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Silicon Graphics F181
Terminology

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Active Matrix
Also known as AMLCD (active matrix liquid crystal display). A liquid crystal display structure in which switching transistors or diodes are attached to each pixel to switch each one on or off. It produces a brighter and sharper display with a broader viewing angle than passive matrix. See TFT.

Aperture Ratio
(or Fill Factor) The ratio between the transmissive portion of a pixel and its surrounding electronics.
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Backlight
The light source for a transmissive LCD, usually an acrylic light pipe edge lit by one or more CCFTs (cold cathode fluorescent tubes). See also Light Pipe.

Bandwidth
The range of signal frequencies the monitor can handle. This determines how much data it can process and therefore how fast it can refresh at higher resolutions.

Birefringence
Refers to the phenomenon of light traveling with different velocities in crystalline materials, depending on the propagation direction and the orientation of the light polarization relative to the crystalline axes.

Brightness
The luminosity of color, which can be expressed as luminous flux (lumen), luminous intensity (candela), luminance (candelas per square meter), and illuminance (lux).
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Candela
The luminous intensity of color. See also Brightness and NIT.

CCFTs
(Cold Cathode Fluorescent Tubes) Tubes that furnish the light for the display. Approximately 2 mm in diameter and 375 mm in length, they are filled with neon, argon, and mercury and their walls are coated with phosphors that emit a mixture of red, green, and blue light depending on the desired color temperature (white balance). In operation, an electrical potential is applied across each lamp, causing the gasses inside to strike a plasma. The plasma emits UV radiation, which excites the phosphor coating on the lamp walls into emitting visible light.

Cell
An assembly consisting of two glass substrates, a perimeter seal, and a liquid crystal layer. The front substrate usually contains a color filter layer. If the cell is an active matrix construction, its back substrate contains thin film transistor switching elements and their associated circuitry.

Cell Gap
The distance between the two LCD glass plates. Typical twisted nematic gaps are 4 to 6 micrometers determined by the molecular twist pitch.

CIE Photopic Curve
A chart developed to show the spectral (color) sensitivity of the average human eye, which is predominantly peaked in the yellow-green region.

Color Calibration
The process of adjusting a display's output characteristics so as to modify its appearance to conform to predetermined standards or settings. Usually accomplished through the use of a color or luminance measuring device and a lookup table (LUT) of values accessible to the computer's graphics controller. See Gamma.

Color Filter
A red-, green-, or blue-dyed gelatin or pigment placed above each LCD subpixel. Combinations of various light levels passing through these color elements can produce all the visible spectral colors.

Color Gamut
The entire range of colors available on a particular device such as a monitor. On an LCD with true 24-bit color, the color gamut is 16,700,000 colors.

Color Resolution
The colors that can be represented on a display depending on the number of Grayscales resolved by the LCD element.

Color Temperature The definition of a monitor's white point, whose chromaticity coordinates can be somewhat arbitrary, existing in color space from red-white to blue-white. Expressed in Kelvins (K), color temperature refers to the amount of light radiated by a perfect thermal radiator. Values at or below 5000K appear reddish; higher numbers, for example 7000K, appear bluish.

Column Drivers
Microelectronic circuits that provide the correct voltages to the individual subpixels through the source lines. For example, 8-bit drivers provide 256 gray shades, or 256 distinct colors per subpixel.

Contrast
The range between the lightest tones and the darkest tones in an image. The lower the number value, the more closely the shades will resemble each other. The higher the number, the more the shades will stand out from each other.

Contrast Ratio
The ratio between the amount of light transmitted by a pixel in its unselected ("off") state and its selected ("on") state. In an AMLCD, this ratio is usually greater than 150:1.

Controller
A digital signal source that puts data in the correct "order" to the display. It provides H and V sync, data enable, clock and 8-bits each of R, G, and B information.

Convergence
The clarity and sharpness of each pixel.
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Dithering
The simulation of more colors and shades in a palette by creating a pattern of dots out of existing colors. In an LCD that does not have true 24-bit color, frequently additional colors are simulated by this method. Dithering cannot produce the same results that a higher color depth (levels of gray or colors) allows, although it can make shaded drawings or images appear more realistic than they otherwise would.

Dot Pitch
The amount of space between each pixel. The smaller the dot pitch, the sharper the image.

Double Domain
A method of achieving an enhanced viewing angle where multiple alignment directions are produced on the same subpixel. Vertical viewing angles can increase from +35/-10 to 40.
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EL
An electroluminescent display where an electric field is applied across a polycrystalline phosphor that stimulates the material and light is emitted. Two types are DC Powder (good appearance, limited life) and AC Thin-Film (good efficiency, grayscale, color). Overlaid phosphors are used for multicolor.

ELD
(Electro-Luminescent Display). An ELD works by sandwiching a thin film of phosphorescent substance between two plates. One plate is coated with vertical wires and the other with horizontal wires, forming a grid. When an electrical current is passed through a horizontal and a vertical wire, the phosphorescent film at the intersection glows, creating the pixel.
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FED
A field emitter display consists of an array of microtips (at a density of thousands beneath each pixel), each of which is essentially a miniature CRT in a vacuum envelope. Can be operated at very high current densities with low drive voltages.

