Patent ID: 7130468

Claim:
A method of monitoring a predetermined scene to detect variations in the scene, said method comprising the steps of: a) establishing an edge image and a reference edge image based on a reference image and a current image detected in a view field of a stationary image capturing device; b) calculating a correlation value for at least one region of the edge image and a corresponding partial image of the reference edge image; c) identifying a change of the at least one region when the correlation value falls below a threshold value; and d) outputting an alarm signal when the at least one region is identified as changed for a predetermined time interval that is longer than a corresponding time interval that the edge image is detected to be changed, further comprising calculating an average quadratic deviation of said at least one region of the edge image and said corresponding partial image of the reference edge image when said correlation value exceeds said threshold value, so that possible brightness differences between said at least one region of the edge image and said corresponding partial image of the reference edge image are eliminated from the calculating; whereby deviations of said at least one region of the edge image from said corresponding partial image of the reference edge image that do not result from image noise and said brightness differences are distinguished.