What is license plate recognition technology?

Abstract: License plate number recognition system is a complete system based on license plate recognition technology. Firstly, the moving vehicle license plate is extracted from the complex background, and then the vehicle license plate is recognized and the license plate number is output through the technologies of license plate extraction, image preprocessing, feature extraction and license plate character recognition. At present, the recognition rate of letters and numbers can reach 96% and the recognition rate of Chinese characters can reach 95%. Below, let's learn more about the relevant knowledge! Working principle of license plate recognition technology

1. Vehicle detection: We can use buried coil detection, infrared detection, radar detection technology, video detection and other methods to sense the passing of vehicles and trigger image capture.

2. Image acquisition: The passing vehicles are recorded and acquired continuously in real time through the high-definition camera capture host.

3. Pretreatment: noise filtering, automatic white balance, automatic exposure, gamma correction, edge enhancement, contrast adjustment, etc.

4. License plate location: scan the gray image after image preprocessing to determine the license plate area.

5. Character segmentation: after locating the license plate area in the image, accurately locate the character area through graying and binarization, and then segment the characters according to the character size characteristics.

6. Character recognition: the segmented characters are scaled and feature extracted, and matched with the standard character expression in the character database template.

7. Result output: output the result of license plate recognition in text format.

Technical difficulties of license plate recognition

1, the file resolution is low, usually because the license plate is far away, sometimes because of the low-end camera;

2. Image blur, especially motion blur;

3. Poor illumination and contrast due to strong light, reflection or shadow;

4. The license plate is (partially) covered, usually with stains on the trailer pole or license plate;

5. The recognition results are different, such as trailers and campers.

6. When the license plate is collected, the lane in the camera perspective changes;

7. Different fonts are common in some grandiose license plates;

8. Ways to avoid license plate recognition.

Trigger mode of license plate recognition technology

1, peripheral coil trigger

Working mode refers to the use of coils, infrared rays or vehicle detectors to transmit signals. After receiving the vehicle trigger signal, the license plate recognition system collects the images of the vehicle and the license plate, and automatically recognizes the license plate for subsequent processing. The advantages of this method are high trigger rate and stable performance. The disadvantage is that the floor needs to be cut and rolled, and the construction amount is large.

2. Video trigger mode

It means that the license plate recognition system uses the image analysis and processing algorithm technology of dynamic moving target sequence to detect the movement of vehicles in the lane in real time, capture the images of vehicles passing by, identify the license plate and carry out subsequent processing. Video trigger mode does not require coils, infrared or other hardware vehicle detectors. The advantage of this method is that it is convenient to construct, and there is no need to cut the ground and lay coils, and there is no need to install automobile detectors and other parts. However, its shortcomings are also very obvious. Due to the limitation of the algorithm, the trigger rate and recognition rate of this scheme are much lower than those of the peripheral coil.

Solution of low recognition rate of license plate recognition technology

1. Replace the camera or adjust the camera angle.

It is generally recommended that the vehicle adjust its front before entering the identification area, so that it can grab the high-definition license plate. The horizontal angle of the camera should be kept between 15 and 20 degrees. The specific details need to adjust the angle of the license plate camera according to the scene environment.

Step 2 increase the speed bump

When the vehicle speed is too fast, it is easy to lose the frame and cannot be recognized, so we can see that most manufacturers' treatment methods are to add speed bumps.

3. Add an auxiliary camera

If the lane is wide, the accuracy of the license plate recognition camera will be low. Generally speaking, the lane design is about 3 meters wide. Too narrow is not convenient for vehicles to pass, and too wide will lead to too large a license plate angle. (Auxiliary camera is recommended for lane width)

4. Add fill light.

When the license plate recognition camera is used outdoors, too strong light will cause the license plate to reflect light, reduce the recognition rate, and the lighting at night is insufficient, so auxiliary lighting is needed. Secondly, in the event of heavy rain, heavy snow and other weather, the license plate recognition rate will be slightly lower than usual.

Application field of license plate recognition technology

1, entrance and exit of parking lot and community

The application of license plate recognition technology in parking lots and residential areas is mainly used to record the license plate number, license plate color and entry and exit time of vehicles, so as to realize the automatic management of vehicles, save manpower and improve efficiency. For example, if it is used in an intelligent community, it can automatically judge whether the driving vehicle belongs to the community or not, and realize automatic time charging for the vehicles in the non-community. In some units, the application can also be combined with the vehicle dispatching system to automatically and objectively record the departure of vehicles in the unit.

2. Expressway toll station

At present, China's expressway construction is advancing by leaps and bounds, extending in all directions, and each exit has a toll station, which is convenient for toll management on the one hand and can help traffic police regulate the traffic on the expressway on the other. The application of license plate recognition technology in the entrance and exit of expressway toll station can greatly facilitate the traffic police to identify the license plate information of illegal vehicles and effectively manage and arrest some illegal vehicles.

3. Application in expressway bayonet

With the increase of highway construction mileage and the overall improvement of people's living standards in China, more and more people buy cars now, which has caused various illegal problems to highways. License plate recognition technology, as a necessary basis for vehicle illegal punishment, can automatically detect and recognize vehicle license plates in videos, the most typical of which is the public security bayonet system. Without license plate recognition technology, the system will not be truly intelligent.

4. Application in urban traffic.

In order to effectively curb the illegal behavior of vehicles running red lights in cities, bayonet detection systems are installed at all intersections in cities, and the most important part of this system is the license plate recognition module. License plate recognition system is mainly to determine the information of illegal vehicles. By capturing the license plate information of all vehicles and comparing it with the database of public security network, it can analyze which vehicles are suspicious, which can reduce illegal activities and control and reduce road traffic accidents.