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An LG flat-panel LCD monitor.
An LG flat-panel LCD monitor. A thin film transistor liquid crystal display ( TFT-LCD) is a variant of Liquid crystal display (LCD which uses Thin film transistor (TFT technology to

A visual display unit, often called simply a monitor or display, is a piece of electrical equipment which displays images generated from the video output of devices such as computers without producing a permanent record. Electrical equipment includes any Machine powered by Electricity. Video is the technology of electronically capturing, Recording, processing storing transmitting and reconstructing a sequence of Still images A computer is a Machine that manipulates data according to a list of instructions. A newer monitor typically consists of a TFT LCD, with most older monitors based around a cathode ray tube (CRT. A thin film transistor liquid crystal display ( TFT-LCD) is a variant of Liquid crystal display (LCD which uses Thin film transistor (TFT technology to The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or ) The monitor comprises the display device, simple circuitry to generate and format a picture from video sent by the signals source, and usually an enclosure. An electronic circuit is a closed path formed by the interconnection of Electronic components through which an Electric current can flow In the fields of communications, Signal processing, and in Electrical engineering more generally a signal is any time-varying or spatial-varying quantity A computer case (also known as the computer chassis, cabinet, tower, box, enclosure, housing or simply case Within the signal source, either as an integral section or a modular component, there is a display adapter to generate video in a format compatible with the monitor. A video card, also known as a graphics accelerator card, display adapter, or graphics card, is a hardware component whose function is to

Contents

Screen size

Main article: Screen size

Diagonal size

The size of a display is typically given as the distance between two opposite screen corners. One problem with this method is that it does not distinguish between the aspect ratios of monitors with identical diagonal sizes, in spite of the fact that a shape of a given diagonal span's area decreases as it becomes less square. The aspect ratio of an Image is its width divided by its height Area is a Quantity expressing the two- Dimensional size of a defined part of a Surface, typically a region bounded by a closed Curve. For example, a 4:3 21" monitor has an area of ~211 square inches, while a 16:9 21" widescreen has an area of only ~188 square inches. A widescreen image is a film computer or television image with a wider and shorter aspect ratio than the standard Academy frame developed during the Classical

This method of size measurement dates from the early days of CRT television when round picture tubes were in common use, which only had one dimension that described display size. When round tubes were used to display rectangular images, the diagonal measurement of these was equivalent to the round tube's diameter, hence this was used.

Another historically problematic practice is the direct measurement of a monitor's imaging element as its quoted size in publicity and advertising materials. Especially on CRT displays, a substantial portion of the imaging element is concealed behind the case's bezel or shroud in order to hide areas outside the monitor's safe area due to overscan. Safe area is a term used in television production to describe the areas of the television picture that can be seen on Television Screens Older televisions Overscan is extra image area around the four edges of a Video image that is not normally seen by the viewer Seen as deceptive, widespread consumer objection and lawsuits eventually forced most manufacturers to instead measure viewable size. On a Computer monitor, the viewable image size or VIS is the actual amount of screen space that is available to display a Picture, without obstruction from

Imaging technologies

19" inch (48.3 cm tube, 45.9 cm viewable) ViewSonic CRT computer monitor.
19" inch (48. 3 cm tube, 45. 9 cm viewable) ViewSonic CRT computer monitor. ViewSonic Corporation is a manufacturer and provider of visual technology specifically CRT monitors Liquid crystal displays Projectors Plasma

As with television, many different hardware technologies exist for displaying computer-generated output:

Cathode ray tube

CRT Computer display pixel array (right).
CRT Computer display pixel array (right). A surface-conduction electron-emitter display (SED is a Flat panel display technology that uses surface conduction Electron emitters for every individual display An Organic Light Emitting Diode ( OLED) also Light Emitting Polymer ( LEP) and Organic Electro Luminescence ( OEL) is any The Penetron is a Cathode ray tube with a voltage-sensitive screen that displays variable colors on layers of Phosphors based on a beam penetration mechanism

