Other Cameras Supporting Study

PTZ cameras have the capability to focus on any part of the scene at any resolution, although this has the drawback of losing awareness of any event occurring at other locations. In the context of unattended baggage detection, the SUBITO project considered the approach of a "guard tour" where a set of positions for the PTZ device with sufficient resolution to achieve robust object detection was defined to create a mosaic of the surveyed scene. The PTZ camera can be controlled to repetitively cover the defined set of views and as such provide a representation for every part of the scene, the update time being dependant on the length of the tour.

To highlight the capability of this type of system, a PTZ sub-system was implemented as defined in the figure shown. A few of the issues relating to this sub-system are discussed below.

PTZ Camera Sub-system

• • PTZ Guard Tour Image Registration - The guard tour approach is subject to the mechanical errors within a camera pointing system and as such no two consecutive images of the same guard tour position will be the same. Thus they must be aligned prior to any image processing algorithm.
• • Background Subtraction - A sequence of images of a guard tour position is used for background image subtraction. An algorithm was especially developed for this purpose and has been published in peer reviewed scientific journals. Any detected foreground is also used to estimate the age of subsequent image foreground. The resulting image contains the age of any detected foreground block.
• • Object identification - The background subtraction output does not include the notion of objects. An additional tool was developed to group the detected foreground 'blocks' into stationary objects that are present in the scene for more than a prior defined time t, in this case 60 seconds. This algorithm is based on age homogeneity with the capability to deal with object occlusion.

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