Motion Capture

In motion capture, literally, motion detection, refers to a tracking method which makes it possible to detect any type of movement as and convert it into a computer-readable format that they analyze the movements, record, process and control applications can use.

An example of such an application is the transmission of human motions in the computer generated 3D models. Examples of other species include the head tracking and eye tracking, for example, to control screen output, or the purpose of analysis and the stereoscopic motion measurement. Another special motion-capture process is the performance capture (literally: Presentation acquisition), which includes the detection of the human face and finger movements, so facial expressions and gestures.

Meanwhile, the motion detection is also common in video games, such as with Kinect, PlayStation Move and the Wii Remote.

Method

There are several methods for motion detection. In principle, two methods can be distinguished between, can also be combined to be used.

When working with optical tracking cameras which active (ie, a signal -emitting ) track or passive markers to be detected person or object. Using the marker moves in the individual camera images may be calculated by triangulation, the position of the markers in 3D. In addition, a marker -free method is possible by means of a pattern recognition in image processing. Stereoscopic methods often make it easier to detect, since the object can be detected from the triangulation of the two ( or more) of the camera position.

Non-optical methods include, for example magnetic tracking, acoustic tracking, accelerometry and gyro sensors.

Precursor

The very first series of photographs by Eadweard Muybridge should be used to analyze human or animal movements. Later photographers and filmmakers brought their models to clearly recognizable flag to simplify the analysis of movements. This technique survived well into video and computer age, the markings still frame by frame by hand were transferred to the analysis software. Applications of this technique were mostly (sports) medicine, accident research ( crash tests ), and rationalization of movements in the working world.

To prepare films, this technique could contribute little, though Muybridge's photos remains a model for animators all over the world. First Max Fleischer invented the rotoscope, a method which was suitable, relatively easy to transfer complex movements in Animation. "The Lord of the Rings " (1978) by Ralph Bakshi was born this way as well as two recent films by Richard Linklater. However, no motion data is generated using rotoscoping, but transmit only the external appearance of the actors (some software support ) in the animation.

Motion capture for animated films

Further processing

After digitization, the raw data using a suitable plugin can be used in current 3-D systems can be imported and processed there. You are transmitted to a virtual skeleton (a type of three-dimensional stick figure ). This skeleton in turn is linked to a wire grid model it follows the recorded movement. The construction of the skeleton ( rigging ) and its link with the figure to be moved ( skinning ) contribute significantly to the credible reproduction of recorded motion data.

After rendering, it looks for the viewer, as if to perform the movements of the original actor, the virtual character. This technique is amplified in computer generated films such as: used " Final Fantasy The Spirits Within " or " Shrek". But also in many new PC and video games (eg, Tony Hawk 's Project 8 or FIFA series from EA Sports ) This technique is use. In addition, with the rock star "LA Noire " both the production, and the marketing focus was games game set on the performance capture technique that finds application in the game. All in the game -existent figures was given by means of performance capturing a realistic face as possible and the accompanying facial expression, to increase the atmospheric effect.

The " quality of motion " of the computer model depends on several factors:

• Number of evaluated, similar movements: The same movement is carried out several times by the player, the movement patterns are compared and a mean value of them is formed.
• " Joints of the computer model ": A computer model is composed of multiple joints and bones (similar to a human). Is the number of joints in the hand and arm of the model is less than that of the agent, so not all data of the real motion can be used. This creates " edgy " movements.
• Detail: In the skeletal animation (as opposed to performance capture, see below) are subtle movements such as muscle strain, does not capture the movement of skin wrinkles and the like through the motion capture systems. The (invisible in itself) motion of the skeleton, there is again only a part of the overall impression of a movement, which therefore depends not only on the quality of the raw data, but also on the technical skill of the animators in the construction of the figure.

The animation of cartoon characters that come to life just by a significant exaggeration of natural movement, has proved in practice to be easier than the lifelike reproduction that would theoretically be possible with the use of motion capture techniques. Studies have shown that animations are perceived as a stranger, the more they strive to conscious realism and avoid exaggeration. This "dimple " in the perception curve is called the Uncanny Valley. Overcoming this " uncanny valley " is not yet valid despite the use of motion capture setups as completely dissolved.

Benefits

Through motion capture complex motion sequences (eg, running, dancing ) with relatively low ( temporal ) effort be realized through other animation methods (such as keyframe animation or engl. Keyframe animation ) difficult, or only with great expenditure of time possible would have been.

Disadvantages

The movements of motion capture can make an artificial impression, even though the underlying data of a natural origin. This is because the so-called retargeting ( transferring animation data on a virtual character with possibly different builds ) is a complex process. Are there differences between the human performer and the computer character in the physiognomy of that data in any form must be converted. Serve the movements of a normal grown human actor, for example, to move a dwarf with very short legs, the decision must be made whether while walking the nature of the movement is transmitted ( then the dwarf is, of course, but it makes very small steps) or the used absolute distance (in this case makes the dwarf giant steps, which may look unnatural or impossible ). Since the fundamental problem with any adaptation of motion capture data to an artificial character is present, this process is actually the most complex part of the whole, if you have a functioning motion capture data. Therefore, the motion data are in larger productions often reworked by experienced animators or even used only as a template for manual work ( Titanic - the term for this is the so-called Rotoanimation ).

Performance Capture

As a performance capture an evolution of the motion-capture technology is called, in which not only the body movement, but also the facial expressions of the actors are scanned. Another feature commonly used to distinguish between motion capture and performance capture is the degree of difference between ingested actor and animated character: If the difference is very small, the movement can be used with little additional work; large differences in complex conversion procedures must transmit the movement to the new figure.

Performance capture animation completely computer-generated characters was used in the following films:

• 2001: Final Fantasy: The Spirits Within ( Director: Hironobu Sakaguchi )
• 2004: The Polar Express ( Director: Robert Zemeckis )
• 2005: Final Fantasy VII: Advent Children ( Director: Tetsuya Nomura )
• 2006: Renaissance ( Directed by Christian Volckman )
• 2006: Monster House (directed by Gil Kenan )
• 2007: Beowulf ( Director: Robert Zemeckis )
• 2009: Disney's A Christmas Carol ( Director: Robert Zemeckis )
• 2009: Avatar - Pandora ( Director: James Cameron )
• Various Barbie fairy tales
• 2010: Tron: Legacy ( Director: Joseph Kosinski )
• 2011: Planet of the Apes (dir. Rupert Wyatt )
• 2011: The Adventures of Tintin - The Secret of the Unicorn (directed by Steven Spielberg )
• 2011: Real Steel (directed by Shawn Levy )
• 2014: Tarzan ( Director: Reinhard Klooss )

Integrated Performance Capture

Movies that vary between individuals recorded in the real world and the computer-generated characters, without a border is visible here.

Movies with individual performance capture characters:

The movie Avatar (2009, directed by James Cameron ) here plays a special role, since large parts of the characters were animated with performance capture. In addition, the camera's were in addition to the motion-capture data of the actors was added in order to transfer them to the virtual environments.