Computer based animation in multimedia ppt

animation techniques in computer graphics ppt and computer animation ppt in computer graphics
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Dr.ShaneMatts,United States,Teacher
Published Date:23-07-2017
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MIT EECS 6.837 Computer Graphics Basics of Computer Animation Skinning/Enveloping Many slides courtesy of Jovan Popovic, Ronen Barzel, and Jaakko Lehtinen Courtesy of Blender Foundation. License CC-BY. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 1 6.837 Matusik Traditional Animation • Draw each frame by hand – great control, but tedious • Reduce burden with cel animation – Layer, keyframe, inbetween, … Image courtesy of Garrett Albright on Wikimedia – Example: Cel panoramas (Disney’s Commons. License: CC-BY-SA. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. Pinocchio) © ACM. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 2 From ACM © 1997 “Multiperspective panoramas for cel animation.”Traditional Animation Principles • The in-betweening, was once a job for apprentice animators. Splines accomplish these tasks automatically. However, the animator still has to draw the keyframes. This is an art form and precisely why the experienced animators were spared the in- betweening work even before automatic techniques. • The classical paper on animation by John Lasseter from Pixar surveys some the standard animation techniques: • "Principles of Traditional Animation Applied to 3D Computer Graphics,“ SIGGRAPH'87, pp. 35-44. • See also The Illusion of Life: Disney Animation, by Frank Thomas and Ollie Johnston. 3Example: Squash and Stretch • Squash: flatten an object or character by pressure or by its own power • Stretch: used to increase the sense of speed and emphasize the squash by contrast © ACM. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. Image adapted from: Lasseter, John. "Principles of Traditional Animation applied to 3D Computer Animation." ACM SIGGRAPH Computer Graphics 21, no. 4 (July 1987): 35-44. 4Example: Timing • Timing affects weight: – Light object move quickly – Heavier objects move slower © ACM. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. • Timing completely changes the interpretation of the motion. 5Computer Animation • How do we describe and generate motion of objects in the scene? © ACM. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. • Two very different contexts: – Production (offline) • Can be hardcoded, entire sequence know beforehand – Interactive (e.g. games, simulators) • Needs to react to user interaction, sequence not known 6Plan • Types of Animation (overview) – Keyframing – Procedural – Physically-based • Animation Controls • Character Animation using skinning/enveloping 7 CERN Types of Animation: Keyframing • Specify scene only at some instants of time • Generate in-betweens automatically © source unknown. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 8Types of Animation: Procedural • Describes the motion algorithmically • Express animation as a function of small number of parameters • Example – a clock/watch with second, minute and hour hands – express the clock motions in terms of a “seconds” variable • the clock is animated by changing this variable • Another example: Grass in the wind, tree canopies, etc. 9Types of Animation: Physically-Based • Assign physical properties to objects – Masses, forces, etc. • Also procedural forces (like wind) • Simulate physics by solving equations of motion – Rigid bodies, fluids, plastic deformation, etc. • Realistic but difficult to control v0 g m 10Another Example • Physically-Based Character Animation – Specify keyframes, solve for physically valid motion that interpolates them by “spacetime optimization” • Anthony C. Fang and Nancy S. Pollard, 2003. Efficient Synthesis of Physically Valid Human Motion, ACM Transactions on Graphics 22(3) 417-426, Proc. SIGGRAPH 2003.http://graphics.cs.cmu.edu/nsp/projects/spacetime/space time.html 11Plan • Types of Animation (overview) – Keyframing – Procedural – Physically-based • Animation Controls • Character Animation using skinning/enveloping 12 CERN Because we are Lazy... • Animation is (usually) specified using some form of low-dimensional controls as opposed to remodeling the actual geometry for each frame. Can you think of examples? 13Because we are Lazy... • Animation is (usually) specified using some form of low-dimensional controls as opposed to remodeling the actual geometry for each frame. – Example: The joint angles (bone transformations) in a hierarchical character determine the pose – Example: A rigid motion is represented by changing the object-to-world transformation (rotation and translation). Courtesy Robert C. Duvall, Duke University. License CC BY-NC-SA. 14Because we are Lazy... • Animation is (usually) specified using some form of low-dimensional controls as opposed to remodeling the actual geometry for each frame. – Example: The joint angles (bone transformations) in a hierarchical character determine the pose – Example: A rigid motion is represented by changing the object-to-world transformation (rotation and translation). “Blendshapes” are keyframes that are just Courtesy Robert C. Duvall, Duke snapshots of the University. License CC BY-NC-SA. entire geometry. 15Example of Higher-Level Controls • Ken Perlin’s facial expression http://mrl.nyu.edu/perlin/experiments/facedemo/ applet • Lower-level controls are mapped to semantically meaningful higher-level ones – “Frown/smile” etc. © Ken Perlin. All rights reserved. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use/. 16 Building 3D models and their animation controls is a major component of every animation pipeline. Building the controls is called “rigging”. 17Articulated Character Models • Forward kinematics describes the positions of the body parts as a function of joint angles – Body parts are usually called “bones” – Angles are the low- dimensional control. • Inverse kinematics specifies constraint locations for bones and solves for joint angles. Courtesy Robert C. Duvall, Duke University. License CC BY-NC-SA. 18Skinning Characters • Embed a skeleton into a detailed character mesh Courtesy of Blender Foundation. License CC-BY. This content is excluded from our Creative Commons license. For more 19 information, see http://ocw.mit.edu/help/faq-fair-use.Skinning Characters • Embed a skeleton into a detailed character mesh • Animate “bones” – Change the joint angles over time – Keyframing, procedural, etc. • Bind skin vertices to bones – Animate skeleton, skin will move with it Courtesy of Blender Foundation. License CC-BY. This content is excluded from our Creative Commons license. For more information, see http://ocw.mit.edu/help/faq-fair-use. Courtesy Robert C. Duvall, Duke University. License CC BY-NC-SA. 20

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