SCIENCE DIRECT

8514/A: A high-resolution video standard for PCs developed by IBM in 1987. It is designed to extend the capabilities of VGA. The 8514/A standard provides a resolution of 1,024 by 768 pixels, which gives it about 2.5 times the pixels of VGA (640 by 480). Like VGA, 8514/A provides a palette of 262,000 colors, of which 256 can be displayed at one time. On monochrome displays, 8514/A provides 64 shades of gray. In its original version, 8514/A relies on interlacing, a technique that makes it possible to provide resolution at low cost. Interlacing, however, carries a performance penalty, so many manufacturers produce noninterlaced 8514/A clones. In 1990, IBM released the Extended Graphics Array (XGA) standard, which supersedes 8514/A. ACTIVE MATRIX DISPLAY: A type of flat-panel display in which the screen is refreshed more frequently than in conventional passive-matrix displays. The most common type of active-matrix display is based on a technology known as TFT (thin film transistor). The two terms, active matrix and TFT, are often used interchangeably. ANALOG MONITOR: The traditional type of color display screen that has been used for years in televisions. In reality, all monitors based on CRT technology (that is, all monitors except flat-panel displays) are analog. Some monitors, however, are called digital monitors because they accept digital signals from the video adapter. EGA monitors, for example, must be digital because the EGA standard specifies digital signals. Digital monitors must nevertheless translate the signals into an analog form before displaying images. Some monitors can accept both digital and analog signals. Most analog monitors are designed to accept signals at a precise frequency. They are therefore called fixed-frequency monitors. However, a special type of monitor, called a multiscanning or multisync monitor, automatically adjusts itself to the frequency of the signals being sent to it. A third type of monitor, called a multifrequency monitor, is designed to accept signals at two or more preset frequency levels. ASPECT RATIO: In computer graphics, the relative horizontal and vertical sizes. For example, if a graphic has an aspect ratio of 2:1, it means that the width is twice as large as the height. When resizing graphics, it is important to maintain the aspect ratio to avoid stretching the graphic out of proportion. AUTOSIZING: Refers to a monitor's ability to accept signals at one resolution and display the image at a different resolution. For example, a VGA video card outputs images at a resolution of 640 by 480. An SVGA monitor, however, can display images at a resolution of only 800 by 600, or even 1,024 by 768. If the monitor supports autosizing, it automatically adjusts the size of the image so that the proportions are correct. Without autosizing, you need to adjust an image manually so that it fills the screen properly. BACKLIGHTING: A technique used to make flat-panel displays easier to read. A backlit display is illuminated so that the foreground appears sharper in contrast with the background. CGA: Abbreviation of color/graphics adapter, an old graphics system for PCs. Introduced in 1981 by IBM, CGA was the first color graphics system for IBM PCs. Designed primarily for computer games, CGA does not produce sharp enough characters for extended editing sessions. CGA's highest-resolution mode is 2 colors at a resolution of 640 by 200. CGA has been superseded by VGA systems, which are backward compatible with CGA. CODEC: Short for compressor/decompressor, a codec is any technology for compressing and decompressing data. Codecs can be implemented in software, hardware, or a combination of both. Some popular codecs for computer video include MPEG, Indeo, Cinepak, QuickTime, and Video for Windows. In telecommunications, a device that encodes or decodes a signal. For example, telephone companies use codecs to convert binary signals transmitted on their digital networks to analog signals converted on their analog networks. The translation of a binary value into a voltage that can be transmitted over a wire. COLOR DEPTH: The number of distinct colors that can be represented by a piece of hardware or software. Color depth is sometimes referred to as bit depth because it is directly related to the number of bits used for each pixel. A 24-bit video adapter, for example, has a color depth of 2 to the 24th power (about 16.7 million) colors. COLOR MONITOR: A display monitor capable of displaying many colors. In contrast, a monochrome monitor can display only two colors -- one for the background and one for the foreground. Color monitors implement the RGB color model by using three different phosphors that appear red, green, and blue when activated. By placing the phosphors directly next to each other, and activating them with different intensities, color monitors can create an unlimited number of colors. In practice, however, the real number of colors that any monitor can display is controlled by the video adapter. COMPOSITE VIDEO: A type of video signal in which all information -- the red, blue, and green signals (and sometimes audio signals as well) -- are mixed together. This is the type of signal used by televisions in the United States (see NTSC). In contrast, most computers use RGB video, which consists of three separate signals for red, green, and blue. In general, RGB video produces sharper images than composite video does. CONVERGENCE: The coming together of two or more disparate disciplines or technologies. For