Frame Rate
The number of times in one second, measured in Hertz (Hz), that a display's system hardware redraws pixels to the monitor screen. With CRT monitors, a series of scanning electron beams (one for each primary color) "write" to their assigned subpixels in a left-to-right, top-to-bottom rasterized scan. In active matrix displays, frame rate is the time period in which all gate electrodes are scanned sequentially from top to bottom until the entire screen is energized. Normally for LCDs, one frame is 1/60 of a second; however, CRT monitors prefer higher values of around 72 Hz because the persistence of the phosphor coating on the inside of the monitor decays unless refreshed quickly. This can result in eye fatigue, either perceived or subliminal, caused by the resulting flicker associated with slower rates. The computer system's graphics rendering rate is usually related to the frame rate.
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Gamma
The relationship between the video input signal and the light output or luminance. See Grayscale. A goal of all image reproduction systems is to reflect and reproduce accurately the tone of the original scene. Display systems generally have inherent nonlinearities in how they reproduce this tone data; these nonlinearities are called natural or "native" gamma. Computer system hardware permits an adjustment or correction of native gamma through the use of LUTs, whose values are collectively called the correction gamma.

Gate Electrode
The "row" electrode in an AMLCD that controls whether a voltage is applied to a liquid crystal subpixel.

GPD
(Gas-Plasma Display). A gas-plasma display works by sandwiching neon gas between two plates. Each plate is coated with a conductive print. The print on one plate contains vertical conductive lines and the other plate has horizontal lines. Together, the two plates form a grid. When electric current is passed through a horizontal and a vertical line, the gas at the intersection glows, creating a point of light, or pixel. You can think of a gas-plasma display as a collection of very small neon bulbs. Images on gas-plasma displays generally appear as orange objects on top of a black background.

Grayscale
An intermediate luminous level of light, between "full on" and "full off," that penetrates a color filter primary. This level, in multiple graduations, is controlled by the magnitude of the voltage that is used to address an LCD subpixel. See Source Electrode.
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HDTV
(High-Definition Television). A new type of television that provides much better resolution than current televisions based on the NTSC standard. There are a number of competing HDTV standards, which is one reason that the new technology has not been widely implemented. All of the standards support a wider screen than NTSC and roughly twice the resolution. To pump this additional data through the narrow TV channels, images are digitized and then compressed before they are transmitted and then decompressed when they reach the TV.

HDTVPlus
A nonstandard display format used to define any display that is 1920x1200, compared to standard HDTV, which is 1920x1080.

Hue
Colors such as red, orange, yellow, green, blue, purple-blue, purple, and red-purple; but not white, gray, or black.

IPS
(In-Plane Switching). Another method of achieving an enhanced viewing angle where the liquid crystal molecules are switched in the plane of the LCD layer rather than orthogonal to it. This method results in excellent viewing angles but negatively impacts aperture ratio and response time, resulting in slower, dimmer displays.

LCD
(Liquid Crystal Displays). These displays are fabricated using semiconductor processes, with each pixel comprising transistors set up in a grid. LCDs are inherently digital displays. In their most common computer application, notebook computers, video drivers take the digital information in the graphics frame buffer and digitally interface to the row and column drivers that set the colors at each pixel in the display.

Light Pipe
A rectangular plate cut from acrylic stock extruded in huge sheets from a melt and located behind the LCD. Used in conjunction with a printed dot extraction pattern to uniformly distribute the light coming from CCF tubes located at its edge(s). See also Backlight.

Luminance
The amount of light emitted or scattered by a surface. Luminance is the weighted average of red, green, and blue color values that provide the perceived brightness of the combination. The English unit of measure for luminance is a foot-lambert (fL) and is defined as one foot-candle falling upon a perfectly diffusing white surface.

LVDS
(Low Voltage Differential Signaling). LVDS is an open standard for digital FPM display defined by two key organizations, the American National Standards Institute/Telecommunications Industry Association/Electronic Industries Association (ANSI/TIA/EIA) and the Institute for Electrical and Electronic Engineering (IEEE). The baseline ANSI/TIA/EIA-644 standard, approved in November 1995, serves as a foundation for the specific implementation of LVDS as an interface to digital displays and is the current notebook computer digital display standard.
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Module
An assembly that comprises the cell plus display drivers that control light and deliver host computer data to the cell, as well as a backlight assembly consisting of fluorescent lamps, light pipes, and associated diffusers and reflectors, all contained within a rigid sheet-metal structure. See Cell.

Monitor
An assembly that consists of the module plus an inverter to power the lamps, a display interface to the CPU, a plastic bezel and stand, and a power supply. See Cell and Module.
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NIT
A unit of photometric luminance equal to one candela/meter^2 or 0.292 fL.