The CRT or cathode ray tube, is the picture tube of a monitor. The cathode ray tube (CRT is a Vacuum tube containing an Electron gun (a source of electrons and a Fluorescent screen with internal or The back of the tube has a negatively charged cathode. The electron gun shoots electrons down the tube and onto a charged screen. An electron gun (also called electron emitter) is an electrical component that produces an Electron beam that has a precise Kinetic energy and is most often The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The screen is coated with a pattern of phosphor dots that glow when struck by the electron stream. A phosphor is a substance that exhibits the phenomenon of Phosphorescence (sustained glowing after exposure to energized particles such as Electrons Each cluster of three dots, one of each color, is one pixel. In Digital imaging, a pixel ( pict ure el ement is the smallest piece of information in an image

The image on the monitor's screen is usually made up from at least tens of thousands of such tiny dots glowing on command from the computer. The closer together the pixels are, the sharper the image on screen can be. The distance between pixels on a computer monitor screen is called its dot pitch and is measured in millimeters. Dot pitch (sometimes called line pitch, phosphor pitch or pixel pitch) is a specification for a Computer display, Computer printer Most monitors have a dot pitch of 0. 28 mm or less.

There are two electromagnets around the collar of the tube which deflect the electron beam. An electromagnet is a type of Magnet in which the Magnetic field is produced by the flow of an electric current. The beam scans across the top of the monitor from left to right, is then blanked and moved back to the left-hand side slightly below the previous trace (on the next scan line), scans across the second line and so on until the bottom right of the screen is reached. In Raster scan equipment an Image is built up by scanning an electron beam from left to right across a screen to produce a visible trace of one Scan line A scan line is one line or row in a Raster scanning pattern such as a video line on a Cathode ray tube (CRT display of a television or computer The beam is again blanked, and moved back to the top left to start again. The vertical blanking interval (VBI also known as the vertical interval or VBLANK, is the time difference between the last line of one frame or field of a Raster This process draws a complete picture, typically 50 to 100 times a second. The number of times in one second that the electron gun redraws the entire image is called the refresh rate and is measured in hertz (cycles per second). The refresh rate (most commonly the "vertical refresh rate" "vertical scan rate" for CRTs is the number of times in a second that display hardware draws The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. It is common in television or very early computer equipment, to use a technique called interlacing, in which all the odd-numbered lines of an image are traced, and then all the even-numbered lines; the circuitry of such an interlaced display need be capable of only half the speed of a non-interlaced display. For the method of incrementally displaying Raster graphics, see Interlace (bitmaps. An interlaced display, particularly at a relatively low refresh rate, can appear to some observers to flicker, and may cause eyestrain.

Performance measurements

The performance parameters of a monitor are:

Comparison

CRT

Pros:

Cons:

LCD

A Samsung 19" LCD monitor.
A Samsung 19" LCD monitor. Implosion is a process in which objects are destroyed by collapsing in on themselves The Samsung Group ( Korean:, Samsung Guerup) is South Korea 's largest company or Chaebol and the world's largest conglomerate

Pros:

Cons:

Plasma

Pros:

Cons:

Penetron

Main article: Penetron

Pros:

Cons:

Problems

Dead pixels

A few LCD monitors are produced with "dead pixels". Defective pixels are pixels on a crystal display (LCD not performing as expected Due to the desire for affordable monitors, most manufacturers sell monitors with dead pixels. Almost all manufacturers have clauses in their warranties which claim monitors with fewer than some number of dead pixels are not broken and will not be replaced. The dead pixels are usually stuck with the green, red, and/or blue subpixels either individually always stuck on or off. Defective pixels are pixels on a crystal display (LCD not performing as expected

Like image persistence, this can sometimes be partially or fully reversed by using the same method listed below, however the chance of success is far lower than with a "stuck" pixel. It can also sometimes be repaired by physically flicking the pixel, however it is always a possibility for someone to use too much force and rupture the weak screen internals doing this.

