Introduction to Computer Graphics CS 445 645 - PowerPoint

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Introduction to Computer Graphics CS 445 645 - PowerPoint Powered By Docstoc
We are going to study how things move and the
creation of computer graphics representations that
look “good enough”

Rendering is: mapping light sources and surfaces to a
vector of pixel colors
Animation is: mapping objects, intentions, and external
forces to a vector of new object positions / orientations
We will not
Develop drawing skills
• but we may study how others draw so we can automate the

Learn how to use Maya
• but we may use Maya as a rendering tool

Hone our video game or moviemaking skills
• but we will study how modern animation technology contributes
  to video games and what elements of moviemaking artistry
  (timing, camera angles, etc.) must reside in animation tools
Study how things move
Who else does this?
 • Biomechanists
    – Physics and sensors
 • Artists
    – Intuition and mind’s eye
Study how things move
We‟ll investigate
• Human walking, running, dancing
• Bicycle riding
• Group behaviors
• Rigid body dynamics
Generate graphics that is “good
                                             Monet                  Picasso
Who else studies this?           La Cathédrale de Rouen (1894)   The Bull (1946)

   • Perceptual psychologists
   • Artists

                 University of
Generate graphics that is “good
We‟ll investigate
• Recent perceptual literature (change blindness)
• Recent computer animation experiments (faking
Completing the mapping
Bridge gap between knowledge of how
things move to how they need to be
• Artists use their minds and hands
• Computer scientists use math and programs
Traditional techniques
• Keyframing (Shoemake)
   – Orientation reps (quaternion, euler)
   – Curve reps (linear, quadratic, wavelets)
   – Interpolation (computing arclength, Gaussian
     Quadrature, SLERP)
• Disney artists (Johnson)
• Timing / storyboarding
Numerical Methods
• Curve fitting (least squares)
• Optimization
   – Simulated annealing (Numerical Recipes)
   – Simplex
   – Spacetime Constraints (Witkin & Kass)
   – Genetic Algorithms (Sims)
   – Neural Networks (Grzeszczuk)
Human Motion
• Motion Capture
  – Retargeting (Gleicher, J. Lee, Z. Popovic, Arikan)
  – Blending (Rose)
  – Abstraction (Unuma)
• Walking
  – Biomechanics (McMahon, Ruina)
  – Gait Generation (Metaxas, van de Panne, Hodgins)
Physical Simulation
• Rigid Body
   – Physics for games (Hecker)
   – Featherstone’s Method
   – Constraint satisfaction
• Integration
   – Runge-Kutta
   – Euler
• Simplification (Chenney, Lin, Popovic)
• Perception (O’Sullivan, Proffitt)
Autonomous Agents
• Behaviors (Thalmann, Badler, Blumberg)
• Group actions (Reynolds, Brogan, Helbing)
Positive afterimage (persistence of vision)
  • the visual stimulus that remains after illumination
    has changed or been removed
Motion blur
  • Persistence of vision causes an object to appear to
    be multiple places at once
Motion Blur
Virtual camera in computer graphics
  usually shoots with infinitely small
  shutter speed
  • No motion blur results

Without motion blur, 30 fps results in fast
 moving objects that look like they are
 strobing, or hopping
What’s the rate?
 Playback rate
   • The number of samples displayed per second
 Sample rate
   • The number of different images per second
                                Sample Rate
        TV Cartoon      30            6
         TV Sitcom      30      30 (on fields)
        CG Lipsync
                        24           12
          on film
Computer graphics rendering can rely on four-
 hundred years of perception research by artists
   • The best animators have is eighty years of Disney

In 1550, after 100 years of refining the art of
   perspective drawing, artists were shocked to think
   that the geometric purity of their modeled world
   didn’t map to recent discoveries of the human eye.
   They couldn’t even imagine how cognition affected
   what one “saw.” 200 more years would pass.
Animation timeline
Persistence of vision
• Thaumotrope (1800s)
• Flipbook
• Zoetrope (1834)
• Shadow puppets

