We investigate the ability of humans to perceive changes in the appearance of images of surface texture caused by the variation of their higher order statistics. We incrementally randomize their phase spectra while holding their first and second order statistics constant in order to ensure that the change in the appearance is due solely to changes in third and other higher order statistics. Stimuli comprise both natural and synthetically generated naturalistic images, with the latter being used to prevent observers from making pixel-wise comparisons. A difference scaling method is used to derive the perceptual scales for each observer, which show a sigmoidal relationship with the degree of randomization. Observers were maximally sensitive to changes within the 20%-60% randomization range. In order to account for this behavior we propose a biologically plausible model that computes the variance of local measurements of phase congruency.
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.
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