Ch-4 Display.txt

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Ch-4 Display.txt
2014-03-29 18:50:37
Aplus Computers Display devices
Chapter 4 Display Devices
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  1. __ is a device called an electron gun shoots a beam of electrons toward the back side of the monitor screen. Color __ often use three guns, one each for red, green, and blue image components. The back of the screen is coated with special chemical dots called phosphors (often zinc sulfide combined with other elements for color variation) that glow when electrons strike them.
  2. __ is the measurement between the same spot in two vertically adjacent dot trios. In other words, it’s the height of the trio added to the distance between the closest extremes of it and the next trio above or below it. Expressed in millimeters or dots per inch, the dot pitch tells how “sharp” the picture can be. The lower the measurement in millimeters or the higher the number of dots per inch, the closer together the phosphors are, and as a result, the sharper the image can be. An average dot pitch is 0.28mm to 0.32mm. Anything closer than 0.28mm is considered exceptional. __ in the flat-panel arena translates to the display’s native resolution.
    Dot Pitch
  3. __ is defined by how many software picture elements (pixels) are used to draw the screen. An advantage of higher resolutions is that more information can be displayed in the same screen area. A disadvantage is that the same objects and text displayed at a higher resolution appear smaller and might be harder to see. Up to a point, the added crispness of higher resolutions displayed on high-quality monitors compensates for the negative aspects. The resolution is described in terms of the visible image’s dimensions, which indicate how many rows and columns of pixels are used to draw the screen. For example, a resolution of 1024 n 768 means 1024 pixels across (columns) and 768 pixels down (rows) were used to draw the pixel matrix.
  4. __ is used to store rendered screen images. The memory required for a screen image varies with the color depth, which is defined as the number of colors in which each pixel can be displayed. A palette with a 24-bit color depth is capable of displaying each pixel in one of 2 24 = 16,777,216 distinct colors. In the preceding example, if you were using 24-bit graphics, meaning each pixel requires 24 bits of memory to store that one screen element, 786,432 pixels would require 18,874,368 bits, or 2,359,296 bytes. Because this boils down to 2.25MB, an early (bordering on ancient) video adapter with only 2MB of RAM would not be capable of such resolution at 24 bits per pixel. Today’s store many screens at a time in order to allow the display of full-motion video.
    Video Memory
  5. An inventor found that when he passed an electric current through a semi-crystalline liquid, the crystals aligned themselves with the current. It was found that by combining transistors with these liquid crystals, patterns could be formed. These patterns could be combined to represent numbers or letters. This screen was very light compared to computer monitors of the day, and it consumed relatively little power. __s are available in either analog or digital interfaces. The analog interface is exactly the same as the VGA interface that was used for analog CRT monitors. Internal digital signals from the computer are rendered and output as analog signals by the video card and are then sent along the same 15-pin connector and associated cable as was used with analog CRT monitors. Digital __s with a digital interface, on the other hand, require no analog modulation by the graphics adapter. They require the video card to support digital output using a different interface, such as DVI, for instance. The advantage is that because the video signal never changes from digital to analog, there is less chance of interference and no conversion-related quality loss. Digital displays are generally sharper than their analog counterparts.
    Liquid Crystal Displays
  6. An __ screen is made up of several independent LCD pixels. A transistor at each pixel location, when switched among various levels, activates two opposing electrodes that align the pixel’s crystals and alter the passage of light at that location to produce hundreds or thousands of shades. The front electrode, at least, must be clear. This type of display is very crisp and easy to look at through nearly all oblique angles, and it does not require constant refreshing to maintain an image because transistors conduct current in only one direction and the pixel acts like a capacitor by holding its charge until it is refreshed with new information. Higher refresh rates are not for prevention of pixel discharge, as in the case of CRTs, plasma displays, and passive-matrix LCDs. Higher rates only result in better video quality, not static-image quality. The major disadvantage of an active-matrix screen is that it requires larger amounts of power to operate all the transistors, one for each grayscale pixel or each red, green, and blue subpixel. Even with the backlight turned off, the screen can still consume battery power at an alarming rate, even more so when conventional fluorescent backlights are employed. The vast majority of LCDs manufactured today are based on active-matrix technology.
