SWE 423: Multimedia Systems

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SWE 423 Multimedia Systems

• Chapter 6 Computer-Based Animation

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Outline

• Introduction
• Producing an Animation
• Specifications of Animations
• Methods of Controlling Animations
• Display of Animations
• Transmission of Animations
• VRML

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Introduction

• An animation covers all changes that have a
  visual effect

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Introduction

• Computer-based animations are produced, edited
  and generated with the help of graphical tools to
  create visual effects
• Multimedia APIs
• Java3D
• Constructs and renders 3D graphics
• Provides a basic set of object primitives (cube,
  splines,...etc.)
• An abstraction layer built on top of DirectX or
  OpenGL
• DirectX
• Windows API that supports video, images, audio,
  and 3D animation
• Most widely used for Windows-based animations
  (video games)
• OpenGL
• Most popular 3D API in use today
• Highly portable

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Introduction

• Computer-based animations are produced, edited
  and generated with the help of graphical tools to
  create visual effects
• Rendering Tools
• 3D Studio Max
• Character animation, game development and visual
  effects production (Sony Playstation)
• Softimage XSI
• For animation and special effects in movies
• Maya
• Softimage competitor
• RenderMan
• Excels in creating complex surface appearances
  and images
• Has been used in many movies.
• Simple/Quick Animation Generators
• GIF Animation Packages
• Looping through several GIF images creates an
  animation
• Gifcon and GifBuilder (Windows) and animate
  (Linux)

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Producing An Animation

• Input Process
• Drawings must be digitized or generated
• Digitizing photos or drawings may require
  post-processing in order to remove any glitches
• Composition Stage
• Individual frames in a completed animation are
  generated by using image composition techniques
  to combine foreground and background elements
• Trailer film is generated from placing
  low-resolution digitized frames in a grid.

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Producing An Animation

• InBetween Process
• Interpolation methods are used to animate the
  movement from one position to another.
• Linear interpolation (lerping) is the simplest
  but the most limited
• E.g. the interpolation of animating throwing a
  ball using three points
• Splines can be used to smoothly vary different
  parameters as a function of time, yet the problem
  is not completely solved (very complex)

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Producing An Animation

• Changing Colors
• Uses the Color LookUp Table (CLUT) or (LUT) of
  the graphics memory and the double buffering
  method
• Two parts of a frame are stored in different
  areas of graphic memory.
• The graphic memory is divided into two fields,
  each having half as many bits per pixel.
• The animation is generated by manipulating the
  CLUT.

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Specification of Animations

• Formal specifications that describe animations
  can be divided into three categories
• Linear-List Notations
• High-Level Programming Language Notations
• Graphical Languages

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Linear List Notations

• Each event is described by a beginning frame
  number, an end frame number and an action event
  that is to be performed.
• Action events may accept input parameters
• For example
• 42, 53, B, ROTATE PALM, 1, 30
• This instruction means......
• SCEne Format (Scefo) specification can be
  considered a superset of linear sets including
  groups and object hierarchies as well as
  transformation abstractions using high-level
  languages constructs.

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High-Level Programming Languages Notations

• Values of variables can be used as parameters for
  animation routines.
• For example, ASAS is a LISP extension that
  includes primitives such as vectors, colors,
  polygons, surfaces, groups, points of view,
  subworlds, and lighting aspects in addition to
  geometrical transformations operating on objects
• For example
• (grasp my-cube) cube is current object
• (cw 0.05) small clock-wise rotation
• (grasp camera) camera is current object
• (right panning-speed) Move it to the right

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Graphical Languages

• Graphical actions cannot be easily described by
  and/or understood from textual scripts.
• Hence, graphical animation languages describe
  animations in a visual manner.
• GENESYS, DIAL and S-Dynamics System are examples
  of such systems.

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Methods of Controlling Animations

• Explicitly Declared
• Procedural
• Constraint-Based
• Analyzing Live Action-Based
• Kinematic and Dynamic

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Explicitly Declared Control

• All events that could occur in an animation are
  declared. This can be done at the
• object level by specifying simple transformations
  (translations, rotations, scaling) to objects
• frame level by specifying key frames and methods
  for interpolating between them.

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Procedural Control

• Based on communication among different objects
  whereby each object obtains knowledge about the
  static/dynamic properties of other objects.
• Can be used to ensure consistency
• For example ....

