License Plate Recognition:Vision-Based Parking Management
Meta Rotenberg and Miriam Silva
The necessity to streamline the ongoing work of parking lots has resulted in the adoption of optical technology, integrating it into sophisticated parking systems. The technology is OCR – Optical Character Recognition – the electronic translation of alphanumeric images into machine-editable text.
The unique application of OCR in the automotive sphere is LPR – License Plate Recognition – reading the license plates on vehicles, and storing the images captured by the cameras as well as the text from the license plate.
In the first phase, the system’s imaging hardware (specialized visual spectrum and infra-red spectrum cameras designed specifically for the task) captures the license plate’s image. In the second phase, the system’s software uses a series of proprietary image manipulation techniques to detect and enhance the number plate’s image, and proprietary OCR to extract the license plate’s alphanumerics.
The software runs on standard PC hardware and can interface with, or be linked to, other applications or databases. For example, the LPR system from Hi-Tech Solutions includes self-developed Recognition Engine software for simple integration into other applications, such as the computerized valet parking and CheckPoint LPR systems of Computerized Valet Parking Systems, a subsidiary of Service Tracking Systems.
In recent years, LPR technology has gained popularity among many parking operators, who use it to automate billing processes, improve customer service, increase productivity and accuracy, minimize liabilities, and enhance facility security.
The LPR system is usually installed at the entrances and exits of a parking facility. The system automatically opens the gate for subscription parking (prepaid members) and calculates the parking fee for visitors. The plate string is used as a key to calculate the parking fee automatically, based on the time difference between exit and entry.
How does it work? For example, in some LPR systems, each vehicle generates one message containing a vehicle number, an optional identification name, the data and time, the lane, and an optional image file path (in .jpg or .bmp formats). Then the system shares the vehicle identifications with other processes such as billing. This can be done either by external communication (RS232) or by application-to-application messages. The latter method is implemented by Dynamic Data Exchange (DDE) or Microsoft Message Queuing (MSMQ) messages that are sent after each identification cycle.
License Plate Recognition technology also can be integrated with valet systems, as well as with standard revenue control systems. For example, one valet system takes a series of images from all sides of the vehicle and stores the license plate information in its archive. The license plate is later used to retrieve the gate event and access the damage inspection images, which are used in cases of damage claims filed by customers.
In office parking garages with motorized doors, the access control unit with the LPR system is usually installed above the motorized door, and only authorized vehicles are allowed to enter. When the vehicle approaches the door, the unit receives the loop detector indication, takes pictures of the plate, performs recognition, compares with a pre-stored database, and opens the gate if found on the list. All these operations are done in a stand-alone compact camera/illumination/computer unit.
Long-term parking lots, such as at airports, also can take advantage of LPR technology. The system is installed at the entrances of a long-term parking lot, records the plate number and associates it with the ticket number. When the car exits the lot, the ticket number is linked to the car number, thus verifying that the ticket is indeed the same as issued while entering. This system reduces fraud and handles cases of missing tickets, a common problem in long-term parking lots.
The automatic identification of the license plate number enables the operators to give discounts and privileges to frequent users. They can register their monthly parkers through without the need to give them Automatic Vehicle Identification (AVI) transponder or proximity cards, which can save thousands of dollars in installation and ongoing costs. In addition, parking operators can register clients for automatic payment. By interfacing with credit card processing applications, the LPR systems can accurately allocate the parking time and process payment when the vehicle exits the facility.
Given today’s increasing security concerns, a parking deck, grade or underground is also one of the most important points of entry and exit to monitor. One system, for example, provides 24-hour surveillance, independent of weather or lighting conditions, and sends alerts to the appropriate people via video, sound, pager or e-mail when the license plate number matches a “blacklist” from the police database or other databases.
Meta Rotenberg is Vice President of Business Development for Hi-Tech Solutions. She can be reached through its website (www.htsol.com). Miriam Silva is Marketing Manager for Computerized Valet Parking Systems; its website is www.cvaletps.com.
Article Abstract from April, 2008