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How do some traditional output devices work

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Cathode Ray Tube (CRT) Invented in 1897 by Karl Ferdinand Braun ... Arrange for red gun to. hit red spot, etc. Requires a lot more ... video signal ... – PowerPoint PPT presentation

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Title: How do some traditional output devices work


1
Output Technologies andUser Interfaces
  • How do some traditional output devices work?
  • Output in the User Interface

2
Agenda
  • Questions?
  • Traditional output technologies
  • Displays (CRT, LCD, plasmas, LED)
  • Some new output technologies
  • WIMP

3
Output Technologies
  • Traditional displays
  • Desktop screens
  • www.howstuffworks.com
  • Later
  • Other modes of output (e.g., sound)
  • Non-desktop scales (smaller and larger)

4
Human Perception and Displays
  • Split a picture into a collection of small dots
    and we can reconstruct it.
  • pixels and resolution
  • 100 dpi on computer screen
  • 1000 dpi for printed material
  • Present consecutive frames of a dynamic scene
    and we can smooth it.
  • 15 frames per second refresh rate

5
Painting a picture
  • Each memory cell controls 1 pixel

1
display surface
Frame buffer
6
Size of Frame Buffer
  • Resolution
  • of pixels
  • 1024 X 768 786432
  • Color
  • Black White 1 bit per pixel
  • Grayscale multiple bits vary intensity
  • Color Depth 3 (R, G B) values

7
True Color
  • Humans can 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.

8
Sources of imagery
  • CRT (cathode ray tube)
  • LCD (liquid crystal display)
  • Gas plasma
  • LED (light emitting diodes)

9
Cathode Ray Tube (CRT)
  • Invented in 1897 by Karl Ferdinand Braun
  • Commonly found in TVs

10
How a B/W CRT works
Phosphor Coating
Vacuum Tube
Deflection Coils
Electron Gun
15-20 Kv
Negative charge
Positive charge
11
How a B/W CRT works
  • Move electron beam in fixed scanning pattern
  • Raster lines across screen

12
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

13
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

14
Problem with CRTs
  • Screen size limitation
  • To increase width, need longer tube
  • Larger display dimmer screen
  • Bulky
  • LCD and Plasma display alternatives

15
How LCDs work
  • 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

16
Types of LCDs
  • Reflective vs. Backlit
  • Common-plane
  • Passive matrix vs. Active matrix

17
ClearType
18
How Plasma Displays Work
  • Plasma is a gas of xenon and neon atoms
  • Small fluorescent tubes providing RGB
  • Matrix of electrodes
  • control fluorescence

19
How an LED works
  • 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

20
Getting Larger
  • Projection systems

21
FogScreen
22
Volumetric Displays
23
Handling Output in a User Interface
  • Windows
  • and other stuff

24
Next Time
  • Input Technologies and Handling
  • Read Design Space for Input
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