Cathode Ray Tube (CRT)

  •  Electron gun shoots beam of electrons toward the back of monitor screen
  • It is coated with chemical dots called phosphors glow when electrons strike them
  • Beam of electrons scans the monitor from left to right, and top to bottom in a raster pattern to create the image.
  • Trio of dot phosphors is grouped in triangle for each hardware picture element
  • Electron beam returns regular to each phosphor to sustain the glow.
  • More dots better quality
  • Dot pitch
    • Measurement between the same spot in two vertically adjacent dot trios
    • Expressed in millimeters or dots per inch
    • Dot pitch tells “sharpness”
    • Software-pixel placement is limited to hardware’s transistor placement
    • Resolution
      • Number of pixelsused to draw the screen.
      • Higher resolutions = more information in the same screen area.
      • indicate rows and columns of pixels on screen

 Liquid Crystal Display (LCD)

  • Crystals align themselves with the current when passed through a semi-crystalline liquid.
  • Combining transistorswith liquid crystals, pattern formed.
  • Patterns combinedto represent numbers or letters.
  • First used in watches, now in monitor, even TV
  • Available in
    • analog (like VGA) :PCs digital signals are converted to analog by video card
    • digital interface: no analog modulation required, generally sharper
  • Backlight makes easier to view
    • Transistor at each pixel, switches to different level changing alignment and producing 1000s of shades
    • crisp, wide viewing angles
    • pixels hold value thus, no refreshing
    • Large power needed
    • pixels in x-y matrix and transistors on the axis
    • circuits controlling rows fire in series to refresh/newly activate pixels on each row in succession
    • circuits controlling the columns are synchronized to fire when that row’s transistor is active
    • refresh required
    • can be muddy
    • DUAL SCAN:
      • Passive matrix split in half and each half refreshed separately
      • quality improved
    • Slower response leading to submarining
    • Lesser viewing angle
  • Antiglare filters brighten, clarifying displays

  LED Displays

  • LCD displays with LED as light sources
  • Each LED can be intelligently controlled for better quality
  • Work on DC power

 Plasma Displays

  • Plasma: Cloud of ionized particles
  • These produce light when electrons change energy levels
  • Electrodes in front and back of sealed chambers with neon gas and mercury vapors
  • Not suitable in high altitude
  • No backlight, produce deeper black
  • 600Hz is refresh rate

 Organic Light Emitting Diode (OLED)

  • Organic light emitting compound placed b/w anode-cathode emits light when excited by current
  • No backlight, deeper black
  • Thin, light weight, flexible
  • Better contrast ratio
  • Reflective thus filters required
  • Active matrix (AMOLED)
  • Passive matrix (PMOLED)
  • Lesser power than LCDs
  • Super AMOLED use one cell TSP thus thinner touch layer over the display
  • Super AMOLED plus has subpixels for clearer display

 Projection Systems

  • condensed video display units with a lighting system that projectsthe VDU’s image onto a screen
  • interactive whiteboards allow presenters to project an image ontothe board as they use virtual markers to electronically draw on the displayed image
  • focusing mechanism is included on the lens


  • 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
  • earlier CRT technology used
  • now 3 LCDs used for separate RGB display
  • Digital light processing optical semiconductors, have roughly as many rotatable mirrors on their surface as pixels in the display resolution


  • Measure of lumens (total visible light that the projector gives off)
  • Image to be projected few feet away
  • Focused on a larger area, the lux—derivative of lumens measuring how much the projector lights up the surface—decreases
  • As we train the projector on a larger surface, the same lumens produce fewer lux.
  • Cannot use light bulbs as light is not constant
  • Chamber contains a metal halide gas that glows bright white when the tungsten filament lights up.
  • Soot inside of the projector bulb is avoided by using a chemical, extending its life and reducing changes in light output.But more expensive


  • Residual heat generated bythe projector bulb can damage the electronics or the bulb itself
  • Occurs if the fan is not allowed to remove enough heat before it stopsrunning
  • Without connection to electrical outlet, fan stops immediately


 Refresh Rate

  • Vertical scan frequency and specifies how many timesin one second the scanning beam of electrons redraws the screen in CRTs
  • Measured in screen draws per second, or Hertz,
  • Refresh rate on smaller monitors (14-16 in) 60-72Hz.
  • LCD TV support 60, 120, 240, 480hzrefresh rates
  • Higher rates = more fluid videomotion.
  • For higher refresh rate, compromise bychoosing a lower resolution.


