CS-184: Computer GraphicsLecture #17: Introduction to AnimationProf. James O’BrienUniversity of California, BerkeleyV2009-F-17-1.02Introduction to Animation•Generate perception of motion with sequence of image shown in rapid succession•Real-time generation (e.g. video game)•Off-line generation (e.g. movie or television)Sunday, November 8, 20093Introduction to Animation•Key technical problem is how to generate and manipulate motion•Human motion•Inanimate objects•Amorphous objects•Control4Introduction to Animation•Technical issues often dominated by aesthetic ones•Violation of realism desirable in some contexts•Animation is a communication tool•Should support desired communication•There should be something to communicateSunday, November 8, 20095StoryAnimationLightingCameraShadingLayoutModelingComputer Animation Pipeline (v 1.1)VoicePostprocessingFor more detailed diagram, see Kerlow p.54FoleyIntroduction to Animation6Introduction to Animation•Key-frame animation•Specification by hand•Motion capture•Recording motion•Procedural / simulation•Automatically generated•Combinations•e.g. mocap + simulationSunday, November 8, 20097Key-framing (manual)•Requires a highly skilled user•Poorly suited for interactive applications•High quality / high expense•Limited applicability From Learning Maya 2.08Motion Capture (recorded)•Markers/sensors placed on subject•Time-consuming clean-up•Reasonable quality / reasonable price•Manipulation algorithms an active research area3Figure 1.1: Optical motion capture systems work by tracking retroreflective markers placed on thebody. Since these markers appear as bright dots to the cameras filming them, they are easy to detect.Multiple cameras are then used to triangulate the position of these markers.as bright dots on the infrared cameras looking at them (see figure 1.1). Optical systems use anumber of such infrared cameras to detect the two dimensional positions of every marker. Becausethe cameras can be calibrated to a known common coordinate system, a marker’s three dimensionalposition can be triangulated from its two dimensional projections on the cameras that see it. Themaximum magnetic field that can be generated by the source and the minimum amount of field thatcan be measured by the markers mean that the markers can not get too far away from the source.Magnetic systems are also prone to magnetic interference generated by metallic objects, which arealmost impossible to avoid. Due to these reasons, optical motion capture systems are more commonthan magnetic ones.Typical optical motion capture systems are quite expensive. To obtain high accuracy,many cameras need to be employed. This is especially true if markers are to move in a large area.This is due to the perspective effect which means projections of father away points move less asthey move in space.In order for a marker to be triangulated, its projection on several cameras need to be found.Since all a camera sees is a cloud of bright dots, the markers corresponding to each other in all cam-era views must be identified. Some motion capture systems accomplish this correspondence using“active” markers that emit an infrared pulse which uniquely identifies every marker. Since theseMotionAnalysis / Performance Capture Studio Okan ArikanSunday, November 8, 20099Motion EditingArikan, Forsyth, O’Brien, SIGGRAPH 200210Motion EditingArikan, Forsyth, O’Brien, SIGGRAPH 2002Sunday, November 8, 200911Model ConstructionKirk, O’Brien, Forsyth, CVPR 200512Simulation•Generate motion of objects using numerical simulation methodsxt+Δt= xt+ Δt vt+12Δt2atgvSunday, November 8, 200913Simulation•Perceptual accuracy required•Stability, easy of use, speed, robustness all important•Predictive accuracy less so•Control desirable14SimulationFeldman, Arikan, O’Brien, SIGGRAPH 2003Sunday, November 8, 200915What to do with animations?•Video tape•Digital video•Print it on yellow sticky notesXVideo Tape•Analog tape formats•VHS/SVHS•Beta SP•3/4” U-matic•Digital tape formats •Digi Beta•DV Tape•DVD (yes, I know DVDs are not tapes)Sunday, November 8, 200916NTSC Standard•Used by DVD, DV, and VHS•720x486 resolution (sort of)•1.33 aspect ratio•Limited color range•30 frames per second (sort of 29.97)•Interlaced video•Overscan regions17Digital Video•Wide range of file formats•QuickTime•MS Audio/Visual Interleaved (AVI) •DV Stream•Bunch ‘o images•Some formats accommodate different CODECs•Quicktime: Cinepak, DV, Sorenson, DivX, etc.•AVI: Cinepak, Indeo, DV, MPEG4, etc.•Some formats imply a given CODEC•MPEG•DV StreamsSunday, November 8, 200918Digital Video•Nearly all CODECs are lossy•Parameter setting important•Different type of video work with different CODECs•Compressors not all equally smart•Compression artifacts are cumulative in a very bad way•Playback issues•Bandwidth and CPU limitations•Hardware acceleration•Missing CODECs (avoid MS CODECs and formats)XPath toTape•Not much of an issue any longer•Cheap ( < $100 ) devices can give good amateur quality output•Pro quality also cheap ( < $5000 )•Beware many cheap solutions over use compression•Good analog tape decks still expensiveSunday, November 8, 200919Editing•Old way:•Multiple expensive tape decks•Slow•Difficult•Error prone•New way:•Non-linear editing software•Premiere, Final Cut Pro, others...•Beware compressed solutions•May take a long time for final encodingInteractive Animation•Video Games20Sunday, November 8, 2009Interactive Animation•“Serious” Games21Interactive Animation•“Serious” Games21Sunday, November 8, 200922Motion Blur•Fast moving things look blurry•Human eye•Finite exposure time in cameras•Without blur: strobing and aliasing•Blur over part of frame interval •Measured in degrees (0..360)•30 tends to often look good23Motion Blur•Easy to do in a sampling framework•Interpolation is an issueInterpolation is an issueMotion Blur ! Cont.Sunday, November 8, 200924Motion Blur•Velocity based blur often works poorlySunday, November 8,
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