Animation timeline
• Muybridge (1885)

• Film projector (Edison, 1891)
Animation Timeline
First Animation
  • 1896, Georges Melies, moving tables
  • 1900, J. Stuart Blackton, added smoke
First celebrated cartoonist
  • Winsor McCay
  • Little Nemo (1911)
  • Gertie the Dinosaur (1914)
Animation Timeline
1910, Bray and Hurd
  • Patented translucent cels (formerly celluloid was
    used, but acetate is used now) used in layers for
  • Patented gray-scale drawings (cool!)
  • Patented using pegs for registration (alignment) of
  • Patented the use of large background drawings and
    panning camera
Bray’s Studio Produced
Max Fleischer – Betty Boop
Paul Terry – Terrytoons
George Stallings – Tom and Jerry
Walter Lantz – Woody Woodpecker

1915, Fleischer patented rotoscoping
  • Drawing images on cells by tracing over previously recorded
    live action (MoCap)
1920, color cartoons
Advanced animation more than anyone else
  • First to have sound in 1928, Steamboat Willie
  • First to use storyboards
  • First to attempt realism
  • Invented multiplane camera
Multiplane Camera

 Camera is mounted above multiple planes
 Each plane holds an animation cel
 Each plane can translate freely on 3 axes
 What is this good for?

  Zooming, moving foreground characters off camera,
  parallax, prolonged shutter allows blurring some layers
  (motion blur)
Stop-motion Animation
Willis O‟Brien – King Kong
Ray Harryhausen – Mighty Joe Young
Nick Park – Wallace and Grommit
Tim Burton – Nightmare Before Christmas
Animation Heritage

• 1963 – Ivan Sutherland’s (MIT) Sketchpad
• 1970 – Evans and Sutherland (Utah) start
  computer graphics program (and Co.)
• 1972 – Ed Catmull’s (Utah) animated hand and
  face (later co-founded Pixar)
• 1970’s – Norm Badler (Penn) Center for
  Modeling and Simulation
  and Jack
Animation Heritage
• 1970‟s – New York Institute of Technology
  (NYIT) produced Alvy Ray Smith (Cofounded
  Pixar and Lucasfilm) and Catmull
• 1980‟s – Daniel and Nadia Magnenant-
  Thalmann (Swiss Universities) become
  European powerhouses
Animation Heritage
• 1980‟s – z-buffer invented, SGI founded, and
  Alias/Wavefront founded
• 1977 – Starwars
• 1982 – Tron (first extensive use of gfx)
• 1982 – Early use of particle systems (Star Trek
  II: The Wrath of Khan)
• 1984 – The Last Starfighter (look for the Cray
  X-MP in credits)
Animation Heritage
• 1986 – Young Sherlock Homes (first use of
  synthetic character in film)
• 1986 – First digital wire removal (Howard the
• 1988 – First digital blue screen extraction
• The Abyss (1989) Terminator II (1991) Casper
  (1995), Men in Black (1997)
Animation Heritage
  • ILM: Jurassic Park (1993), Jumangi (1995),
    Mars Attacks (1996), Flubber (1997), Titanic
  • Angel Studios: Lawnmower Man (1992)
  • PDI: Batman Returns (1995)
  • Tippett Studio: Dragonheart (1996), Starship
    Troopers (1997)
  • Disney: Beauty and the Beast (1991), Lion
    King (1994), Tarzan (1999)
  • Dreamworks: Antz, Prince of Egypt
  • Pixar: Toy Story, A Bug‟s Life, Monster‟s Inc.
Americans are hardest working
   Recent history
United Nations report from Sept 1, 2003
•   $/worker-year
     – US = $60,728, Belgium (top EU) = $54,333
•   hours/worker-year
     – US = Japan = 1825, EU = 1300 – 1800
•   $/worker-hour
     – Norway, France, Belgium, US
        $38      $35     $34 $32
•   Why is US on top of $/worker-year?
     – Best economies encourage widespread use of communications and
       information technology
     – Even though we’re fat, dumb, and happy – we don’t take month-long vacations
       and one-year maternity breaks
Let’s talk about computer
Must generate 30 frames per second of
 animation (24 fps for film)
Issues to consider:
  • Is the goal to replace or augment the artist?
     – What does the artist bring to the project?
  • Is the scene/plot fixed or responsive to user?
     – What can we automate?
Animation – A broad Brush
Traditional Methods
• Cartoons, stop motion

