UBI 516 Advanced Computer Graphics

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UBI 516 Advanced Computer Graphics

• Aydin Öztürk
• ozturk_at_ube.ege.edu.tr
• http//www.ube.ege.edu.tr/ozturk

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Administrivia

• Syllabus
• Instructor/TA coordinates
• Prereqs
• Texts
• Assignments
• Topic list

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Textbook

• Computer Graphics with OpenGL
• Third Edition
• Hearn and Baker

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The Basics

• Computer graphics generating 2D images of a 3D
  world represented in a computer.
• Main tasks
• modeling creating and representing the geometry
  of objects in the 3D world
• rendering generating 2D images of the objects
• animation describing how objects change in time

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Why Study Computer Graphics?

• Graphics is cool
• I like to see what Im doing
• I like to show people what Im doing
• Graphics is interesting
• Involves simulation, algorithms, architecture
• Ill never get an Oscar for my acting
• But maybe Ill get one for my CG special effects
• Graphics is fun

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Graphics Applications

• Entertainment Cinema

Pixar Monsters Inc.
Square Final Fantasy
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Graphics Applications
Entertainment Cinema
Final Fantasy (Square, USA)
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Graphics Applications

• Entertainment Games

GT Racer 3
Polyphony Digital Gran Turismo 3, A Spec
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Graphics Applications

• Video Games

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Graphics Applications

• Medical Visualization

The Visible Human Project
MIT Image-Guided Surgery Project
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Graphics Applications

• Computer Aided Design (CAD)

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Graphics Applications

• Scientific Visualization

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Graphics Applications

• Everyday Use
• Microsofts Whistler OS will use graphics
  seriously
• Graphics visualizations and debuggers
• Visualize complex software systems

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Everyday use
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Everyday use
Window system and large-screen interaction
metaphors (François Guimbretière)
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Education
Outside In (Geometry Center, University of
Minnesota)
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Current Technologies
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Impact of Computers

• Moores Law
• Power of a CPU doubles every 18 months / 2 years

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Impact of Video Games (Nvidia)

• Number of transistors on GPU doubles each 6
  months.
• Three times Moores Law
• Good article on Jen-Hsun Huang, Nvidia CEO
  http//www.wired.com/wired/archive/10.07/Nvidia_pr
  .html

Worldwide revenues
Retro flashback???
7 Billion Man
5.6 Billion Man
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Impact of Video Games

• But
• Video game sales is roughly same as Hollywood box
  office
• Americans bought 3.2 billion in VCRs and DVDs in
  2002
• Total revenues to movie studios is 5 times total
  video game revenues

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Future of Consoles

• 33 million PS2s (in 2002)
• 3.9 million Xboxes (in 2002)
• MSFT still losing lots of per console
• Predicted 200 million PDA/Cell game players in
  2005

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Display technologies

• Cathode Ray Tubes (CRTs)
• Most common display device today
• Evacuated glass bottle
• Extremely high voltage

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CRT details

• 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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Electron Gun

• Contains a filament that, when heated, emits a
  stream of electrons
• Electrons are focused with an electromagnet into
  a sharp beam and directed to a specific point of
  the face of the picture tube
• The front surface of the picture tube is coated
  with small phospher dots
• When the beam hits a phospher dot it glows with a
  brightness proportional to the strength of the
  beam and how long it is hit

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CRT characteristics

• Whats the largest (diagonal) CRT youve seen?
• Why is that the largest?
• Evacuated tube massive glass
• Symmetrical electron paths (corners vs. center)
• How might one measure CRT capabilities?
• Size of tube
• Brightness of phosphers vs. darkness of tube
• Speed of electron gun
• Width of electron beam
• Pixels?

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Display technologies CRTs

• Vector Displays
• Anybody remember Battlezone? Tempest?

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Display Technologies CRTs

• Vector Displays
• Early computer displays basically an
  oscilloscope
• Control X,Y with vertical/horizontal plate
  voltage
• Often used intensity as Z
• Name two disadvantages
• Just does wireframe
• Complex scenes cause visible flicker

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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
• Scan line A row of pixels

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Display technologies CRTs

• Raster Displays
• Black and white television an oscilloscope with
  a fixed scan pattern left to right, top to
  bottom
• As beam sweeps across entire face of CRT, beam
  intensity changes to reflect brightness
• Analog signal vs. digital display

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Display technologies CRT

• Can a computer display work like a black and
  white TV?
• Must synchronize
• Your program makes decisions about the intensity
  signal at the pace of the CPU
• The screen is painted at the pace of the
  electron gun scanning the raster
• Solution special memory to buffer image with
  scan-out synchronous to the raster. We call this
  the framebuffer.
• Digital description to analog signal to digital
  display

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Display Technologies CRTs

• Phosphers
• Flourescence Light emitted while the phospher is
  being struck by electrons
• Phospherescence Light emitted once the electron
  beam is removed
• Persistence The time from the removal of the
  excitation to the moment when phospherescence has
  decayed to 10 of the initial light output

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Display Technologies CRTs

• Refresh
• 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, phospher
  persistence, lighting...

