Introduction and Display Technologies

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Introduction andDisplay Technologies

• Chapter 1 and
• Sections
• 2-1 to 2-4(somewhat outdated)

Most of these slides have been prepared by Dr
Ahmed Bashandy and some of the material have been
adapted from university of Virginia and MIT
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We will Study

• Graphics Fundamentals
• Graphics programming algorithms
• Graphics data structures
• Some of
• Color and human vision
• Applied geometry and modeling
• Applied numerical computing
• DirectX in the sections

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We will NOT study

• Paint and Imaging packages (Adobe Photoshop)
• Art and Movies
• CAD packages (AutoCAD)
• Packages
• Rendering packages (Lightscape)
• Modeling packages (3D Studio MAX)
• Animation packages (Digimation)
• Graphics Modeling and Languages (RenderMan)

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Why Computer Graphics
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Why Computer Graphics

• What computers do....
• process, transform, and communicate information
• Visual communication is very appealing to humans
• Computer graphics is a method of communication
• Computer Graphics is...
• the technology for presenting information
• Applied geometry and modeling
• Applied numerical computing

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Many Application for Graphics

• Education
• CAD
• Entertainment
• Medicine
• Communication
• Games

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Medicine

• Precision and correctness
• Remote medicine
• Teaching and diagnosis (CAT, MRI)
• Modeling of medical data

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Computer Aided Design

• Wide range of processes from the design of
  tooling fixtures to manufacturing.
• Architectural and product designs
• Verify tolerances and design from CAD tools
  directly

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Education and Scientific Visualization

• Biology and Chemistry visualization
• Mathematicians use computer graphics to explore
  abstract and high-dimensional functions and
  spaces.
• Physicists explore both microscopic and
  macroscopic worlds.

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Graphical User Interface

• Graphical elements such as windows, fonts,
  cursors, menus, and icons
• Translation, scaling, rotation of graphical
  elements
• Humans prefer appealing interfaces

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Display Devices
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Display Technologies

• Cathode Ray Tubes (CRTs) A CRT is an evacuated
  glass tube, with a heating element on one end and
  a phosphor coated screen on the other
• Most common display device
• (until recently)
• Evacuated glass bottle (lastof the vacuum tubes)
• Heating element (filament)
• Electrons pulled towards anode focusing cylinder
• Vertical and horizontal deflection plates
• Beam strikes phosphor coating on front of tube

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CRTs Overview

• CRT technology hasnt changed much in 50 years
• Early television technology
• requires synchronization between video signal and
  electron beam vertical sync pulse
• Early computer displays
• avoided synchronization using vector algorithm
• flicker and refresh were problematic

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CRTs Vector Displays

• Vector displays
• Early computer displays basically an
  oscilloscope
• Control X,Y with vertical/horizontal plate
  voltage
• Often used intensity as Z
• Show http//graphics.lcs.mit.edu/classes/6.837/F9
  8/Lecture1/Slide11.html
• Name two disadvantages
• Just does wireframe
• Complex scenes results in visible flicker

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CRTs Raster Displays

• Raster Displays (early 70s)
• like television, scan all pixels in regular
  pattern
• use frame buffer (video RAM) to eliminate sync
  problems
• RAM
• ¼ MB (256 KB) cost 2 million in 1971
• Do some math
• 1280 x 1024 screen resolution 1,310,720 pixels
• Monochrome color (8 bits per pixel) requires 160
  KB
• High resolution color (24 bits per pixel)
  requires 5.2 MB

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CRTs Raster Displays

• Black and white television an oscilloscope with
  a fixed scan pattern left to right, top to
  bottom
• Paint entire screen 30 times/sec
• Actually, TVs paint top-to-bottom 60 times/sec,
  alternating between even and odd scanlines
• This is called interlacing. Its a hack. Why do
  it?
• To paint the screen, computer needs to
  synchronize with the scanning pattern of raster
• Solution special memory to buffer image with
  scan-out synchronous to the raster. We call this
  the framebuffer.

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CRTs Raster Displays
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CRTs Raster Displays

• Raster Displays
• Frame must be refreshed to draw new images
• As new pixels are struck by electron beam, others
  are decaying
• Electron beam must hit all pixels frequently to
  eliminate flicker
• Critical fusion frequency
• Typically 60 times/sec
• Varies with intensity, individuals, phosphor
  persistence, lighting...

