1. Computer Animation

2. Animation Animate = “to give life to” Specify, directly or indirectly, how ‘thing’ moves in time and space

3. Angel Games

4. Animation Applications Special Effects (Movies, TV) Video Games Virtual Reality Simulation, Training, Military Medical Robotics, Animatronics Visualization Communication

5. Frame Rates Film24 fps Imax48 fps NTSC TV30 fps (interlaced) PAL TV25 fps (interlaced) HDTV60 fps Computer~60 fps

6. Animation How do we describe and generate motion of object in the scene?

7. Animation File Formats SoftwareFile Format Director.dir &.dcr Animator Pro.fli Studio Max.max SuperCard and Director.pics Windows Audio Video Interleaved.avi Macintosh.qt &.mov Motion Video.mpeg CompuServe.gif Flash.swf Shockwave.dcr

8. Web Page Animation File Formats (1) GIF Files –GIF89a’s ability to store a sequence of images has been used to provide a cheap and cheerful form of small animation for Web page advertisements.

9. Web Page Animation File Formats (2) GIF Shortcomings: However, even when GIF animation is properly implemented and enabled, it has many shortcomings. 1)Sound can not be added. 2)Colour palette is restricted to 256. 3)Images are losslessly compressed.

10. QuickTime For animation of any duration, especially if it is accompanied by sound, the best result will be achieved using a video format, and QuickTime has become the standard.

11. Heritage of Animation Persistence of vision: discovered about 1800s –Zoetrope or “wheel of life” –Flip-book

12. Heritage of Animation Camera to make lifeless things move –Meleis 1890 using simple tricks –Emil Cohl (1857-1938, French)

13. Disney: Animation as an art form Innovations –Story board to review story –Pencil sketch to review motion –Multi-plane camera stand –Color (not first to use color) –Sound! Steamboat Willie (1928)

14. Two main categories Computer-assisted animation –2D & 2 1/2 D –Inbetweening –Inking, virtual camera, managing data, etc Computer generated animation –Low level techniques Precisely specifying motion –High level techniques Describe general motion behavior

15. Low level techniques Shape interpolation (in-betweening) Have to know what you want

16. High level techniques Generate motion with set of rules or constraints –Physically based motion http://www.cs.berkeley.edu/~job/Projects/SoundGen/video.html

17. Why animation works The eye cannot register images faster than approximately 60 frames per second (30 is just about adequate) If a gap in the projection occurs, the eye seems to perform spatial interpolation over the gap

18. Animation and Frame Rates TV video builds 30 entire frames or pictures every second. Movies are shot at a shutter rate of 24 frames per second, but using projections tricks the flicker is increased to 48. On some projectors each frame is shown 3 times before the next frame, for a total of 72 flickers per second which helps eliminate the flicker effect. Cel Animation – plays at 24 frames per second.

19. Displaying animation sequences To achieve smooth animation, a sequence of images (frames) have to be presented on a screen with the speed of at least 30 per second Animations frames can be –pre-computed in advance and pre-loaded in memory –computed in real time (e.g. movement of the cursor)

20. Raster animation This is the most common animation technique Frames are copied very fast from off-screen memory to the frame buffer Copying can be applied to –complete frames –only parts of the frame which contain some movement

21. Examples

23. Double buffering Used to achieve smooth animation The next frame of animation is computed to an off-screen buffer at the same time when the current frame is transferred to the frame buffer.

24. 2-D Animation Two types: Cel animation Path animation

25. Cel Animation Made famous by Disney 24 frames per second therefore a minute may require as many as 1,440 separate frames. It is based on changes that occur from one frame to the next. Cel stands for celluloid which is a clear sheet with images drawn on them. The celluloid images are place on a background that is usually stationary. The background remain fixed as the images changes.

26. Cel Animation Those elements in a scene that might move are drawn on sheets of transparent material known as ‘cel’, and laid over a background drawn separately.

