Animation CS 551 / 651

AnimationCS 551 / 651

Perception of Physically Perception of Physically Simulated HumansSimulated Humans

Perception of Physically Perception of Physically Simulated HumansSimulated Humans

Hodgins et al., 1998

Assignment 1 Suggestions

Emphasize development of physics codeEmphasize development of physics code• Even without graphics (simulate a 2D disk on a plane)Even without graphics (simulate a 2D disk on a plane)

– Apply force (hard coded) to COM to show how Apply force (hard coded) to COM to show how forceforceaccaccvelvelchange in positionchange in position

– Apply force offset from COM to show ang. effectsApply force offset from COM to show ang. effects

– Just use printf to verify successJust use printf to verify success

• 2D dynamics (linear and angular) + integrator2D dynamics (linear and angular) + integrator

– Start with EulerStart with Euler

Emphasize development of physics codeEmphasize development of physics code• Even without graphics (simulate a 2D disk on a plane)Even without graphics (simulate a 2D disk on a plane)

– Apply force (hard coded) to COM to show how Apply force (hard coded) to COM to show how forceforceaccaccvelvelchange in positionchange in position

– Apply force offset from COM to show ang. effectsApply force offset from COM to show ang. effects

– Just use printf to verify successJust use printf to verify success

• 2D dynamics (linear and angular) + integrator2D dynamics (linear and angular) + integrator

– Start with EulerStart with Euler


Test collision code in simplest scenarioTest collision code in simplest scenario

• 2D Disk hitting a wall2D Disk hitting a wall

– Just use distance from COM to plane to measure Just use distance from COM to plane to measure collisioncollision

Test collision code in simplest scenarioTest collision code in simplest scenario

• 2D Disk hitting a wall2D Disk hitting a wall

– Just use distance from COM to plane to measure Just use distance from COM to plane to measure collisioncollision


Scale to 3DScale to 3D

• Extension to 3D should go smoothlyExtension to 3D should go smoothly

• You could stay in an environment without graphicsYou could stay in an environment without graphics

• Don’t need file loader to initialize modelsDon’t need file loader to initialize models

– Just define one in codeJust define one in code

Scale to 3DScale to 3D

• Extension to 3D should go smoothlyExtension to 3D should go smoothly

• You could stay in an environment without graphicsYou could stay in an environment without graphics

• Don’t need file loader to initialize modelsDon’t need file loader to initialize models

– Just define one in codeJust define one in code


Adding on the restAdding on the rest

• File loader (use simple models)File loader (use simple models)

• Runge-KuttaRunge-Kutta

• InterfaceInterface

– Start simple (without any toolkit, just control the Start simple (without any toolkit, just control the vector using GLUT mouse tracking – aimed vector using GLUT mouse tracking – aimed straight into monitor)straight into monitor)

Adding on the restAdding on the rest

• File loader (use simple models)File loader (use simple models)

• Runge-KuttaRunge-Kutta

• InterfaceInterface

– Start simple (without any toolkit, just control the Start simple (without any toolkit, just control the vector using GLUT mouse tracking – aimed vector using GLUT mouse tracking – aimed straight into monitor)straight into monitor)

Paper CategoriesPerceptionPerception

Creating motion automatically using optimizationCreating motion automatically using optimization

SimulationSimulation

• Multilink systemsMultilink systems

• Simplification of simulationSimplification of simulation

Motion captureMotion capture

• Blending and reusing segmentsBlending and reusing segments

KinematicsKinematics

Low-level motion like walking/running/jumpingLow-level motion like walking/running/jumping

• Gait generation, abstraction, reuse, biomechanicsGait generation, abstraction, reuse, biomechanics

High-level motion like generating pathsHigh-level motion like generating paths

Generating group behaviorsGenerating group behaviors

PerceptionPerception

Creating motion automatically using optimizationCreating motion automatically using optimization

SimulationSimulation

• Multilink systemsMultilink systems

• Simplification of simulationSimplification of simulation

Motion captureMotion capture

• Blending and reusing segmentsBlending and reusing segments

KinematicsKinematics

Low-level motion like walking/running/jumpingLow-level motion like walking/running/jumping

• Gait generation, abstraction, reuse, biomechanicsGait generation, abstraction, reuse, biomechanics

High-level motion like generating pathsHigh-level motion like generating paths

Generating group behaviorsGenerating group behaviors

Perception

How should we render our objects?How should we render our objects?

