In many camera surveillance situations it is important to detect activity, such as presence of objects or motion, at large distances. For natural reasons, objects which are located far away from the camera will be small in images captured by the camera. For instance, they may only cover a few pixels in the images. In order to detect activity at large distances, it is thus necessary to, e.g., be able to detect objects which appear as small in the captured images.
However, detecting small objects usually comes at the cost that false detections increase. This has to do with the fact that there is noise in the images captured by the camera. The noise may easily be mistaken for being a small object and vice versa, thereby leading to false detections. In order to reduce the false detections, video processing algorithms for object detection, motion detection, and/or object tracking, include parameters for such things as intensity change thresholds and noise filtering, including morphological filters to remove small detections. The parameters are typically set so that false detections caused by noise are removed while there is still enough sensitivity to detect actual activity. In other words, there is a trade-off between detection range and avoiding false detections.
The problem of detecting and identifying objects at a large distance has been recognized. In order to solve the problem, it has been suggested to use a thermal camera to identify a position coordinate of a person. The position coordinate is then input to a control method for controlling a second camera, and in particular the direction and zoom thereof, to capture an enlarged image of the person.
Such a method of has the drawback that the second camera is controlled to change its direction and zoom level to follow a specific target object. Accordingly, such method is only suitable for detecting one object at a time.
There is thus room for improvements. In particular, there is a need for alternative methods which allow detection at large ranges at the same time as false detections are reduced.