Chrysalis - A Single Source Video Motion Capture System
By: John Li and Jung Yoon
Faculty Advisor: Camillo J. Taylor
In the last few years, many researchers have studied human motion for the purpose of digital 3D reconstruction. A wide spectrum of commercial applications such as character animation, games, sport performance analysis, and surveillance systems motivate this research. However, research focuses typically on either special cameras  or special outfits with embedded sensors . These solutions usually demonstrate a high degree of accuracy and reliability at significant cost. Ideally, the capture of motion data should be easily available and affordable for the typical computer user. In that sense, developing a tracking system that can render from a single video source is an enticing idea.
The Chrysalis project seeks to develop just such a simple, inexpensive, and accurate video motion capture system. This paper will discuss how the Chrysalis project can develop from a simple avi video file, the type created from any retail digital camera, a 3D reconstruction of the human figurers in the video. In developing such a system, the developers needed to overcome several significant challenges such as the non-linear movement of limbs, ambiguities in mapping from 2D image measurements to 3D model configurations and self occlusion problems. The Chrysalis project makes several important assumptions in overcoming these difficulties. First, the relative bone lengths must be known a priori. Second, the scope of rendering is limited to a square mat whose vertices are pinpointed by the user. Lastly, the subject must be of significant distance away from the camera so that the self-occlusion problem causes minimal effects. The paper will discuss in greater detail later the importance of each assumption and their specific impacts.
In comparison to previous work on this subject, the Chrysalis project makes one important improvement. As discussed earlier, the Chrysalis system seeks to make motion capture as simple and as inexpensive as possible. The project does this by simplifying the interface as well as the requirements needed to use the system. For example, the project does not use any additional external equipment besides a simple retail digital camera. Although the project does not develop rendering in as much detail as available retail solutions, the project at its core creates a well developed base for accurate motion capture and future development.