    Active matrix
  7. A __ display does not have a dedicated transistor for each pixel or subpixel but instead a matrix of conductive traces. In simplified terms for a single pixel, when the display is instructed to change the crystalline alignment of a particular pixel, it sends a signal across the x- and y-coordinate traces that intersect at that pixel, thus turning it on. More realistically, circuits controlling the rows fire in series to refresh or newly activate pixels on each row in succession. The circuits controlling the columns are synchronized to fi re when that row’s transistor is active and only for the pixels that should be affected on that row. Once a pixel’s charge is gone, the pixel begins to return to normal, or decay, requiring a refresh to make it appear static. Angles of visibility and response times (the time to change a pixel) suffer greatly with passive-matrix LCDs. Because neighboring pixels can be affected through a sort of “crosstalk,” passive-matrix displays can look a bit “muddy.”
    Passive matrix
  8. __ is a variation of the passive-matrix display. The classic passive-matrix screen is split in half to implement a dual-scan display. Each half of the display is refreshed separately, leading to increased quality. Although dual scan improves on the quality of conventional passive-matrix displays, it cannot rival the quality produced by active matrix. The main differences between active matrix and typical passive matrix are image quality and viewing angle. Because the computer takes hundreds of milliseconds to change a pixel in passive-matrix displays (compared with tens of milliseconds or less in active-matrix displays), the response of the screen to rapid changes is poor, causing, for example, an effect known as submarining : On a computer with a passive-matrix display, if you move the mouse pointer rapidly from one location to another, it will disappear from the first location and reappear in the new location without appearing anywhere in between. The poor response rate of passive-matrix displays also makes them suboptimal for displaying video. If you move toward the side of a passive-matrix LCD, you eventually notice the display turning dark. In contrast, active-matrix LCDs have a viewing angle wider than 179 degrees. In fact, if you didn’t know better, you’d think a passive-matrix display was a standard display with a privacy filter on it. A privacy filter is a panel that fits over the front of a display and, through a polarization affect, intentionally limits the viewing angle of the monitor. The filters were used with CRTs and continue to be produced for the variety of LCD and plasma panels being used as computer monitors. These same filters, as well as specialty versions, can act as antiglare filters , brightening and clarifying the image appearing on the monitor’s screen.
    Dual scan
  9. __ are merely LCD panels with light emitting diodes as light sources instead of the fluorescent bulbs used by conventional LCD monitors. No doubt, the new technology would not be nearly as marketable if they were referred to merely as LCDs. The general consumer would not rush to purchase a new display that goes by the same name as their current display. Nevertheless, calling these monitors __ displays is analogous to calling the conventional LCD monitors fluorescent displays; it’s simply the backlight source, not the display technology. Because there are many individually controlled __ in an __ display, sometimes as many as there are transistors in the LCD panel, the image can be intelligently backlit to enhance the quality of the picture. Additionally, there is no need for laptops with __ displays to convert the DC power coming into the laptop to the AC needed to power traditional fluorescent backlights because __s operate on DC power like the rest of the laptop. As a result, these systems have no inverter board __ displays rival plasma displays in clarity and variations in luminance.
    LED Displays
  10. The __ refers to a cloud of ionized (charged) particles—atoms and molecules with electrons in an unstable state. This electrical imbalance is used to create light from the changes in energy levels as they achieve balance. __ panels (PDPs) create just such a cloud from an inert gas, such as neon, by placing electrodes in front of and behind sealed chambers full of the gas and vaporized mercury. This technology of running a current through an inert gas to ionize it is shared with neon signs and fluorescent bulbs. Because of the pressurized nature of the gas in the chambers, __s are not optimal for high-altitude use, leading to CRTs and LCDs being more popular for high-altitude applications, such as aboard aircraft, where __s can be heard to buzz the way fluorescent bulbs sometimes do. Because of the temporary emission of light that this process produces, plasma displays have more in common with CRTs than they do with LCDs. In fact, as with CRTs, phosphors are responsible for the creation of light in the shade of the three primary colors, red, green, and blue. Because the pixels produce their own light, no backlight is required with plasma displays, also a feature shared with CRTs. The phosphor chemicals in CRTs and PDPs can be “used up” over time, reducing the overall image quality. The heat generated by CRTs and __s can lead to a loss of phosphorescence in the phosphor chemicals, which results in images burning into the screen. Advancements in the chemistry of plasma phosphors have reduced this tendency in recent years. The refresh rate for plasma displays has always been in the 600Hz range so that the decay of the glow of the cells within each pixel (subpixel) is not perceptible until such time as the image calls for that cell to turn off as well as to ensure fluid video motion. Refresh Rate but note that this rate is approximately 10 times that which is necessary to avoid the human eye’s perception of the glow’s decay. The result is a display that produces the state of the art in video motion fluidity. Higher refresh rates in LCDs lead to an unwanted artificial or noncinematic quality to video known as the “soap-opera effect.” __s do not suffer from this effect. PDPs can also produce deeper black colors than fluorescent-backlit LCD panels because the backlight cannot be completely blocked by the liquid crystal, thus producing hues that are grayer than black. LCDs backlit with LEDs, however, are able to completely dim selective areas or the entire image. Because of the relative cost-effectiveness to produce __s of the same size as a given LCD panel, plasma displays historically enjoyed more popularity in the larger-monitor market. That advantage is all but gone today, resulting in more LCDs being sold today than plasma displays.