Stuck pixels

LCD monitors, while lacking phosphor screens and thus immune to phosphor burn-in, have a similar condition known as image persistence, where the pixels of the LCD monitor can "remember" a particular color and become "stuck" and unable to change. A phosphor is a substance that exhibits the phenomenon of Phosphorescence (sustained glowing after exposure to energized particles such as Electrons Image Persistence is the term used for the LCD and Plasma display equivalent of screen burn. Unlike phosphor burn-in, however, image persistence can sometimes be reversed partially or completely. This is accomplished by rapidly displaying varying colors to "wake up" the stuck pixels. Defective pixels are pixels on a crystal display (LCD not performing as expected

Phosphor burn-in

Phosphor burn-in is localised aging of the phosphor layer of a CRT screen where it has displayed a static bright image for many years. A phosphor is a substance that exhibits the phenomenon of Phosphorescence (sustained glowing after exposure to energized particles such as Electrons This results in a faint permanent image on the screen, even when powered off. In severe cases it can even be possible to read some of the text, though this only occurs where the displayed text remained the same for years.

This was once a common phenomenon in single purpose business computers. It can still be an issue with CRT displays when used to display the same image for years at a time, but modern computers aren't normally used this way any more, so the problem is not a significant issue. The issue seems to have become exaggerated in popular opinion. The only systems that suffered the defect were ones displaying the same image for years, and with these the presence of burn-in was not a noticeable effect when in use, since it coincided with the displayed image perfectly. It only became a significant issue in 3 situations:

Screen savers were developed as a means to avoid burn-in, but are redundant for CRTs today, despite their popularity. A screensaver is a type of computer program initially designed to prevent " Phosphor burn-in " on CRT and plasma Computer

Phosphor burn-in can be gradually removed on damaged CRT displays by displaying an all white screen with brightness & contrast turned up full. This is a slow procedure, and is usually effective.

Plasma burn-in

Burn-in re-emerged as an issue with early plasma displays, which are more vulnerable to this than CRTs. Screen savers with moving images may be used with these to minimise localised burn. Periodic change of the colour scheme in use also helps.

Glare

Glare is a problem caused by the relationship between lighting and screen, or by using monitors in bright sunlight. LCDs and flat screen CRTs are less prone to reflected glare than conventional curved CRTs, and aperture grille CRTs, which are curved on one axis only, are less prone to it than other CRTs curved on both axes.

If the problem persists despite moving the monitor or adjusting lighting, a filter using a mesh of very fine black wires may be placed on the screen to reduce glare and improve contrast. These filters were popular in the late 1980s. They do also reduce light output.

The above will only work against reflective glare, direct glare (such as sunlight) will completely wash out most monitors' internal lighting, and can only be dealt with by use of a hood or transreflective LCD.

Color misregistration

With exceptions of correctly aligned video projectors and stacked LEDs, most display technologies, especially LCD, have an inherent misregistration of the color channels, that is, the centers of the red, green, and blue dots do not line up perfectly. An Organic Light Emitting Diode ( OLED) also Light Emitting Polymer ( LEP) and Organic Electro Luminescence ( OEL) is any Subpixel rendering depends on this misalignment; technologies making use of this include the Apple II from 1976,[1] and more recently Microsoft (ClearType, 1998) and XFree86 (X Rendering Extension). Subpixel rendering is a way to increase the apparent resolution of a computer's Liquid crystal display (LCD by rendering pixels to take account the screen type's physical properties Year 1976 ( MCMLXXVI) was a Leap year starting on Thursday (link will display full calendar of the Gregorian calendar. Microsoft Corporation is an American multinational Computer technology Corporation, which rose to dominate the Home computer ClearType is the Microsoft implementation of Subpixel rendering technology aiming to improve the appearance of text on certain types of Computer display Year 1998 ( MCMXCVIII) was a Common year starting on Thursday (link will display full 1998 Gregorian calendar) XFree86 is an implementation of the X Window System. It was originally written for Unix-like Operating systems on IBM PC compatibles and is now The X Rendering Extension ( Render or XRender) is an X Window System extension to implement Porter-Duff image compositing in the X server

Incomplete spectrum

RGB displays produce most of the visible color spectrum, but not all. This can be a problem where good color matching to non-RGB images is needed. This issue is common to all monitor technologies with 3 color channels.