example, the so-called fax revolution was produced by a convergence of telecommunications technology, optical scanning technology, and printing technology. In graphics, convergence refers to how sharply an individual color pixel on a monitor appears. Each pixel is composed of three dots -- a red, blue, and green one. If the dots are badly misconverged, the pixel will appear blurry. All monitors have some convergence errors, but they differ in degree. CRT: Abbreviation of cathode-ray tube, the technology used in most televisions and computer display screens. A CRT works by moving an electron beam back and forth across the back of the screen. Each time the beam makes a pass across the screen, it lights up phosphor dots on the inside of the glass tube, thereby illuminating the active portions of the screen. By drawing many such lines from the top to the bottom of the screen, it creates an entire screenful of images. CSTN: Short for color super-twist nematic, an LCD technology developed by Sharp Electronics Corporation. Unlike TFT, CSTN is based on a passive matrix, which is less expensive to produce. The original CSTN displays developed in the early 90's suffered from slow response times and ghosting. Recent advances in the technology, however, have made CSTN a viable alternative to active-matrix displays. New CSTN displays offer 100ms response times, a 140 degree viewing angle, and high-quality color rivaling TFT displays - all at about half the cost. DDC: Short for Display Data Channel, a VESA standard for communication between a monitor and a video adapter. Using DDC, a monitor can inform the video card about its properties, such as maximum resolution and color depth. The video card can then use this information to ensure that the user is presented with valid options for configuring the display. DIGITAL MONITOR: A monitor that accepts digital rather than analog signals. All monitors (except flat-panel displays) use CRT technology, which is essentially analog. The term digital, therefore, refers only to the type of input received from the video adapter. A digital monitor then translates the digital signals into analog signals that control the actual display. Although digital monitors are fast and produce clear images, they cannot display continuously variable colors. Consequently, only low-quality video standards, such as MDA, CGA, and EGA, specify digital signals. VGA and SVGA, on the other hand, require an analog monitor. Some monitors are capable of accepting either analog or digital signals. DISP SCREEN: The display part of a monitor. Most display screens work under the same principle as a television, using a cathode ray tube (CRT). Consequently, the term CRT is often used in place of display screen. DLP: Short for Digital Light Processing, a new technology developed by Texas Instruments used for projecting images from a monitor onto a large screen for presentations. Prior to the development of DLP, most computer projection systems were based on LCD technology which tends to produce faded and blurry images. DLP uses tiny mirrors housed on a special kind of microchip called a Digital Micromirror Device (DMD). The result is sharp images that can be clearly seen even in a normally lit room. DOT PITCH: A measurement that indicates the vertical distance between each pixel on a display screen. Measured in millimeters, the dot pitch is one of the principal characteristics that determines the quality of display monitors. The lower the number, the crisper the image. The dot pitch of color monitors for personal computers ranges from about 0.22 mm to 0.42 mm. DSTN: Short for double-layer supertwist nematic, a passive-matrix LCD technology that uses two display layers to counteract the color shifting that occurs with conventional supertwist displays. DUAL -SCAN DISPLAY: A type of passive-matrix LCD display that provides faster refresh rates that conventional passive-matrix displays by dividing the screen into two sections that are refreshed simultaneously. Dual-scan displays are not as sharp or bright as active-matrix displays, but they consume less power. EGA: Abbreviation of enhanced graphics adapter, a graphics display system for PCs introduced by IBM in 1984. EGA supports 16 colors from a palette of 64 and provides a resolution of 640 by 350. This is better than CGA but not as good as VGA. ELD: A technology used to produce a very thin display screen, called a flat-panel display, used in some portable computers. 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 vertical wire, the phosphorescent film at the intersection glows, creating a point of light, or pixel. Other types of flat-panel displays include LCD displays and gas-plasma displays, both of which are more common than ELDs. ELF EMISSION: ELF stands for extremely low frequency, and ELF emissions are magnetic fields generated by common electrical appliances. There is considerable debate about whether ELF emissions from computer monitors pose a threat. Some European countries have adopted regulations controlling the amount of allowable emission. The most well-know regulation is Sweden’s MPR II standard. You can play it safe by buying MPR II-compliant monitors. FIXED FREQUENCY MONITOR: A monitor that can only accept signals in one frequency range. In contrast, multiscanning monitors automatically adjust themselves to the frequency at which data is being sent. FLAT TECHNOLOGY MONITOR: Often abbreviated as FTM, flat technology monitors are monitors that have a flat display screen to reduce glare. Conventional display screens are curved, which makes them more susceptible to reflections from external light sources. Do not confuse flat technology monitors with flat-panel displays. Flat-panel displays are the display screens used in laptops and other portable computers. FLAT PANEL DISPLAY: A very thin display screen used in portable computers. Nearly all modern flat-panel displays use LCD technologies. Most LCD screens are backlit to make them easier to read in bright environments. GAS PLASMA DISPLAY: A type of thin display screen, called a flat-panel display, used in some portable computers. 