog to digital TV standards. Digital compression methods such as MPEG-2 and MPEG-4 allow the bandwidth of a single analogue TV channel (6 MHz in the US) to carry up to 5 standard-definition or up to 2 high-definition digital TV channels instead. Most developed nations have plans in place for a transition to digital television, but not necessarily or exclusively HDTV; for example, on 17th February 2009, the US intends to terminate all full-power terrestrial analog broadcasting (although some smaller local stations have later deadlines), with both standard definition TV (SDTV) and HDTV being allowed. ^[8]

Current HDTV broadcast standards include ATSC (US and Canada) and DVB (Europe, and most of the rest of the world). HDTV can also provide 5.1-channel surround sound audio using e.g. the Dolby Digital (AC-3) format.

Zero-power (bistable) LCD displays

Zero-power (bistable) displays

The zenithal bistable device (ZBD), developed by QinetiQ (formerly DERA), can retain an image without power. The crystals may exist in one of two stable orientations (Black and “White”) and power is only required to change the image. ZBD Displays is a spin-off company from QinetiQ who manufacture both grayscale and color ZBD devices.

A French company, Nemoptic, has developed another zero-power, paper-like LCD technology which has been mass-produced since July 2003. This technology is intended for use in applications such as Electronic Shelf Labels, E-books, E-documents, E-newspapers, E-dictionaries, Industrial sensors, Ultra-Mobile PCs, etc. Zero-power LCDs are a category of electronic paper.

Kent Displays has also developed a “no power” display that uses Polymer Stabilized Cholesteric Liquid Crystals (ChLCD). The major drawback to the ChLCD is slow refresh rate, especially with low temperatures.

In 2004 researchers at the University of Oxford demonstrated two new types of zero-power bistable LCDs based on Zenithal bistable techniques.^[16]

Several bistable technologies, like the 360° BTN and the bistable cholesteric, depend mainly on the bulk properties of the liquid crystal (LC) and use standard strong anchoring, with alignment films and LC mixtures similar to the traditional monostable materials. Other bistable technologies (i.e. Binem Technology) are based mainly on the surface properties and need specific weak anchoring materials.

[edit] Drawbacks

Two IBM ThinkPad laptop screens viewed at an extreme angle.

LCD technology still has a few drawbacks in comparison to some other display technologies:

• While CRTs are capable of displaying multiple video resolutions without introducing artifacts, LCDs produce crisp images only in their “native resolution” and, sometimes, fractions of that native resolution. Attempting to run LCD panels at non-native resolutions usually results in the panel scaling the image, which introduces blurriness or “blockiness” and is susceptible in general to multiple kinds of HDTV blur. Many LCDs are incapable of displaying very low resolution screen modes (such as 320×200) due to these scaling limitations.

• Although LCDs typically have more vibrant images and better “real-world” contrast ratios (the ability to maintain contrast and variation of color in bright environments) than CRTs, they do have lower contrast ratios than CRTs in terms of how deep their blacks are. A contrast ratio is the difference between a completely on (white) and off (black) pixel, and LCDs can have “backlight bleed” where light (usually seen around corners of the screen) leaks out and turns black into gray. However, as of December 2007, the very best LCDs can approach the contrast ratios of plasma displays in terms of delivering a deep black.

• LCDs typically have longer response times than their plasma and CRT counterparts, especially older displays, creating visible ghosting when images rapidly change. For example, when moving the mouse quickly on an LCD, multiple cursors can sometimes be seen.

• Some LCDs have significant input lag. If the lag delay is large enough, such displays can be unsuitable for fast and time-precise mouse operations (CAD, FPS gaming) as compared to CRT displays or smaller LCD panels with negligible amounts of input lag. Short lag times are sometimes emphasized in marketing.

• LCD panels using TN tend to have a limited viewing angle relative to CRT and plasma displays. This reduces the number of people able to conveniently view the same image – laptop screens are a prime example. Usually when looking below the screen, it gets much darker; looking from above makes it look lighter. Many panels such as 22″ and 24″ LCDs which are based on the IPS, MVA, or PVA panels have much improved viewing angles; typically the color only gets a little brighter when viewing at extreme angles.

• Consumer LCD monitors tend to be more fragile than their CRT counterparts. The screen may be especially vulnerable due to the lack of a thick glass shield as in CRT monitors.