    Plasma Displays
  11. __, unlike LED displays, really are the image-producing parts of the display, not just the light source. In much the same way as a plasma cell places an excitable material between two electrodes, __s are self-contained cells that use the same principle to create light. An organic light-emitting compound forms the heart of the __ and is placed between an anode and a cathode, which produce a current that runs through the electroluminescent compound, causing it to emit light. An __, then, is the combination of the compound and the electrodes on each side of it. The electrode in the back of the __ cell is usually opaque, allowing a rich black display when the __ cell is not lit. The front electrode should be transparent to allow the emission of light from the __. If thin-film electrodes and a flexible compound are used to produce the __s, an __ display can be made flexible, allowing it to function in novel applications where other display technologies could never. Because of the thin, lightweight nature of the panels, __ displays can both replace existing heavy full-color LED signs. LEDs create light and have been used in recent years for business, home, and automotive interior lighting and automotive headlamps. __s are LEDs, organic as they may be, and produce light as well. They, too, have already made their way into the interior lighting market. As with LCD panels, __ panels can be classified as active matrix or passive matrix.
    OLED Displays
  12. __ can be thought of as condensed video display units with a lighting system that projects the VDU’s image onto a screen or other flat surface for group viewing.
    Projection Systems
  13. __ television, in which a projector is built into a cabinet behind a screen onto which the image is projected in reverse so that an observer in front of the TV can view the image correctly. Early __ TVs as well as ceiling-mounted home-theater units used CRT technology to drive three filtered light sources that worked together to create an RGB image. Later __ systems, including most modern portable projectors, implement LCD gates. These units shine a bright light through three LCD panels that adjust pixels in the same manner as an LCD monitor, except the projected image is formed as with the CRT projector by synchronizing the combination and projection of the red, green, and blue images onto the same surface.
    Rear Projection
  14. __ is another popular technology that keeps rear-projection TVs on the market and benefits portable projectors as well, allowing some projectors to be extremely small. Special __ chips, referred to as optical semiconductors, have roughly as many rotatable mirrors on their surface as pixels in the display resolution. A light source and colored filter wheel or colored light sources are used to rapidly switch among primary, and sometimes secondary, colors in synchronization with the chip’s mirror positions, thousands of times per second.
    Digital Light Processing
  15. __ is measured in lumens. A lumen (lm) is a unit of measure for the total amount of visible light that the projector gives off, based solely on what the human eye can perceive and not also on invisible wavelengths. When the rated brightness of the projector, in lumens, is focused on a larger area, the lux —a derivative of lumens measuring how much the projector lights up the surface on which it is focused—decreases; as you train the projector on a larger surface (farther away), the same lumens produce fewer lux.
  16. __ lamps like the ones found in projection systems do more with less by using a smaller electrical discharge to produce far more visible light. A strong quartz chamber holds the filament in a projector lamp and can be seen inside the outer bulb. It contains a metal halide (where the word halogen comes from) gas that glows bright white when the tungsten filament lights up. Depositing the soot on the inside of the projector bulb is avoided by using a chemical process that attracts the soot created back to the filament where it once again becomes part of the filament, extending its life and reducing changes in light output. Expect to pay considerably more for projector bulbs than for standard bulbs of a comparable wattage. The metal halide gases used in projector bulbs are more expensive than the noble gases used in standard bulbs.