Passive Matrix
LCDs that are addressed by a multiplexed drive time-sharing system using a voltage equalization method. Passive matrix LCDs are usually dimmer and have a narrower viewing angle than active matrix LCDs, because as the number of scan lines increases, the viewing angle narrows and the contrast ratio is reduced.

Pixel
The smallest addressable unit on a display screen. The resolution of a monitor is determined by the number of pixels covering the width and height of the complete on-screen image.

In storage, pixels are made up of one or more bits. The greater this bit depth, the more shades or colors can be represented. Grayscale and color displays typically use from 4 to 24 bits per pixel, providing from 16 to 16 million colors.

On screen, pixels are made up of one or more dots of color (subpixels). For grayscale, the pixel is energized with different intensities, creating a range from dark to light. Color systems use a red, green, and blue dot per pixel, each of which is energized to different intensities, creating a range of colors perceived as the mixture of these dots. Black is all three dots dark, white is all dots light.

Pixel Clock
The pixel clock that resides in the LCD is critical to ensure that as each line is scanned, the red, green, and blue components of each pixel precisely align with each other. If there is a slight error in the clock, this error accumulates as the line is scanned from the left to the right edge of the display.

Pixel Pitch
The distance from the edge of one pixel to the similar edge on an adjacent pixel.

Pixel Resolution
The number of addressable pixels in a display. Several standard display sizes are:

VGA:640 x 480
SVGA:800 x 600
XGA:1024 x 768
SXGA:1280 x 1024
SXGA-Wide:1600 x 1024
UXGA:1600 x 1200
HDTV:1920 x 1080
UXGA-Wide:1920 x 1200
QXGA:2056 x 1536


Primary Colors
In light (and in monitors, which produce light) they are the colors (red, green, and blue) that cannot be produced by any combination of other colors. Conversely, any color can be produced by mixing the three RGB primary colors.
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Refresh Rate
How many times per second the screen is refreshed (redrawn).

Response Time
The speed at which the orientation of a liquid crystal material can change in response to a charging/discharging cycle. Typically noted as "rise plus fall," for twisted-nematic structures, this time ranges from 20 to 50 ms.

Row Driver
Response Time (or Gate driver) The switch for turning the thin film transistor (TFT) on or off.

Saturation
The vividness of a color.

Source Electrode
The "column" electrode in an AMLCD that determines the amount of voltage to be applied to an LCD subpixel. The magnitude of this voltage determines the gray level to which that subpixel transmits light to its respective color filter primary. See Grayscale.

Subpixel
In a color monitor, each pixel is made out of 3 subpixels that have either red, green, or blue color filters. Each subpixel is energized with different intensities, creating a range of colors perceived as the mixture of these dots.

SVGA
Super video graphics array is a set of graphics standards designed to offer greater resolution than VGA. There are several varieties of SVGA, each providing a different resolution. All SVGA standards support a palette of 16 million colors, but the number of colors that can be displayed simultaneously is limited by the amount of video memory available. The SVGA standards are developed by a consortium of monitor and graphics manufacturers called VESA.

SXGA
(Super Extended Graphics Adapter) A graphics standard offering a display resolution of 1280x1024 pixels. SXGA-Wide has a display resolution of 1600x1024.
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TFT
(Thin Film Transistor) An a-Si, p-Si, or CdSe used as a switch to a charge storage device beneath each subpixel of an AMLCD.. A type of LCD flat-panel display screen, in which each pixel is controlled by from one to four transistors. The TFT technology provides the best resolution of all the flat-panel techniques, but it is also the most expensive. TFT screens are sometimes called active-matrix LCDs.

TMDS
(Transition Minimized Differential Signaling). TMDS is similar to LVDS in concept but very different in execution. TMDS is a proprietary specification defined by Silicon Image, Inc. TMDS is the generic form of Silicon Image's PanelLink interface technology. VESA is currently exploring the definition of TMDS as an open standard, but today it remains proprietary to Silicon Image.

TTL
(Transistor-Transistor Logic). A common type of digital circuit in which the output is derived from two transistors. The term is commonly used to describe any system based on digital circuitry, as in TTL monitor.

UXGA
(Ultra Extended Graphics Adapter). A graphics standard offering a display resolution of 1600x1200 pixels.

VGA
(Video Graphics Array). VGA has become one of the de facto standards for PCs. In text mode, VGA systems provide a resolution of 720 by 400 pixels. In graphics mode, the resolution is either 640 by 480 (with 16 colors) or 320 by 200 (with 256 colors). VGA remains the lowest common denominator among PC displays.

Viewing Angle
The bounding angles generated from a point normal to the display surface within which can be found acceptable contrast ratios and linear grayscales.

XGA
(Extended Graphics Array). A high-resolution graphics standard introduced by IBM in 1990. XGA was designed to replace the older 8514/A video standard. It provides the same resolutions (640 by 480 or 1024 by 768 pixels), but supports more simultaneous colors (65,000 compared to 8514/A's 256 colors). In addition, XGA allows monitors to be noninterlaced.
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