• To what end?To what end?

– VerisimilitudeVerisimilitude

– Mechanical accuracyMechanical accuracy

– ImpressionismImpressionism

• What about motion?What about motion?

How should we render our objects?How should we render our objects?

• To what end?To what end?

– VerisimilitudeVerisimilitude

– Mechanical accuracyMechanical accuracy

– ImpressionismImpressionism

• What about motion?What about motion?

Is simplicity better?

AdvantagesAdvantages

• Abstraction is easierAbstraction is easier

• Obfuscations are removedObfuscations are removed

DisadvantagesDisadvantages

• Complementary features are removedComplementary features are removed

– Edges, critical featuresEdges, critical features

• May look “wrong”May look “wrong”


• Abstraction is easierAbstraction is easier

• Obfuscations are removedObfuscations are removed


• Complementary features are removedComplementary features are removed

– Edges, critical featuresEdges, critical features

• May look “wrong”May look “wrong”

Is complexity better?


• Details provide perceptual cuesDetails provide perceptual cues

• This is the way we perceive things in real worldThis is the way we perceive things in real world


• Difficult to get the details rightDifficult to get the details right

• May distract from basic motionMay distract from basic motion


• Details provide perceptual cuesDetails provide perceptual cues

• This is the way we perceive things in real worldThis is the way we perceive things in real world


• Difficult to get the details rightDifficult to get the details right

• May distract from basic motionMay distract from basic motion

We have no idea…

We turn to different expertsWe turn to different experts

• PsychologistsPsychologists

• Automated computer visionAutomated computer vision

We turn to different expertsWe turn to different experts

• PsychologistsPsychologists

• Automated computer visionAutomated computer vision

Psychologists

Kubovy and Proffitt @ UVaKubovy and Proffitt @ UVa• Perception of patterned dot animationsPerception of patterned dot animations

– Models of perceptionModels of perception

• Perception as it relates to actionPerception as it relates to action

– We perceive because it helps us to actWe perceive because it helps us to act

Attacks the perception question within well-Attacks the perception question within well-defined psychological modelsdefined psychological models

Kubovy and Proffitt @ UVaKubovy and Proffitt @ UVa• Perception of patterned dot animationsPerception of patterned dot animations

– Models of perceptionModels of perception

• Perception as it relates to actionPerception as it relates to action

– We perceive because it helps us to actWe perceive because it helps us to act

Attacks the perception question within well-Attacks the perception question within well-defined psychological modelsdefined psychological models

Computer Vision

Martin and Acton @UVaMartin and Acton @UVa

• Low-level visionLow-level vision

– How do we detect edges, shadows, primitivesHow do we detect edges, shadows, primitives

• High-level visionHigh-level vision

– How do we compose “things” from primitivesHow do we compose “things” from primitives

Martin and Acton @UVaMartin and Acton @UVa

• Low-level visionLow-level vision

– How do we detect edges, shadows, primitivesHow do we detect edges, shadows, primitives

• High-level visionHigh-level vision

– How do we compose “things” from primitivesHow do we compose “things” from primitives

Still no solid answers

Vision and psychology provide models of Vision and psychology provide models of perception that influence graphics perception that influence graphics

Graphics permits isolated experimentation Graphics permits isolated experimentation with perception modelswith perception models

The three fields move forward togetherThe three fields move forward together

Vision and psychology provide models of Vision and psychology provide models of perception that influence graphics perception that influence graphics

Graphics permits isolated experimentation Graphics permits isolated experimentation with perception modelswith perception models

The three fields move forward togetherThe three fields move forward together

What’s amazing about us?

Perceiving friendsPerceiving friends

• Just two moving lights on ankles is enoughJust two moving lights on ankles is enough

• Just two seconds is requiredJust two seconds is required

Perceiving pendulaPerceiving pendula

• Humans thought moving dots were connected via Humans thought moving dots were connected via flexible bar, not rigid pendulumflexible bar, not rigid pendulum

Perceiving friendsPerceiving friends

• Just two moving lights on ankles is enoughJust two moving lights on ankles is enough

• Just two seconds is requiredJust two seconds is required

Perceiving pendulaPerceiving pendula

• Humans thought moving dots were connected via Humans thought moving dots were connected via flexible bar, not rigid pendulumflexible bar, not rigid pendulum

Hodgins’ comparison

Is there a difference?Is there a difference?Is there a difference?Is there a difference?