• Dead pixels can occur when the screen is damaged or pressure is put upon the screen; few manufacturers replace screens with dead pixels for free.

• Horizontal and/or vertical banding is a problem in some LCD screens. This flaw occurs as part of the manufacturing process, and cannot be repaired (short of total replacement of the screen). Banding can vary substantially even among LCD screens of the same make and model. The degree is determined by the manufacturer’s quality control procedures.

• The cold-cathode fluorescent bulbs typically used for back-lights in LCDs contain mercury. LED backlit LCD displays are mercury-free.

Quality control LCD panels

Some LCD panels have defective transistors, causing permanently lit or unlit pixels which are commonly referred to as stuck pixels or dead pixels respectively. Unlike integrated circuits (ICs), LCD panels with a few defective pixels are usually still usable. It is also economically prohibitive to discard a panel with just a few defective pixels because LCD panels are much larger than ICs. Manufacturers have different standards for determining a maximum acceptable number of defective pixels. The maximum acceptable number of defective pixels for LCD varies greatly. At one point, Samsung held a zero-tolerance policy for LCD monitors sold in Korea.^[11] Currently, though, Samsung adheres to the less restrictive ISO 13406-2 standard.^[12] Other companies have been known to tolerate as many as 11 dead pixels in their policies.^[13] Dead pixel policies are often hotly debated between manufacturers and customers. To regulate the acceptability of defects and to protect the end user, ISO released the ISO 13406-2 standard.^[14] However, not every LCD manufacturer conforms to the ISO standard and the ISO standard is quite often interpreted in different ways.

Examples of defects in LCDs

LCD panels are more likely to have defects than most ICs due to their larger size. In the example to the right, a 300 mm SVGA LCD has 8 defects and a 150 mm wafer has only 3 defects. However, 134 of the 137 dies on the wafer will be acceptable, whereas rejection of the LCD panel would be a 0% yield. The standard is much higher now due to fierce competition between manufacturers and improved quality control. An SVGA LCD panel with 4 defective pixels is usually considered defective and customers can request an exchange for a new one. Some manufacturers, notably in South Korea where some of the largest LCD panel manufacturers, such as LG, are located, now have “zero defective pixel guarantee”, which is an extra screening process which can then determine “A” and “B” grade panels. Many manufacturers would replace a product even with one defective pixel. Even where such guarantees do not exist, the location of defective pixels is important. A display with only a few defective pixels may be unacceptable if the defective pixels are near each other. Manufacturers may also relax their replacement criteria when defective pixels are in the center of the viewing area.

LCD panels also have defects known as mura, which look like a small-scale crack with very small changes in luminance or color.^[15]

Active matrix LCD technologies

Main article: TFT LCD, Active-matrix liquid crystal display

[edit] Twisted nematic (TN)

Twisted nematic displays contain liquid crystal elements which twist and untwist at varying degrees to allow light to pass through. When no voltage is applied to a TN liquid crystal cell, the light is polarized to pass through the cell. In proportion to the voltage applied, the LC cells twist up to 90 degrees changing the polarization and blocking the light’s path. By properly adjusting the level of the voltage almost any grey level or transmission can be achieved.

For a more comprehensive description refer to the section on the twisted nematic field effect.

[edit] In-plane switching (IPS)

In-plane switching is an LCD technology which aligns the liquid crystal cells in a horizontal direction. In this method, the electrical field is applied through each end of the crystal, but this requires two transistors for each pixel instead of the single transistor needed for a standard thin-film transistor (TFT) display. This results in blocking more transmission area, thus requiring a brighter backlight, which will consume more power, making this type of display less desirable for notebook computers.

[edit] Vertical alignment (VA)

Vertical alignment displays are a form of LC displays in which the liquid crystal material naturally exists in a horizontal state removing the need for extra transistors (as in IPS). When no voltage is applied the liquid crystal cell, it remains perpendicular to the substrate creating a black display. When voltage is applied, the liquid crystal cells shift to a horizontal position, parallel to the substrate, allowing light to pass through and create a white display. VA liquid crystal displays provide some of the same advantages as IPS panels, particularly an improved viewing angle and improved black level.

Passive-matrix and active-matrix addressed LCDs

LCDs with a small number of segments, such as those used in digital watches and pocket calculators, have individual electrical contacts for each segment. An external dedicated circuit supplies an electric charge to control each segment. This display structure is unwieldy for more than a few display elements.