    High-intensity discharge
  17. Although it doesn’t take long for the fan to stop running on its own, this is a phase that should never be skipped to save time. With projector bulbs one of the priciest consumables in the world of technology, doing so may cost you more than a change in your travel arrangements.
    Cooling Down
  18. Measured in screen draws per second, or Hertz, the __ indicates how much effort is being put into keeping the screen lit. The larger a monitor gets, the higher the refresh rate needs to be to reduce eyestrain and perceivable flicker. The __ is a characteristic of the LCD, generally not an adjustment to be made. LCD televisions that support 120Hz refresh rates are common, but it’s easy to find those rated for 60Hz, 240Hz, and 480Hz as well. Higher __ translate to more fluid video motion. The __ you select must be supported by both your graphics adapter and your monitor because the adapter drives the monitor. If a monitor supports only one __, it does not matter how many different rates your adapter supports you will be able to choose only the one common __. It is important to note that as the resolution you select increases, the higher supported refresh rates begin to disappear from the selection menu. If you want a higher __, you might have to compromise by choosing a lower resolution.
    Refresh Rate
  19. The number of horizontal dots by the number of vertical dots that make up the rows and columns of your display. There are software and hardware resolutions. If you are using an LCD, for best results you should use the monitor’s native resolution. Some systems will scale the image to avoid distortion, but others will try to fill the screen with the image, resulting in distortion. On occasion, you might find that increasing the resolution beyond the native resolution results in the need to scroll the Desktop in order to view other portions of it. In such instances, you cannot see the entire Desktop all at the same time.
  20. You may find yourself in a position where you need to use two monitors on the same computer simultaneously. You might need to change settings for the external device, such as the resolution or the device’s virtual orientation with respect to the built-in display, which affects how you drag objects between the screens. Microsoft calls its multi-monitor feature Dual View. You have the option to extend your Desktop onto a second monitor or to clone your Desktop on the second monitor. You can use one graphics adapter with multiple monitor interfaces or multiple adapters. However, as of Vista, Windows Display Driver Model (WDDM) version 1.0 required that the same driver be used for all adapters. This doesn’t mean that you cannot use two adapters that fit into different expansion slot types, such as PCIe and AGP. It just means that both cards have to use the same driver. Incidentally, laptops that support external monitors use the same driver for the external interface as for the internal LCD attachment. Version 1.1, introduced with Windows 7, relaxed this requirement. WDDM is a graphics-driver architecture that provides enhanced graphics functionality that was not available before Windows Vista, such as virtualized video memory, preemptive task scheduling, and sharing of Direct3D surfaces among processes.
    Multiple Displays
  21. __ is the reduction of the magnetic field of an object. It is generally impossible to completely neutralize an object’s magnetic field, so reducing it is the objective. One application of __ is to randomize the magnetic domains on the surface of a magnetic storage medium, such as a hard disk drive. __ the drive makes previously saved information all but unrecoverable. This, however, is a discussion of display devices, and as such, __ has a related but different implication. Because CRTs use magnetic fields to guide the electron beams to their intended targets, and LCDs do not, __ a monitor is strictly a CRT-related practice. Due to the fact that you cannot completely eradicate the magnetic field of an object, repeated degaussing of a CRT monitor is not advised. In fact, the monitor can be damaged by degaussing it more than once in a short period of time.
  22. This video technology had a 256KB of video memory on board and could display 16 colors at 640 n 480, 640 n 350, and 320 n 200 pixels or, using mode 13h of the VGA BIOS, 256 colors at 320 n 200 pixels. One unique feature of __ is that it’s an analog technology, unlike the preceding and subsequent standards. In __-based technologies is that graphics adapters output and monitors receive an analog signal over the cable. __ builds a dynamic palette of 256 colors, which are chosen from various shades and hues of an 18-bit palette of 262,114 colors. When only 16 colors are displayed, they are chosen from the 256 selected colors. The reason for moving away from the original digital signal is because for every power of 2 that the number of colors in the palette increases, you need at least one more pin on the connector. A minimum of 4 pins for 16 colors is not a big deal, but a minimum of 32 pins for 32-bit graphics become a bit unwieldy. The cable has to grow with the connector, as well, affecting transmission quality and cable length. __, on the other hand, requires only 3 pins, one each for red, green, and blue modulated analog color levels, not including the necessary complement of ground, sync, and other control signals. For this application, 12 to 14 of the 15 pins of a __ connector are adequate.
