License Plate Recognition System's Technical Route

The process of using computer vision to identify license plates usually includes five steps: vehicle image acquisition, license plate positioning, character segmentation, optical character recognition, and output recognition results. The vehicle image acquisition method determines the technical route for license plate recognition. The two main technical routes that international ITS use are natural light and infrared light image acquisition and recognition. Natural light and infrared light do not have adverse psychological effects on the human body, nor do they generate new electronic pollution to the environment. It is a green environmental protection technology.

The natural light route refers to the use of natural light during the day, the use of auxiliary light sources at night, the collection of vehicle true color images with color cameras, and the use of color image analysis methods to identify license plates. The natural light color recognition technology line is consistent with the human photographic light habits, and true color images can reflect true image information of the vehicle and its surrounding environment. It can not only be used to identify vehicle license plates, but also can be used to identify vehicle license plate colors and vehicle flow. , vehicle models, car colors and other vehicle characteristics. With an image captured by a camera, all front-end basic video information collection, identification, and artificially assisted image forensic discrimination can be achieved at the same time, and an interface can be reserved for the future intelligent traffic system engineering.

The infrared light path refers to the use of the license plate's optical characteristics of reflection and infrared light. An infrared camera is used to collect the vehicle's gray image. Due to the infrared characteristics, the vehicle image can only see the license plate, and then the black and white image processing method is used to identify the license plate. The 950nm infrared illuminator captures a very good reflective license plate image. Because infrared light is invisible, it does not have a visual impact on the driver. In addition, the infrared lighting device provides constant light, and the captured images are the same, whether it is the brightest time of the day or the darkest time of the day. The only exception is that during the daytime, some of the details around the license plate are sometimes seen because of the influence of the external light of the sun during sunny weather. The disadvantage of using an infrared lamp is that the captured license plate image is not colored, it cannot acquire the image of the entire vehicle, and it relies heavily on the license plate reflective material.