Research from 'Human Motion Based on Actor Physique Using Motion Capture' by Jong Sze Joon

Basic Details:

JONG, S. J. (2008), Human Motion Based on Actor Physique Using Motion Capture, Germany: VDM Publishing.

2.

• Motion Capture (Mocap) has some very useful applications for many types of users. Its purpose is not simply to duplicate the movements of an actor, as some people have naively stated (Trager, 1994). By employing specific Mocap application, this research studies realistic human motion of various subject with different physical attributes.
• Every individual has his/her own pattern of movement based on the nature of his/her physique, and yet every repetitive movement is always different in a slightly distinct manner.
• If a repetitive motion cycle of a particular individual can be sampled, it is clear that every time the cycle is repeated, the exact same algorithm of movement will not be achieved. For instance, when a person swings his hand from up to down and repeats the motion for a few times, the duration, velocity, angle, distance and level of the each swing are different.
• These subtle nuances in every biological motion serve as the essence to define realistic motion. It illuminates the identity of the person's behavioural pattern thus providing ideal characteristics that distinguishes every other individual.
• According to Pullen (2002), the term 'Motion Capture' generally refers to any method for obtaining data that describes the motion of a human or animal. 
• As the availability of Mocap data has increased, there has been more and more interest in using it as a basis  for creating computer animations where life-like motion is required.
• There are still various difficulties that arise based on its application, such as the question of the accuracy of the capture data and how much artificial data is filled in during the "clean up" process.

2-3.

• There are other cases whereby human motion data is not suitable to be applied to a non-human character. As a result, the art of keyframe animation is still being practiced.

3.

• Mocap is perhaps the most widely used technique for acquiring realistic motion. Recent production of feature films such as King Kong, The Matrix trilogy, Star Wars, The Polar Express and the Lord of the Rings trilogy, to name a few, employ Mocap techniques.
• Hyper-realistic virtual Computer-generated (CG) characters will be an element of the future of digital storytelling.
• One of the highest demands of Mocap is the gaming industry.
• Mocap is used to create 3D character animation and natural simulations in a performance oriented way.
• Mocap is also known as "Performance Animation".
• Its sole purpose is not simply to duplicate the movements of an actor or animator, but also as a process of taking and recording a human's emotion.

4.

• According to White (1986) and Ratner (2003), a similar technique, which is commonly used in animation production, called "Rotoscoping", was later invented in 1915 by Max Fleischer, a cartoonist; in an attempt to automate the production of animated cartoons by painstakingly traced the image of the live-action movement and captured film frame by frame onto paper in his series "Out of the Inkwell".
• In the early 20th century, this technique was used in traditional 2D cell animation by animators who traced individual frames of film to create individual frames of drawn animation.
• Later in 1930's Walt Disney and his animators employed it carefully and very effectively in 'Snow White and the Seven Dwarfs', 'Sleeping Beauty' and other animated feature-films. The technique has since developed into automated tracking functions, mostly within compositing softwares.
• In the mid 1980's, the type of Mocap used was really an extension of rotoscoping where an actor's movements were filmed from more than one view.
• Markers were attached to the subject and visible on the film, and were then manually encoded as corresponding points on the 3D representation of the character in the computer. This process is called 'Photogammetry'.
• Even though rotoscoping and Mocap are based on the same principles, the execution of the two is different. In the case of rotoscoping, artists trace human motion but interpret it with the model of the animated character.
• In the case of Mocap, human motion is copied and the data is directly applied to the animated character.

4-5.

• The temptation to use this captured motion and call it "animation" has led computer animators who practiced the art of traditional animation to regard Mocap as "Satan's Rotoscope" or "Devil's Rotoscope" (a term widely used by many though attributed to Steph Greenberg, 2000)

5.

• Mocap is now globally projected more into Computer Generated character animation. Basically, the Mocap system enables the animator to record the precise movement of a human subject in time and space for immediate or delayed analysis and playback, which can later be modified and applied to an existing 3D character model in any 3D platform.
• However, no matter how advanced the technology, the most important thing about Mocap is the actor's ability to act.
• This is supported by Grifter's (2000) statement that animation is not only about the timing, weight and 'character' of the motion; it is about acting and performance. This is one of the main reasons Mocap is regarded as 'Performance Animation'.
• From a more subjective point of view, White (1986) and Williams (2001) remarked that the goal of animation is not to create human-like motion, but to impart unique personalities to animated characters, to give them the "illusion of life".
• Both rotoscope and Mocap impose human motion on animated characters, which make them seem subtle and lifeless in comparison to those animated or hand-keyframed by skilled artists.
• This is because actors cannot break the law of reality and physics to fill in the Principles of Animation applied in a keyframe animation.