Small monochrome displays such as those found in personal organizers, or older laptop screens have a passive-matrix structure employing super-twisted nematic (STN) or double-layer STN (DSTN) technology—the latter of which addresses a color-shifting problem with the former—and color-STN (CSTN)—wherein color is added by using an internal filter. Each row or column of the display has a single electrical circuit. The pixels are addressed one at a time by row and column addresses. This type of display is called passive-matrix addressed because the pixel must retain its state between refreshes without the benefit of a steady electrical charge. As the number of pixels (and, correspondingly, columns and rows) increases, this type of display becomes less feasible. Very slow response times and poor contrast are typical of passive-matrix addressed LCDs.

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 addressed displays of the same size, and generally have quicker response times, producing much better images.

LCD monitor Specifications

Important factors to consider when evaluating an LCD monitor:

• Resolution: The horizontal and vertical size expressed in pixels (e.g., 1024×768). Unlike CRT monitors, LCD monitors have a native-supported resolution for best display effect.
• Dot pitch: The distance between the centers of two adjacent pixels. The smaller the dot pitch size, the less granularity is present, resulting in a sharper image. Dot pitch may be the same both vertically and horizontally, or different (less common).
• Viewable size: The size of an LCD panel measured on the diagonal (more specifically known as active display area).
• Response time: The minimum time necessary to change a pixel’s color or brightness. Response time is also divided into rise and fall time. For LCD Monitors, this is measured in btb (black to black) or gtg (gray to gray). These different types of measurements make comparison difficult.
• Refresh rate: The number of times per second in which the monitor draws the data it is being given. A refresh rate that is too low can cause flickering and will be more noticeable on larger monitors. Many high-end LCD televisions now have a 120 Hz refresh rate (current and former NTSC countries only). This allows for less distortion when movies filmed at 24 frames per second (fps) are viewed due to the elimination of telecine (3:2 pulldown). The rate of 120 was chosen as the least common multiple of 24 fps (cinema) and 30 fps (TV).
• Matrix type: Active or Passive.
• Viewing angle: (coll., more specifically known as viewing direction).
• Color support: How many types of colors are supported (coll., more specifically known as color gamut).
• Brightness: The amount of light emitted from the display (coll., more specifically known as luminance).
• Contrast ratio: The ratio of the intensity of the brightest bright to the darkest dark.
• Aspect ratio: The ratio of the width to the height (for example, 4:3, 16:9 or 16:10).
• Input ports (e.g., DVI, VGA, LVDS, or even S-Video and HDMI).

[edit] Brief history

• 1888: Friedrich Reinitzer (1858-1927) discovers the liquid crystalline nature of cholesterol extracted from carrots (that is, two melting points and generation of colors) and published his findings at a meeting of the Vienna Chemical Society on May 3, 1888 (F. Reinitzer: Beiträge zur Kenntniss des Cholesterins, Monatshefte für Chemie (Wien) 9, 421-441 (1888)).^[1]

• 1904: Otto Lehmann publishes his work “Liquid Crystals”.

• 1911: Charles Mauguin describes the structure and properties of liquid crystals.

• 1936: The Marconi Wireless Telegraph company patents the first practical application of the technology, “The Liquid Crystal Light Valve”.

• 1962: The first major English language publication on the subject “Molecular Structure and Properties of Liquid Crystals”, by Dr. George W. Gray.^[2]

• 1962: Richard Williams of RCA found that liquid crystals had some interesting electro-optic characteristics and he realized an electro-optical effect by generating stripe-patterns in a thin layer of liquid crystal material by the application of a voltage. This effect is based on an electro-hydrodynamic instability forming what is now called “Williams domains” inside the liquid crystal.^[3]

• 1964: In the fall of 1964 George H. Heilmeier, then working in the RCA laboratories on the effect discovered by Williams realized the switching of colors by field-induced realignment of dichroic dyes in a homeotropically oriented liquid crystal. Practical problems with this new electro-optical effect made Heilmeier to continue work on scattering effects in liquid crystals and finally the realization of the first operational liquid crystal display based on what he called the dynamic scattering mode (DSM). Application of a voltage to a DSM display switches the initially clear transparent liquid crystal layer into a milky turbid state. DSM displays could be operated in transmissive and in reflective mode but they required a considerable current to flow for their operation.^[4][5][6]

Pioneering work on liquid crystals was undertaken in the late 1960s by the UK’s Royal Radar Establishment at Malvern. The team at RRE supported ongoing work by George Gray and his team at the University of Hull who ultimately discovered the cyanobiphenyl liquid crystals (which had correct stability and temperature properties for application in LCDs).