27. Path Animation Moves an object along a predetermined path on the screen The path can be a straight line or have a number of curves. Starts with keyframes (the first and last frame of an action). The series of frames in between the keyframes are drawn in a process called tweening. Tweening requires calculating the number of frames between keyframes and the path the action takes, and then actually takes, and then sketches a series of progressively different outlines.

28. 3-D Animation 3-D Animation involves three steps: modeling, animation, and rendering Modeling – the process of creating objects and scenes Animation – the process of defining the object’s motion Rendering – the final step in creating 3-D animation. Morphing is the process of blending two images into a series of images Warping allows you to distort a single image Warping Virtual reality (VR) creates an environment that surrounds the user so that they become part of the experience.

29. Hybrid Forms of Animation Mixing cel and 3-D Combining animation with live footage such as Jurassic Park. Add time -> 4D

30. Steps of a simple computer animation 1. Creating animation sequences –object definition –path specification (for an object or a camera) –key frames –in-betweening 2. Displaying the sequences –raster animation –colour-table animation

31. Object definition In simple manual systems, the objects can be simply the artist drawings In computer-generated animations, models are used Examples of models: –a "flying logo" in a TV advert –a walking stick-man –a dinosaur attacking its prey in Jurassic Park

32. Character Development 300 Drawings

33. Character Development 40 Sculptures

34. Character Development Computer Models

35. Storyboarding Explicitly define –Scenes –Camera shots –Special effects –Lighting –Scale Used as guide by animators

36. Layout and Look Build scenery Match colors

37. Path specification Impression of movement can be created for two basic situations, or for their combination: –static object, moving camera –static camera, moving object The path defines the sequence of locations (for either the camera or the object) for the consecutive time frames

38. Static object, moving camera F3 F1 F2 F4 Time F5

39. Static camera, moving object F1F2F3F4

40. It is important to remember that when the object moves along the path, not only its position changes, but also its orientation X Y Z

41. Keyframing Describe motion of objects as a function of time from a set of key object positions. In short, compute the inbetween frames. ACM © 1987 “Principles of traditional animation applied to 3D computer animation”

47. Keyframe Animation Set target positions for vertices at “key” frames in animations Linearly interpolate vertex positions between targets at intervening frames Lots can go wrong (like the feet) Can be fixed by adding key frames Piecewise linear approach to animation Need same number and configuration of vertices at key frames for intervening frames to make sense Often need to find correspondences between two collections of vertices

48. Keyframe Animation Set target positions for vertices at “key” frames in animations Linearly interpolate vertex positions between targets at intervening frames Lots can go wrong (like the feet) Can be fixed by adding key frames Piecewise linear approach to animation Need same number and configuration of vertices at key frames for intervening frames to make sense Often need to find correspondences between two collections of vertices

49. Key frames Compute first a small number of key frames Interpolate the remaining frames in-between these key frames (in-betweening) Key frames can be computed –at equal time intervals –according to some other rules –for example when the direction of the path changes rapidly

50. In-betweening The simplest method of in-betweening is linear interpolation Interpolation is normally applied to the projected object points

51. 1 2 Key frame k 1’ 2’ Key frame k+1 3 3’ added point Halfway frame

52. In-betweening - example Given coordinates of a 2D point –key frame n:(x n,y n ) –key frame n+1: (x n +1,y n +1) –time interval between the two key frames: 1/10 second To get smooth animation, needs at least 30 frames per second Solution: insert at least further 2 frames between the given two key frames

54. Keyframes and In-Betweening BeforeAfterIn-betweens

55. Calculating in-between frames using linear interpolation  x = (x n+1 - x n ) / 3  y = (y n+1 - y n ) / 3 for ( i=1; i<3; i++ ) { x i = x n + i *  x y i = y n + i *  y }

56. Example: Interpolating Positions Given positions: find curve such that

57. Linear Interpolation Simple problem: linear interpolation between first two points assuming : The x-coordinate for the complete curve in the figure:

