Backgroundless detection of pedestrians in cluttered conditions based on monocular images: a review

The significant progress in visual surveillance has been motivated by the need to emulate some of the human ability to monitor activity in human-made environments, particularly in the contexts of security and safety. The rapid rise in numbers of cameras installed in public and private places makes such automation desirable, at least to reduce CCTV workload. Real-world applications of visual surveillance impose the need of robust real-time solutions, able to deal with a wide range of circumstances and environmental conditions. Conventional approaches work based on what has become known as motion (or change) detection followed by tracking (in single or multiple camera systems). Objects of interest are represented by rectangular blobs and decisions on whether something might be interesting are made on rules or learned patterns of presence and trajectories of such blobs. There is growing interest in looking `inside the box` for applications that are concerned with detailed human activity recognition and with robust detection of people even when image backgrounds change, as is the case of a moving camera. In this study, the authors consider the general problem of robust pedestrian detection irrespective of background, reviewing the state of the art, showing some representative results and suggesting ways forward.