motion capture technology
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Overview:
Definition of Motion Capture History of Mocap Rotoscoping Types of Motion Capture Mechanical Optical Electromagnetic Marker Placement Production Pipeline Applications of MoCap Examples
What is Motion Capture?
Motion capture is the process of recording human movement through specialised camera’s, and mapping
them onto a character model.
Also known as “Mo-Cap, Real-Time Animation” or “Performance Capture”
The Motion Capture began in late 1800’s when Etienne Jules Marey and Eadweard Muybridge performed motion studies on various animals and humans
History of Motion Capture
Etienne Jules Marey’sMotion Capture Suit
Eadweard Muybridge
•Historically, Motion
Capture in animated
movies was created
using the extension of "ROTOSCOPING" technique.
Eadweard Muybridge (1830-1904)
“Father of the motion picture” several cameras – successive
pictures photographs of human and animal
motion zoopraxiscope (zoogyroscope,
zoetrope) – a device for playing still images in sequence
Rotoscope
Allow animators to trace cartoon character over
photographed frames of live performances
• invented by Max Fleischer in 1915
RotoscopeAllow animators to trace cartoon character over
photographed frames of live performances
• invented by Max Fleischer in 1915
• 2D manual motion capture
A horse animated by rotoscoping from Muybridge’s photos
Rotoscoping
“rotoscoping can be thought of as a primitive form or precursor to motion capture, where the motion is ‘captured’ painstakingly by hand.” - Sturman
“3D Rotoscoping”: measuring 3D positions, orientations,
velocities or accelerations automatically
Current motion capture systems
• Electromagnetic
• Electromechanical
• Fiber optic
• Optical
Current Motion Capture Technologies
This approach has a central magnet with several receivers attached to the actor’s body. The receivers capture and record the actors movements and save them to the computer. This motion capture method can be hindered by nearby metal objects if they are large enough and depending on the power of magnets being used. A suit with magnetic sensors
Electromagnetic systems
Electromagnetic sensors placed on joints of moving object
Measures orientation and position of sensor relative to electromagnetic field generated by transmitter
No occlusion, multiple subjects
Electromagnetic interference, small volume
Pros
• measure 3D positions and orientations
• no occlusion problems
• can capture multiple subjects simultaneously
Cons
• magnetic perturbations (metal)
• small capture volume
• cannot capture deformation (facial expression)
• hard to capture small bone movement (finger movement)
• not as accurate as optical MoCap systems
Electromagnetic MoCap
Electromechanical Motion Capture uses Potentiometers on the aforementioned plastic exoskeleton that an actor must “wear”, and then act out his or her movements. This is very accurate and transmits real-time data at a far greater range than any other technology.
A gypsy3 prosthetic suite
Pros
• Measure 3D orientations
• No occlusion problems
• Can capture multiple subjects simultaneously
• Large capture volume
• Portable and outdoors capture (e.g. skiing)
Cons
• Getting 3D position info is not easy
• Cannot capture facial expression
• Hard to capture small bone movement (finger motion)
• Not as accurate as optical MoCap system
Electromechanical Mocap
• Reflective markers
• Multiple cameras
digitize different views
of performance
• High speed capture
• High data accuracy
• Occlusion
• Position sensitive
cameras
• Limited volume
Optical capture advantages
freedom of movement high quality capture Can Capture Facial Expression high throughput
fast sampling (200 fps at a high resolution) can capture fast motions can have a large capture space can capture many markers
disadvantages occlusion, markers are can be hidden from the camera
additional performers will increase occlusion may be able to add redundant cameras
marker crossover, which marker are you looking at?
cost $$$ extensive post processing (the marker’s have to be located and identified)
Major Optical PlayersMotion Analysis
Films Lord of the Rings King Kong Matrix Final Fantasy
Games NBA Live 2004 Grand Theft Auto III Mortal Kombat 4 (Midway)
Films Polar Express Harry Potter and the
Prisoner of Azkaban The Hulk Spider Man
Games All-Star Baseball 2002 Buffy the Vampire Slayer Everquest II NHL 2K3 (Mocap by
Red Eye Studio)
Production Pipeline
Sensor Calibration
Subject Calibration
Record Movements
Compute the position and orientation of camera/transmitter
Place markers on body, compute skeleton structure(lengths of links)
Marker positions (and orientations) varying over time
Marker Data Cleanup
Convert to Joint Angles
Occlusion and correspondence problemsOcclusion and
correspondence problems
Mapping to characters
Direct Mapping or retargetting
Process of Motion Capture (1)
• Recording area is constructed (often blue screen or green screen area)
• Cameras are set up to record the actors movement
• Cameras map 360 degree image of the person
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Process of Motion Capture (2)
• Suit fitted with nodes
• Camera follows nodes
• Triangulates information
• DATA is recorded and ready to be manipulated
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Process of Motion Capture (3)
• DATA given to an animator
• Manipulation of digital skeleton
• Helps character creation
Entertainment: Live Action Films
Computer generated characters in live action films (e.g. Battle Droids and many others in Star Wars Prequels, Gollum in The Lord of the Rings, King Kong in King Kong , Davy Jones in Pirates of Caribbean)
Entertainment: 3D computer animations
Characters in computer animated files (e.g. Polar Express, Monster House)
Kochadaiyaan (India's first photorealistic performance capture film) //After all he is Rajnikanth!!
Entertainment: Video Games
Video games by Electronic Arts, Gremlin, id, RARE, Square, Konami, Namco, and others, (e.g. Enemy Territory, Devil May Cry,FIFA)
Medicine Medicine (e.g., gait analysis, rehabilitation)
Sports medicine (e.g. injury prevention, performance analyses, performance enhancement)
Gait Analysis Service
Science / Engineering
Engineering (e.g., Biped robot developments)
Ergonomic product design
Military (e.g., field exercises, virtual instructors, and role-playing games)