With respect to the first invention, there is heretofore known a tracking and surveillance system which uses a computer for applying image processing to images picked up by a plurality of cameras to thereby track and supervise (surveille) an object such as a human figure or the like. In such a tracking and surveillance system, when characteristics, lighting environments, installation conditions, etc. of the cameras are different from one another, images of one and the same object (e.g. human figure or the like) picked up by the cameras respectively, especially colors of the object, are different in appearance in accordance with the cameras. Accordingly, in order to track an object with a plurality of cameras, it is necessary to associate one and the same object with colors which appears to be different in accordance with the plurality of cameras, that is, it is necessary to keep color constancy. In the tracking and surveillance system according to the background art, color information of an object is used for calibrating the color of the object between the plurality of cameras to thereby obtain consistency of one and the same object picked up by the plurality of cameras. Accordingly, accuracy in consistency of the object between the plurality of cameras is improved so that accuracy in tracking the object between the plurality of cameras is improved.
In such a tracking and surveillance system, when, for example, there is a change of lighting environment, it is necessary to update color information of the object in accordance with the change of lighting environment. As a method of detecting a change of lighting environment, there is heretofore known a method in which a deviation between corresponding pixels of two image regions is detected in order to detect an image change. For example, this method has been described in U.S. Pat. No. 4,779,095. As another method of detecting a change of lighting environment, there is also known a method in which video is stored to detect the beginning of a new scene so that detection of a scene change is achieved by use of a representative value of a video signal. For example, this method has been described in U.S. Pat. No. 4,823,184. As an another method of detecting a change of lighting environment, there is further known a method in which feature vectors of many images are generated on the basis of characteristics of the images respectively so that a scene change is detected when a value obtained by calculation of a difference between the vectors (a value having a feature of the object) varies in accordance with each image. For example, this method has been described in U.S. Pat. No. 4,912,770.
However, in the tracking and surveillance system according to the background art, when, for example, an object to be tracked is added, color information of the object is added correspondingly. In this case, even when color information of the same object as the newly added object has been already held, the color information of the object is added as the object is added. When the color information of the object unnecessary for color correction is added in this manner, the amount of color information of the object increases excessively. That is, since the amount of information used for color correction increases as the amount of color information of the object increases, the time required for color correction becomes so long that the operation of color correction becomes unstable.
Moreover, when lighting environment changes, the color information of the object which has been used up to now cannot be used so that the amount of unnecessary color information increases correspondingly. Moreover, when lighting environment changes, it is necessary to obtain new color information in accordance with the change of lighting environment. The background-art method of detecting a change of lighting environment is however unsuitable for real-time processing because the load imposed on calculation is very large.
With respect to the second invention, a device using color information of a human figure or an object is often used as a background-art device of tracking and searching for a human figure or an object by using a camera. When color information is used, there is a method in which a specific color pattern such as a color chart is once photographed by an installed camera in order to correct the individual difference between cameras and the influence of lighting environment so that a camera pattern is introduced individually. For example, such a technique has been described in JP-A-11-186487.
However, a surveillance system is frequently installed in any place regardless of indoor installation or outdoor installation. Particularly in outdoor installation, appearance of the color of an object to be supervised varies every moment in accordance with time, weather, etc. because of a dynamic change of sunlight, etc. For this reason, it is necessary to update dynamically the camera parameter which has been once introduced into the installed camera. Moreover, automatic update of the camera parameter is requisite in consideration of the number of installed cameras and the diversification of sunlight environment.