Display interfaces

Computer terminals

Main article: Computer terminal

Early CRT-based VDUs (Visual Display Units) such as the DEC VT05 without graphics capabilities gained the label glass teletypes, because of the functional similarity to their electromechanical predecessors. A computer terminal is an electronic or electromechanical hardware device that is used for entering data into and displaying data from a Computer or a Computing The VT05 was the first free-standing CRT Computer terminal from Digital Equipment Corporation. Computer graphics are Graphics created by Computers and more generally the Representation and Manipulation of Pictorial Data A teleprinter (

Some historic computers had no modern display, using a teletype, modified electric typewriter, or printer instead.

Composite signal

Early home computers such as the Apple II and the Commodore 64 used a composite signal output to drive a CRT monitor or TV. This resulted in degraded resolution due to compromises in the broadcast TV standards used. This method is still used with video game consoles. The Commodore monitor had S-Video input to improve resolution.

Digital monitors

Early digital monitors are sometimes known as TTLs because the voltages on the red, green, and blue inputs are compatible with TTL logic chips. Transistor–transistor logic ( TTL) is a class of Digital circuits built from Bipolar junction transistors (BJT and Resistors It is called Later digital monitors support LVDS, or TMDS protocols. Low-voltage differential signaling, or LVDS, is an electrical signaling system that can run at very high speeds over inexpensive Twisted-pair copper cables Transition Minimized Differential Signaling ( TMDS) is a technology for transmitting high-speed serial data and is used by the DVI and HDMI video interfaces

TTL monitors

IBM PC with green monochrome display.
IBM PC with green monochrome display.
An amber monochrome computer monitor, manufactured in 2007, which uses a 15-pin SVGA connector just like a standard color monitor.
An amber monochrome computer monitor, manufactured in 2007, which uses a 15-pin SVGA connector just like a standard color monitor.

Monitors used with the MDA, Hercules, CGA, and EGA graphics adapters used in early IBM PC's (Personal Computer) and clones were controlled via TTL logic. The Monochrome Display Adapter ( MDA, also MDA card, Monochrome Display and Printer Adapter, MDPA) introduced in 1981 was IBM The Hercules Graphics Card ( HGC) was a computer Graphics controller which through its popularity became a widely supported display standard. The Color Graphics Adapter ( CGA) originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter The Enhanced Graphics Adapter (EGA is the IBM PC Computer display standard specification located between CGA and VGA in terms of graphics Transistor–transistor logic ( TTL) is a class of Digital circuits built from Bipolar junction transistors (BJT and Resistors It is called Such monitors can usually be identified by a male DB-9 connector used on the video cable. The D-subminiature or D-sub is a common type of Electrical connector used particularly in Computers Calling them "subminiature" was appropriate The disadvantage of TTL monitors was the limited number of colors available due to the low number of digital bits used for video signaling.

Modern monochrome monitors use the same 15-pin SVGA connector as standard color monitors. They are capable of displaying 32-bit grayscale at 1024x768 resolution, making them able to interface with modern computers.

TTL Monochrome monitors only made use of five out of the nine pins. Monochrome monitors are a type of computer display which were very common in the early days of computing from the 1960s through the 1980s before the color monitors became popular One pin was used as a ground, and two pins were used for horizontal/vertical synchronization. The electron gun was controlled by two separate digital signals, a video bit, and an intensity bit to control the brightness of the drawn pixels. Only four shades were possible; black, dim, medium or bright.

