How do some traditional output devices work

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Output Technologies

• How do some traditional output devices work?

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Agenda

• Questions
• CoWeb
• Homework overview (Khai)
• Traditional output technologies
• Displays (CRT, LCD, LED, plasma)

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Homework 1
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Output Technologies

• Traditional displays
• Desktop screens
• Later
• Other modes of output (e.g., sound)
• Non-desktop scales (smaller and larger)

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Human Perception and Displays

• Split a picture into a collection of small dots
  and we can reconstruct it.
• pixels and resolution
• Present consecutive frames of a dynamic scene
  and we can smooth it.
• gt 15 frames per second refresh rate

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Painting a picture

• Each memory cell controls 1 pixel

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display surface
Frame buffer
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Size of Frame Buffer

• Resolution - of pixels
• 1024 X 768
• Black White 1 bit per pixel
• Grayscale multiple bits vary intensity
• Color Depth 3 (R, G B) values

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True Color

• Humans can only distinguish 28 different
  gradations for each of R, G B
• 3 bytes or 24-bits is all you need
• For transparency, we can add an extra byte.

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Color lookup tables (CLUTs)

• Extra piece of hardware
• Use value in FB as index into CLUT
• e.g. 8 bit pixel gt entries 0255
• Each entry in CLUT has full RBG value used to
  drive 3 guns

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Sources of imagery

• LED (light emitting diodes)
• CRT (cathode ray tube)
• LCD (liquid crystal display)
• Gas plasma

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How an LED works
http//www.howthingswork.com/led.htm

• Invented in 1962 by Nick Holonyak, Jr.
• Electrons moving through semiconductor diode emit
  light.
• Long-lasting, durable and efficient
• Some examples
• Jumbo TVs, traffic lights, optical mouse, remote
  controls, entertainment devices

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Cathode Ray Tube (CRT)
http//www.howstuffworks.com/tv2.htm

• Invented in 1897 by Karl Ferdinand Braun
• Commonly found in TVs

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How a B/W CRT works
Phosphor Coating
Vacuum Tube
Deflection Coils
Electron Gun
15-20 Kv
Negative charge
Positive charge
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How a B/W CRT works

• Move electron beam in fixed scanning pattern
• Raster lines across screen
• Each spot along horizontal lines intensity is
  modulated to get pixels

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How color CRTs work

• Use 3 electron guns
• For each pixel place 3 spots of phosphor (glowing
  R, G, B)
• Arrange for red gun to hit red spot, etc.
• Requires a lot more precision than simple B/W
• Use shadow mask behind phosphor spots to help

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Problem with CRTs

• Screen size limitation
• 36 diagonal
• Bulky
• LCD and Plasma display alternatives

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How LCDs work
http//www.howstuffworks.com/lcd.htm

• Liquid Crystals
• discovered in 1888 by Reinitzer
• liquid and solid characteristics
• sensitive to temp electricity
• Layers of crystal line up
• along grooves of a surface
• relative to neighboring layers (spiral)
• electricity can untwist layers
• Paired polarized plates and electric field

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Types of LCDs

• Reflective vs. Backlit
• Common-plane
• Passive matrix vs. Active matrix

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How Plasma Displays Work
http//www.howstuffworks.com/plasma-display1.htm

• Plasma is a gas of xenon and neon atoms
• Small fluorescent tubes providing RGB
• Matrix of electrodes control fluorescence

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TVs vs. Computer Monitors

• TVs use composite video signal
• Horizontal-, vertical-sync and intensity (for B/W
  or RGB) all combined
• Computer monitor has VGA interface
• 15-pin standard that separates signals
• DVI is an emerging new standard

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Printers

• Dot matrix
• Ink Jet
• Laser