SketchIt: Basketball Video Retrieval Using Ball Motion Similarity

A prototype basketball video retrieval system is presented in this paper. Retrieval is based on the similarity of ball motion in the clip with that in the query. The system uses a query-by-sketch paradigm, where the user provides a sketch of the desired ball trajectory. The video data is pre-processed to make the ball motion invariant to camera translation. The next stage is dimensionality reduction wherein we model the ball motion as a set of parabolic trajectories. An R-tree is used to index these parabolic representations and search for similar trajectories in a low dimension parametric space. The query is processed to obtain its parametric representation, and a nearest neighbor search is performed for similar parabolas. These query results are then post-processed by assigning scores based on various similarity criteria. The system could be extended to other types of videos and moving objects. As a proof of concept, the system was tested for ball trajectories in basketball video.