CGA monitors used four digital signals to control the three electron guns used in color CRTs, in a signalling method known as RGBI, or Red Green and Blue, plus Intensity. Red is any of a number of similar Colors evoked by light consisting predominantly of the longest wavelengths of Light discernible by the human eye in the wavelength Green is a Color, the perception of which is evoked by light having a spectrum dominated by energy with a Wavelength of roughly 520–570- nm. Blue is a Colour, the Perception of which is evoked by In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a Light source in a particular direction per unit Solid Each of the three RGB colors can be switched on or off independently. The intensity bit increases the brightness of all guns that are switched on, or if no colors are switched on the intensity bit will switch on all guns at a very low brightness to produce a dark grey. A CGA monitor is only capable of rendering 16 colors. The CGA monitor was not exclusively used by PC based hardware. The Commodore 128 could also utilize CGA monitors. The Commodore 128 ( C128, CBM 128, C=128) home / Personal computer was the last 8-bit machine which was commercially Many CGA monitors were capable of displaying composite video via a separate jack.

EGA monitors used six digital signals to control the three electron guns in a signalling method known as RrGgBb. Unlike CGA, each gun is allocated its own intensity bit. This allowed each of the three primary colors to have four different states (off, soft, medium, and bright) resulting in 64 colors.

Although not supported in the original IBM specification, many vendors of clone graphics adapters have implemented backwards monitor compatibility and auto detection. For example, EGA cards produced by Paradise could operate as an MDA, or CGA adapter if a monochrome or CGA monitor was used in place of an EGA monitor. Many CGA cards were also capable of operating as MDA or Hercules card if a monochrome monitor was used.

Single color screens

Display colors other than white were very popular on monochrome monitors in the 1980s. These colors were more comfortable on the eye. This was particularly an issue at the time due to the lower refresh rates in use at the time causing flicker, plus the use of less comfortable color schemes than used with most of today's software.

Green screens were the most popular color, with orange displays also available. 'Paper white' was also in use, which was a warm white.

Modern technology

Analog monitors

Most modern computer displays can show an infinite number of different colors in the RGB color space by changing red, green, and blue analog video signals in continuously variable intensities. A computer is a Machine that manipulates data according to a list of instructions. An RGB color space is any additive Color space based on the RGB color model. Analog video is a Video signal transferred by Analog signal. It contains the Luminance (brightness and Chrominance (color of the image which These have been almost exclusively progressive scan since the middle 1980s. Progressive or noninterlaced scanning is a method for displaying storing or transmitting Moving images in which all the lines of each frame are drawn in While many early plasma and liquid crystal displays have exclusively analog connections, all signals in such monitors pass through a completely digital section prior to display.

While many similar connectors (13W3, BNC, etc…) were used on other platforms, the IBM PC and compatible systems long ago standardized on the VGA connector. DB13W3 (also known simply as 13W3) is a particular style of D-subminiature connector commonly used as an analog video interface connector that was The BNC ( Bayonet Neill Concelman) connector is a very common type of RF connector used for terminating Coaxial cable. A VGA connector as it is commonly known (other names include RGB connector D-sub 15 mini sub D15 and mini D15 is a three-row 15 pin DE-15. All of these connectors deliver nearly flawless high resolution video which vastly outclasses that of a TV.

Digital and analog combination

The first popular digital monitor connectors, such as DVI-I and the various breakout connectors based on it, include both analog signals compatible with VGA and digital signals compatible with new flatscreen displays in the same connector. The Digital Visual Interface ( DVI) is a Video interface standard designed to maximize the visual quality of digital Display devices such as Flat panel A breakout box (BoB is usually a Box, in which a compound Electrical connector is separated or "broken out" into its component connectors A VGA connector as it is commonly known (other names include RGB connector D-sub 15 mini sub D15 and mini D15 is a three-row 15 pin DE-15. This made the connector nearly painless for users of both technologies.

