CHAPTER 4: DISPLAY DEVICES
UNDERSTANDING DISPLAY TYPES AND SETTINGS
VIDEO DISPLAY TYPES
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
- 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
- ACTIVE MATRIX:
- 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
- PASSIVE MATRIX:
- 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
- LCD displays with LED as light sources
- Each LED can be intelligently controlled for better quality
- Work on DC power
- 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
- 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
- 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
- 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
UNDERSTANDING DISPLAY TYPES AND SETTINGS
VIDEO DISPLAY TYPES
- 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
ADVANCED VIDEO RESOLUTIONS AND CONCEPTS
Advancements after VGA adapter occurred in memory and firmware of adapter, not the connector or analog functionality.
- 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
- 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.
- 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
- Configure and apply BIOS settings
- Differentiate between motherboard components, their purposes, and properties
- Compare and contrast RAM types and features
- Install and configure expansion cards
- Expansion cards
- Motherboard Components
- Computer Ports and Connections
- Optical Disk Storage Options
- Motherboard Processors and Memory
- PERIPHERALS AND EXPANSION
- Custom Configurations