Light sensor and thresholding method for minimizing transmission of redundant data

A data thresholding method that minimizes the amount of processing required of a processor coupled to a light sensor that controls the shutter, gain, and pedestal settings of the cameras used to image a vehicle license plate, and hence adjusts the contrast level between the background and the vehicle license plate to adapt the cameras to varying lighting conditions, said method comprising the steps of:

• detecting the intensity of ambient light energy viewed by a license plate camera using a light sensor;
• programming a detection threshold of the light sensor so that output signals from the light sensor are generated only when the intensity of ambient light energy transitions across a predetermined threshold;
• generating message reports from the light sensor when the ambient light energy transitions across the predetermined threshold;
• transmitting the message reports to the processor;
• and
• generating control signals in the processor that are applied to the camera to adjust the shutter, gain, and pedestal settings of the camera to adapt the camera to the changed lighting condition.

A light sensor employed in a toll road revenue collection system, said light sensor comprising:

• a replica license plate that reflects ambient light energy;
• a light detector that senses the ambient light energy reflected from the replica license plate;
• and
• a microprocessor responsive to the ambient light energy sensed by said light detector for generating message reports indicative of a change in the sensed ambient light energy sufficient to cause the sensed ambient light energy to transition across a predetermined threshold, wherein said message reports are utilized by said toll road revenue collection system for controlling a camera operable to image vehicle license plates.