A New Iris Control Mechanism for Traffic Monitoring System

Most of the image-based traffic monitoring system (ITMS) adopts auto iris lens to control the amount of incoming light to camera. Auto iris mechanism measures total light energy in camera’s field of view (FOV) and controls iris opening mechanically and inversely proportional to the light energy perceived. Thus, under counterlight, it causes the reduction of incoming light to produce dark scene where brighter one is desirable. To overcome this difficulty, some camera provides a function to define a region of interest (ROI) in FOV and measures light energy only in ROI. Thus, if we leave out counterlight area from ROI, the iris may properly be controlled. However, in ITMS, it frequently happens that large vehicle with white or black roof passes under camera, covers most of the FOV, and results in undesirable iris change. In this paper, we suggest a new iris control mechanism, called user-controlled iris (UCI), in which iris control depends only on background brightness. Since UCI is not sensitive to counterlight or foreground object’s brightness, it can maintain the optimal environment for vehicle detection for ITMS.