• Digital inbetweens

Motion Capture
• What you record is what you get

• Animate what you can model (with equations)
Computer Animation

 Traditional animation technique
 Dependent on artist to generate „key‟
 Additional, „inbetween‟ frames are drawn
  automatically by computer
 How are we going to interpolate?

  From “The computer in the visual arts”, Spalter, 1999
Linear Interpolation

 Simple, but discontinuous velocity
Nonlinear Interpolation

 Smooth ball trajectory and continuous velocity, but loss of timing

 Adjust the timing of the inbetween frames. Can be automated
 by adjusting the stepsize of parameter, t.
Style or
Interpolating time
  captures accuracy
  of velocity
Squash and stretch
 replaces motion
 blur stimuli and
 adds life-like
Ease-in and
 ease-out is like
 squash and
Can we
 automate the
 inbetweens for
                    “The Illusion of Life, Disney Animation”
                              Thomas and Johnson
More squash and stretch
and Staging
Don‟t surprise the
Direct their
  attention to what‟s
Follow Through
Audience likes to see resolution of action
Discontinuities are unsettling
Secondary Motion
Characters should exist in a real
Extra movements should not detract
Many parameters can be interpolated to
 generate animation
Simple interpolation techniques can only
  generate simple inbetweens
More complicated inbetweening will require
 a more complicated model of animated
 object and simulation
  • Animator has exacting control (Woody’s face)
  • Interpolation hooks must be simple and direct
     – Remember the problems with Euler angle interp?
  • Time consuming and skill intensive
  • Difficult to reuse and adjust
Sports video games
  • Madden Football
Many movie characters
  • Phantom Menace
Motion Capture Strengths
Exactly captures the motions of the actor
  • Michael Jordan’s video game character will capture
    his style
Easy to capture data
Motion Capture Weaknesses
Noise, noise, noise!
Magnetic system inteference
Visual system occlusions
Mechanical system mass
Tethered (wireless is available now)
Motion Capture Weaknesses

 Aligning motion data with CG character
   • Limb lengths
   • Idealized perfect joints
   • Foot sliding
 Reusing motion data
   • Difficult to scale in size (must also scale in time)
   • Changing one part of motion
Motion Capture Weaknesses

 Blending segments
   • Motion clips are short (due to range and tethers)
   • Dynamic motion generation requires blending at
     run time
   • Difficult to manage smooth transition

Inanimate video game objects
  • GT Racer cars
  • Soapbox about why this is so cool
Special effects
  • Explosions, water, secondary motion
  • Phantom Menace CG droids after they were cut in
Procedural Animation
Very general term for a technique that puts
 more complex algorithms behind the
Technique attempts to consolidate artistic
 efforts in algorithms and heuristics
Allows for optimization and physical
Procedural Animation Strengths
Animation can be generated „on the fly‟
Dynamic response to user
Write-once, use-often
Algorithms provide accuracy and exhaustive
  search that animators cannot
Procedural Animation
We‟re not great at boiling human skill down
 to algorithms
  • How do we move when juggling?
Difficult to generate
Expensive to compute
Difficult to force system to generate a
  particular solution
  • Bicycles will fall down
Fundamental Animation
Fundamental Animation
Squash and Stretch
Slow In and Slow Out
Secondary Action
Squash and Stretch
More squash and stretch
Timing – is everything!
Timing = speed of action
Relays the idea behind the
Too fast:
• might not notice at all
• Might not understand what’s
• might not pay enough attention
Too slow:
• Sense of action can be lost
• can become boring
Defines weight of the object
• Heavy objects accelerate slowly
• Size in general should correspond to the mass
Shows emotional state
Identical key frames can have different
Timing example
Two key frames
• Head leaning toward the right shoulder
• Head over left shoulder, chin slightly raised
Vary the number of in-between frames, 0 to
Very different ideas can be communicated
Timing example, cont.
  0: hit by tremendous force
  1: hit by a brick, frying pan
  2: nervous tick, muscle spasm
  3: dodging a brick, frying pan
  4: giving a crisp order “Move it !”
  5: friendly “Over here. Come on - hurry”
  6: sees a sports car he always wanted
  7: tries to get a better look at something.
  8: searches for a book on a shelf
  9: appraises, considering thoughtfully
  10: stretches a sore muscle
  Example from: Thomas and Johnson “Disney animation –
  the illusion of life”

