Digital Media Concepts/Motion Capture

computer character animation

Motion Capture
In the 19th century, when photographer Eadweard Muybridge studied the motion of humans and animals through stop-motion photography. The basic principles of his study would soon serve filmmakers when MaxFleischer invented something called a rotoscope in 1915. In essence, a camera would project a single frame onto an easel so that the animator could then draw over it, Frame by frame, to better capture realistic movement for the on-screen character.

Uses Of Motion Capture In Computers
The use of motion capture for computer character animation is relatively new, having begun in late 1970's, and only now beginning to become widespread motion capture is the recording of human body movement ( or other movements) for immediate or delayed analysis and playback. The information captured can be as general as the simple position of the body in space or as complex as the deformations of the face and muscle masses. The motion of capture for computer character animation involves the mapping of human motion onto the motion of computer character. The mapping can be direct, such as human arm motion controlling a character's arm motion, or indirect, such as human hand and finger patterns controlling a character's skin color or emotional state. The idea of copying human motion for the animated character is, of course, not new. To get the convincing motion of the human character in snow white, Disney studios ever since. In the late 1970's, when it began to feasible to animate character by a computer, animators adopted tradition technique, including rotoscoping. At the New York Institute of technology Computer Graphic lab, Rebbeca Allen used a half-silvered mirror to superimpose videotapes of real dancers onto the computer screen to pose a computer-generated dancer for Twyla Tharp's " the catherine wheel. The Computer used these pose as keys for generating a smooth animation. Rotoscoping is by no means an automatic process and the complexity of human motion required for "catherine wheel," necessitated the setting of keys every few frames. as such, Rotoscoping can be thought of as primitive form or precursor to motion capture, wheel the motion is " captured" painstakingly by hand.

Advantages Of Motion Capture
advantages over live action A movie that contains so large amounts of CGI that the actors would have to stay in front of a blue screen and interact the director can choose any angle he desired from a screen, including angles that would have been hard or impossible in a live action movie. limitless possibilities for rotating effect. customers make-up,body-size, and age can be changed to whatever is needed. There is no need to have light, color and filters in mind when filming the motions, as this will be added digitally later. Advantages over live action a movie that contains so large amount of CGI that actors would have to stay in front of a blue screen and interact with invisible computer animated characters which are added later, trying to fit into a computer animated world, it is sometimes less problematic to make everything digital, including the actors. This way, all element would fit together naturally and have the same visual look.

Technology Of Motion capture
There are a few different ways of capturing a motion, the most commonly used are optical motion capture, electromagnetic system. An optical motion capture uses the camera to record an actor performance movements. The number of cameras used differently for the system, but most systems use 4 cameras or more. The camera used, are often very high-performance cameras capturing rate to 2000 frames per second. When using a high capturing rate, the movement from Frame to the next will be very small. The actors wear a suite of markers that later will be scanned for in the video clip. The markers are made of some material intended to stand out from the surrounding, often some reflecting material or LED:s. The cameras are 4 placed at different angles toward the actors and a sequence is filmed which afterward can be analyzed, and the positions of the markers stored in a computer. The different inputs from the camera are then combined and processed, and a three-dimensional representation is produced. This output is known as motion capture and can be analyzed or applied to 3D-character. The PROCESS Of using an optical system is that is capable of recording the most complex motion with the least deterioration in quality. It also allows the actor to move unhindered, without any suit or other measurements devices attached to the body. The problems with optical motion capture are when the markers get occluded. Also, the processing time is very high, and data produced by an optical motion capture must often be adjusted and cleaned up. This combined with the demanding calculations make it a non-real time system.

Cost of an optical capture system
.An Optical motion capture system often costs between $100,000 and $250,000. [1, 2] In an electromagnetic system, the actor wears a suit with magnetic sensors attach to it. The systems then produce an electromagnetic field, using a magnetic field generator. The sensors return both their position and rotation and due to that only 10-20 markers are needed to record the whole body. Advantages with the Electromagnetic system are that the data is clean and the processing time is very low. I.e. it can be used in real-time applications like television or VR. The disadvantage is the sensitivity of the sensors that easily can pick up electromagnetic noise as well as the presence of ferrous metals. Also, some equipment is required and can be disturbing for some movements. The magnetic sensors are often linked to a computer using cables, and that will restrict both movements and range. An electromagnetic system costs between $5,000 and $150,000 Electromechanical systems let the actor wear a mechanical suit that is composed of potentiometers measuring the joint angles and extensions. The system’s processing-time is very fast and there is no electromagnetic interference. The disadvantages are that the suit is encumbering and heavy. Also the mechanical components get worn out by time resulting in less accurate data.

Motion capture Market
Motion capture has a wide field of usage. Although motion capture most often is associated with the entertainment industry, such as movies and videogames, there are several otherotio usage areas. Examples are in medicine, sports, industry and military. In Medicine motion capture is used to perform gait analysis, these are studies of human motion. The advantage of using motion capture is that you separate the different mechanisms used when for example performing a walk cycle, thereby it is simple to detect abnormalities and changes. Motion capture can also be a useful help when creating ergonomic workstations or motions. On the sports market motion capture is used as a analyzer of athletes in order to improve their performances. The most common sport using motion capture is Golf. The swing of a golfer can be captured using motion capture and then analyzed or compared to a professional golfers swing. The advantage gained from motion capture compared to video capture is that you get a three dimensional view from motion capture. 5 Motion capture can be very useful in different industries because it can quickly measure small fast movements and therefore be used as a process controller. It can also be used to analyze vibrations on equipment or vehicles or as a tool in virtual industrial design. Motion capture can also be used in the military to contribute to the training of military personnel. Military field exercises, virtual instructors, and role-playing games are just some of the possibilities that the Motion capture system can provide. However, the entertainment market is the market that has made motion capture a common term. Almost all videogames containing human motion uses motion capture to accurately generate animated characters. It is a cost effective method that produces realistic motions compared to manually animate the character. Television and feature films use motion capture mostly to create digital stuntmen, these are animated character that perform stunts that are impossible for a live actor. Motion capture can also be used to create cartoons and give the cartoon characters realistic movements in a effective way.[3]