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Color CRTs

• Color CRTs are much more complicated
• Requires manufacturing very precise geometry
• Uses a pattern of color phosphors on the screen
• Why red, green, and blue phosphors?
• We will see later that the human eye contains
  cells that sense these 3 colors

Delta electron gun arrangement
In-line electron gun arrangement
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Color CRTs

• Color CRTs have
• Three electron guns
• A metal shadow mask to differentiate the beams

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Raster CRTs Pros and Cons

• Raster CRT pros
• Allows solids, not just wireframes
• Leverages low-cost CRT technology (i.e., TVs)
• Bright! Display emits light
• Cons
• Requires screen-size memory array
• Discreet sampling (pixels)
• Practical limit on size (call it 40 inches)
• Bulky

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Display Technology LCDs

• Liquid Crystal Displays (LCDs)
• LCDs organic molecules, naturally in crystalline
  state, that liquefy when excited by heat or E
  field
• When LCDs are used as optical (light) modulators
  they are actually changing polarization. In their
  unexcited or crystalline state the LCDs rotate
  the polarization of light by 90 degrees. In the
  presence of an electric field, LCDs behave like a
  liquid and align the small electrostatic charges
  of the molecules with the impinging E field.

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Display Technology LCDs

• Liquid Crystal Displays (LCDs)
• LCDs, like phosphors, remain "on" for some time
  after the E field is applied. Thus the image is
  persistent like a CRT's, but this lasts just
  until the crystals can realign themselves, thus
  they must be constantly refreshed, again, like a
  CRT.

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Display Technology LCDs

• Transmissive reflective LCDs
• LCDs act as light valves, not light emitters, and
  thus rely on an external light source.
• Laptop screen backlit, transmissive display
• Palm Pilot/Game Boy reflective display

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Display Technology Plasma

• Plasma display panels
• Similar in principle to fluorescent light tubes
• Small gas-filled capsules are excited by
  electric field,emits UV light
• UV excites phosphor
• Phosphor relaxes, emits some other color

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Display Technology Plasma

• Plasma Display Panel Pros
• Large viewing angle
• Good for large-format displays
• Fairly bright
• Cons
• Expensive
• Large pixels (1 mm versus 0.2 mm)
• Phosphors gradually deplete
• Less bright than CRTs, using more power
• For more details visit http//www.howstuffworks.co
  m/lcd4.htm

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Display Technology DMD

• Digital Micromirror Devices (projectors)
• A DMD chip has on its surface several hundred
  thousand microscopic mirrors
• Arranged in a rectangular array correspond to the
  pixels in the image to be displayed.
• Individually rotated 10-12, to an on or off
  state.
• Fast on-off to produce grey scale
• Mirrors made out of aluminium16 mm across.
• Mirrors mounted on hinge, the axle is fixed and
  literally twists in the middle

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Display Technology DMDs

• Microelectromechanical (MEM) devices, fabricated
  with VLSI techniques

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Display Technology DMDs

• DMDs are truly digital pixels
• Vary grey levels by modulating pulse length
• Color multiple chips, or color-wheel
• Great resolution
• Very bright
• Flicker problems

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Display Technologies Organic LED Arrays

• Organic Light-Emitting Diode (OLED) Arrays
• The display of the future? Many think so.
• OLEDs function like regular semiconductor LEDs
• But with thin-film polymer construction
• Thin-film deposition of organic, light-emitting
  molecules through vapor sublimation in a vacuum.
• Dope emissive layers with fluorescent molecules
  to create color.
• Not grown like a crystal, no high-temperature
  doping
• Thus, easier to create large-area OLEDs

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Display Technologies Organic LED Arrays

• OLED pros
• Transparent
• Flexible
• Light-emitting, and quite bright (daylight
  visible)
• Large viewing angle
• Fast (lt 1 microsecond off-on-off)
• Can be made large or small

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Display Technologies Organic LED Arrays

• OLED cons
• Not quite there yet (96x64 displays)
• Cell phones (especially back display)
• Not very robust, display lifetime a key issue
• Currently only passive matrix displays
• Passive matrix Pixels are illuminated in
  scanline order (like a raster display), but the
  lack of phosphorescence causes flicker
• Active matrix A polysilicate layer provides thin
  film transistors at each pixel, allowing direct
  pixel access and constant illumination
• Hard to compete with LCDs, a moving target
• See http//www.youtube.com/watch?vmGVbEBOzACs
  for more info

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Framebuffers

• So far weve talked about the physical display
  device
• How does the interface between the device and the
  computers notion of an image look?
• Framebuffer A memory array in which the computer
  stores an image
• On most computers, separate memory bank from main
  memory (why?)
• Many different variations, motivated by cost of
  memory

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Display Technologies CRTs

• Raster Displays
• Raster A rectangular array of points or dots
• Pixel One dot or picture element of the raster
• Scanline A row of pixels
• Rasterize find the set of pixels corresponding
  to a 2D shape (line, circle, polygon)
• Scan Conversion Rasterize

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