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 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. Although gas-plasma displays produce very sharp monochrome images, they require much more power than the more common LCD displays. GENLOCK: Short for generator locking device, a genlock is a device that enables a composite video machine, such as a TV, to accept two signals simultaneously. A genlock locks one set of signals while it processes the second set. This enables you to combine graphics from a computer with video signals from a second source such as a video camera. GRAPHICS ACCELERATOR: A special type of video adapter that contains its own processor to boost performance levels. These processors are specialized for computing graphical transformations, so they achieve better results than the general-purpose CPU used by the computer. In addition, they free up the computer’s CPU to execute other commands while the graphics accelerator is handling graphics computations. The popularity of graphical applications, and especially multimedia applications, has made graphics accelerators not only a common enhancement, but a necessity. Most computer manufacturers now bundle a graphics accelerator with their mid-range and high-end systems. Aside from the graphics processor used, the other characteristics that differentiate graphics accelerators are: memory: Graphics accelerators have their own memory, which is reserved for storing graphical representations. The amount of memory determines how much resolution and how many colors can be displayed. Some accelerators use conventional DRAM, but others use a special type of video RAM (VRAM), which enables both the video circuitry and the processor to simultaneously access the memory. bus: Each graphics accelerator is designed for a particular type of video bus. As of 1995, most are designed for the PCI bus. register width: The wider the register, the more data the processor can manipulate with each instruction. 64-bit accelerators are already becoming common, and we can expect 128-bit accelerators in the near future. GRAPHICS COPROCESSOR: A microprocessor specially designed for handling graphics computations. Most graphics accelerators include a graphics coprocessor. GRAPHICS MODE: Many video adapters support several different modes of resolution, all of which are divided into two general categories: character mode and graphics mode. In character mode, the display screen is treated as an array of blocks, each of which can hold one ASCII character. In graphics mode, the display screen is treated as an array of pixels. Characters and other shapes are formed by turning on combinations of pixels. Of the two modes, graphics mode is the more sophisticated. Programs that run in graphics mode can display an unlimited variety of shapes and fonts, whereas programs running in character mode are severely limited. Programs that run entirely in graphics mode are called graphics-based programs. GRAY SCALING: The use of many shades of gray to represent an image. Continuous-tone images, such as black-and-white photographs, use an almost unlimited number of shades of gray. Conventional computer hardware and software, however, can only represent a limited number of shades of gray (typically 16 or 256). Gray-scaling is the process of converting a continuous-tone image to an image that a computer can manipulate. While gray scaling is an improvement over monochrome, it requires larger amounts of memory because each dot is represented by from 4 to 8 bits. At a resolution of 300 dpi, you would need about 6 megabytes to represent a single 8½ by 11-inch page using 256 shades of gray. This can be reduced somewhat through data compression techniques, but gray scaling still requires a great deal of memory. Many optical scanners are capable of gray scaling, using from 16 to 256 different shades of gray. However, gray scaling is only useful if you have an output device -- monitor or printer -- that is capable of displaying all the shades. Most color monitors are capable of gray scaling, but the images are generally not as good as on dedicated gray-scaling monitors. Note that gray scaling is different from dithering. Dithering simulates shades of gray by altering the density and pattern of black and white dots. In gray scaling, each individual dot can have a different shade of gray. HERCULES GRAPHICS: A graphics display system for PCs developed by Van Suwannukul, founder of Hercules Computer Technology. Suwannukul developed the system so that he could produce his doctoral thesis on PC equipment using his native Thai alphabet. First offered in 1982, the original Hercules system filled a void left by IBM's MDA (monochrome display adapter) system. MDA produces high-resolution monochrome text but cannot generate graphics. Hercules systems generate both high-resolution text and graphics for monochrome monitors. The resolution is 720 by 348.