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Display Technologies CRTs

• Raster Displays
• Interlaced Scanning
• Assume can only scan 30 times / second
• To reduce flicker, divide frame into two fields
  of odd and even lines

1/30 Sec
1/30 Sec
1/60 Sec
1/60 Sec
1/60 Sec
1/60 Sec
Field 1
Field 2
Field 2
Field 1
Frame
Frame
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Display Technologies CRTs

• CRT timing
• Scanning (left to right, top to bottom)
• Vertical Sync Pulse Signals the start of the
  next field
• Vertical Retrace Time needed to get from the
  bottom of the current field to the top of the
  next field
• Horizontal Sync Pulse Signals the start of the
  new scan line
• Horizontal Retrace The time needed to get from
  the end of the current scan line to the start of
  the next scan line

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What is a pixel?

• Wood chips Chrome spheres Trash

Daniel Rozin NYU (movies) http//fargo.itp.tsoa
.nyu.edu/danny/art.html
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Display Technology 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?

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

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

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Display Technology Raster

• 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
• Finicky (convergence, warp, etc)

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CRTs A Review

• CRT technology hasnt changed much in 50 years
• Early television technology
• high resolution
• 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 A Review

• 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 (binary) requires 160 KB
• High resolution color requires 5.2 MB

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Movie Theaters

• U.S. film projectors play film at 24 fps
• Projectors have a shutter to block light during
  frame advance
• To reduce flicker, shutter opens twice for each
  frame resulting in 48 fps flashing
• 48 fps is perceptually acceptable
• European film projectors play film at 25 fps
• American films are played as is in Europe,
  resulting in everything moving 4 faster
• Faster movements and increased audio pitch are
  considered perceptually acceptable

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Viewing Movies at Home

• Film to DVD transfer
• Problem 24 film fps must be converted to
• NTSC U.S. television interlaced 29.97 fps 768x494
  
• PAL Europe television 25 fps 752x582
• Use 32 Pulldown
• First frame of movie is broken into first three
  fields (odd, even, odd)
• Next frame of movie is broken into next two
  fields (even, odd)
• Next frame of movie is broken into next three
  fields (even, odd, even)

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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
• Crystalline state twists polarized light 90º.

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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
• Crystalline state twists polarized light 90º

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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 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

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Display Technology DMD / DLP

• Digital Micromirror Devices (projectors) or
  Digital Light Processing
• Microelectromechanical (MEM) devices, fabricated
  with VLSI techniques

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Display Technology DMD / DLP

• 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 they emit light
• Thin-film deposition of organic, light-emitting
  molecules through vapor sublimation in a vacuum.
• Dope emissive layers with fluorescent molecules
  to create color.

http//www.kodak.com/global/en/professional/produc
ts/specialProducts/OEL/creating.jhtml
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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
• Available for cell phones and car stereos

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Display Technologies Organic LED Arrays

• OLED cons
• Not very robust, display lifetime a key issue
• Currently only passive matrix displays
• Passive matrix Pixels are illuminated in
  scanline order, but the lack of phospherescence
  causes flicker
• Active matrix A polysilicate layer provides thin
  film transistors at each pixel, allowing direct
  pixel access and constant illum.

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Additional Displays

• Display Walls (Princeton)

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Additional Displays

• Stereo

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Video Controllers

• Graphics Hardware
• Frame buffer is anywherein system memory

Frame buffer Cartesian Coordinates
CPU
Video Controller
System Memory
Monitor
System Bus
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Video Controllers

• Graphics Hardware
• Permanent place forframe buffer
• Direct connection tovideo controller

Frame buffer Cartesian Coordinates
CPU
Video Controller
System Memory
Frame Buffer
Monitor
System Bus
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Video Controllers

• The need for synchronization

CPU
Video Controller
System Memory
Frame Buffer
Monitor
synchronized
System Bus
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Video Controllers
previous
current

• The need for synchronization
• Double buffering

CPU
Video Controller
System Memory
Double Buffer
Monitor
synchronized
System Bus
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Raster Graphics Systems
Figure 2.29 from Hearn and Baker
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Frame Buffer
Frame Buffer
Figure 1.2 from Foley et al.
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Frame Buffer Refresh
Refresh rate is usually 30-75Hz
Figure 1.3 from FvDFH
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Direct Color Framebuffer

• Store the actual intensities of R, G, and B
  individually in the framebuffer
• 24 bits per pixel 8 bits red, 8 bits green, 8
  bits blue
• 16 bits per pixel ? bits red, ? bits green, ?
  bits blue

DAC
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Color Lookup Framebuffer

• Store indices (usually 8 bits) in framebuffer
• Display controller looks up the R,G,B values
  before triggering the electron guns

Color Lookup Table
0
DAC
14
Pixel color 14
R G B
Frame Buffer
1024
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A Graphics System
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Todays Interfaces

• What is spatial dimensionality of computer
  screen?
• What is dimensionality of mouse input?
• How many degrees of freedom (DOFs) define the
  position of your hand in space?
• Space ball