We present an approach to track human subjects using an articulated human framework. First, we describe the articulated hierarchical human model. Second, we develop a stochastic hierarchical, partitioned, particle filter based on the natural structure and limb dependency of the human body. We apply this to track human subjects in video sequences using likelihoods adapted to the hierarchical process. Finally, we evaluate the effectiveness of the described approach using publicly available datasets.

Bidirectional Texture Functions (BTF) are commonly thought to provide the most realistic perceptual experience of materials from rendered images. The key to providing efficient compression of BTFs is the decision as to how much of the data should be preserved. We use psychophysical experiments to show that this decision depends critically upon the material concerned. Furthermore, we develop a BTF derived metric that enables us to automatically set a material's compression parameters in such a way as to provide users with a predefined perceptual quality. We investigate the correlation of three different BTF metrics with psychophysically derived data. Eight materials were presented to eleven naive observers who were asked to judge the perceived quality of BTF renderings as the amount of preserved data was varied. The metric showing the highest correlation with the thresholds set by the observers was the mean variance of individual BTF images. This metric was then used to automatically determine the material-specific compression parameters used in a vector quantisation scheme. The results were successfully validated in an experiment with six additional materials and eighteen observers. We show that using the psychophysically reduced BTF data significantly improves performance of a PCA-based compression method. On average, we were able to increase the compression ratios, and decrease processing times, by a factor of four without any differences being perceived.

This paper considers the link between tracking algorithms and high-level human behavioural analysis, introducing the action primitives model that recovers symbolic labels from tracked limb configurations. The model consists of similar short-term actions, action primitives clusters, formed automatically and then labelled by supervised learning. The model allows both short actions and longer activities, either periodic or aperiodic. New labels are added incrementally. We determine the effects of model parameters on the labelling of action primitives using ground truth derived from a motion capture system. We also present a representative example of a labelled video sequence.

For navigation and obstacle detection, it is necessary to develop robust and efficient algorithms to compute ego-motion and model the changing scene. These algorithms must cope with the high video data rate from the input sensor. In this paper, we present an approach to achieve improved motion tracking from a monocular image sequence acquired by a camera attached to a pedestrian. The human gait is modelled from the motion history of the camera, and used to predict the feature positions in successive frames. This is encoded within a maximum a posteriori (MAP) framework to seek fast and robust motion estimation. Experimental results show how use of the gait model can reduce the computational load by allowing longer gaps between successive frames, while retaining the robust ability to track features.