Computer AnimationLet’s talk about computer animationSlide 3KeyframingSlide 5Linear InterpolationNonlinear InterpolationEasingStyle or Accuracy?Traditional MotivationMore squash and stretchAnticipation and StagingFollow ThroughCombinedSecondary MotionInterpolationSlide 17MoviesPowerPoint PresentationExamplesMotion Capture StrengthsMotion Capture WeaknessesSlide 23Slide 24Slide 25Slide 26Slide 27Procedural AnimationProcedural Animation StrengthsProcedural Animation WeaknessesSlide 31Computer AnimationCS 445/645Fall 2001Let’s talk about computer animation•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?Computer AnimationKeyframing•Traditional animation technique•Dependent on artist to generate ‘key’ frames•Additional, ‘inbetween’ frames are drawn automatically by computerKeyframingFrom “The computer in the visual arts”, Spalter, 1999How are we going to interpolate?Linear InterpolationSimple, but discontinuous velocityNonlinear InterpolationSmooth ball trajectory and continuous velocity, but loss of timingEasingAdjust the timing of the inbetween frames. Can be automated by adjusting the stepsize of parameter, t.Style or Accuracy?•Interpolating timecaptures accuracyof velocity•Squash and stretchreplaces motionblur stimuli andadds life-likeintentTraditional Motivation•Ease-in andease-out is likesquash andstretch•Can weautomate theinbetweens forthese?“The Illusion of Life, Disney Animation”Thomas and JohnsonMore squash and stretchAnticipation and Staging•Don’t surprise theaudience•Direct their attention to what’simportantFollow Through•Audience likes to see resolution of action•Discontinuities are unsettlingCombinedSecondary Motion•Characters should exist in a real environment•Extra movements should not detractInterpolation•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 simulationInterpolation•Strengths–Animator has exacting control (Woody’s face)•Weaknesses–Interpolation hooks must be simple and direct•Remember the problems with Euler angle interp?–Time consuming and skill intensive–Difficult to reuse and adjustMovies•Cartoon Physics•Homer3DExamples•Sports video games–Madden Football•Many movie characters–Phantom Menace•CartoonsMotion Capture Strengths•Exactly captures the motions of the actor–Michael Jordan’s video game character will capture his style•Easy to capture dataMotion 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•Reusing motion data–Difficult to scale in size (must also scale in time)–Changing one part of motionMotion 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 transitionMovies•Animating Aliens•Retargeting Motion – Siggraph ‘98•Siggraph ‘99 Papers TapeExamples•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 halfProcedural Animation•Very general term for a technique that puts more complex algorithms behind the scenes•Technique attempts to consolidate artistic efforts in algorithms and heuristics•Allows for optimization and physical simulationProcedural 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 cannotProcedural Animation Weaknesses•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 downMovies•Humming Along•Siggraph
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