Digital monitors

Newer connectors are being made which have digital only video signals. Many of these, such as HDMI and DisplayPort, also feature integrated audio and data connections. The High-Definition Multimedia Interface ( HDMI) is a compact audio/video connector interface for transmitting uncompressed digital streams DisplayPort is a digital display interface standard (approved May 2006 current version 1 One less popular feature most of these connectors share are DRM encrypted signals. Digital rights management ( DRM) is a generic term that refers to Access control technologies used by hardware manufacturers publishers and Copyright holders

Configuration and usage

Multiple monitors

Main article: Multi-monitor
Two Apple flat-screen monitors used as an extended desktop.
Two Apple flat-screen monitors used as an extended desktop. Multi-monitor, also known as Multi-display, Multi-head and Dual-Monitor are synonymous terms referring to the use of multiple physical display Multi-monitor, also known as Multi-display, Multi-head and Dual-Monitor are synonymous terms referring to the use of multiple physical display

More than one monitor can be attached to the same device. Each display can operate in two basic configurations:

Multiple video sources

Multiple devices can be connected to the same monitor using a video switch, in the case of computers, this usually takes the form of a "Keyboard Video Mouse switch" (KVM) switch, which is designed to switch all of the user interface devices for a workstation between different computers at once. A KVM switch (with KVM being an abbreviation for Keyboard Video or Visual Display Unit Mouse) is a hardware device that allows a user to control multiple Computers

Virtual displays

Main article: Virtual desktop
Screenshot of the Spaces environment under Mac OS X.
Screenshot of the Spaces environment under Mac OS X. A virtual desktop is a term used usually within the WIMP paradigm to describe ways in which a Computer 's Desktop environment is expanded through the use Spaces is a Virtual desktop feature developed by Apple Inc and is an integral part of Mac OS X v10

Much software and video hardware support the ability to create additional, virtual pieces of desktop, commonly known as workspaces.

Additional features

Power saving

Most modern monitors contain a power saving mode that will switched to if no video input signal is received. Modern operating systems can thus power down a monitor after a specified period of inactivity. This also extends the service life of the monitor.

Some monitors will also switch themselves completely off after a time period on standby.

Most modern laptops provide a method of gradually dimming the screen after periods of inactivity, or when the battery is in use. This is to extend battery life, and reduce wear.

Integrated accessories

Many monitors have other accessories (or connections for them) integrated. This places standard ports within easy reach and eliminates the need for another separate hub, camera, microphone, or set of speakers. In Computer hardware, a 'port' serves as an interface between the computer and other computers or peripheral devices A USB hub is a device that allows many USB devices to be connected to a single USB port on the host computer or another hub Webcams ( web cameras) are small cameras (usually though not always Video cameras, whose images can be accessed using the World Wide Web, instant Computer speakers, or multimedia speakers, are external speakers commonly equipped with a low-power internal amplifier Integrated accessories are often of substandard quality.

Directional screen

Narrow viewing angle screens are used in some security conscious applications.

Autopolyscopic screen

Main article: Autostereoscopy

A specially designed directional screen which generates 3D images without headgear, distortion or eyestrain. Autostereoscopy is a method of displaying three-dimensional images that can be viewed without the use of special headgear or glasses on the part of the user

Touch screen

These monitors use touching of the screen as an input method. Items can be selected or moved with a finger, and finger gestures may be used to convey commands. This does however mean the screen needs frequent cleaning due to image degradation from fingerprints.

Tablet screens

Main article: Graphics tablet/screen hybrid

A combination of a monitor with a graphics tablet. A graphics tablet/screen hybrid (or tablet/LCD hybrid Tablet LCD Monitor) is a Graphics tablet that incorporates an LCD into the tablet itself allowing the user A graphics tablet (or digitizing tablet, graphics pad, drawing tablet) is a computer Input device that allows one to hand-draw images and graphics Such devices are typically unresponsive to touch, but may offer sensitivity to one or more special tools' pressure, tilt, controls, opposite ends, and multiple tools.

Major manufacturers

See also

References

  1. ^ GRC | The Origins of Sub-Pixel Font Rendering

External links

Screenless video describes systems for transmitting visual information from a video source without the use of a screen.

Dictionary

visual display unit

-noun

  1. An early computer display, consisting of a screen (or monitor) and keyboard connected, as a terminal, to a mainframe or minicomputer
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