Automatic license plate detection and character extraction with adaptive threshold and projections
- Daniel González Balderrama, Osslan Osiris Vergara Villegas, Vianey Guadaupe Cruz Sánchez
- In Proceedings of the 7th conference on Circuits,
Automatic license/number plate recognition is a specific application of optical character recognition. Typically employed by law enforcement agencies, the uses for automatic license plate recognition have grown tremendously since its inception. Automatic license plate recognition may be used to cite individuals who violate traffic signals or drive in excess of the speed limit, as a method of electronic toll collection, to place a suspect at a scene, or identify uninsured motorist (when combined with a database search). License plate recognition may be complicated by frames that obscure parts of the plate, debris, complex backgrounds, and a wide variety of fonts. Furthermore, license plates are not configured in a standard format; license plates typically vary across issuing states and countries. Recognition systems must also account for rotation in the plane if a license plate is improperly mounted (this is more likely to occur after an accident). Difficulties also occur in the acquisition phase. Many systems acquire license plate images in the near-infrared spectrum and providing proper illumination is challenging. Also, cameras must be equipped with extremely shutter speeds to capture objects moving at very fast speeds. Motion blur and noise make character recognition (and most other areas of computer vision) difficult. Acquisition devices may only have one chance to capture the target, so it is imperative that images are of good quality.