Shape matching has many applications in computer vision, such as shape classification, object recognition, object detection, and localization. In 2D cases, shape instances are 2D closed contours and matching two shape contours can usually be formulated as finding a one-to-one dense point correspondence between them. However, in practice, many shape contours are extracted from real images and may contain partial occlusions. This leads to the challenging partial shape matching problem, where we need to identify and match a subset of segments of the two shape contours. In this paper, we propose a new MCMC (Markov chain Monte Carlo) based algorithm to handle partial shape matching with mildly non-rigid deformations. Specifically, we represent each shape contour by a set of ordered landmark points. The selection of a subset of these landmark points into the shape matching is evaluated and updated by a posterior distribution, which is composed of both a matching likelihood and a prior distribution. This prior distribution favors the inclusion of more and consecutive landmark points into the matching. To better describe the matching likelihood, we develop a contour-subdivision technique to highlight the contour segment with highest matching cost from the selected subsequences of the points. In our experiments, we construct 1,600 test shape instances by introducing partial occlusions to the 40 shapes chosen from different categories in MPEG-7 dataset. We evaluate the performance of the proposed algorithm by comparing with three well-known partial shape matching methods.

The seven papers in this special section focus on shape analysis and its application in image understanding.

This paper presents a new methodology for improving the tracking of multiple targets in complex scenes. The new method,Motion Parameter Sharing, incorporates social motion information into tracking predictions. This is achieved by allowing a tracker to share motion estimates within groups of targets which have previously been moving in a coordinated fashion. The method is intuitive and, as well as aiding the prediction estimates, allows the implicit formation of 'social groups' of targets as a side effect of the process. The underlying reasoning and method are presented, as well as a description of how the method fits into the framework of a typical Bayesian tracking system. This is followed by some preliminary results which suggest the method is more accurate and robust than algorithms which do not incorporate the social information available in multiple target scenarios.