    Video Graphics Array
  23. This video technology could support 16 colors at a resolution of 800 n 600 (the VESA standard), but it soon expanded to support 1024 n 768 pixels with 256 colors. __ has been a term used loosely for any resolution and color palette to exceed that of standard VGA. This even includes the resolution presented next, XGA. New names still continue to be introduced, mainly as a marketing tool to tout the new resolution du jour. While display devices must be manufactured to support a certain display resolution, one of the benefits of analog video technology was that later VGA monitors could advance along with the graphics adapter, in terms of the color palette. The analog signal is what dictates the color palette, and the standard for the signal has not changed since its VGA origin. This makes VGA monitors’ color limitations a nonissue. Such a topic makes sense only in reference to graphics adapters.
    Super VGA
  24. __ could support 256 colors at 1024 n 768 pixels or 65,536 colors at 800 n 600 pixels. It was a different design, optimized for GUIs of the day such as Windows or OS/2. It was also an interlaced technology when operating at the 1024 n 768 resolution, meaning that rather than scan every line one at a time on each pass to create the image, it scanned every other line on each pass, using the phenomenon known as “ persistence of vision ” to produce what appears to our eyes as a continuous image. The advertised refresh rate specifies the frequency with which all odd or all even rows are scanned. The drawback to interlacing is that the refresh rate used on a CRT has to be twice the minimum comfort level for refreshing an entire screen. Otherwise, the human eye will interpret the uncomfortably noticeable decay of the pixels as flicker. Therefore, a refresh rate of 120Hz would result in a comfortable effective refresh rate of 60Hz. Unfortunately, 84Hz was a popular refresh rate for interlaced display signals, resulting in an entire screen being redrawn only 42 times per second, a rate below the minimum comfort level.
    Extended Graphics Array
  25. Whenever a known technology is preceded by the letter W, you can assume roughly the same vertical resolution but a wider horizontal resolution to accommodate 16:10 wide-screen formats (16:9 for LCD and plasma televisions). Preceding the technology with the letter Q indicates that the horizontal and vertical resolutions were each doubled, making a final number of pixels 4 times (quadruple) the original. To imply 4 times each, for a fi nal resolution enhancement of 16 times, the letter H for hexadecatuple is used. __ will have a resolution of 2048 n 1536. If Ultra XGA (UXGA) has a resolution of 1600 n 1200 and an aspect ratio of 4:3, then __ has a resolution of 1920 n 1200 and a 16:10 aspect ratio.
    Quadruple XGA QXGA/ Wide UXGA WUXGA
  26. LCD, plasma, OLED, and other flat-panel displays is that they have a single fixed resolution Unlike CRT monitors, which can display a crisp image at many resolutions within a supported range, flat-panel monitors have trouble displaying most resolutions other than their __. The __ comes from the placement of the transistors in the hardware display matrix of the monitor. For a __ of 1680 n 1050, for example, there are 1,764,000 transistors (LCDs) or cells (PDPs and OLED displays) arranged in a grid of 1680 columns and 1050 rows.
    Native Resolution
  27. The __ is the measure of the ratio of the luminance of the brightest color to that of the darkest color the screen is capable of producing. Do not confuse __ with contrast.
    Contrast Ratio
  28. __, on the other hand, is an adjustable setting on all monitors that changes the relative brightness of adjacent pixels. The more contrast, the sharper and edgier the image. Reducing the __ too much can make the image appear washed out.
  29. __ is realized by reducing power to the backlight for darker images. The downside was that the original backlight being a single fluorescent bulb meant that the signal to the brighter LCD pixels had to be amplified to compensate for the uniform dimming of the backlight. This occasionally resulted in over-compensation manifested as areas of extreme brightness, often artificial in appearance. This practice tends to wash out the lighter colors and make white seem like it’s glowing, which is hardly useful to the user. Today’s LED backlights, however, are controlled either in zones made up of a small number of pixels or individually per pixel, resulting in trust-worthy high dynamic contrast ratios. The environment where the monitor will be used must be taken into account when considering whether to place a lot of emphasis on contrast ratio. In darker areas, a high contrast ratio will be more noticeable. In brighter surroundings, widely varying contrast ratios do not make as much of a difference.
    Dynamic Ratio