  • Number of horizontal dots by vertical dots that make up the rows and columns
  • Adjusting display settings that are recommendedfor monitor can alleviate scrolling effect
  • Adapters come with utilities for changing settings like refresh rate, resolution

 Multiple Displays

  • Sometimes need touse two monitors on same computer simultaneously
  • We can have same display on all the screens or we can extend one screen on multiple displays
  • Might need to change settings for external device, like resolution or the device’s orientation with respect to the built-in display
  • Microsoft calls its multimonitor feature Dual View


  • Reduction of the magnetic field of an object
  • Degaussing the drive makes previously savedinformation all but unrecoverable
  • CRTs use magnetic fields to guide the electron beams, LCDs do not, thusstrictly CRT-related practice.
  • Monitor can be damaged by degaussing it morethan once in short period
  • Constant bombardment of the metallic shadow results image discolorationand rainbow effects
  • Later-generation CRTs have an internal degaussing coil
  • Activate coil each time unit is turned on.
  • External degaussing devices exist
  • Excessive electromagnetic energy can permanentlydamage CRT



  • difference: highest resolution and maximum number of colors
  • amount of memory of pre-VGA adapters was fixed, thus resolution and number of colors was fixed
  • Newerwith expandable memory
  • 24-bit color palettes, Truecolor made of 17 million colors, number of colors the human eye can distinguish
  • Latest commercial video standards continue to grow in resolution


  • first video technology for PCs (black-and-white for DOS)
  • First adapter Monochrome Display Adapter (MDA) displayed text, no graphics with resolution  720×350
  • Hercules Graphics Card (HGC), resolution of 720×350,could display graphics and text
  • Text Mode: displayingpredawn characters from onboard library
  • Graphics Mode:drawing individual pixels for graphics.
  • Modes switchable
  • These modes of operation used today

 Color Graphics Adapter (CGA)

  • displays 16-color text
  • Displays 320x200graphics with only four colors per mode.
  • 3 fixed and a selectable 4th
  • CGA’s 640x200graphics resolution has 2 colors—black and one from palette-of-16.

 Enhanced Graphics Adapter (EGA)

  • display 16 colors from palette-of-64
  • With CGA resolutions and 640n350 mode.
  • digital data pins on the 9-pin D-subminiatureconnector accounted for 6 of 9 pins

Video Graphics Array (VGA)

  • 256KB of video memory on board
  • display16 colors at 640×480, 640×350, and 320×200 pixels
  • It became base standard for color PC video.
  • Analog technology, graphics adapters output and monitors receive an analog signal
  • palette-of-256 colors chosen from 18-bit palette of 262,114 colors
  • more pins needed in digital for every 2-to-the-power increase in color
  • VGA requires only 3 pins, for RGB
  • Video card must support the monitor



 Advancements after VGA adapter occurred in memory and firmware of adapter, not the connector or analog functionality.

 Super VGA

  • Introduced to advance VGA
  • Support 16 colors at resolution of 800×600, but expanded to 1024×768 pixels with 256 colors
  • VGA monitorscan advance along with graphics adapter and color palette

 Extended Graphics Array (XGA)

  • Available only as Micro Channel Architecture (MCA) expansionboard
  • XGA supports 256 colors at 1024n768 pixelsor 65,536 colors at 800n600 pixels
  • Optimized for GUIs of theday like Windows or OS/2.
  • It scans every other line on each pass, using the phenomenon knownas “persistence of vision” appears to our eyes as continuous image
  • Refresh rate specifies frequency with which all odd/even rows arescanned
  • Refresh rateof 120Hz would result in refresh rate of 60Hz

 More Recent Video Standards

  • Preceded by the letter W :same vertical but a wider horizontal resolution toaccommodate 16:10 wide-screen formats
  • Letter Q :horizontal and vertical resolutions eachdoubled for 4 times (quadruple)
  • Letter H:4 times each for (16 times) hexadecatuple is used.
  • Therefore, if XGA has a resolution of 1024×768, then QXGA will have a resolutionof 2048×1536.
  • Needbetter technology, more video memory to display even slightly higher resolutions
  • Starting with SXGA, advanced resolutions can be paired with 32-bit graphics,with the 24-bit Truecolor palette and other 8 bitsfor noncolor features

 Nonadjustable Characteristics

  Native Resolution

  • Flat-panel displays have a single fixed resolution:native resolution.
  • Resolution other than native resolution can distort picture like blurred text, elliptical circles,etc
  • LCD computer monitors before use of wide-screen monitors became pervasive.

 Contrast Ratio

  • Ratio of luminance of brightest color to darkest color the screen is capable of producing
  • Different fromcontrast.
  • Contrast is an adjustable setting
  • LCDs have low contrast ratios.
  • A display with low contrastratio won’t show “true black” very well, and the other colors will look washed out
  • Lower contrast ratios mean difficult viewing images fromthe side
  • Ratios for smaller LCD monitors around 500:1
  • Today’s LED backlights controlled in zones or individually per pixel, resulting in high dynamic contrast ratios
  • In darker areas, a high contrast ratiowill be more noticeable.
  • In brighter surroundings, varying contrast ratios do not makea difference

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