• 1970: On December 4, 1970, the twisted nematic field effect in liquid crystals was filed for patent by Hoffmann-LaRoche in Switzerland, (Swiss patent No. 532 261) with Wolfgang Helfrich and Martin Schadt (then working for the Central Research Laboratories) listed as inventors.^[4] Hoffmann-La Roche then licensed the invention to the Swiss manufacturer Brown, Boveri & Cie who produced displays for wrist watches during the 1970′s and also to Japanese electronics industry which soon produced the first digital quartz wrist watches with TN-LCDs and numerous other products. James Fergason at the Westinghouse Research Laboratories in Pittsburgh while working with Sardari Arora and Alfred Saupe at Kent State University Liquid Crystal Institute filed an identical patent in the USA on April 22, 1971.^[7] In 1971 the company of Fergason ILIXCO (now LXD Incorporated) produced the first LCDs based on the TN-effect, which soon superseded the poor-quality DSM types due to improvements of lower operating voltages and lower power consumption.
• 1972: The first active-matrix liquid crystal display panel was produced in the United States by T. Peter Brody.^[8]

• 2008: LCD TVs are the main stream with 50% market share of the 200 million TVs forecasted to ship globally in 2008 according to Display Bank.^{[citation needed]}

A detailed description of the origins and the complex history of liquid crystal displays from the perspective of an insider during the early days has been published by Joseph A. Castellano in “Liquid Gold, The Story of Liquid Crystal Displays and the Creation of an Industry” ^[9].

The same history seen from a different perspective has been described and published by Hiroshi Kawamoto, available at the IEEE History Center.^[10]

[edit] Color displays

A subpixel of a color LCD

Simulation of an LCD monitor up close

Comparison of the OLPC XO-1 display (left) with a typical color LCD. The images show 1×1 mm of each screen. A typical LCD addresses groups of 3 locations as pixels. The XO-1 display addresses each location as a separate pixel.

In color LCDs each individual pixel is divided into three cells, or subpixels, 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 analog electron beam employed in CRTs do not hit exact ‘subpixels’.

Color components may be arrayed in various pixel geometries, depending on the monitor’s usage. If 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.

To reduce smudging in a moving picture when pixels do not respond quickly enough to color changes, so-called pixel overdrive may be used.

Liquid crystal display (LCD)

A liquid crystal display (LCD) is a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is often utilized in battery-powered electronic devices because it uses very small amounts of electric power.

Contents [hide] 1 Overview 2 Specifications 3 Brief history 4 Color displays 5 Passive-matrix and active-matrix addressed LCDs 6 Active matrix technologies 6.1 Twisted nematic (TN) 6.2 In-plane switching (IPS) 6.3 Vertical alignment (VA) 7 Quality control 8 Zero-power (bistable) displays 9 Drawbacks 10 See also 10.1 LCD technologies 10.2 Other display technologies 10.3 Display applications 10.4 Manufacturers 11 References 12 External links – Tutorials 12.1 General information

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[edit] Overview

LCD alarm clock

Each pixel of an LCD typically consists of a layer of 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 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 unidirectionally rubbed using, for example, a cloth. The direction of the liquid crystal alignment 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. In a twisted nematic device (still 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. Because the liquid crystal material is birefringent, light passing through one polarizing filter is rotated by the liquid crystal helix as it passes through the liquid crystal layer, allowing it to pass through the second polarized filter. Half of the incident light is absorbed by the first polarizing filter, but otherwise the entire assembly is reasonably transparent.

LCD with top polarizer removed from device and placed on top, such that the top and bottom polarizers are crossed.

When a voltage is applied across the electrodes, a torque acts to align the liquid crystal molecules parallel to the electric field, distorting the helical structure (this is resisted by elastic forces since the molecules are constrained at the surfaces). This reduces the rotation of the polarization of the incident light, and the device appears gray. 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 the liquid 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.