Unattended camera devices are increasingly being used in various intelligent transportation systems (ITS) for applications such as surveillance, toll collection, and photo enforcement. In these fielded systems, a variety of factors can cause camera obstructions and persistent view changes that may adversely affect their performance. Examples include camera misalignment, intentional blockage resulting from vandalism, and natural elements causing obstruction, such as foliage growing into the scene and ice forming on the porthole. In addition, other persistent view changes resulting from new scene elements of interest being captured, such as stalled cars, suspicious packages, etc. might warrant alarms. Since these systems are often unattended, it is often important to automatically detect such incidents early. In this paper, we describe innovative algorithms to address these problems. A novel approach that uses the image edge map to detect near-field obstructions without a reference image of the unobstructed scene is presented. A second algorithm that can be used to detect more generic obstructions and persistent view changes using a learned scene element cluster map is then discussed. Lastly, an approach to detect and distinguish persistent view changes from changes in the orientation of the fixed camera system is explained. Together, these algorithms can be useful in a variety of camera-based ITS.
Raghavan, A.; Price, R.; Liu, J. J. Detection of scene obstructions and persistent view changes in transportation camera systems. 15th International IEEE Conference on Intelligent Transportation Systems (ITSC); 2012 September 16-19; Anchorage, AK.