The Shape of Animations Jason Harrison (Fiddling with the algorithms of Jeffery Boyd and Jim Little, and the animations of Jessica Hodgins, James O’Brien and Jack Tumblin)
Animation Metrics l “rate” animations by using metrics l use comparisons for databases, analysis, description... l aim for metrics based on human perceptual processes l Start with “Shape of Motion”
Shape of Motion l Jeffery Boyd and Jim Little l analysing video without models l optical flow l time varying signals l relative phases of signals l feature vector
N+1 frames... optical flow time-varying scalars scalar sequences phases {s 11, s 12,…, s 1n }{s 12, s 22,…, s 2m }{s n1, s n2,…, s nm } 11 22 mm... (phase reference) (s 1, s 2, …, s m ) feature vector(F 1, F 2, …, F m-1 ) phase features F 1 = 1 - m F 2 = 2 - m F m-1 = m-1 - m... “Shape of Motion”: Data Flow
Scalars computed l x coordinate of centroid l x coordinate of centroid weighted by |(u,v)| l y coordinate of centroid weighted by |(u,v)| l weighted centroid x - unweighted centroid x l weighted centroid y - unweighted centroid y l aspect ratio l aspect ratio weighted by |(u,v)| l aspect - weighted aspect l x coordinate of centroid weighted by |u| l y coordinate of centroid weighted by |u| l x coordinate of centroid weighted by |v| l y coordinate of centroid weighted by |v|
Boyd and Little’s Experiment l 6 participants l Walk for about 15 minutes l Toss first 2 passes l Analyse 7 passes l Compare between participants (control variable)
Example Gait (total sequence is 76 frames long)
Results aspect ratio x coordinate of centroid
Human Perceptions and Judgements of Motions l Jessica Hodgins, James O'Brien, and Jack Tumblin at Georgia Tech l participant study l dynamics model used to simulate runner l wireframe and polygonal models l camera moves steadily with runner
Animations: l 72 4-second running animations (36 of each model) l shoulder swing l motion computed dynamically l currently lost on /imager/raid
“Shape of Animations”: Data Flow l remove moving floor (chroma key) l crop and scale down by half l convert to grey scale l compute optical flow l compute fundamental frequency l pick good reference signal for phase l compute feature vectors
Fundamental Frequency l Median frequency of sequences for an animation l (min/max/ave/median) Stick figure animation
Any patterns? phase
One pattern x coordinate of centroid aspect ratio
Future Work l order sequences based on features? l clustering, rankings? l automatic analysis? l polygonal versus stick models?
Effect of Rendering Models? l geometry and surface appearances l lighting l camera position, parameters and movement l should resolution and frame rate be an issue?