Observational testsTorso rotationTorso rotation

• Keep head looking forward, but rotate torso and armsKeep head looking forward, but rotate torso and arms

Arm MotionArm Motion

• Make arm swing more forward / backwardMake arm swing more forward / backward

– Adjust dynamics accordinglyAdjust dynamics accordingly

– How much?How much?

NoiseNoise

• Randomly perturb joint angles (waist, shoulders, neck)Randomly perturb joint angles (waist, shoulders, neck)

– No dynamicsNo dynamics


Torso rotationTorso rotation

• Keep head looking forward, but rotate torso and armsKeep head looking forward, but rotate torso and arms

Arm MotionArm Motion

• Make arm swing more forward / backwardMake arm swing more forward / backward

– Adjust dynamics accordinglyAdjust dynamics accordingly


NoiseNoise

• Randomly perturb joint angles (waist, shoulders, neck)Randomly perturb joint angles (waist, shoulders, neck)

– No dynamicsNo dynamics


How the simulation works

Experimental protocol

Watch animations in pairsWatch animations in pairs

• 4 seconds of one then 4 seconds of a mate4 seconds of one then 4 seconds of a mate

Indicate similarity or difference within pairIndicate similarity or difference within pair

• forced choiceforced choice

• Could you forget what first looked like?Could you forget what first looked like?

Approx. 25 people per conditionApprox. 25 people per condition

Varied the orderVaried the order

• Avoids ordering effects (learning during experiment)Avoids ordering effects (learning during experiment)

Watch animations in pairsWatch animations in pairs

• 4 seconds of one then 4 seconds of a mate4 seconds of one then 4 seconds of a mate

Indicate similarity or difference within pairIndicate similarity or difference within pair

• forced choiceforced choice

• Could you forget what first looked like?Could you forget what first looked like?

Approx. 25 people per conditionApprox. 25 people per condition

Varied the orderVaried the order

• Avoids ordering effects (learning during experiment)Avoids ordering effects (learning during experiment)

Experimental protocol

Animations rendered in same wayAnimations rendered in same way

• Could this have made a difference?Could this have made a difference?

– Is there a rendering that is conducive to stick Is there a rendering that is conducive to stick figures?figures?

– What tricks would people use to identify motions?What tricks would people use to identify motions?

Played from VHS at 30 fpsPlayed from VHS at 30 fps

• Can’t have any effects from rendering blipsCan’t have any effects from rendering blips

Animations rendered in same wayAnimations rendered in same way

• Could this have made a difference?Could this have made a difference?

– Is there a rendering that is conducive to stick Is there a rendering that is conducive to stick figures?figures?

– What tricks would people use to identify motions?What tricks would people use to identify motions?

Played from VHS at 30 fpsPlayed from VHS at 30 fps

• Can’t have any effects from rendering blipsCan’t have any effects from rendering blips

Results

On average, people were better with manHOn average, people were better with manHOn average, people were better with manHOn average, people were better with manH

Results

But how did rendering affect each person’s But how did rendering affect each person’s ability?ability?But how did rendering affect each person’s But how did rendering affect each person’s ability?ability?

There’s a trick!

Take-away messages

Don’t read too much into these resultsDon’t read too much into these results

• Each experiment may be differentEach experiment may be different

• More detailed model was also more human-likeMore detailed model was also more human-like

Standardization of animation environments Standardization of animation environments might be good for comparisonmight be good for comparison

• Difficult to compare improvements from year to yearDifficult to compare improvements from year to year

Don’t read too much into these resultsDon’t read too much into these results

• Each experiment may be differentEach experiment may be different

• More detailed model was also more human-likeMore detailed model was also more human-like

Standardization of animation environments Standardization of animation environments might be good for comparisonmight be good for comparison

• Difficult to compare improvements from year to yearDifficult to compare improvements from year to year

What else matters?

