License plate recognition system has two trigger methods, one is peripheral trigger, the other is the video trigger.

Peripheral triggering mode of work refers to the use of coils, infrared or other detectors to detect the vehicle through the signal, the vehicle license plate recognition system to receive the vehicle trigger signal, the vehicle image acquisition, automatic identification plate, and follow-up processing. The method has the advantages of high triggering rate and stable performance. The disadvantage is that the coil is cut on the ground and the construction amount is large.

Video triggering means that the license plate recognition system uses dynamic moving target sequence image analysis and processing technology to detect the vehicle movement status in real time and to capture the vehicle image when the vehicle passes the vehicle and identify the vehicle license plate for subsequent processing. Video triggering eliminates the need for coil, infrared or other hardware vehicle detectors. The method has the advantages of convenient construction, no need to cut the ground to lay the coil, and does not need to install the vehicle inspection parts and the like, but the disadvantages are also quite remarkable. Due to the limitation of the algorithm, the trigger rate and the recognition rate of the scheme are higher than that of the peripherals Trigger is much lower.

1) Indirect method: It refers to identifying the license plate and relevant information by identifying the information of the license plate stored in the IC card or bar code installed on the car. IC card technology to identify high accuracy, reliable operation, you can work around the clock, but it is expensive package of equipment, hardware equipment is very complex, not suitable for remote operations; bar code technology with identification speed, high accuracy, reliability and cost more Low advantage, but high requirements for the scanner. In addition, both need to develop a unified national standards, and can not check the car, bar code is consistent, but also the technical shortcomings, which give promotion in a short time difficult.

2) Direct method: Image-based license plate recognition technology is a direct method, is a passive license plate smart identification method that can be used in any vehicle-specific launch license plate signal transmission equipment, the state of the vehicle or stationary vehicle License plate number for non-contact information collection and real-time intelligent identification. Compared with indirect method recognition system, firstly, this system saves equipment placement and large amount of capital, thereby improving economic efficiency. Second, due to the adoption of advanced computer application technology, it can improve the recognition speed and better solve the real-time Problem; again, it is based on images for recognition, so identification of errors in the system can be addressed through human engagement, whereas other approaches are difficult to interact with.