Symmetry-driven accumulation of local features for human characterization and re-identification

Abstract

This work proposes a method to characterize the appearance of individuals exploiting body visual cues. The method is based on a symmetry-driven appearance-based descriptor and a matching policy that allows to recognize an individual. The descriptor encodes three complementary visual characteristics of the human appearance: the overall chromatic content, the spatial arrangement of colors into stable regions, and the presence of recurrent local motifs with high entropy. The characteristics are extracted by following symmetry and asymmetry perceptual principles, that allow to segregate meaningful body parts and to focus on the human body only, pruning out the background clutter. The descriptor exploits the case where we have a single image of the individual, as so as the eventuality that multiple pictures of the same identity are available, as in a tracking scenario. The descriptor is dubbed Symmetry-Driven Accumulation of Local Features (SDALFs). Our approach is applied to two different scenarios: re-identification and multi-target tracking. In the former, we show the capabilities of SDALF in encoding peculiar aspects of an individual, focusing on its robustness properties across dramatic low resolution images, in presence of occlusions and pose changes, and variations of viewpoints and scene illumination. SDALF has been tested on various benchmark datasets, obtaining in general convincing performances, and setting the state of the art in some cases. The latter scenario shows the benefits of using SDALF as observation model for different trackers, boosting their performances under different respects on the CAVIAR dataset.