Camera movementCamera movement

Ground planeGround plane

Motion blurMotion blur

Secondary motion (clothing / hair)Secondary motion (clothing / hair)

ShadowsShadows

Camera movementCamera movement

Ground planeGround plane

Motion blurMotion blur

Secondary motion (clothing / hair)Secondary motion (clothing / hair)

ShadowsShadows

Additional commentary

Experiments are essential for graphicsExperiments are essential for graphics

• Yet rarely conductedYet rarely conducted

• How is graphics evaluated?How is graphics evaluated?

– The SIGGRAPH “aaahhhh” factorThe SIGGRAPH “aaahhhh” factor

Experiments are essential for graphicsExperiments are essential for graphics

• Yet rarely conductedYet rarely conducted

• How is graphics evaluated?How is graphics evaluated?

– The SIGGRAPH “aaahhhh” factorThe SIGGRAPH “aaahhhh” factor

Additional commentary

Creating experiments is dicey businessCreating experiments is dicey business• Have to include psychologists who are experts of Have to include psychologists who are experts of

experiment designexperiment design

• Make sure enough subjects are includedMake sure enough subjects are included

• You need to understand the domain so well that you You need to understand the domain so well that you know the answer before the experiments are know the answer before the experiments are completecomplete

– Many pretrials were conducted to refine amounts of Many pretrials were conducted to refine amounts of noise to add (to avoid making it too easy or hard)noise to add (to avoid making it too easy or hard)

Creating experiments is dicey businessCreating experiments is dicey business• Have to include psychologists who are experts of Have to include psychologists who are experts of

experiment designexperiment design

• Make sure enough subjects are includedMake sure enough subjects are included

• You need to understand the domain so well that you You need to understand the domain so well that you know the answer before the experiments are know the answer before the experiments are completecomplete

– Many pretrials were conducted to refine amounts of Many pretrials were conducted to refine amounts of noise to add (to avoid making it too easy or hard)noise to add (to avoid making it too easy or hard)

Follow-up paper

Bodenheimer et al., 1999 Eurographics Bodenheimer et al., 1999 Eurographics Animation WorkshopAnimation Workshop

How does noise influence perception?How does noise influence perception?

Bodenheimer et al., 1999 Eurographics Bodenheimer et al., 1999 Eurographics Animation WorkshopAnimation Workshop

How does noise influence perception?How does noise influence perception?

How to add noise to simulation?

SensorsSensors

• When the arm reaches angle When the arm reaches angle , trigger reaction, trigger reaction

Control gainsControl gains

• How stiff/strong are the musclesHow stiff/strong are the muscles

Output torquesOutput torques

• How regular and well-behaved are the musclesHow regular and well-behaved are the muscles

Control parametersControl parameters

• When does the arm swing backwardsWhen does the arm swing backwards

SensorsSensors

• When the arm reaches angle When the arm reaches angle , trigger reaction, trigger reaction

Control gainsControl gains

• How stiff/strong are the musclesHow stiff/strong are the muscles

Output torquesOutput torques

• How regular and well-behaved are the musclesHow regular and well-behaved are the muscles

Control parametersControl parameters

• When does the arm swing backwardsWhen does the arm swing backwards

Output torques

Noise inserted here didn’t work wellNoise inserted here didn’t work well

• Instantaneous noise was quickly corrected with Instantaneous noise was quickly corrected with subsequent countertorquessubsequent countertorques

Noise inserted here didn’t work wellNoise inserted here didn’t work well

• Instantaneous noise was quickly corrected with Instantaneous noise was quickly corrected with subsequent countertorquessubsequent countertorques

What kind of noise?

Variability of human motion is tied to large Variability of human motion is tied to large movements of the bodymovements of the body

• Not a random sinusoidal noise functionNot a random sinusoidal noise function

• Not a white noiseNot a white noise

Variability of human motion is tied to large Variability of human motion is tied to large movements of the bodymovements of the body

• Not a random sinusoidal noise functionNot a random sinusoidal noise function

• Not a white noiseNot a white noise

Experimental scenario

Watch 10 movies of varying noise and select Watch 10 movies of varying noise and select the one that looks most “natural”the one that looks most “natural”Watch 10 movies of varying noise and select Watch 10 movies of varying noise and select the one that looks most “natural”the one that looks most “natural”

Animation CS 551 / 651

Documents

Transcript of Animation CS 551 / 651