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Motion Capture


Published on Dec 24, 2016

Abstract

In technical terms "Motion capture (Mocap) is sampling and recording motion of humans, animals, and inanimate objects as 3D data", but in simple terms “Recording of motion and playback” OR "One way of acting out an animation" is Motion Capture. So in this paper we are going to present technical as well as simple aspects of Motion Capture like from simple history of Mocap to technical process of Mocap, simple applications of mocap to technical aspects of Mocap.

In this paper first thing that would be cleared is that Mocap is not new technology it is used since 1872 when Edward Muybridge performs Flying Horse experiment to know that if a horse ever had all four feet off the ground while trotting? So Muybridge placed cameras to capture movements of running horse and takes multiple pictures of horse and proved that statement true. After that Etienne-Jules Marey became the First person to analyze human and animal motion with video. After all these main-frame motion capture started when in 1915 Rotoscoping which is described in this paper later comes in animation techniques and it changed whole meaning of animation. Then process of basic motion capture and some techniques used i.e. how motion or movements of an actor are captured using various markers, sensors, cameras and mechanical or magnetic suits and then how these recorded data is converted and applied on a virtual actor to perform same movements. Then some applications like films, animation, medical etc. are discussed and at last a brief about some pros and cons of Mocap is stated.so overall in this paper we tried to give basic knowledge on mocap so that a non-technical or normal person can also understand that how mocap is started and how it is useful or popular now days.

INTRODUCTION:

"Motion Capture" is the term used to describe the process of recording human movement and translating that movement onto a digital model. It is used in military, entertainment, sports, medical applications for validation of computer vision and robotics. In film making it refers to recording the actions of human actors, and using that information to animate digital character models in 2D or 3D computer animation. When it includes face, fingers and captures subtle expressions, it is often referred to as performance capture in motion capture sessions.

Movements of one or more actors are sampled many times per second,although with most techniques motion capture records only the movement of actors , not his or her visual appearance this animation data is mapped to a 3D model so that the model performs the same actions as the actor. This is comparable to the older technique of rotoscope such as 1978 "The Lord Of Rings" animated film where visual appearance of the motion of an actor was filmed,then the film is used as guide for the frame by frame motion of the hand-drawn animated character.

Camera movements can also be motion captured so that a virtual camera in the scene will pan, tilt, or dolly around the stage driven by a camera operator while the actor is performing, and the motion capture system can capture the camera and props as well as the actor's performance. This allows the computer-generated characters, images and sets to have the same perspective as the video images from the camera. A computer processes the data and displays the movements of the actor, providing the desired camera positions in terms of objects in the set. Retroactively obtaining camera movement data from the captured footage is known asmatch moving or camera tracking.

Research and development of digital MOCAP technology started in pursuit of medical and military applicationsin the 1970s. The CGI industry discovered the technology’s potentials in the 1980s. Since someof this book’s readers weren’t born in the 1980s, let’s recall the 1980s. In the 1980s there were floppydisks that were actually floppy and most computers were equipped with monochrome monitors, somewith calligraphic displays. To view color images, for example rendered animation frames, images had tobe sent to a “frame buffer,” which was often shared by multiple users due to its cost. Large computerswere housed in ice cold server rooms. The noise of dot matrix printers filled offices. Ray-tracing and radio city algorithms were published in the 1980s. Renderers based on these algorithms required asupercomputer or workstations to render animation frames in a reasonable amount of time.

Personal computers weren’t powerful enough. (Ray-tracing and radio city didn’t become widely available untilthe computing power improved.) CPUs, memories, storage devices, and applications were more expensive than today. Wave front Technologies developed and marketed the first commercial off-the-shelf3D computer animation software in 1985. Only a handful of computer animation productioncompanies existed. Most of the animations that they produced were “flying logos” for TV commercialsor TV programme’s opening sequences. These were often 15 to 30 seconds long per piece. The readerswho saw “Brilliance” (also called “Sexy Robot”) in the 1980s probably still remember the astonishmentof seeing a computer generated character, a shiny female robot, moving like a real human being.

“Brilliance” was produced by Robert Abel and Associates for the National Canned FoodInformation Council and was aired during the 1985 Super Bowl. They invented their own methodfor capturing motion for the project. They painted black dots on 18 joints of a female model andphotographed her action on a swivel stool from multiple angles. The images were imported intoSilicon Graphics workstations and a number of applications were employed to extract the informationnecessary to animate the CGI robot. They didn’t have enough computing power to renderframes for the 30 second piece in house. So, in the final 2 weeks before the project deadline theyborrowed VAX 11/750 computers around the country to render. The final product was a groundbreaking piece and is regarded as a milestone in the history of CGI.

ROTOSCOPING:

A Rotoscoping is a device that enables animators to trace live action movement, frame by frame, for use in animation.This method is called "Rotoscoping".