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Constraint-Based Control

• Many objects movements in the real world are
  determined by other objects which they come in
  contact with
• E.g. presence of strong wind or fast moving large
  objects
• Instead of explicit declaration, constraints
  based on the environment can be used to control
  objects motion.
• Example Systems Sketchpad and ThingLab.

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Analyzing Live Action-Based Control

• Control is achieved by examining the motions of
  objects in the real world.
• Rotoscoping is a technique where animators trace
  live action movement, frame by frame, for use in
  animated films.
• Originally, pre-recorded live-film images were
  projected onto a frosted glass panel and redrawn
  by an animator.
• This projection equipment is called a Rotoscope.
• Another way is to attach indicators to key points
  on the body of a human actor.
• For example the data glove gesture language for
  hearing-impaired people

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Kinematic and Dynamic Control

• Kinematics refer to the position and velocity of
  points
• The cube is at the origin at time t 0.
  Thereafter, it moves with constant acceleration
  in the direction (1 meter, 1 meter, 5 meters)
• Dynamics takes into account the physical laws
  that govern kinematics
• Newton laws for the movement of large objects
• Euler-Lagrange equations for fluids
• A particle moves with an acceleration
  proportional to the forces acting on it.
• For example At time t 0, the cube is at
  position (0 meter, 100 meter, 0 meter). The cube
  has a mass of 100 grams. The force of gravity
  acts on the cube.

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Display of Animation

• To display animations with raster systems, the
  animated objects must be scan-converted and
  stored as pixmap in the frame buffer.
• Scan conversion must be done at least 10 times
  per second to ensure smooth visual effects.
• The actual scan-conversion must take a small
  portion of 10 times/second in order to avoid
  distracting ghost effect
• Double buffering is used to avoid the ghost
  effect

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Display of Animation

• Example
• Load CLUT to display values as background color
• Scan-convert object into image0
• Load CLUT to display only image0
• Repeat
• Scan-convert object into image1
• Load CLUT to display only image1
• Rotate object data structure description
• Scan-convert object into image0
• Load CLUT to display only image0
• Rotate object data structure description
• Until (termination condition)

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Transmission of Animation

• Two forms of transmission
• Symbolic representation of an animation is
  transmitted together with the operations
  performed on the object.
• The receiver displays the animation.
• Transmission is fast since text is much smaller
  than pixmaps
• Display is slow since the pixmap has to be
  generated from their descriptions.
• The pixmap representations are transmitted and
  displayed
• Transmission time is longer.
• Display is faster.

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VRML

• Virtual Reality Modeling Language
• Describes 3D interactive worlds and objects that
  can be used together with the World Wide Web.
• Illustrations, product definitions or virtual
  reality presentations can be generated on the
  Web.
• History of VRML
• May 1994 At the first Int. Conf. on the WWW, the
  idea of a platform-independent standard for 3-D
  WWW applications originated
• October 1994 VRML 1.0 was presented at the
  second Int. Conf. on the WWW.
• VRML 1.0 defined the parameters for creating 3D
  objects that can travel across the Internet.
• August 1995 VAG (Vrml Architecture Group) was
  established

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VRML

• History of VRML
• January 1996 VAG called for proposals for VRML
  2.0. Each of the following submitted their own
• Apple Out of this World
• Sun Holoweb
• German National Research Center for Information
  Technology (GMD) and others Dynamic Worlds
• IBM Japan Reactive Virtual Environment
• Microsoft Active VRML
• Silicon Graphics Inc. (SGI), Sony, and others
  Moving Worlds
• August 1996 VRML 2.0 in its final form was
  presented in SIGGRAPH 96.

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VRML Capabilities

• VRML is capable of representing static and
  animated objects as well as hyperlinks to other
  media such as sound, motion pictures and still
  pictures
• There are three ways of navigating though a
  virtual world
• Walk Movement over the ground at eye-level
• Fly Movement at any height
• Examine Rotating an object in order to closely
  examine it.

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VRML Example

• Color interpolator
• This example interpolates in a 10-second long
  cycle from red to green to blue
• DEF myColor ColorInterpolator
• key 0.0, 0.5, 1.0
• keyValue 1 0 0, 0 1 0, 0 0 1 red, green,
  blue
• DEF myClock TimeSensor
• cycleInterval 10.0 10 second animation
• loop TRUE animation in endless loop