License plate recognition - LPR

LPR – License Plate Recognition is sometimes known by various other terms

  • Automatic Number Plate Recognition - ANPR
  • Automatic License Plate Recognition - ALPR
  •  Automatic License Plate Reader – ALPR
  • Care Plate Recognition – CPR
  • Lecture Automatique de Plaques d’immatriculation (LAPI – Tiếng Pháp)
  • Mobile License Plate Reader (MLPR)
  • Vehicle license Plate Recognition (VLPR)
License Plate Recognition is a technology that uses optical character recognition on images to read vehicle registration plates.
Optical Character Recognition (OCR)  is the mechanical or electronic conversion of images of typed, handwritten or printed text into machine-encoded text. It is widely used as a form of data entry from printed paper data records, whether passport documents, invoices, bank statements, computerized receipts, business cards, mail, printouts of static-data, or any suitable documentation. It is a common method of digitizing printed texts so that it can be electronically edited, searched, stored more compactly, displayed on-line, and used in machine processes such as machine translation, text-to-speech, key data and text mining.

License plate recognition involves capturing photographic video or images of license plates, whereby they are processed by a series of algorithms that are able to provide an alpha numeric conversion of the captured license plate images into a text entry.

Perhaps the core dependence of any License Plate Recognition system is the effectiveness of its algorithms. The algorithms are quite meticulous and typically require hundreds of thousands lines of software code to compensate for such complexities. Large mathematical models are constructed and computer modeling may be done using super computer systems to account for multiple scenarios.
2018 04 18 1  LPR with Barrie

Six step:

1. License Plate Localization: Localizing is an algorithmic function that determines what aspect of the vehicle's image is the license plate. (What is problem?) The algorithm searches for a similar background color of unified proportion and contrast as a means to differentiate objects on a vehicle.

2. License Plate Sizing and Orientation: Components of algorithms that adjust for the angular skew of the license plate image to accurately sample, correct, and proportionally recalculate to an optimal size.

3. Normalization: Algorithm for regulating the contrast and brightness of the captured license plate image.

4. Character segmentation: Algorithm that locates the separate alpha numeric characters on a license plate. Character Segmentation separates each letter or number where it is subsequently processed by optical character recognition(OCR) algorithms.

5. Optical character recognition (OCR): Algorithm for Translating the captured image into an alpha numeric text entry.

6. Syntactical /Geometrical analysis:  Algorithm to verify alpha numeric information and arrangement with a specific rule set. The algorithms operate sequentially with instructions being executed in milliseconds. The successful completion of each algorithm is required before subsequent algorithms can be operational.

Apply :

  • Parking - the plate number is used to automatically enter pre-paid members and calculate parking fee for non-members (by comparing the exit and entry times). The optional driver face image can be used to prevent car hijacking.
  • Access Control - a gate automatically opens for authorized members in a secured area, thus replacing or assisting the security gaurd. The events are logged on a database and could be used to search the history of events.
  • Tolling - the car number is used to calculate the travel fee in a toll-road, or used to double-check the ticket.
  • Border Control - the car number is registered in the entry or exits to the Country, and used to monitor the border crossings. It can short the border crossing turnaround time and cut short the typical long lines.
  • Stolen cars - a list of stolen cars or unpaid fines is used to alert on a passing 'hot' cars. The 'black list' can be updated in real time and provide immediate alarm to the police force. The LPR system is deployed on the roadside, and performs a real-time match between the passing cars and the list. When a match is found a siren or display is activated and the police officer is notified with the detected car and the reasons for stopping the car.
  • Enforcement - the plate number is used to produce a violation fine on speed or red-light systems The manual process of preparing a violation fine is replaced by an automated process which reduces the overhead and turnaround time. The fines can be viewed and paid on-line.
  • Traffic control - the vehicles can be directed to different lanes according to their entry permits (such as in University complex projects). The system effectively reduces traffic congestions and the number of attendents.
The License Plate Recognition (LPR) system has been implemented in Viet Nam (for urban roads):
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