Surveillance systems are used in a number of security applications to monitor buildings, equipment, and other locations of importance. Some systems use standard cameras that produce rectilinear images. Rectilinear images are undistorted wherein the coordinates are made up of right lines. Additionally, a single rectilinear image needs only a minimum amount of processing, if any, before being displayed to the viewer. Although these systems produce undistorted images, the field of view of standard cameras is limited. Therefore, a surveillance system may require numerous cameras to cover the entire area of interest. Adding additional cameras increases the complexity and cost of the surveillance system. Further, in many instances, the system must merge the images coming from the multiple cameras into a single panoramic style image.
To avoid the complexity and cost problems associated with multiple standard camera systems, other surveillance systems use hemispherical cameras with a “fish-eye” lens to create a hemispherical image. Hemispherical cameras and the resulting hemispherical images provide a much wider field of view as compared to standard cameras capturing rectilinear images. The wider field of view means that the number of required cameras may be reduced. In addition, using hemispherical cameras eliminates the task of merging multiple images to create a single image of the area of interest. The drawback to hemispherical images is that they are somewhat distorted, making monitoring and detection more difficult. As shown in FIG. 2, objects in hemispherical images tend to have a flattened appearance. Objects within the image, especially those at the edges of the image, are distorted.
To aide in monitoring and detection, several prior art systems exist that transform a distorted hemispherical image into a rectilinear image. The resulting rectilinear image is provides a less distorted view of the area of interest. One such prior art system generates panoramic views from Omni Directional Video Sensors (ODVS). The ODVS is a standard video camera directed towards an optical mirror. The camera captures the hemispherical reflection off of the mirror to generate a hemispherical image. This prior art system uses algorithms to transform the incoming ODVS image into a rectilinear image. The prior art system then displays the rectilinear image to the user. The drawback of this system is that the algorithms used rely on the optical characteristics of the camera and lens. Specifically, the algorithm requires knowledge of the focal lengths of the camera, and the shape and angular characteristics of the lens. Therefore, if a given camera or lens needs to be changed, the algorithms must be adjusted accordingly.
In addition to the above mentioned prior art, there are several prior art software packages that are capable of transforming a hemispherical image into a rectilinear image. One example of such a product is titled Capture Software 4.0 and is produced by Nikon. These software packages are only meant for post-processing transformation and many work only with images taken with certain types of cameras having particular optical characteristics. For example, Capture Software 4.0 specifically works with Nikon Digital SLR cameras.
Although all of the above prior art systems are capable of providing a rectilinear image, whether the image starts as a rectilinear image or a hemispherical image, all suffer from limitations and drawbacks. None of the systems are capable of easily producing a real time, wide viewing area, rectilinear image that is independent of the optical characteristics of the camera.