6.

• Mocap is used for games production, television, film production and education.
• Industry is increasingly depending on Mocap to produce fast yet realistic animation for their characters.
• The demand on gaming and feature-films enabled animation companies to allocate sufficient budget to apply Motion Capture application into their production.
• Mocap technology is frequently used in digital puppetry systems to aid in the performance of Computer-Generated characters in real-time.

7.

• In spite of the limitations, Mocap seems to have a positive response in the local animation industry and most likely the usage of Mocap will increase in the near future. This theory is subject to change based on the job market of the industry.

8.

• Most animators are often particularly concerned about the subtle detail such as slight nuances within a character's motion. This is because the nuances often define the level of realism in animation.
• Most key-frame methods practiced are difficult to achieve realistic motion due to the interpolation variables of tweening between keys.
• Realistic motions performed by human do not translate by those type of curves in animation.

9.

• Increased interest in using the information in Mocap data to assist animators in the creation of a character's base motion. If the animator required additional predefined movements for the character sets, the base data can be reduced or retargeted using a standard 3D application.

10.

• When adapting data to virtual characters, the animation will look more realistic in the sense that proper weight allocation manages the movements of the character.

39.

• The prominent twelve Principles of Animation by animators Thomas and Johnston (1981) serve as a fundamental guideline to most of animators, traditional cell animators, computer animators, or even Mocap animators.
• The Mocap animators, however, use these principles at different occasions throughout the animation process and in different ways than the other animators.
• A Mocap animator should consider the methods of application upon certain principles within the animation process. There are three distinct points within the process, the preparation stage, the capture session itself, and the post processing stage.
• Squash and Stretch: This is the first principle that cannot be achieved by a performer. Some people have attempted to add this property to captured motion data either by hand or procedurally, but the results have not been promising.

40.

• Timing: The performance, whether animated or acted, has to have the right timing to convey the necessary perception.
• Anticipation: A good performer can show anticipation to a certain degree, but is limited by the law of physics.
• Staging: A principle of filmmaking in general, the layout of the scene and positioning of the camera and characters are equally important in animation and live action performance.
• Follow-through and overlapping action: The opposite of anticipation.
• Straight-ahead action and pose-to-pose action: In computer animation, most of the characters' motions are created using a variation of the pose-to-pose action method, creating key poses for different parts instead of posing the whole character at a particular frame. This is done by creating keyframes and letting the software produce the in-between frames by some kind of interpolation defined by the animator.

41.

• Motion Capture is completely straight-ahead action; as such, it generates keyframes at every frame. This makes it very difficult to modify. Pose-to-pose action can be achieved through Motion Capture by selecting significant keyframes, deleting the rest, and allowing the computer to do the in-between as before.
• Ease-in and ease-out: Principles are based on real-world physics, so they can easily be achieved by capturing the motion of a live performance.
• Arcs: Another principle aimed at emulating realistic movement, which can be represented as a set of different types of arcs. When using keyframe animation, these curves are usually smooth between keyframes. With motion data, however, they are coarse and noisy, representing the natural nuances of realistic motion.
• Secondary motion: Secondary motion represents a lot of extra work with keyframe animation, whereas with Mocap it is a part of the performance. One has to be able to collect it, however, which may not be captured by an Optical system if markers are added to the clothes, but an electromagnetic tracker or electromechanical suit would not be able to collect that kind of data easily.

42.

• Exaggeration: The principle of exaggeration implies approaching or crossing the boundaries of physical reality in order to enhance or dramatise the character's performance. We must decide if capturing a live performance would be acceptable, or even feasible, for the level of exaggeration needed.
• Appeal: This principle applies for both live action and animation.
• Personality: When using Mocap, this is the number one reason to use a talented performer, as opposed to just anybody who can move.