58. Linear Interpolation Two Problems with Linear Interpolation –Unnatural movement Nothing really moves like this – motion begins and ends instantaneously, with objects attaining their full velocity as soon as they start to move, and maintaining it until they stop. Solution: using hand-made animation

59. Polynomial Interpolation An n-degree polynomial can interpolate any n+1 points. The Lagrange formula gives the n+1 coefficients of an n-degree polynomial that interpolates n+1 points. The resulting interpolating polynomials are called Lagrange polynomials. parabola

60. Easing In The object accelerate from a standstill to its final velocity.

61. (Hodkins, http://www.cc.gatech.edu/classes/cs8113a_98_spring/principles.pdf)

63. Rigid body animation Rigid body animation uses standard 3D transformations At least 30 frames per second to achieve smooth animation Computing each frame would take too long

64. (Hodkins, http://www.cc.gatech.edu/classes/cs8113a_98_spring/principles.pdf)

65. Robotic Arm Example Fingers first Then wrist Then elbow Finally, shoulder

66. x y T1T1 R1R1 R2R2 R3R3 P Find the new location of P (P’) after some translations T 1, T 2, T 3, T 4 and rotations R 1, R 2, and R 3. Express in terms of a matrix product, i.e. P’ = R 1 R 2 R 3 P T2T2 T3T3 T4T4 Robotic Arm Example

67. x y P T4T4 P’ P’ = T 4 P

68. x y Robotic Arm Example P’ P’’ = R 3 P’ = R 3 T 4 P P’’ R3R3

69. x y Robotic Arm Example P’’’ = T 3 P’’ = T 3 R 3 T 4 P P’’ T3T3 P’’’

70. x y Robotic Arm Example P 4 = R 2 P’’’ = R 2 T 3 R 3 T 4 P P’’’ P4P4 R2R2

71. x y Robotic Arm Example P4P4 T2T2 P5P5 P 5 = T 2 P 4 = T 2 R 2 T 3 R 3 T 4 P

72. x y Robotic Arm Example P5P5 P6P6 R1R1 P 6 = R 1 P 5 = R 1 T 2 R 2 T 3 R 3 T 4 P

73. x y Robotic Arm Example P6P6 P7P7 T1T1 P 7 = T 1 P 6 = T 1 R 1 T 2 R 2 T 3 R 3 T 4 P

74. x y Robotic Arm Example P6P6 P7P7 T1T1 P 7 = T 1 P 6 = T 1 R 1 T 2 R 2 T 3 R 3 T 4 P T1T1 R1R1 R2R2 R3R3 T2T2 T3T3 T4T4

75. x y Robotic Arm Example P 7 = T 1 P 6 = T 1 R 1 T 2 R 2 T 3 R 3 T 4 P P7P7 T1T1 R1R1 R2R2 R3R3 T2T2 T3T3 T4T4

76. 3D Transforms x y x’x’ y’y’ T x y x’x’ y’y’ z z’ T Pretty much exactly the same as 2D transforms

77. Physically Based Animation Assign physical properties to objects (masses, forces, inertial properties) Simulate physics by solving equations Realistic but difficult to control v0v0 mg

84. 84 Topics in Animation Scripted Animation –Keyframe interpolation, articulated models, inverse kinematics, deformations, … Procedural Animation –Particle Systems, Flocks, Crowds, Cloth, Fire, Smoke, Water, … Motion capture –Filtering, editing, retargeting, stitching,…

85. Procedural animation describes the motion algorithmically express animation as a function of small number of parameters Example: a clock with second, minute and hour hands –hands should rotate together –express the clock motions in terms of a “seconds” variable –the clock is animated by varying the seconds parameter

86. 86 Procedural animation

87. 87 Scripted Animation

88. 88 Motion capture

89. Motion Capture Usually uses optical markers and multiple high-speed cameras Triangulate to get marker 3D position Faces or joints You must observe someone do something

90. (Hodkins, http://www.cc.gatech.edu/classes/cs8113a_98_spring/)