  Action has three parts
   • Preparation for the action (anticipation)
   • Action itself
   • Termination of the action (follow through)

  Need anticipation to:
   • Make actions natural
      – Muscle movement (kicking a ball)
   • Prepare audience for the following action
   • Direct attention to another part of the screen
Slow action: can use little
• Meaning is carried by the
  action itself
Fast action: need more
• Need to know what’s going to
  happen even before the action
Exaggerated anticipation:
• Emphasize extreme weight /
  action difficulty
Follow-Thru and Overlapping
Follow through
Actions rarely come to sudden stops
There are leading parts, other participating
parts and appendages
Action starts by leading part
Main action follows
Appendages continue to move longer
• Heavy ones drag along longer
Follow Through
Audience likes to see resolution of action
Discontinuities are unsettling
Overlapping action
Add variations to timing of loose parts
• Little extra actions make it more interesting

New action starts BEFORE previous one stops
• Full stops are rare

locking open door:
• Start walking to the door
• Before coming to the door, reach for the door
• Before completely closing, reach for the key, etc.
Slow in and slow out
Even spacing between
frames = constant
Better to have gradual
acceleration and
slowing down
Bouncing Ball Example
  The ball on the left
  moves at a constant
  speed with no
  The ball in the center
  does slow in and out
  with a squash/stretch.
  The ball on the right
  moves at a constant
  speed with
 Visual path should be an
 • Rather than a straight line
Exaggeration and secondary
Keep it balanced
Have some natural elements
and some exaggerated ones
Secondary action – results
directly from primary action
• Gives natural complexity
                                The secondary action of Luxo
• Can be missed if happens in    Jr's forward motion is the
  the middle of major move       rippling of his power cord.
Should be obvious but kept
Secondary Action
Appeal & Personality
Basic Camera Shots
Wide Shot/Establishing Shot/Long Shot
Medium Shot
Close Up Shot
Cutaway Shot/Over the Shoulder
Two Shot/Three Shot
Length of shot
Wide Shot/Establishing
Medium Shot
Close Up Shot
Extreme Close Up
Two Shot/Three Shot
Cutaway Shot

               Cutaway (CA)
           Acutaway is a shot that's usually of
           something other than the current action.
           It could be a different subject (eg. this
           cat when the main subject is its owner),
           a close up of a different part of the
           subject (eg. the subject's hands), or just
           about anything else.
           The cutaway is used as a "buffer"
           between shots (to help the editing
           process), or to add interest/information.
Basic Camera Moves
Zoom In
Zoom Out
Pan Right, Pan Left
Action in the frame.
Follow the action/rolling shot.
Standard Movie Openings
Movie Opening 1    Movie Opening 2
Wide Shot          Tight Close-Up
Zoom to Medium     Out to Medium
Some Action.       Action
Zoom to close-up   Zoom to close-up
Out to Medium.     Out to Medium
Most Bond Films    Run with it.
                   Raiders of Lost Ark

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