Motion Capture

Different Types Of Motion Capture

Motion Capture technology can be achieved by using the following three types of techniques:

1.Mechanical motion capture

2.Optical motion capture

3.Magnetic motion capture

Now although this technique is effective, it still contains some problems (weight, Cost). But against any doubt that the motion capture will become one of the basic tools of animation.

3.1 Mechanical Motion capture:

This technique of motion capture is achieved through the use of an exoskeleton. Each joint is then connected to an angular encoder. The value of movement of each encoder (rotation etc...) is recorded by a computer that by knowing the relative position encoders (and therefore joints) can rebuild these movements on the screen using software. An offset is applied to each encoder. because it is very difficult to match exactly their position with that of the real relationship (and especially in the case of human movements).
Motion Capture using Exo Skeleton
Fig 3.1 Mechanical Motion Capture using Exo skeleton

3.1.1 Advantages and Disadvantages

1.This technique offers high precision and it has the advantage of not being influenced by external factors (such as quality or the number of cameras for Optical MOCAP).

2.But the catch is limited by mechanical constraints related to the implementation of the encoders and the exoskeleton. It should be noted that the exoskeleton generally use wired connections to connect the encoders to the computer. For example, there is much more difficult to move with a fairly heavy exoskeleton and connected to a large number of simple son with small reflective sphere. The freedom of movement is rather limited.

3.The accuracy of reproduction of the movement depends on the position encoders and modeling of the skeleton. It must match the size of the exoskeleton at each morphology. The big disadvantage comes from the coders themselves because if they are of great precision between them it cannot move the object to capture in a so true. In effect, then use the method of optical positioning to place the animation in a decor. Finally, each object to animate to need an exoskeleton over it is quite complicated to measure the interaction of several exoskeleton. Thereby bringing about a scene involving several people will be very difficult to implement.

3.2 Magnetic motion capture:

Magnetic motion capture is done through a field of electro-Magenta is introduced in which sensors are coils of sensors electriques, Les son are represented on a place mark in 3 axes x,y,z. To determine their position on the capture field disturbance created by a son through an antennathen we can know its orientation.
Motion Capture
Fig 3.2 Magnetic Field Transmitter Source

3.2.1Advantages and disadvantages

1.The advantage of this method is that data captured is accurate and no further calculationsexcluding from the calculation of position is useful in handling.

2.But any metal object disturbs the magnetic field and distorts the data.

3.3 Optical Motion Capture:

The capture is based on optical shooting several synchronized cameras, the synthesis of coordinates (x, y) of the same object from different angles allows to deduce the coordinates (x, y, z). This method involves the consideration of complex problems such as optical parallax. distortion lens used, etc. The signal thus undergoes many interpolations. However. a correct calibration of these parameters will help in high accuracy of data collected.To determine their position on the capture field disturbance created by a son through an antennathen we can know its orientation.

Motion Capture
Fig 3.3 Camera emitting Infrared Radiations

The operating principle is similar to radar: the cameras emit radiation usually infrared, reflected by the markers and then returned to the same cameras. Checking the information of each camera (minimum two cameras ) to determine the position of markers in virtual space.

APPLICATIONS:

5.1. Entertainment

1.Computer generated characters in live action films like avatar, polar express.

2.Games using motion capture technology such as prince of persia, grand theft auto 5 etc.

5.2. Medicine

1.For gait analysis, rehabilitation.

2. Injury prevention, performance analysis, performance enhancement in sports.

5.3 Science / Engineering

1.In Engineering for Biped robot developments.

2. In Military for field exercises, virtual instructors and role-playing games.

ADVANTAGES

Motion capture offers several advantages over traditional computer animation of a 3D model

1. More rapid, even real time results can be obtained. In entertainment applications this can reduce the costs of key frame-based animation.

2. The amount of work does not vary with the complexity or length of the performance to the same degree as when using traditional techniques. This allows many tests to be done with different styles or deliveries.

3. Comlpex movement and realistic physical interactions such as secondary motions, weight and exchange of forces can be easily recreated in a physically accurate manner.

4. The amount of animation data that can be produced within a given time is extremely large when compared to traditional animation techniques. This contributes to both cost effectiveness and meeting production deadlines.

5. Potential free software and third party solutions reducing its costs.

CONCLUSION:

Although the motion capture requires some technical means, we can quite get what to do ityourself at home in a reasonable cost that can make your own short film. Motion capture is a major in the field of cinemas as you can reprocess the image in a more simple in fact it is easier to modify an image captured a classic scene, all although this is too expensive, but it is also a major asset in medicine, for example it can be used to measure the benefit of a transaction via recording of the movement of patient before or after the operation (such as in the case of application prosthesis or simply at a medical classic in the future perhaps).

BIBLIOGRAPHY:

http://www.fogscreen.com

http://www.google.com http://wikipedia.com

http://www.engadget.com/tag/interface/












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